the impact of tropical land-use change on downstream

REVIEW Open Access

The impact of tropical land-use change ondownstream riverine and estuarine waterproperties and biogeochemical cycles areviewYasuaki Tanaka Elizerberth Minggat and Wardina Roseli

Abstract

Tropical primary forests have been disappearing quickly to make use of the land for commercial purposes Land-usechange has an impact on downstream aquatic processes but those impacts have mainly been studied intemperate climate regions The present article reviews the impacts of various tropical land-use changes caused byhuman activities on downstream riverine and estuarine water properties and biogeochemical cycles focusingespecially on the behaviors of nitrogen (N) and phosphorus (P) Logging of tropical primary forests subsequentestablishment of pasture lands and occasional wildfire or intentional burning have decreased terrestrial N fixationand increased the discharge of P combined with soils which has lowered the NP ratio of dissolved inorganicnutrients in the adjacent stream waters and downstream rivers Agricultural fertilizers and aquacultural practicesbasically cause nutrient enrichment in downstream riverine and estuarine waters changing the NP ratio dependingon the source Finally urbanization causes eutrophication in many tropical estuaries where a halocline forms easilybecause of a warm temperature throughout the year and the water at the bottom of the estuary tends to becomehypoxic or anoxic Overall the impact of land-use change on aquatic processes may be more serious in tropicalregions than in temperate or cold climate regions because of (1) a higher biomass and nutrient stock in originaltropical forests (2) higher precipitation more frequent episodic flooding and warmer temperatures in tropicalregions and (3) certain practices that are rapidly expanding in tropical regions such as land-based aquacultureVarious land-use changes are causing downstream nutrient enrichment or disturbance of the nutrient balance attropical land-sea interfaces and the overall NP ratios in the aquatic ecosystem seem to be declining Nonetheless ifproper management is conducted and the discharge of nutrients and soils ceases tropical aquatic systems mayhave the potential to recover faster than those in other climate regions because of their abundant precipitation andwarm temperature Long-term monitoring and more attention to elemental stoichiometry are important areas forfuture research

Keywords Deforestation Land-use change Eutrophication Water quality Hypoxia Environmental monitoringAquatic conservation Water resources

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Correspondence yasuakitanakaubdedubnEnvironmental and Life Sciences Faculty of Science Universiti BruneiDarussalam Jalan Tungku Link Gadong BE1410 Brunei Darussalam

Tanaka et al Ecological Processes (2021) 1040 httpsdoiorg101186s13717-021-00315-3

IntroductionPrimary forests have been globally cut down with in-creasing human populations and expanding commercialland use in particular tropical forests have been lost fas-ter than those in other climate regions during the pastseveral decades (Gibbs et al 2010 Miettinen et al 2011Achard et al 2014 Rosa et al 2016) As a result for ex-ample the eastern lowlands of Sumatra and the peat-lands of Borneo lost approximately half of their peatswamps for conversion to industrial plantations from2000 to 2010 (Miettinen et al 2011) and the BrazilianAmazon lost 15 of the primary forest by 2010 (Maiaand Schons 2020) Not only inland forests but alsocoastal forests have been cut down quickly Tropicalcoasts and estuaries are often bordered by mangrove for-ests but it was estimated that 35 of global mangroveswere already lost from 1980 to 2000 (Valiela et al 2001)although recently the rate seems to be declining (Friesset al 2019) At the global level the gross loss of tropicalforests has been estimated to be 8 million ha per yearfrom 1990 to 2010 (05 annually Achard et al 2014)These deforested lands have been replaced with com-mercial lands for various purposes agricultural fields(eg rice soybeans and oil palm) aquaculture ponds orranching and poultry farms depending on the demandsof the region (Chen et al 2013 Richards and Friess2016)Generally tropical forests and their soil have higher

carbon (C) and nitrogen (N) stocks than those in otherclimate regions because of active photosynthesis andbiological N fixation throughout the year (Clevelandet al 1999 Jobbaacutegy and Jackson 2000 Hedin et al 2009Cloern et al 2014) Organic litter is fragmented into dis-solved and particulate organic matter (DOM and POMrespectively) and is mineralized into carbon dioxide(CO2) by bacteria faster in the tropics because of warmertemperatures (Wetterstedt et al 2010) When precipita-tion and throughfall pass through forest soils the con-centration of dissolved organic carbon (DOC) in the soilsolution gradually declines with soil depth because DOCtends to be adsorbed to soil particles (McDowell 1998)Because of organic matter decomposition the ammo-nium (NH4

+) concentration is relatively high in the sur-face soil but is gradually oxidized into nitrate (NO3

minus) assoil water moves downstream as groundwater (McDow-ell et al 1995 McDowell 1998) Phosphate (PO4

3minus) isalso regenerated from organic matter decompositionbut PO4

3minus tends to be adsorbed to soil and does not per-colate deeply into groundwater (McDowell et al 1995McDowell 1998) Thus stream waters surrounded bytropical primary forest and its downstream river and es-tuarine waters are usually enriched with dissolved inor-ganic carbon (DIC) and NO3

minus (McDowell 1998Miyajima et al 2009 Brookshire et al 2012 Noriega and

Araujo 2014) DIC and N exports from undisturbedtropical watersheds are generally higher than those fromtemperate watersheds because of the higher stock of or-ganic matter and active bacterial mineralization in theforest (Hedin et al 2009 Sarma et al 2011 Abril et al2014) However along with the disappearance of tropicalprimary forests less organic matter is produced on landand more organic matter is discharged downstream byincreased erosion which results in a reduction in thestock of soil organic C and N (Brown and Lugo 1990Brouwer and Riezebos 1998 Don et al 2011 Drakeet al 2019 Hattori et al 2019) Therefore the impact ofdeforestation on downstream limnological processes isexpected to be greater in tropical regions than in otherclimate regionsConversely artificial nutrient loading such as the ap-

plication of fertilizers increases with human land useafter deforestation because many human activities in-volve the use of nutrients (Downing et al 1999) In agri-culture more than half of applied fertilizers are oftennot recovered by plants but can accumulate in soilsvolatilize to the atmosphere or leach from the land toambient streams and rivers through groundwater or sur-face water runoff (Rocha et al 2019) The impact of fer-tilizers may remain in the soil even after several decades(Sebilo et al 2013) The fluxes of total N (TN) or NO3

minus

in rivers are correlated with population densities in thewatershed and TN fluxes have increased by 2- to 20-fold in temperate rivers since industrialization (Howarthet al 1996) although the trend is specific to the catch-ment and is also highly affected by climatic drivers suchas hydrology and temperature (Argerich et al 2013)The discharge of total phosphorus (TP) and PO4

3minus hasalso been increasing with wastewater discharge artificialdrainage systems and erosion (Nieminen et al 2017Williams and King 2020) Because tropical regions oftenexperience more rainfall than other climate regionsmore N and phosphorus (P) might be discharged withwater from tropical landsThe impacts of land-use change on downstream

aquatic processes have mainly been studied in temperateregions and some reviews are available (Howarth et al2011 Statham 2012 Bauer et al 2013) However re-views of the impacts on tropical regions are scarce(Downing et al 1999 Camara et al 2019 Thomaz et al2020) even though the impacts are expected to be dif-ferent from those seen in other climate regions as intro-duced above To summarize our present understandingof changing tropical aquatic processes the present art-icle reviews the impacts of various tropical land-usechanges on the water properties and biogeochemical cy-cles in adjacent streams rivers and estuaries We fo-cused on six major land-use changes (1) logging ofprimary forests (2) pasture including ranching (3)

Tanaka et al Ecological Processes (2021) 1040 Page 2 of 21

agriculture (4) forest fire including intentional burning(5) aquaculture and (6) urbanization affected by varioustypes of wastewaters We collected published literaturemainly from Google Scholar and focused on studies thatdirectly compared water properties or biogeochemicalcycles between sites affected or unaffected by land-usechange In the present review tropical regions were de-fined as the warmest areas in the Koumlppen-Geiger climateclassification (roughly between 20deg N and 20deg S Peelet al 2007)

LoggingTropical land-use change starts from deforestation bylogging primary forests At this stage both above- andbelowground plant biomasses are drastically and quicklyremoved from the land where the soil is dug up andloosened Subsequent transportation of timber by trac-tors further disturbs the ground which causes runoff ofsurface water and soils downstream after rainfall (Nyk-vist et al 1996 Chappell et al 2004) Moreover totalevaporation (or evapotranspiration) from the land maybe reduced due to less vegetation and more rainwaterflows into the adjacent streams and rivers after logging(Chappell et al 2005 Ling et al 2016) The groundwaterbaseflow also increases because of the reduced uptake ofinfiltrated rainwater by terrestrial plants In the BukitBerembun catchments in Peninsular Malaysia the aver-age water yield increased by 50minus70 after commerciallogging (Nik and Harding 1992 Chappell et al 2005)The increased volume and velocity of water flows erodestream banks making the stream increasingly wider(Iwata et al 2003 Neill et al 2006)

Most previous studies on the effects of logging ondownstream riverine water properties have focused onthe monitoring of suspended solids (SS) or turbidity andincreases in these water variables have been recorded atmany study sites during and after logging (Table 1) Theincrease in SS and turbidity is mainly caused by soilsbut dissolved inorganic nutrients (eg NO3

minus and PO43minus)

minerals (eg K+ Mg2+ and Ca2+) and organic matterare also discharged from soils (Table 1) Because terres-trial plant-derived organic matter generally has a higherCN ratio than aquatic microbes in rivers the dischargeof terrestrial organic matter from logging sites increasesthe CN ratio of total organic matter in the river (Wardet al 2015 Zhang et al 2019) In the ChanghuajiangRiver basin China the CN ratio of POM increased from7 to 10 during the wet season where more terrestrialparticles were discharged downstream due to high pre-cipitation and strong soil erosion (Zhang et al 2019) Inaddition the NP ratio of tropical plant leaves is occa-sionally very high due to the active N fixation of the for-est ecosystem compared to temperate or cold climateregions (Hedin et al 2009) This finding suggests thatthe NP ratio of POM in the downstream river might behigher in tropical regions than expected in other climateregionsRiver water pH can also be altered due to terrestrial

inputs because most soils in the humid tropics are acidic(eg pH = 45minus64 Grip et al 2005) This acidity hasboth biological and chemical causes microbial processes(eg aerobic oxidation methanogenesis sulfate reduc-tion nitrification) enrich the soil pore water with H+

and various forms of oxidized C and N (eg CO2 CH4NO3

minus) (Melling et al 2005 Riacuteos-Villamizar et al 2017)

Table 1 A summary of the effects of logging on the downstream riverine and estuarine water properties The arrows indicate thatthe subsequent water properties increased (uarr) decreased (darr) or did not change (rarr) See the list of abbreviations for waterproperties

Study sites Effects on downstream waterproperties

Sources

Bukit Berembun rivers Negri Sembilan Malaysia uarr SS turbidity NO3minus PO4

3minus Chappell et al (2004 2005)

Bukit Tarek streams Selangor Malaysia uarr EC SS turbidity Gomi et al (2006) Marryanna et al (2007)

Danum Valley rivers Sabah Malaysia uarr SS Douglas et al (1992) Greer et al (1996) Nainaret al (2017)

Mendolong catchment Sabah Malaysia uarr EC TN NO3minus NH4

+ DOCdarr DOCDON

Malmer and Grip (1994)

Baleh River Sarawak Malaysia uarr pH SS DOrarr TPdarr NO3

minus PO43minus Chl a

Ling et al (2016)

Batam River Sarawak Malaysia uarr SS turbidity Ling et al (2017)

Rivers Seram Indonesia uarr SS Cecil et al (2003)

Bongan River East Kalimantan Indonesia uarr SS de Jong et al (2015)

Bukit Baka Experimental Catchment Central KalimantanIndonesia

uarr SS Suryatmojo et al (2014)

Purus river Amazonas Brazil darr pH Riacuteos-Villamizar et al (2017)


and weathering of parent material may also directly acid-ify adjacent aquatic systems by reacting with precipita-tion or moisture For example acid sulfate soil (ASS) iswidely distributed in tropical regions and is stable underanoxic conditions However when ASS is exposed tooxygen (atmosphere) with water which is often drivenby logging during a rainy season ASS starts to be oxi-dized producing H+ and causing severe acidification ofthe downstream rivers (Sammut et al 1996 Vuai et al2003 Van Ha et al 2011) In the Kahayan River in Cen-tral Kalimantan Indonesia the surface water pHdropped to as low as 3 due to ASS during a rainy season(Haraguchi 2007)Because P combines with certain soil minerals (eg

calcium iron and aluminum) enhanced soil runoff dueto logging would involve a drastic transportation of Pfrom the surface land to the downstream aquatic ecosys-tem decreasing the NP ratio (Chappell et al 2005) Inthe downstream estuary suspended particulate P de-sorbs from the soil particles and PO4

3minus becomes avail-able for primary producers (Zhang and Huang 2011 Linet al 2012 Nguyen et al 2019a) The sorptiondesorp-tion of P is chemically affected by the water temperatureand salinity PO4

3minus desorption is enhanced with decreas-ing temperature or increasing salinity (Zhang and Huang2011) However in a turbid tropical estuary of SaigonVietnam the SS concentration was the greatest factor indetermining the P content in the water because of thehigh flocculation of cohesive sediments (Nguyen et al2019a) These properties of P indicate the importance ofthe management of soil discharge from logging sites toprevent P overloading in downstream aquatic ecosys-tems All the above types of runoff (ie water soil or-ganic matter and nutrients) would be alleviated byriparian vegetation because the vegetation zone func-tions as a filter (Williams et al 1997 Gomi et al 2006de Souza et al 2013)The effects of logging on downstream riverine and es-

tuarine water could last for months to years until theterrestrial soil is gradually stabilized and plants regrownaturally or artificially During the recovery period thedischarge of N and P into the adjacent river seems to re-turn to the original level before logging earlier thanother mineral ions (eg K+ Ca2+ Mg2+) (Malmer andGrip 1994 Chappell et al 2005) For example in the riv-ers of the Mendolong catchment Malaysia the concen-tration of NO3

minus returned to the original level within 2years after clear felling but the K+ concentration wasstill high even after 5 years (Malmer and Grip 1994)This difference suggests that N and P often limit thegrowth of terrestrial vegetation after logging and thusare subject to active absorption by the vegetation for re-growth while other minerals such as K+ are relativelysufficient for plants because they are continuously

leached from soil and rock through weathering (Malmerand Grip 1994 McDowell 1998 Chappell et al 2005)However from a longer-term viewpoint the removal ofterrestrial vegetation and the gradual erosion of soils de-crease the storage of nutrients and minerals on land(Recha et al 2012 Hattori et al 2019) which wouldeventually lower the concentration of these ions in thedownstream river and estuarine waterTo summarize this section logging increases the dis-

charge of terrestrial soils including nutrients and or-ganic matter that are stored in the forest (Table 2)Because tropical forest soils store larger biomass stocksthan those of other climate regions the impact of log-ging on organic matter and nutrient discharge would begreater in tropical regions especially when episodicheavy rainfall occurs The discharge of soils might in-crease the CN ratio of organic matter and decrease theNP ratio of dissolved inorganic nutrients in the down-stream river and estuary (Table 2) The increase in tur-bidity caused by soil and organic matter might reduceaquatic photosynthesis in the downstream river and es-tuary but in contrast the discharged nutrients have thepotential to increase productivity The final productivitywould be determined by the balance of these effects

Pastures and ranchesAfter deforestation the land is often changed to pastureby natural sprouts or seedings of a target species ofgrass The grown pasture may be repeatedly burned toremove unwanted weeds and used for ranches (Neillet al 2001 2017) If fertilizers are not added to pasturelands nutrient stocks in the soil may gradually declinefrom the original stock in primary forests (Hattori et al2019 Loacutepez-Poma et al 2020) Because of deforestationand conversion to pasture the primary production andstanding stock of biomass are decreasing globally ontropical lands (Erb et al 2016) Ranching of avicultureswine and cattle for livestock production is the majoruse of pasture lands especially in Latin America Brazilalone accounts for almost half of the livestock

Table 2 A summary of the common effects of tropical land-use change on the downstream riverine and estuarine waterproperties The arrows indicate that the water properties wouldincrease (uarr) decrease (darr) or not change (rarr) See the list ofabbreviations for water properties

Land use SS TN TP OCON TNTP DO

Logging uarr uarr uarr uarr darr darr

Pasture and ranching uarr uarrdarr uarr darr darr darr

Agriculture uarr uarr uarr darr uarrdarr darr

Burning uarr uarr uarr uarr uarrdarr darr

Aquaculture uarrdarr uarr uarrdarr darr uarrdarr rarr

Urbanization uarr uarr uarr darr darr darr


production in Latin America and the Caribbean (OECDFAO 2019)Because of its extensive area and long history the im-

pacts of the conversion of tropical primary forest to pas-ture on adjacent stream waters have been frequentlystudied in the Amazon region (de Mello et al 2020 Tho-maz et al 2020 Table 3) In the Amazonian state of Ron-docircnia Brazil forest reserves were logged from 1987 to1990 and were mostly planted with Brachiaria grass spe-cies for extensive cattle ranching (Thomas et al 2004Noacutebrega et al 2018) The planted grasses had low prod-uctivity compared to the primary forest (Noacutebrega et al2018) Due to the conversion from primary forest tograsses decreased canopy densities allowed more sunlightto reach streams which increased the temperature andprimary production in the stream water (Thomas et al2004 Lorion and Kennedy 2009) Most of the measuredorganic and nutrient contents in the stream waters werehigher alongside pastures than the streams surrounded byprimary forest during the dry season although the differ-ence was smaller or negligible during the wet season be-cause of the dilution by rainwater (Biggs et al 2004 Neillet al 2006 Thomas et al 2004 Deegan et al 2011Noacutebrega et al 2018) Higher POM and DOM would bederived from aquatic vegetation which became dominanton the stream banks in pastures due to increased lightavailability (Neill et al 2001 Noacutebrega et al 2018) NH4

+

and PO43minus also increased through the mineralization of

the organic matter produced by aquatic vegetation in thestream which led to lower dissolved oxygen (DO) in thewater (Thomas et al 2004)Conversely NO3

minus may decrease in the pasture streamsbecause less N fixation mineralization and nitrificationcould occur on the pasture lands than in the originalprimary forest (Neill et al 2001 Thomas et al 2004Table 3) The reduced NO3

minus concentration lowered theNP ratio of dissolved inorganic nutrients in the streamwaters of the Amazon regions shifting from a P limita-tion in forest streams to an N limitation in pasturestreams for aquatic primary producers (Neill et al 2001Figueiredo et al 2020) A similar reduction in NP ratiosin stream waters was also observed in pasture-dominated watersheds in Panama (Valiela et al 2013)Because tropical primary forests have high N fixationand provide excess N downstream (McDowell 1998 He-din et al 2009 Brookshire et al 2012) this reduction inNO3

minus and the NP ratio would be more impactful intropical regions than in other climate regions The totalfluxes of these nutrients would be greatly affected bywater discharge and therefore long-term monitoring isimportant to observe seasonal changes and to assess an-nual budgets (Williams et al 1997 Noacutebrega et al 2018)Pasture lands are often used for ranching to raise live-

stock animals The grazing of grass by those animals

Table 3 A summary of the effects of the conversion of primary forest to pastures and ranches on the downstream riverine andestuarine water properties The arrows before the water properties indicate that the subsequent water properties increased (uarr)decreased (darr) or did not change (rarr) See the list of abbreviations for the water properties

Study sites Effects on downstream water properties Sources

Rayu River Sarawak Malaysia rarr pH NO3minus NO2

minus NH4+ PO4

3minus Iwata et al (2003)

Rivers Queensland Australia uarr PON NO3minus Furnas (2003)

Rondocircnia Amazon Basin Brazil uarr TDN TDP PP Biggs et al (2004)

uarr SS POC PON DON PO43minus

rarr TDN NH4+

darr NO3minus TDNTDP DINDIP DO

Neill et al (2001)

uarr SS POC PON NH4+ PO4

3minus Chl adarr NO3

minus DOThomas et al (2004)

darr NO3minus DINDIP DO Neill et al (2006)

uarr SS NH4+ PO4

3minus

darr NO3minus DINDIP DO

Deegan et al (2011)

Paragominas streams Paraacute Brazil uarr pH DOdarr NO3

minusFigueiredo et al (2010)

Novo Progresso (Amazon) and Campo Verde (Cerrado) Brazil uarr TOC DOC TN NO3minus Noacutebrega et al (2018)

Sarapuiacute River Basin Satildeo Paulo Brazil uarr SS turbidity TPrarr TN

de Mello et al (2018a)

Sixaola River streams Limoacuten Costa Rica uarr Chl a Lorion and Kennedy (2009)

Veraguas rivers and estuaries Panama uarr SS Chl ararr PO4

3minus

darr NO3minus NH4

+ DINDIP

Valiela et al (2013 2014)

Streams Puerto Rico uarr Turbidity TN TPrarr DO

Uriarte et al (2011)


generally enhances (1) the cycling of plant decompos-ition and nutrient regeneration through digestion andexcretion by animals (Assmann et al 2017 Arnuti et al2020) and (2) soil erosion from fragile stream banks(McCulloch et al 2003 Brodie and Mitchell 2005) Dungnutrients are recycled by terrestrial plants or utilized asmanure fertilizer for agriculture (Sileshi et al 2017) butsome of them can flow into adjacent streams with pre-cipitation In the Amazon catchment the fluxes of totalinorganic C (TIC) and TN increased by 5 and 37 timesrespectively in the streams surrounded by pasture landswith extensive cattle ranching compared to those in pri-mary forests (Noacutebrega et al 2018) This increase in TICwas caused by the practice of liming (CaCO3) in the pas-ture to raise the pH of the indigenous acidic soils Ameta-analysis of the chemical composition of animalmanure from sub-Saharan countries showed that 77 ofmanure had NP ratios less than 5 which is lower thanthe NP requirement of major crops (Sileshi et al 2017)When plants take up available nutrients the NP ratio ofthe residue would decrease further The accumulation ofP relative to N was also found in subtropical pastureswith livestock grazing in Florida USA (Ho et al 2018)The discharge of these P-rich residues into streams mayshift the limitation factor from P to N for primary pro-duction in downstream aquatic ecosystems (Jennerjahnet al 2008 see ldquoAgriculturerdquo)If deforested lands or pasture lands are abandoned

they will gradually regenerate trees by natural seeding orartificial plantations as secondary forests Generally ittakes a longer time for tropical lands to recover theirfloral and faunal diversity than temperate lands becauseof the higher diversity in the original tropical forest(Meli et al 2017) In the Rayu River catchment of Bor-neo Malaysia slash-and-burn agricultural practices wereperformed until 1989 but then the area was protected asa national park and a secondary forest was redevelopedIn 1998 the dissolved inorganic nutrients electrical con-ductivity (EC) and pH in the stream water of the sec-ondary forest were no longer different from those of theoriginal primary forest (Iwata et al 2003) However thestream substrates were finer and the banks were moreeroded in the secondary forest most likely because ofthe loss of the riparian primary forest during the initialdeforestation Because of this physical alteration of habi-tats the diversity and abundance of aquatic organisms(eg periphyton aquatic insects shrimp and fish) werestill lower in the streams surrounded by the secondaryforest than in those surrounded by the primary forest(Inoue et al 2003 Iwata et al 2003) These observationssuggest that even if secondary forest develops the recov-ery of aquatic habitats and ecosystems would take a lon-ger time than that of chemical water properties (Feioet al 2015)

To summarize this section the conversion of primaryforest to pasture lands enables more sunlight to reachthe ground and adjacent lotic ecosystems increasing thetemperature and primary production in the water Be-cause terrestrial N fixation declines with deforestationthe NO3

minus concentration and the NP ratio of dissolvedinorganic nutrients in the downstream riverine and estu-arine waters would decrease (Table 2) and this reduc-tion would be more drastic in tropical regions than inother climate regions Ranching further decreases the NP ratio in the water due to the input of animal excretionBoth aquatic primary production and the input of ani-mal excretion increase DOM and POM in downstreamrivers and estuaries causing high turbidity and low DOin the water (Table 2)

AgriculturePrimary forests are frequently converted to lands foragriculture in tropical regions The net agricultural pro-duction in Southeast Asia has increased by approxi-mately 3 per year over the past several decades(OECDFAO 2017) In Southeast Asia rice cultivationwas the main agricultural activity until the 1980s butthe percentage of rice production to the total agricul-tural production has been decreasing for the past 40years instead palm oil and poultry production are in-creasing because of the higher income they generate(OECDFAO 2017) In Latin America and the Carib-bean soybeans are the major agricultural products andtheir production has increased fourfold during the past40 years (OECDFAO 2019) As seen in logging and pas-ture lands agricultural lands also cause increased runoffof surface water and soil In the Nandi district Kenyathe water runoff increased twofold after the primary for-est was converted to croplands (Recha et al 2012)In agricultural fields synthetic fertilizers which are

commonly composed of soluble inorganic nutrients (egammonium chloride diammonium phosphate potas-sium chloride) or organic nutrients that decompose rap-idly such as urea are frequently used althoughnatural organic fertilizer (eg animal manure and vege-table compost) has recently received attention (Dinget al 2019) Synthetic fertilizers are created to quicklydissolve and be efficiently absorbed by crop plants butin general only 10minus50 of applied N and P fertilizersare recovered as crop harvests (Prasertsak et al 2002Chen et al 2008 Ding et al 2019) The remaining Npercolates through soil into groundwater dischargeswith surface water runoff or it is released into the at-mosphere through volatilization (eg NH3) or denitrifi-cation (eg N2 and N2O) (Downing et al 1999 Rivettet al 2008 Maranguit et al 2017) Conversely P tendsto remain in the surface soil or be discharged with sedi-ment as surface runoff because of its ability to bind to


certain soil minerals (Faithful and Finlayson 2005 Zhangand Huang 2011 Nguyen et al 2019a)In the Brazilian Amazon and Cerrado the major crops

are soybean maize corn and cotton and the effects offertilizers on the adjacent stream water quality have beenfrequently reported (Figueiredo et al 2010 Silva et al2011 Riskin et al 2017 Neill et al 2017 Figueiredo et al2020 de Mello et al 2020) After the land use shifted frompasture to agriculture the concentration of most of themeasured nutrients minerals and EC increased while DOdecreased in the stream surrounded by agricultural fieldswith the use of fertilizers (Figueiredo et al 2010 Silvaet al 2011 de Mello et al 2018b Table 4) Even thoughthe concentration appeared to be unaffected the impactof fertilizer may become obvious when annual export ismeasured In the Brazilian state of Mat Grosso the nutri-ent concentration in stream waters was not affected bysoybean cropping compared to primary forest but the an-nual export of nutrients was higher from soybean fieldsthan the forest watershed because of the increased waterdischarge from the soybean fields (Riskin et al 2017)Oil palm plantations are one of the most extensive

agricultural crops in the tropics and consume the largestamount of commercial fertilizers in Southeast Asia(Maranguit et al 2017) but the effects on adjacentstreams or rivers have not been well studied (Ah Tunget al 2009 Comte et al 2012 2015 Gandaseca et al2015 Table 4) Because of fertilizer use the rivers sur-rounded by new oil palm plantations in SarawakMalaysia had higher NH4

+ and biological and chemicaloxygen demands (BOD and COD respectively) than thecontrolled forest sites (Gandaseca et al 2015) The sur-face runoff from the mature oil palm farms of PapuaNew Guinea also had higher NH4

+ concentrations thanthe controlled sites and the nutrient and water balanceimplied that a considerable amount of N was lost asdeep drainage by leaching (Banabas et al 2008) Thegroundwater collected from the well in the oil palmplantation of Sabah Malaysia had high NH4

+ and K+

concentrations which were likely derived from fertilizer(Ah Tung et al 2009) The NO3

minus concentration was notsignificantly affected by fertilizer at these oil palm sitesin Southeast Asia demonstrating that nitrification is nota major process in N transformation in these agriculturallands Because of the high precipitation in SoutheastAsia fertilizer-derived NH4

+ could be discharged intostreams and rivers before being oxidized into NO3

minus Atan oil palm plantation in Sumatra Indonesia the use oforganic fertilizer caused a high BOD and COD level inthe adjacent stream water which also suggests a shortresidence time of fertilizer-derived organic matter in thesurface soil (Comte et al 2015)Conversely NO3

minus may become the major fertilizer-derived nutrient in regions where precipitation

percolates and travels underground as groundwater witha relatively long residence time In northern QueenslandAustralia sugarcane and banana cultivation have beenthe major industries over the last century and the detailshave been reviewed in several articles (Furnas 2003 Bro-die and Mitchell 2005 Davis et al 2016) In brief theuse of fertilizer in this region increased the NO3

minus con-centration in the groundwater through nitrification(Thorburn et al 2003) and fertilizer-derived NO3

minus flo-wed into adjacent streams and rivers as baseflow (Mitch-ell et al 2001 2009) The NP ratio of dissolvedinorganic nutrients in the Tully River was much higherthan the Redfield ratio (NP = 16) throughout the year(Faithful and Finlayson 2005) indicating that P limitedaquatic primary production in the river High NP ratiosof dissolved inorganic nutrients in groundwaters or riverwaters affected by agricultural fertilizers have also beenreported in many other tropical and subtropical regionseg Hawaii (USA) Java (Indonesia) Okinawa (Japan)and Satildeo Paulo (Brazil) where the major N form is NO3

minus

(Blanco et al 2010 Bishop et al 2017 Taniwaki et al2017 Oehler et al 2018)The impact of fertilizer would also be different de-

pending on the type of fertilizer in the KalladaRiver India where a large part of the catchment isdominated by agricultural plantations (eg ricecoconut tea and rubber) low NP ratios of dissolvedinorganic nutrients were measured in the down-stream river region (Jennerjahn et al 2008) The ra-tio of NO3

minus to PO43minus ranged from 29 to 80 the

lowest value was measured during the wet seasonThis low NP ratio seems to have been caused bythe use of organic fertilizers such as urea and ma-nure in this region (Jennerjahn et al 2008) Similareffects are expected to occur by ranching as men-tioned in the above sectionTo summarize this section the effect of agricultural

fertilizer on the adjacent stream and river waters isnot straightforward but is affected by various factors(eg chemical composition and amount of fertilizersoil properties precipitation) Simply speaking iffertilizer-derived nutrients are quickly flushed down-stream with rainfall the NP ratio in the dischargedwater would be affected by the residue of thefertilizer In contrast if fertilizer-derived nutrients re-main in the soil or percolate into groundwater with along residence time the groundwater would have highNP ratios of dissolved inorganic nutrients because Ptends to be chemically trapped in soils Consideringthe climate of tropical regions the former case couldoccur more commonly or frequently than in other cli-mate regions Regardless of which case occurs down-stream primary production would increase due tofertilizer-derived nutrients


Wildfire and intentional burningHumid tropical forests are generally resistant to burningbut the transition from primary to secondary forestsshrubs pastures and agricultural plantations increasesthe frequency of fires (da Silva et al 2018 Adriantoet al 2020) Not only natural wildfires but alsointentional burning to remove weeds for agriculture maytrigger extensive fires In Southeast Asia 50 of forestswere affected by fire from 2003 to 2017 (Reddy et al2019) The area of forest fires increased 36-fold in theAmazon region from 1984 to 2016 (da Silva et al 2018)Forest fires provoke airborne release and deposition ofsuspended matter and gaseous chemicals causing exten-sive haze in tropical regions (Tacconi 2016)

The effects of forest wildfire or intentional burning onthe adjacent stream and river water quality have beenstudied well in temperate regions such as North Amer-ica but they have not been frequently studied in tropicalregions (Earl and Blinn 2003 Smith et al 2011 Rustet al 2018) Basically terrestrial organic matter is com-busted into ash black carbon or volatized chemicalswhich are released into the atmosphere or transportedinto the adjacent aquatic ecosystem The compositionand amount of ash or black carbon (including both or-ganic and inorganic matter) change with thetemperature and duration of burning a higher combus-tion completeness decreases the organic matter contentand increases the relative content of minerals (Audry

Table 4 A summary of the effects of agriculture on the downstream riverine and estuarine water properties When most minerals(eg Na+ Mg2+ Clminus K+ Ca2+) increased they were collectively described as EC increased The arrows before the water propertiesindicate that the subsequent water properties increased (uarr) decreased (darr) or did not change (rarr) See the list of abbreviations forthe water properties


Sources

Jambi estuary rivers Sumatra Indonesia uarr SS TOC Sanderson and Taylor (2003)

Streams at the Petapahan area Sumatra Indonesia rarr DIN TP Comte et al (2015)

Rivers at Sibu and Tatau Sarawak Malaysia uarr COD NH4+

darr pH DOGandaseca et al (2015)

Rajang River Sarawak Malaysia uarr SSdarr pCO2

Muumlller-Dum et al (2019)

Sundar River Sarawak Malaysia uarr EC turbidity NH4+ COD Rosli et al (2020)

Groundwater at Tawau Sabah Malaysia uarr NH4+

rarr NO3minus

Ah Tung et al (2009)

Buyhang watershed streams Leyte Philippines uarr Turbiditydarr NO3

minus PO43minus

Dessie and Bredemeier (2013)

Surface runoff at Sangara and Dami Papua New Guinea uarr NH4+

rarr NO3minus

Banabas et al (2008)

Tully River Queensland Australia uarr SS PON NO3minus PO4

3minus

rarr DON PP DOPMitchell et al (2001) Furnas (2003)

Tully and Murray Rivers Granite Creek QueenslandAustralia

uarr SS TN TP Faithful and Finlayson (2005)

Herbert River Queensland Australia uarr SS TN TP Bramley and Roth (2002) Mitchell et al(1997)

Cudgen Catchment New South Wales Australia uarr pHdarr pCO2

Jeffrey et al (2016)

Kallada River and Ashtamudi estuary Kerala India uarr SS NO3minus PO4

3minus

darr DINDIPJennerjahn et al (2008)

Nawuni Catchment Ghana uarr Turbidity NH4+ Tahiru et al (2020)

Federal District streams Brasilia Brazil uarr EC NO3minus NO2

minus NH4+

rarr DON PO43minus

darr DO

Silva et al (2011)

Tanguro Ranch Mat Gross Brazil uarr EC SS DOC NH4+ PO4

3minus Riskin et al (2017)

Paragominas streams Paraacute Brazil uarr EC pH turbidity NO3minus

rarr PO43minus

darr DO

Figueiredo et al (2010)

Sarapuiacute River Basin Satildeo Paulo Brazil uarr SS turbidity POM TN TP De Mello et al (2018a b)

Streams Puerto Rico uarr DO TP Uriarte et al (2011)


et al 2014 Bodiacute et al 2014) Because ash is easily dis-charged from burnt forests with surface water runoffafter rainfall (Malmer and Grip 1994 Ice et al 2004Dittmar et al 2012) episodic heavy rainfall that fre-quently occurs in tropical regions could cause a morerapid loss of nutrients and organic matter from the landcompared with temperate regions (Marques et al 2017)In the Mendolong catchments of northern Borneo

Malaysia the effects of the conversion of humid primaryforest to Acacia mangium plantations as well as agricul-tural use have been monitored since 1985 (Malmer1992 Nykvist et al 1996) After clear felling the practiceof intentional burning increased the concentration ofash and major nutrients in the adjacent streams andhigh concentrations were detected in the baseflow evenafter 3 years (Malmer and Grip 1994 Malmer 1996Table 5) The CN ratio of organic matter in the streamwater increased with burning (Malmer and Grip 1994)which suggests that more terrestrial organic matter wascarried downstream as ash or black carbon than beforeburning (Bodiacute et al 2014 Marques et al 2017) More-over less vegetation due to burning would decrease theuptake and retention of NO3

minus in the soil and mightincrease NO3

minus leaching to downstream river waters(Rhoades et al 2019) Ash and soil samples collectedfrom burnt land showed that more N than P was lostduring combustion (Kauffman et al 1995 1998 Mur-phy et al 2006) suggesting that more N is leachedthan P and that the NP ratio increases in the down-stream groundwater or river water after burning Theimpact of burning on nutrient discharge would bemitigated by retention and uptake by riparian vegeta-tion indicating the importance of riparian manage-ment (Williams et al 1997 Malmer 2004 de Souzaet al 2013)In the tropical savanna of northern Australia (Kakadu

National Park) fires in the late dry season caused highconcentrations of total suspended solids (TSS) volatilesuspended solids (VSS) N and P in the adjacent stream

after episodic storms and runoff but fires in the earlydry season did not have similar impacts (Townsend andDouglas 2000 2004 Table 5) Because leaf litter andvegetation accumulate during the preceding wet seasonash and soil are retained by the litter and nutrients areabsorbed by the remaining vegetation in the early dryseason (Townsend and Douglas 2004) Conversely inthe late dry season a lower canopy cover and less vege-tation and litter caused higher overland flows of ash andwater which increased the concentration of the above-mentioned water quality variables in the stream (Town-send and Douglas 2000) These observations showedthat the impacts of wildfire on the adjacent water prop-erties are affected by the season of the fire and that for-est management in the late dry season is especiallyimportant to prevent destructive wildfires and subse-quent drastic changes in the downstream riverine andestuarine water propertiesThe combustion of terrestrial biomass transports nu-

trients to adjacent rivers and the coastal sea through theatmosphere (ie dry and wet depositions) During exten-sive forest fires in Southeast Asia in 2006 N and P con-centrations in both dry (aerosol) and wet (rainwater)depositions increased in Singapore (Sundarambal et al2010a) These depositions would considerably increasenutrient concentrations in coastal seawater and mightincrease the productivity of phytoplankton (Sundarambalet al 2010b) Because the volatilization temperature of Nis much lower than that of P (Bodiacute et al 2014) more Nwould be lost during combustion and the NP ratio inatmospheric deposition is expected to decrease after fireeventsTo summarize this section the frequency and area of

wildfires or intentional burning are increasing in tropicalregions because of the conversion of primary forests topasture and agricultural lands Combustion changes thechemical compositions of terrestrial material and in-creases its mobility into adjacent streams and rivers Be-cause of the discharge of plant-derived materials and the

Table 5 A summary of the effects of wildfire or burning on the downstream riverine and estuarine water properties The arrowsbefore the water properties indicate that the subsequent water properties increased (uarr) decreased (darr) or did not change (rarr) Seethe list of abbreviations for the water properties


Sources

Mendolong catchment Sabah Malaysia uarr TN NO3minus NH4

+ TP PO43minus DOC Grip et al (1994) Malmer and Grip (1994)

Malmer (1996)

uarr TN NO3minus NH4

+

rarr PO43minus

Malmer (2004)

Rain waters and aerosol deposition during smoke hazeevents Singapore

uarr TN NO3minus + NO2

minus NH4+ TP PO4

3minus Sundarambal et al (2010a b)

Kakadu National Park catchments Northern Territory Australia uarr SS TN TP Townsend and Douglas (2000)

uarr TNrarr SS TP

Townsend and Douglas (2004)


leaching of N the downstream river waters would havea higher CN ratio of organic matter and a higher NPratio of dissolved inorganic nutrients than those beforeburning (Table 2) Tropical lands might lose organicmatter and nutrients more quickly than other climate re-gions because of frequent heavy rainfall events in thetropics

AquacultureDue to the global consumption of seafood aquaculturalproduction is currently almost equivalent to capturefisheries Production from inland (land-based) aquacul-ture where earthen ponds are created or culture tanksare placed on land is almost twice as high as that frommarine aquaculture and increased by 30 from 2011 to2016 worldwide (FAO 2018) Asia alone accounted for93 of global inland aquacultural production in 2016(FAO 2018) Because aquaculture ponds are usually lo-cated beside coasts and estuaries to obtain and releasewater efficiently mangroves and coastal forests are themajor vegetation types that have been lost due to land-based aquaculture On the coast of Hainan China 76of the mangrove loss was attributed to the creation ofnew aquaculture ponds (Herbeck et al 2020) The dif-ference in water properties between the influent and ef-fluent through an aquaculture pond is considered apotential impact of this practice on the downstreamenvironment

Land-based aquaculture usually involves the feeding oforganic pellets to raise target species as fast as possible(Rout and Bandyopadhyay 1999 Correia et al 2014)However a large part of the feed is not recovered as har-vests but is wasted with the water discharged from thepond or accumulates in the sediment of the pond (Jack-son et al 2003 Islam et al 2004 Anh et al 2010)Therefore most studies have shown that the effluentfrom aquaculture ponds tends to be eutrophic comparedto the influent that enters the pond (Table 6) This eu-trophication is largely composed of DOM and POM ra-ther than dissolved inorganic nutrients such as NH4

+

(Jackson et al 2003 Costanzo et al 2004 Islam et al2004 Molnar et al 2013) For example the total dis-solved and particulate organic nitrogen (DON and PONrespectively) accounted for approximately 60minus80 of thetotal N in the effluents from shrimp ponds in Queens-land Australia (Jackson et al 2003 Costanzo et al2004) a value of 98 was reported for shrimp pondsalong the west coast of New Caledonia (Thomas et al2010) and a value of 70 was reported for shrimp pondsin Hainan China (Herbeck et al 2013) These high per-centages of organic N relative to inorganic N are mostlikely caused by extra feed pellets feces excreted fromcultured organisms andor the microbes that proliferatein the pond (Jackson et al 2003 Thomas et al 2010Herbeck et al 2013)Laboratory experiments showed the release of N with

different chemical forms specific to the source while

Table 6 A summary of the effects of aquaculture on the downstream riverine and estuarine water properties The arrows beforethe water properties indicate that the subsequent water properties increased (uarr) decreased (darr) or did not change (rarr) See the listof abbreviations for the water properties


Shrimp and fish ponds Wenchang and Wenjiao EstuaryHainan China

uarr DOC DON DOCDON DIN NH4+ PO4

3minusChl ararr NO3

minus NO2minus

darr SS POC PN POCPN DINPO43minus

Herbeck et al (2013) Herbeck et al(2011)

Shrimp ponds Can Gio Vietnam uarr pH POC TN DINdarr SS POCPON

Vivier et al (2019)

uarr SS pH TN TP BOD CODrarr DO NH4

+Anh et al (2010)

Shrimp ponds the Bay of Bengal Bangladesh uarr TN NO3minus NO2

minus NH4+ Chl a

rarr DO pHdarr SS TP PO4

3minus

Islam et al (2004)

Shrimp ponds Cardwell Queensland Australia uarr TN PON DON NH4+ Chl a Jackson et al (2003)

uarr SS TN NO3minus NH4

+ TP DINDIP Chl ararr PO4

3minusCostanzo et al (2004)

Shrimp ponds Saint Vincent Bay New Caledonia uarr TN PON DON TDN NH4+ TP PP TDP

PO43minus

Molnar et al (2013)

Shrimp ponds Teremba Bay Chambeyron Bay New Caledonia uarr SS turbidity POC TN PON TP Chl ararr DIN DIP

Thomas et al (2010)

Fish and shrimp ponds Hawaii USA uarr SS turbidity TN NH4+ TP Chl a

darr NO3minus NO2

minus

uarrdarr PO43minus

Ziemann et al (1992)

Tanaka et al Ecological Processes (2021) 1040 0 of 21

cultured shrimp released a mixture of NH4+ and DON

(including urea) formulated feed pellets released moreDON compounds than shrimp (Burford and Williams2001) Because these pellet-derived DON compoundswould be chemically more complex than urea (eg pro-teins and peptidoglycan remnants) the DON leachedfrom feed pellets was less degradable for microbial com-munities in the water than shrimp-derived DON (mainlyurea) These results suggest that when aquaculturalwastewaters are discharged to adjacent rivers or estuar-ies the impact of pellet-derived DON may be differentfrom that of organism-derived DON and may reach far-ther downstream from the source (Thuy et al 2011Vivier et al 2019)Among inorganic N species in aquaculture ponds

NH4+ usually constitutes the largest proportion and

NO3minus and NO2

minus are much lower (Jackson et al 2003Costanzo et al 2004 Thomas et al 2010 Herbeck et al2013) NH4

+ is directly excreted from cultured organ-isms and is also produced through the degradation of la-bile DON such as urea contained in their feces(Ziemann et al 1992 Burford and Williams 2001) Rela-tively low proportions of NO3

minus and NO2minus in aquaculture

ponds indicate that (1) NH4+ is quickly absorbed by

phytoplankton or discharged from the pond before nitri-fication proceeds (Jackson et al 2003) (2) nitrification isnot a major process of N transformation in aquacultureponds because the process mainly occurs only at the aer-obic sediment surface (Hargreaves 1998) andor (3)even if NO3

minus is produced through nitrification NO3minus is

again reduced through dissimilatory nitrate reductioninto NH4

+ (DNRA) in anoxic pond sediment (Molnaret al 2013) DNRA is generally enhanced by hightemperature high organic matter and sulfate availabilityall of which are likely to occur in the sediment oftropical aquaculture ponds in brackish and coastalareas (Christensen et al 2003 Nizzoli et al 2006Dong et al 2011) In fact the proportion of DNRA tototal NO3

minus reduction (DNRA + denitrification) in-creased in the sediment receiving effluents fromshrimp ponds in New Caledonia which resulted in ahigher retention of N within the sediment due to thecoupling of nitrification and NO3

minus reduction (Molnaret al 2013)It should be noted that the concentration of NH4

+

often increased but PO43minus was relatively constant or

even decreased in some aquaculture ponds leading toelevated NP ratios of dissolved inorganic nutrients inthe pond water (Ziemann et al 1992 Costanzo et al2004 Islam et al 2004 Table 6) For example the NPratio of dissolved inorganic nutrients increased from 14(influent) to 214 (effluent) in shrimp ponds in Queens-land Australia (Costanzo et al 2004) Increased NP ra-tios would be caused by the retention of P in the pond

sediment and microbes (Reddy et al 1999) While N isrelatively mobile and transformed by bacteria throughnitrification or reduction (eg DNRA and denitrifica-tion) P needs to be stored in bacterial cells (eg nucleicacids and phospholipids) to maintain their basic cellularstructures In addition inorganic P tends to be chem-ically bound with minerals such as Ca2+ and the formedparticulate solids are deposited on the sediment underlow water turbulence These processes would lead to theaccumulation of P in aquaculture pond sediments grad-ually increasing the NP ratio of dissolved inorganic nu-trients in the water column In the sediment receivingaquacultural effluents in New Caledonia the NP ratio ofdissolved inorganic nutrient fluxes from sediment to theoverlying water was 42 which was much higher than theNP ratio of organic matter fluxes (82) indicating thatPO4

3minus was retained in the sediment (Molnar et al 2013)In downstream aquatic ecosystems receiving aquacul-tural effluents with high NP ratios the growth of phyto-plankton might be limited by the availability of P(Costanzo et al 2004)However even if P tends to be trapped in the pond

compared to N this does not mean that aquaculturalpractices do not cause P enrichment in the downstreamenvironment providing feed pellets basically has the po-tential to increase the enrichment of both N and P (Zie-mann et al 1992 Herbeck et al 2013 Molnar et al2013 Table 6) In fact the water quality in aquacultureponds is affected by many factors the chemical compos-ition and feeding amount of feed pellets (Rout and Ban-dyopadhyay 1999 Correia et al 2014) the density andspecies of cultured organisms (Ziemann et al 1992Thomas et al 2010) and the aeration and water resi-dence time (exchange rate) in the pond (Hopkins et al1993 Martinez-Coacuterdova et al 1997) Modifications ofaquacultural systems using microbial activities or engin-eering techniques to minimize environmental impactshave been reviewed in previous articles (Hargreaves2006 Mook et al 2012 van Rijn 2013 Martiacutenez-Coacuter-dova et al 2015 Li et al 2020)To summarize this section a considerable portion of

feed pellets may be discharged from aquaculture pondsas organic matter While organism-derived urea isquickly decomposed pellet-derived organic matter mightbe less degradable and the impact of the effluent mightreach far downstream from the aquaculture site Thedischarge of NH4

+ derived from cultured organisms sup-plies another major impact on the downstream ecosys-tem because the nutrients contained in the freshwaterprovided from tropical primary forests are mainly NO3

minusBecause inland aquacultural practices are rapidlyexpanding in tropical regions especially in SoutheastAsia these changes in aquatic processes will further in-crease in the future


UrbanizationWith the increasing human population tropical regionshave urbanized faster than other climate regions (Mont-gomery 2008) Deforested tropical lands may be used forbuilding private houses commercial facilities and indus-trial plants where wastewaters are sometimes directlydischarged into the adjacent environment withoutproper treatment The chemical compositions of thesewastewaters differ depending on the source but varioustypes of wastewaters from different sources are com-monly mixed in urbanized rivers and estuaries (Davisand Koop 2006 Cunha et al 2011 Fontana et al 2014Peyman et al 2017) Even if wastewater is treated at atreatment plant it is technically difficult to remove alldissolved inorganic nutrients from the water whichcould cause eutrophication of the downstream aquaticecosystem (Burford et al 2012b) Other sources reviewedin the above sections such as agricultural lands may stillaffect urbanized areas through surface water runoff andor groundwater seepage if the source is locatedupstreamThe effects of urbanization on riverine and estuarine

water quality have been studied at many sites in tropicalregions (Table 7) Because these previous studies havealready reported water quality variables such as nutrientconcentration this section mainly focuses on the charac-teristics of biogeochemical or microbial processes intropical regions that could differ from those in cooler re-gions Typically the organic matter contained in eu-trophic riverine or estuarine water is first decomposedby aerobic bacteria if DO is available where nutrientssuch as NH4

+ are regenerated and DO is consumed(Peacuterez-Villalona et al 2015) Because the temperature isusually higher in tropical regions than in other climateregions bacterial respiration (DO consumption) and or-ganic matter decomposition proceed more rapidly intropical waters (Scofield et al 2015 Follstad Shah et al2017) While DOM is mainly consumed in the watercolumn POM tends to sink down to the river or estuaryfloor and undergo decomposition at the bottom Thedifferent patterns of water properties and biological ac-tivities with depth would be especially obvious in estuar-ies where a halocline and stratification often occur(Martin et al 2010 Shivaprasad et al 2013) The tenden-cies toward stratification formation and DO depletionare highly dependent on the physical structure of thewater path (eg depth flow rate and vertical mixing) Awater body is easily stratified in a warm deep calm estu-ary but not in a fast-flowing shallow upstream riverThe degree of autotrophy or heterotrophy and theresulting DO concentration and pCO2 in the water arealso controlled by these physical factors (Cotovicz Jret al 2015 Guenther et al 2017 Santos and De Paula2019) Because nutrient-enriched wastewater is quickly

flushed downstream in the latter case eutrophicationand subsequent algal blooms or hypoxia usually becomeapparent in the former case where the residence time ofwater is sufficient (Perez et al 2011 Romo et al 2013John et al 2020)Under hypoxic or anoxic conditions anaerobic micro-

bial processes such as denitrification become dominantBecause denitrification proceeds faster under warmertemperatures (eg 25minus35 degC Myrstener et al 2016Meng et al 2019) eutrophic tropical rivers and estuaries(especially sediment) experience active denitrificationthroughout the year In an urbanized estuary in PuertoRico 21 of N was lost from the sediment through de-nitrification when organic matter was decomposed(Peacuterez-Villalona et al 2015) However denitrificationmight be gradually limited by the availability of NO3

minus

because the microbial production of NO3minus (= nitrifica-

tion) is expected to decrease under oxygen-depletedconditions (Koop-Jakobsen and Giblin 2010) Moreoverdenitrification may be inhibited by sulfate-reducing bac-teria because sulfide inhibits the final process of denitri-fication (Gardner and McCarthy 2009) This inhibition islikely to occur in the sediment of eutrophic estuaries be-cause of the intrusion of seawater (Rysgaard et al 1999)Anammox (anaerobic ammonium oxidation) is an-

other process that potentially removes N from aquaticecosystems under oxygen-depleted conditions whereNH4

+ and NO2minus are converted to N2 Because a high

NH4+ availability and DO depletion are basic require-

ments for anammox eutrophic rivers and estuaries (es-pecially sediment) are expected to be a hotspot of thisbacterial activity (Liu et al 2020) Moreover most ana-mmox bacteria prefer a warm temperature which makestropical aquatic environments further suitable for ana-mmox to actively proceed (Tomaszewski et al 2017) Al-though anammox was previously considered minorcompared to denitrification the recently revised isotopetechnique revealed that 64minus86 of the total N loss inthe seagrass sediment at Shaws Bay Australia wascaused by anammox (Salk et al 2017) A higher contri-bution of anammox than denitrification to the total Nloss was also reported in the sediment from oyster farm-ing in the Wallis Lake estuary Australia (Erler et al2017) although the balance between anammox and de-nitrification is not consistent among studies (Dong et al2011 Jiao et al 2018 Tan et al 2019) The proportionof anammox and denitrification is affected by variousenvironmental factors such as DO and salinity (Jianget al 2017 Liu et al 2020) Although relatively smallcontributions of microbial N removal through anammoxand denitrification have been reported in cooler regions(Mulholland et al 2009 Hellemann et al 2017 Liu et al2020) the removal of N may be more significant in trop-ical environments because of the warmer temperature


Table 7 A summary of the effects of urbanization on the downstream riverine and estuarine water properties When most minerals(eg Na+ Mg2+ Clminus K+ Ca2+) increased they were collectively described as EC increased The arrows before the water propertiesindicate that the subsequent water properties increased (uarr) decreased (darr) or did not change (rarr) See the list of abbreviations forthe water properties


Malacca river Malacca Malaysia uarr EC pH SS turbidity BOD CODdarr DO

Hua (2017)

Penchala River Selangor Malaysia uarr EC NH4+ BOD COD

rarr pHdarr DO

Mahazar et al (2013)

Kuantan Belat and Galing River Malaysia uarr EC pH DIN NH4+ TP COD

darr DO NO3minus

Kozaki et al (2016)

Day River Red River Delta Vietnam uarr TN NH4+ TP PO4

3minus Chl adarr TNTP DO

Hoang et al (2018)

Day River Red River Delta Vietnam uarr DOC NH4+ PO4

3minus pCO2 Chl a Duc et al (2009)

Saigon-Dongnai Rivers Vietnam uarr POC TN NH4+ TP PO4

3minus Chl a Nguyen et al (2019b)

Can Gio estuary Vietnam uarr pCO2

darr DODavid et al (2018)

Can Tho Mekong Delta Vietnam uarr Turbidity TN NH4+ PO4

3minus CODrarr NO3

minus NO2minus

darr DO

Wilbers et al (2014)

Brantas River Basin Java Indonesia uarr DON NO3minus PO4

3minus Jennerjahn et al (2004)

Ciliwung watershed Jakarta Indonesia uarr TP BOD CODdarr DO

Permatasari et al (2017)

Kholpetua-Arpangashia riversSundarbans Bangladesh

uarr NH4+ PO4

3minus

rarr NO3minus

darr DO

Rahaman et al (2013)

Manimala River Kerala India uarr EC NO3minus NO2

minus TP PO43minus

darr DOPadmalal et al (2012)

Piracicaba River Satildeo Paulo Brazil uarr NH4+ pCO2

rarr SS NO3minus

darr DO

Ballester et al (1999)Martinelli et al (1999)

Streams Satildeo Paulo Brazil uarr PO43minus

darr DO NO3minus

Silva et al (2012)

Streams Satildeo Paulo Brazil uarr TN NH4+ TP BOD Cunha et al (2011)

Monjolinho basin Satildeo Carlos Brazil uarr EC turbidity TN NO3minus TP PO4

3minus BODdarr DO

Bere and Tundisi (2011)

Guanabara Bay Rio de Janeiro Brazil uarr DO NH4+ PO4

3minus Chl adarr pCO2

Cotovicz Jr et al (2015)

Streams Rio de Janeiro Brazil uarr TN NH4+ TP

darr TNTPTromboni and Dodds (2017)

Una River Satildeo Joseacute da Vitoacuteria Brazil uarr EC SS turbidity PON DON NO2minus NH4

+PP DOP PO4

3minus

rarr pHdarr DO

Santos and De Paula (2019)

Urban streams Federal District Brazil uarr Turbidity DOC NO3minus NO2

minus NH4+

darr DOSilva et al (2011)

Cachoeira River estuary Bahia Brazil uarr NH4+ PO4

3minus Chl adarr DO DINDIP

Silva et al (2013)

Madeira River Rondocircnia Brazil uarr TDN TDP Biggs et al (2004)

Streams Puerto Rico uarr Turbidity TN TPdarr DO


Streams Mayaguumlez Puerto Rico uarr ECdarr DO

Wengrove and Ballestero (2012)

Riacuteo Pedras Watershed Puerto Rico uarr EC DOC DON NH4+ PO4

3minus

darr DO NO3minus

De Jesuacutes-Crespo and Ramiacuterez (2011) Potter et al (2013)Ramiacuterez et al (2014)


(Peacuterez-Villalona et al 2015) However it should also benoted that N losses in the form of N2 (anammox and de-nitrification) are usually much lower than nutrient re-generation and would not considerably eliminate N fromthe aquatic ecosystem (Gardner and McCarthy 2009Molnar et al 2013 Erler et al 2017 Salk et al 2017Domangue and Mortazavi 2018)While N follows a pathway of release into the atmos-

phere through anammox or denitrification P tends toremain in the aquatic system or to flow downstream byattaching to sediment particles and this property of Psorption becomes stronger at higher temperatures(Zhang and Huang 2011 Nguyen et al 2019a) This dif-ference between N and P gradually lowers the NP ratioin water or sediments in tropical estuaries (Cotovicz Jret al 2013) Therefore the discharge of wastewater fromurban areas would accelerate the decrease in the NP ra-tio because (1) sewage itself generally has a low NP ratiocompared to freshwater from pristine forests and (2)after organic matter is decomposed eutrophic oxygen-depleted conditions potentially promote microbial N re-moval through anammox and denitrification (Sarmaet al 2009 Dong et al 2011 Hoang et al 2018 Tanet al 2019) At the sites upstream of the Day RiverVietnam much lower TNTP ratios (a minimum of 29)than the Redfield ratio (NP = 16) were measured andwere attributed to sewage discharge agricultural and in-dustrial water runoff and denitrification (Hoang et al2018) In addition a low TNTP ratio (10) was detectedin the streams of the State of Rio de Janeiro Brazilwhich was considered to be due to the discharge ofphosphate-based detergents from the ambient urbanizedarea (Tromboni and Dodds 2017) Although many pris-tine tropical rivers have high NP ratios of dissolved in-organic nutrients where primary production is limitedby the availability of P (McDowell et al 2019 Nguyenet al 2019b) these impacts of urbanization might grad-ually shift the metabolic conditions to N limitation Thepotential to decrease NP ratios with these microbial andchemical processes would be basically higher in tropicalenvironments than in other climate regions due to thewarmer temperatureTo summarize this section urbanized rivers and estuar-

ies that receive a variety of wastewaters typically have highconcentrations of nutrients and minerals and low concen-trations of DO (Table 2) The TNTP ratio in the waterwould decrease with these eutrophication processes be-cause excess P is often discharged as wastewater and aportion of the N is lost from the aquatic ecosystemthrough anammox and denitrification under hypoxic oranoxic conditions The decline in NP ratios would bemore severe in tropical regions than in other climate re-gions because N removal and P sorption processes are fa-cilitated under warm temperature conditions

Conclusions and future researchThe present review shows that the impact of tropicalland-use change on downstream rivers and estuaries isspecific to the land use and human practices carried outon land but overall it appears that the impact is oftenmore serious and the biogeochemical processes aremore enhanced in tropical regions than in temperate orcold regions This difference derives mainly from thecharacteristics of the tropics (1) tropical primary forestshave a higher biomass and nutrient stocks supported byactive photosynthesis and N fixation (2) tropical regionshave a higher precipitation more frequent episodicflooding and warmer temperatures and (3) certain prac-tices such as land-based aquaculture are rapidly expand-ing in tropical regionsThe actual impacts that downstream rivers and estuar-

ies receive from changing land use depend on the inten-sity of each land-use effect therefore it is not easy toquantitatively evaluate the combined effects (Davis et al2016 Hapsari et al 2020) For example nutrient dis-charge may not enhance downstream primary produc-tion if sufficient light is not available for phytoplanktondue to high precipitation and subsequent discharge ofterrestrial soils (Burford et al 2012a) The combined ef-fects of land-use change and climate-related precipita-tion change should also be considered in the actualenvironment (Hapsari et al 2020) Because these land-use changes are usually extensive and nonpoint sourcessuch as groundwater seepage also contribute to down-stream water properties it is challenging to understandthe proportions of each land-use impact and their com-bination The test of stable isotopes (eg δ13C and δ15N)might be a useful tool to identify the source and contri-bution of wastewater (Taillardat et al 2020)Impacts such as eutrophication or imbalanced nutrient

supplies due to these tropical land-use changes wouldnot recover quickly even if the cause was removed A re-cent meta-analysis showed that terrestrial biogeochem-ical functions recovered more slowly after agriculturalpractices than after logging most likely due to fertilizeruse (Meli et al 2017) Another meta-analysis on coastalecosystem restoration projects showed that even 10years after the reduction or cessation of anthropogenicnutrient inputs the recovery completeness was only 24of the original baseline condition (McCrackin et al2017) Because most of the data used for this analysiswere from temperate climate regions such as Europeand North America there may be some differences attropical sites For example the high annual precipitationand occasional intensive rainfall in tropical regionswould help eutrophic ecosystems flush away accumu-lated nutrients downstream Additionally if denitrifica-tion or anammox proceeds faster at warmertemperatures N might be removed from the eutrophic


site more quickly than in temperate cases However as ittakes a longer time for tropical lands to recover theiroriginal biodiversity than temperate lands (Meli et al2017) the aquatic processes in the downstream riverand estuary might also require a longer time for recoveryin tropical regions To evaluate recovery from eutrophi-cation or disturbance of nutrient balance long-termmonitoring of more than 10 years is necessary but suchcases cannot be found in tropical regions at this timeAnother important aspect for future research is the

change in elemental stoichiometry such as the CNP ra-tio Most previous studies have measured the concentra-tion of target variables but reports of the impact onelement stoichiometry are relatively scarce In temperateestuaries primary production was expected to shift fromN limitation to P limitation because of the increased in-puts and retention of N (Howarth et al 2011) althoughthe limiting nutrients would be highly affected by re-gional factors The present review has shown that the NP ratio in tropical estuaries may decline with changes inland use due to different loading and removal processesbetween N and P Additionally the CN ratio of theavailable organic matter predominantly affects microbialprocesses of N transformation (eg DNRA anammoxdenitrification) (Erler et al 2017) Thus more researchwith accurate measurements of elemental ratios isneeded to evaluate the ecological impacts of tropicalland-use change on downstream aquatic processes

AbbreviationsBOD Biological oxygen demand Chl a Chlorophyll a COD Chemicaloxygen demand DIN Dissolved inorganic nitrogen DIP Dissolved inorganicphosphorus DOC Dissolved organic carbon DON Dissolved organicnitrogen DOP Dissolved organic phosphorus EC Electrical conductivityOC Organic carbon ON Organic nitrogen pCO2 Partial pressure of CO2POC Particulate organic carbon POM Particulate organic matterPON Particulate organic nitrogen PP Particulate phosphorus SS Suspendedsolids TDN Total dissolved nitrogen (= DON + DIN) TDP Total dissolvedphosphorus (= DOP + DIP) TN Total nitrogen TOC Total organic carbonTP Total phosphorus

AcknowledgementsWe are grateful to two anonymous reviewers for providing manysuggestions and recommendations to improve this article

Authorsrsquo contributionsYT had a concept for this article YT EM and WR performed the literaturesearch and collection YT drafted and revised the manuscript All authorsread and approved the final manuscript

FundingThis study was financially supported by the research grants (No CRGWG(013)170601 and UBDRSCHURCNIG402020001) funded by UniversitiBrunei Darussalam

Availability of data and materialsNot applicable

Declarations

Ethics approval and consent to participateNot applicable

Consent for publicationNot applicable

Competing interestsThe authors declare that they have no competing interests

Received 29 January 2021 Accepted 26 May 2021

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Christensen PB Glud RN Dalsgaard T Gillespie P (2003) Impacts of longlinemussel farming on oxygen and nitrogen dynamics and biologicalcommunities of coastal sediments Aquaculture 218(1ndash4)567ndash588 httpsdoiorg101016S0044-8486(02)00587-2

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Erler DV Welsh DT Bennet WW Meziane T Hubas C Nizzoli D Ferguson AJP(2017) The impact of suspended oyster farming on nitrogen cycling andnitrous oxide production in a sub-tropical Australian estuary Estuar CoastShelf Sci 192117ndash127 httpsdoiorg101016jecss201705007

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Figueiredo RO Cak A Markewitz D (2020) Agricultural impacts onhydrobiogeochemical cycling in the Amazon is there any solution Water12(3)763 httpsdoiorg103390w12030763

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fluxes at a hypereutrophic tropical estuary Mar Ecol 38(2)1ndash12 httpsdoiorg101111maec12423

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Hargreaves JA (1998) Nitrogen biogeochemistry of aquaculture pondsAquaculture 166(3ndash4)181ndash212 httpsdoiorg101016S0044-8486(98)00298-1

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Hedin LO Brookshire ENJ Menge DNL Barron AR (2009) The nitrogen paradox intropical forest ecosystems Annu Rev Ecol Evol Syst 40613ndash635 httpsdoiorg101146annurevecolsys37091305110246

Hellemann D Tallberg P Bartl I Voss M Hietanen S (2017) Denitrification in anoligotrophic estuary a delayed sink for riverine nitrate Mar Ecol Prog Ser58363ndash80 httpsdoiorg103354meps12359

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Herbeck LS Unger D Krumme U Liu SM Jennerjahn TC (2011) Typhoon-inducedprecipitation impact on nutrient and suspended matter dynamics of a


tropical estuary affected by human activities in Hainan China Estuar CoastShelf Sci 93(4)375ndash388 httpsdoiorg101016jecss201105004

Herbeck LS Unger D Wu Y Jennerjahn TC (2013) Effluent nutrient and organicmatter export from shrimp and fish ponds causing eutrophication in coastaland back-reef waters of NE hainan tropical China Cont Shelf Res 5792ndash104httpsdoiorg101016jcsr201205006

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Howarth R Chan F Conley D Garnier J Doney SC Marine R Billen G (2011)Coupled biogeochemical cycles eutrophication and hypoxia in temperateestuaries and coastal marine ecosystems Front Ecol Environ 9(1)18ndash26httpsdoiorg101890100008

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Ice GG Neary DG Adams PW (2004) Effects of wildfire on soils and watershedprocesses J For 102(6)16ndash20 httpsdoiorg101093jof102616

Inoue M Iwata T Nakano S Doi A Miyasaka H (2003) Fish assemblagecomposition abundance-habitat relationships and habitat use in tropical rainforest streams Sarawak Borneo effects of past deforestation Biosph Conserv5(2)71ndash86 doi 1020798biospherecons52_71

Islam MS Sarker MJ Yamamoto T Wahab MA Tanaka M (2004) Water andsediment quality partial mass budget and effluent N loading in coastalbrackishwater shrimp farms in Bangladesh Mar Pollut Bull 48(5ndash6)471ndash485httpsdoiorg101016jmarpolbul200308025

Iwata T Nakano S Inoue M (2003) Impacts of past riparian deforestation onstream communities in a tropical rain forest in Borneo Ecol Appl 13(2)461ndash473 httpsdoiorg1018901051-0761(2003)013[0461IOPRDO]20CO2

Jackson C Preston N Thompson PJ Burford M (2003) Nitrogen budget andeffluent nitrogen components at an intensive shrimp farm Aquaculture218(1ndash4)397ndash411 httpsdoiorg101016S0044-8486(03)00014-0

Jeffrey LC Maher DT Santos IR McMahon A Tait DR (2016) Groundwater acidand carbon dioxide dynamics along a coastal wetland lake and estuarycontinuum Estuaries Coasts 39(5)1325ndash1344 httpsdoiorg101007s12237-016-0099-8

Jennerjahn TC Ittekkot V Kloumlpper S Adi S Purwo Nugroho S Sudiana N YusmalA Prihartanto G-HB (2004) Biogeochemistry of a tropical river affected byhuman activities in its catchment Brantas River estuary and coastal waters ofMadura Strait Java Indonesia Estuar Coast Shelf Sci 60(3)503ndash514 httpsdoiorg101016jecss200402008

Jennerjahn TC Soman K Ittekkot V Nordhaus I Sooraj S Priya RS Lahajnar N(2008) Effect of land use on the biogeochemistry of dissolved nutrients andsuspended and sedimentary organic matter in the tropical Kallada River andAshtamudi estuary Kerela India Biogeochemistry 90(1)29ndash47 httpsdoiorg101007s10533-008-9228-1

Jiang X Hou L Zheng Y Liu M Yin G Gao J Li X Wang R Yu C Lin X (2017)Salinity-driven shifts in the activity diversity and abundance of anammoxbacteria of estuarine and coastal wetlands Phys Chem Earth 9746ndash53httpsdoiorg101016jpce201701012

Jiao L Wu J He X Wen X Li Y Hong Y (2018) Significant microbial nitrogen lossfrom denitrification and anammox in the land-sea interface of lowpermeable sediments Int Biodeterior Biodegrad 13580ndash89 httpsdoiorg101016jibiod201810002

Jobbaacutegy EG Jackson RB (2000) The vertical distribution of soil organic carbonand its relation to climate and vegetation Ecol Appl 10(2)423ndash436 httpsdoiorg1023072641104

John S Muraleedharan KR Revichandran C Azeez SA Seena G Cazenave PW(2020) What controls the flushing efficiency and particle transport pathwaysin a tropical Estuary Cochin Estuary Southwest coast of India Water 12(3)908 httpsdoiorg103390w12030908

Kauffman JB Cummings DL Ward DE (1998) Fire in the Brazilian Amazon 2Biomass nutrient pools and losses in cattle pastures Oecologia 113(3)415ndash427 httpsdoiorg101007s004420050394

Kauffman JB Cummings DL Ward DE Babbitt R (1995) Fire in the BrazilianAmazon 1 Biomass nutrient pools and losses in slashed primary forestsOecologia 104(4)397ndash408 httpsdoiorg101007BF00341336

Koop-Jakobsen K Giblin AE (2010) The effect of increased nitrate loading onnitrate reduction via denitrification and DNRA in salt marsh sedimentsLimnol Oceanogr 55(2)789ndash802 httpsdoiorg104319lo20105520789

Kozaki D Rahim MHA Wan Ishak MF Yusoff MM Mori M Nakatani N Tanaka K(2016) Assessment of the river water pollution levels in Kuantan Malaysiausing ion-exclusion chromatographic data water quality indices and landusage patterns Air Soil Water Res 91ndash11 httpsdoiorg104137ASWRS33017

Li Z Yu E Zhang K Gong W Xia Y Tian J Wang G Xie J (2020) Water treatmenteffect microbial community structure and metabolic characteristics in afield-scale aquaculture wastewater treatment system Front Microbiol 11930httpsdoiorg103389fmicb202000930

Lin P Chen M Guo L (2012) Speciation and transformation of phosphorus and itsmixing behavior in the Bay of St Louis estuary in the northern Gulf ofMexico Geochim Cosmochim Acta 87283ndash298 httpsdoiorg101016jgca201203040

Ling TY Soo CL Liew JJ Nyanti L Sim SF Grinang J (2017) Application ofmultivariate statistical analysis in evaluation of surface river water quality of atropical river J Chem 20175737452ndash5737413 httpsdoiorg10115520175737452

Ling TY Soo CL Sivalingam JR Nyanti L Sim SF Grinang J (2016) Assessment ofthe water and sediment quality of tropical forest streams in upperreaches of the Baleh River Sarawak Malaysia subjected to loggingactivities J Chem 20168503931ndash8503913 httpsdoiorg10115520168503931

Liu C Hou L Liu M Zheng Y Yin G Dong H Liang X Li X Gao D Zhang Z(2020) In situ nitrogen removal processes in intertidal wetlands of theYangtze Estuary J Environ Sci 9391ndash97 httpsdoiorg101016jjes202003005

Loacutepez-Poma R Pivello VR de Brito GS Bautista S (2020) Impact of the conversionof Brazilian woodland savanna (cerradatildeo) to pasture and Eucalyptusplantations on soil nitrogen mineralization Sci Total Environ 704135397httpsdoiorg101016jscitotenv2019135397

Lorion CM Kennedy BP (2009) Riparian forest buffers mitigate the effects ofdeforestation on fish assemblages in tropical headwater streams Ecol Appl19(2)468ndash479 httpsdoiorg10189008-00501

Mahazar A Othman MS Kutty AA Desa MNM (2013) Monitoring urban riverwater quality using macroinvertebrate and physico-chemical parameterscase study of Penchala river Malaysia J Biol Sci 13(6)474ndash482 httpsdoiorg103923jbs2013474482

Maia AG Schons SZ (2020) The effect of environmental change on out-migrationin the Brazilian Amazon rainforest Popul Environ 42(2)183ndash218 httpsdoiorg101007s11111-020-00358-2

Malmer A (1992) Water-yield changes after clear-felling tropical rainforest andestablishment of forest plantation in Sabah Malaysia J Hydrol 134(1-4)77ndash94httpsdoiorg1010160022-1694(92)90029-U

Malmer A (1996) Hydrological effects and nutrient losses of forest plantationestablishment on tropical rainforest land in Sabah Malaysia J Hydrol 174(1-2)129ndash148 httpsdoiorg1010160022-1694(95)02757-2

Malmer A (2004) Streamwater quality as affected by wild fires in natural andmanmade vegetation in Malaysian Borneo Hydrol Process 18(5)853ndash864httpsdoiorg101002hyp1255

Malmer A Grip H (1994) Converting tropical rainforest to forest plantation inSabah Malaysia Part II Effects on nutrient dynamics and net losses instreamwater Hydrol Process 8(3)195ndash209 httpsdoiorg101002hyp3360080303

Maranguit D Guillaume T Kuzyakov Y (2017) Land-use change affectsphosphorus fractions in highly weathered tropical soils Catena 149(1)385ndash393 httpsdoiorg101016jcatena201610010

Marques JSJ Dittmar T Niggemann J Almeida MG Gomez-Saez GV Rezende CE(2017) Dissolved black carbon in the headwaters-to-ocean continuum of


Paraiacuteba do Sul River Brazil Front Earth Sci 51ndash12 httpsdoiorg103389feart201700011

Marryanna L Siti Aisah S Saiful Iskandar K (2007) Water quality response to clearfelling trees for forest plantation establishment at Bukit Tarek FR Selangor JPhys Sci 18(1)33ndash45

Martin GD Muraleedharan KR Vijay JG Rejomon G Madhu NV Shivaprasad AHaridevi CK Nair M Balachandran KK Revichandran C Jayalakshmy KVChandramohanakumar N (2010) Formation of anoxia and denitrification inthe bottom waters of a tropical estuary southwest coast of IndiaBiogeosciences Discuss 7(2)1751ndash1782 httpsdoiorg105194bgd-7-1751-2010

Martinelli LA Krusche AV Victoria RL Camargo PB Bernardes M Ferraz ESMoraes JM Ballester VM (1999) Effect of sewage on the chemicalcomposition of Piracicaba River Brazil Water Air Soil Pollut 110(9)67ndash79httpsdoiorg101023A1005052213652

Martiacutenez-Coacuterdova LR Emerenciano M Miranda-Baeza A Martiacutenez-Porchas M(2015) Microbial-based systems for aquaculture of fish and shrimp anupdated review Rev Aquac 7(2)131ndash148 httpsdoiorg101111raq12058

Martinez-Coacuterdova LR Villarreal-Colmenares H Porchas-Cornejo MA Naranjo-Paramo J Aragon-Noriega A (1997) Effect of aeration rate on growth survivaland yield of white shrimp Penaeus vannamei in low water exchange pondsAquac Eng 16(1ndash2)85ndash90 httpsdoiorg101016S0144-8609(96)01010-2

McCrackin ML Jones HP Jones PC Moreno-Mateos D (2017) Recovery of lakesand coastal marine ecosystems from eutrophication a global meta-analysisLimnol Oceanogr 62(2)507ndash518 httpsdoiorg101002lno10441

McCulloch M Fallon S Wyndham T Hendy E Lough J Barnes D (2003) Coralrecord of increased sediment flux to the inner Great Barrier Reef sinceEuropean settlement Nature 421(6924)727ndash730 httpsdoiorg101038nature01361

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McDowell WH Lugo AE James A (1995) Export of nutrients and major ions fromCaribbean catchments J N Am Bentol Soc 14(1)12ndash20 httpsdoiorg1023071467721

McDowell WH McDowell WG Potter JD Ramiacuterez A (2019) Nutrient export andelemental stoichiometry in an urban tropical river Ecol Appl 29(2)e01839httpsdoiorg101002eap1839

Meli P Holl KD Rey Benayas JM Jones HP Jones PC Montoya D Mateos DM(2017) A global review of past land use climate and active vs passiverestoration effects on forest recovery PLoS ONE 12(2)e0171368 httpsdoiorg101371journalpone0171368

Melling L Hatano R Kah JG (2005) Methane fluxes from three ecosystems intropical peatland of Sarawak Malaysia Soil Biol Biochem 37(8)1445ndash1453httpsdoiorg101016jsoilbio200501001

Meng J Li J Li J Nan J Deng K Antwi P (2019) Effect of temperature onnitrogen removal and biological mechanism in an up-flow microaerobicsludge reactor treating wastewater rich in ammonium and lack in carbonsource Chemosphere 216186ndash194 httpsdoiorg101016jchemosphere201810132

Miettinen J Shi C Liew SC (2011) Deforestation rates in insular Southeast Asiabetween 2000 and 2010 Glob Chang Biol 17(7)2261ndash2270 httpsdoiorg101111j1365-2486201102398x

Mitchell A Reghenzani J Faithful J Furnas M Brodie J (2009) Relationshipsbetween land use and nutrient concentrations in streams draining a lsquowet-tropicsrsquo catchment in northern Australia Mar Freshw Res 60(11)1097ndash1108httpsdoiorg101071MF08330

Mitchell AW Bramley RGV Johnson AKL (1997) Export of nutrients andsuspended sediment during a cyclone-mediated flood event in the HerbertRiver catchment Australia Mar Freshw Res 48(1)79ndash88 httpsdoiorg101071MF96021

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Miyajima T Tsuboi Y Tanaka Y Koike I (2009) Export of inorganic carbon fromtwo Southeast Asian mangrove forests to adjacent estuaries as estimated bythe stable isotope composition of dissolved inorganic carbon J Geophys Res114(G1)G01024 httpsdoiorg1010292008JG000861

Molnar N Welsh DT Marchand C Deborde J Meziane T (2013) Impacts of shrimpfarm effluent on water quality benthic metabolism and N-dynamics in amangrove forest (New Caledonia) Estuar Coast Shelf Sci 117(2)12ndash21httpsdoiorg101016jecss201207012

Mook WT Chakrabarti MH Aroua MK Khan GMA Ali BS Islam MS Abu HassanMA (2012) Removal of total ammonia nitrogen (TAN) nitrate and totalorganic carbon (TOC) from aquaculture wastewater using electrochemicaltechnology a review Desalination 2851ndash13 httpsdoiorg101016jdesal201109029

Mulholland PJ Hall ROJ Sobota DJ Dodds WK Findlay SEG Grimm NB HamiltonSK McDowell WH OrsquoBrien JM Tank JL Ashkenas LR Cooper LW Dahm CNGregory SV Johnson SL Meyer JL Peterson BJ Poole GC Valett HM WebsterJR Arango CP Beaulieu JJ Bernot MJ Burgin AJ Crenshaw CL Helton AMJohnson LT Niederlehner BR Potter JD Sheibley RW Thomas S M (2009)Nitrate removal in stream ecosystems measured by 15N additionexperiments denitrification Limnol Oceanogr 54(3)666ndash680 doi httpsdoiorg104319lo20095430666

Muumlller-Dum D Warneke T Rixen T Muumlller M Baum A Christodoulou A Oakes JEyre BD Notholt J (2019) Impact of peatlands on carbon dioxide (CO2)emissions from the Rajang River and Estuary Malaysia Biogeosciences 16(1)17ndash32 httpsdoiorg105194bg-16-17-2019

Murphy JD Johnson DW Miller WW Walker RF Carroll EF Blank RR (2006)Wildfire effects on soil nutrients and leaching in a Tahoe Basin watershed JEnviron Qual 35(2)479ndash489 httpsdoiorg102134jeq20050144

Myrstener M Jonsson A Bergstroumlm AK (2016) The effects of temperature andresource availability on denitrification and relative N2O production in boreallake sediments J Environ Sci 4782ndash90 httpsdoiorg101016jjes201603003

Nainar A Bidin K Walsh RPD Ewers RM Reynolds G (2017) Effects of differentland-use on suspended sediment dynamics in Sabah (Malaysian borneo) - aview at the event and annual timescales Hydrol Res Lett 11(1)79ndash84 httpsdoiorg103178HRL1179

Neill C Deegan LA Thomas SM Cerri CC (2001) Deforestation for pasture altersnitrogen and phosphorus in small Amazonian streams Ecol Appl 11(6)1817ndash1828 httpsdoiorg1018901051-0761(2001)011[1817DFPANA]20CO2

Neill C Deegan LA Thomas SM Haupert CL Krusche AV Ballester VM Victoria RL(2006) Deforestation alters the hydraulic and biogeochemical characteristicsof small lowland Amazonian streams Hydrol Process 20(12)2563ndash2580httpsdoiorg101002hyp6216

Neill C Jankowski KJ Brando PM Coe MT Deegan LA Macedo MN Riskin SHPorder S Elsenbeer H Krusche AV (2017) Surprisingly modest water qualityimpacts from expansion and intensification of large-scale commercialagriculture in the Brazilian Amazon-Cerrado Region Trop Conserv Sci 101ndash5httpsdoiorg1011771940082917720669

Nguyen TTN Neacutemery J Gratiot N Garnier J Strady E Tran VQ Nguyen ATNguyen TNT Golliet C Aimeacute J (2019a) Phosphorus adsorptiondesorptionprocesses in the tropical Saigon River estuary (Southern Vietnam) impactedby a megacity Estuar Coast Shelf Sci 227106321 httpsdoiorg101016jecss2019106321

Nguyen TTN Neacutemery J Gratiot N Strady E Tran VQ Nguyen AT Aimeacute J Peyne A(2019b) Nutrient dynamics and eutrophication assessment in the tropicalriver system of Saigon ndash Dongnai (southern Vietnam) Sci Total Environ 653370ndash383 httpsdoiorg101016jscitotenv201810319

Nieminen M Sallantaus T Ukonmaanaho L Nieminen TM Sarkkola S (2017)Nitrogen and phosphorus concentrations in discharge from drained peatlandforests are increasing Sci Total Environ 609974ndash981 httpsdoiorg101016jscitotenv201707210

Nik AR Harding D (1992) The effects of selective logging methods on water yieldand streamflow parameters in Peninsular Malaysia J Trop For Sci 5(2)130ndash154

Nizzoli D Welsh DT Fano EA Viaroli P (2006) Impact of clam and mussel farmingon benthic metabolism and nitrogen cycling with emphasis on nitratereduction pathways Mar Ecol Prog Ser 315151ndash165 httpsdoiorg103354meps315151

Noacutebrega RLB Guzha AC Lamparter G Amorim RSS Couto EG Hughes HJJungkunst HF Gerold G (2018) Impacts of land-use and land-cover changeon stream hydrochemistry in the Cerrado and Amazon biomes Sci TotalEnviron 635259ndash274 httpsdoiorg101016jscitotenv201803356

Noriega C Araujo M (2014) Carbon dioxide emissions from estuaries of northernand northeastern Brazil Sci Rep 4(1)6164 httpsdoiorg101038srep06164

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Padmalal D Remya SI Jyothi SJ Baijulal B Babu KN Baiju RS (2012) Water qualityand dissolved inorganic fluxes of N P SO4 and K of a small catchment riverin the Southwestern Coast of India Environ Monit Assess 184(3)1541ndash1557httpsdoiorg101007s10661-011-2059-x

Peel M Finlayson B McMahon T (2007) Updated world map of the Koumlppen-Geiger climate classification Hydrol Earth Syst Sci 11(5)1633ndash2007 httpsdoiorg105194hess-11-1633-2007

Perez BC Day JW Justic D Lane RR Twilley RR (2011) Nutrient stoichiometryfreshwater residence time and nutrient retention in a river-dominatedestuary in the Mississippi delta Hydrobiologia 658(1)41ndash54 httpsdoiorg101007s10750-010-0472-8

Peacuterez-Villalona H Cornwell JC Ortiz-Zayas JR Cuevas E (2015) Sedimentdenitrification and nutrient fluxes in the San Joseacute Lagoon a tropical Lagoonin the highly urbanized San Juan Bay Estuary Puerto Rico Estuaries Coasts38(6)2259ndash2278 httpsdoiorg101007s12237-015-9953-3

Permatasari PA Setiawan Y Khairiah RN Effendi H (2017) The effect of land usechange on water quality a case study in Ciliwung Watershed IOP Conf SerEarth Environ Sci 54012026 httpsdoiorg1010881742-65967551011001

Peyman N Travakloy Sany SB Tajfard M Hashim R Rezayi M Karlen DJ (2017)The status and characteristics of eutrophication in tropical coastal waterEnviron Sci Process Impacts 19(8)1086ndash1103 httpsdoiorg101039c7em00200a

Potter JD McDowell WH Helton AM Daley ML (2013) Incorporating urbaninfrastructure into biogeochemical assessment of urban tropical streams inPuerto Rico Biogeochemistry 121(1)271ndash286 httpsdoiorg101007s10533-013-9914-5

Prasertsak P Freney JR Denmead OT Saffigna PG Prove BG Reghenzani JR(2002) Effect of fertilizer placement on nitrogen loss from sugarcane intropical Queensland Nutr Cycl Agroecosyst 62(3)229ndash239 httpsdoiorg101023A1021279309222

Rahaman SMB Sarder L Rahaman MS Ghosh AK Biswas SK Siraj SMS Huq KAHasanuzzaman AFM Islam SS (2013) Nutrient dynamics in the Sundarbansmangrove estuarine system of Bangladesh under different weather and tidalcycles Ecol Process 229 httpsdoiorg1011862192-1709-2-29

Ramiacuterez A Rosas KG Lugo AE Ramos-Gonzaacutelez OM (2014) Spatio-temporalvariation in stream water chemistry in a tropical urban watershed Ecol Soc19(2)45

Recha JW Lehmann J Todd Walter M Pell A Verchot L Johnson M (2012)Stream discharge in tropical headwater catchments as a result of forestclearing and soil degradation Earth Interact 16(13)1ndash18 httpsdoiorg1011752012EI0004391

Reddy CS Bird NG Sreelakshmi S Manikandan TM Asra M Krishna PH Jha CSRao PVN Diwakar PG (2019) Identification and characterization of spatio-temporal hotspots of forest fires in South Asia Environ Monit Assess191(Suppl 3)791 httpsdoiorg101007s10661-019-7695-6

Reddy KR Kadlec RH Flaig E Gale PM (1999) Phosphorus retention in streamsand wetlands a review Crit Rev Environ Sci Technol 29(1)83ndash146 httpsdoiorg10108010643389991259182

Rhoades CC Chow AT Covino TP Fegel TS Pierson DN Rhea AE (2019) Thelegacy of a severe wildfire on stream nitrogen and carbon in headwatercatchments Ecosystems 22(3)643ndash657 httpsdoiorg101007s10021-018-0293-6

Richards DR Friess DA (2016) Rates and drivers of mangrove deforestation inSoutheast Asia 2000ndash2012 Proc Natl Acad Sci USA 113(2)344ndash349 httpsdoiorg101073pnas1510272113

Riacuteos-Villamizar EA Piedade MTF Junk WJ Waichman AV (2017) Surface waterquality and deforestation of the Purus river basin Brazilian Amazon IntAquat Res 9(1)81ndash88 httpsdoiorg101007s40071-016-0150-1

Riskin SH Neill C Jankowski K Krusche AV McHorney R Elsenbeer HMacedo MN Nunes D Porder S (2017) Solute and sediment export fromAmazon forest and soybean headwater streams Ecol Appl 27(1)193ndash207 httpsdoiorg101002eap1428

Rivett MO Buss SR Morgan P Smith JWN Bemment CD (2008) Nitrateattenuation in groundwater a review of biogeochemical controlling

processes Water Res 42(16)4215ndash4232 httpsdoiorg101016jwatres200807020

Rocha KF Mariano E Grassmann CS Trivelin PCO Rosolem CA (2019) Fate of 15Nfertilizer applied to maize in rotation with tropical forage grasses Field CropsRes 23835ndash44 httpsdoiorg101016jfcr201904018

Romo S Soria J Fernaacutendez F Ouahid Y Baroacuten-Solaacute Aacute (2013) Water residencetime and the dynamics of toxic cyanobacteria Freshw Biol 58(3)513ndash522httpsdoiorg101111j1365-2427201202734x

Rosa IMD Smith MJ Weam OR Purves D Ewers RM (2016) The environmentallegacy of modern tropical deforestation Curr Biol 26(16)2161ndash2166 httpsdoiorg101016jcub201606013

Rosli N Gandaseca S Gerusu GJ Heng RKJ Ahmed OH Idris MH Mohamad PaziAM (2020) Quality of tropical river water in different catchments of canopycover Malaysian For 83(1)128ndash148

Rout RK Bandyopadhyay S (1999) A comparative study of shrimp feed pelletsprocessed through cooking extruder and meat mincer Aquac Eng 19(2)71ndash79 httpsdoiorg101016S0144-8609(98)00034-X

Rust AJ Hogue TS Saxe S McCray J (2018) Post-fire water-quality response in thewestern United States Int J Wildland Fire 27(3)203ndash216 httpsdoiorg101071WF17115

Rysgaard S Thastum P Dalsgaard T Christensen PB Sloth NP (1999) Effectsof salinity on NH4

+ adsorption capacity nitrification and denitrificationin Danish estuarine sediments Estuaries 22(1)21ndash30 httpsdoiorg1023071352923

Salk KR Erler DV Eyre BD Carlson-Perret N Ostrom NE (2017) Unexpectedly highdegree of anammox and DNRA in seagrass sediments description andapplication of a revised isotope pairing technique Geochim CosmochimActa 21164ndash78 httpsdoiorg101016jgca201705012

Sammut J White I Melville MD (1996) Acidification of an estuarine tributary ineastern Australia due to drainage of acid sulfate soils Mar Freshw Res 47(5)669ndash684 httpsdoiorg101071MF9960669

Sanderson PG Taylor DM (2003) Short-term water quality variability in twotropical estuaries central Sumatra Estuaries 26(1)156ndash165 httpsdoiorg101007BF02691702

Santos DA De Paula FCF (2019) Diel changes in aquatic biogeochemistry of apristine stream receiving untreated urban sewage at Brazilian rainforestEnviron Sci Pollut Res 26(12)12324ndash12334 httpsdoiorg101007s11356-019-04386-w

Sarma VVSS Gupta SNM Babu PVR Acharya T Harikrishnachari N VishnuvardhanK Rao NS Reddy NPC Sarma VV Sadhuram Y Murty TVR Kumar MD (2009)Influence of river discharge on plankton metabolic rates in the tropicalmonsoon driven Godavari estuary India Estuar Coast Shelf Sci 85(4)515ndash524httpsdoiorg101016jecss200909003

Sarma VVSS Kumar NA Prasad VR Venkataramana V Appalanaidu S SrideviB Kumar BSK Bharati MD Subbaiah CV Acharyya T Rao GDViswanadham R Gawade L Manjary DT Kumar PP Rajeev K NPC RSarma VV Kumar MD Sadhuram Y TVR M (2011) High CO2 emissionsfrom the tropical Godavari estuary (India) associated with monsoon riverdischarges Geophys Res Lett 38(8)L08601 httpsdoiorg1010292011GL046928

Scofield V Jacques SMS Guimaratildees JRD Farjalla VF (2015) Potential changes inbacterial metabolism associated with increased water temperature andnutrient inputs in tropical humic lagoons Front Microbiol 6310 httpsdoiorg103389fmicb201500310

Sebilo M Mayer B Nicolardot B Pinay G Mariotti A (2013) Long-term fate ofnitrate fertilizer in agricultural soils Proc Natl Acad Sci USA 110(45)18185ndash18189 httpsdoiorg101073pnas1305372110

Shivaprasad A Vinita J Revichandran C Reny PD Deepak MP Muraleedharan KRKumar KRN (2013) Seasonal stratification and property distributions in atropical estuary (Cochin estuary west coast India) Hydrol Earth Syst Sci 17(1)187ndash199 httpsdoiorg105194hess-17-187-2013

Sileshi GW Nhamo N Mafongoya PL Tanimu J (2017) Stoichiometry of animalmanure and implications for nutrient cycling and agriculture in sub-SaharanAfrica Nutr Cycl Agroecosyst 107(1)91ndash105 httpsdoiorg101007s10705-016-9817-7

Silva DML Camargo PB McDowell WH Vieira I Salomatildeo MSMB Martinelli LA(2012) Influence of land use changes on water chemistry in streams in thestate of Satildeo Paulo southeast Brazil An Acad Bras Cienc 84(4)919ndash930httpsdoiorg101590S0001-37652012000400007

Silva JSO da Bustamante MMC Markewitz D Krusche AV Ferreira LG (2011)Effects of land cover on chemical characteristics of streams in the Cerrado


region of Brazil Biogeochemistry 105(1)75ndash88 httpsdoiorg101007s10533-010-9557-8

Silva MAMEcirc Eccedila GF Santos DF Guimaratildees AG Lima MC de Souza MFL (2013)Dissolved inorganic nutrients and chlorophyll a in an estuary receivingsewage treatment plant effluents Cachoeira River estuary (NE Brazil) EnvironMonit Assess 185(7)5387ndash5399 httpsdoiorg101007s10661-012-2953-x

Smith HG Sheridan GJ Lane PNJ Nyman P Haydon S (2011) Wildfire effects onwater quality in forest catchments a review with implications for watersupply J Hydrol 396(1ndash2)170ndash192 httpsdoiorg101016jjhydrol201010043

Statham PJ (2012) Nutrients in estuaries mdash An overview and the potentialimpacts of climate change Sci Total Environ 434213ndash227

Sundarambal P Balasubramanian R Tkalich P He J (2010a) Impact of biomassburning on ocean water quality in Southeast Asia through atmosphericdeposition field observations Atmos Chem Phys 10(23)11323ndash11336httpsdoiorg105194acp-10-11323-2010

Sundarambal P Tkalich P Balasubramanian R (2010b) Impact of biomass burningon ocean water quality in Southeast Asia through atmospheric depositioneutrophication modeling Atmos Chem Phys 10(23)11337ndash11357 httpsdoiorg105194acp-10-11337-2010

Suryatmojo H Fujimoto M Kosugi K Mizuyama T (2014) Runoff and soil erosioncharacteristics in different periods of an intensive forest management systemin a tropical Indonesian rainforest Int J Sustain Dev Plan 9(6)830ndash846httpsdoiorg102495SDP-V9-N6-830-846

Tacconi L (2016) Preventing fires and haze in Southeast Asia Nat Clim Change6(7)640ndash643 httpsdoiorg101038nclimate3008

Tahiru AA Doke DA Baatuuwie BN (2020) Effect of land use and land coverchanges on water quality in the Nawuni Catchment of the White Volta BasinNorthern Region Ghana Appl Water Sci 10(8)1ndash14 httpsdoiorg101007s13201-020-01272-6

Taillardat P Marchand C Friess DA Widory D David F Ohte N Nakamura T VinhTV Thanh-Nho N Ziegler AD (2020) Respective contribution of urbanwastewater and mangroves on nutrient dynamics in a tropical estuaryduring the monsoon season Mar Pollut Bull 160111652 httpsdoiorg101016jmarpolbul2020111652

Tan E Zou W Jiang X Wan X Hsu TC Zheng Z Chen L Xu M Dai M Kao SJ(2019) Organic matter decomposition sustains sedimentary nitrogen loss inthe Pearl River Estuary China Sci Total Environ 648508ndash517 httpsdoiorg101016jscitotenv201808109

Taniwaki RH Cassiano CC Filoso S de Barros Ferraz SF de Camargo PB MartinelliLA (2017) Impacts of converting low-intensity pastureland to high-intensitybioenergy cropland on the water quality of tropical streams in Brazil SciTotal Environ 584ndash585339ndash347 httpsdoiorg101016jscitotenv201612150

Thomas SM Neill C Deegan LA Krusche AV Ballester VM Victoria RL (2004)Influences of land use and stream size on particulate and dissolved materialsin a small Amazonian stream network Biogeochemistry 68(2)135ndash151httpsdoiorg101023BBIOG000002573466083b7

Thomas Y Courties C El Helwe Y Herbland A Lemonnier H (2010) Spatial andtemporal extension of eutrophication associated with shrimp farmwastewater discharges in the New Caledonia lagoon Mar Pollut Bull 61(7ndash12)387ndash398 httpsdoiorg101016jmarpolbul201007005

Thomaz EL Nunes DD Watanabe M (2020) Effects of tropical forest conversionon soil and aquatic systems in southwestern Brazilian Amazonia a synthesisEnviron Res 183109220 httpsdoiorg101016jenvres2020109220

Thorburn PJ Biggs JS Weier KL Keating BA (2003) Nitrate in groundwaters ofintensive agricultural areas in coastal Northeastern Australia Agric EcosystEnviron 94(1)49ndash58 httpsdoiorg101016S0167-8809(02)00018-X

Thuy HTT Nga LP Loan TTC (2011) Antibiotic contaminants in coastal wetlandsfrom Vietnamese shrimp farming Environ Sci Pollut Res 18(6)835ndash841httpsdoiorg101007s11356-011-0475-7

Tomaszewski M Cema G Ziembińska-Buczyńska A (2017) Influence oftemperature and pH on the anammox process a review and meta-analysisChemosphere 182203ndash214 httpsdoiorg101016jchemosphere201705003

Townsend SA Douglas MM (2000) The effect of three fire regimes on streamwater quality water yield and export coefficients in a tropical savanna(northern Australia) J Hydrol 229(3-4)118ndash137 httpsdoiorg101016S0022-1694(00)00165-7

Townsend SA Douglas MM (2004) The effect of a wildfire on stream waterquality and catchment water yield in a tropical savanna excluded from fire

for 10 years (Kakadu National Park North Australia) Water Res 38(13)3051ndash3058 httpsdoiorg101016jwatres200404009

Tromboni F Dodds WK (2017) Relationships between land use and streamnutrient concentrations in a highly urbanized tropical region of Brazilthresholds and riparian zones Environ Manage 60(1)30ndash40 httpsdoiorg101007s00267-017-0858-8

Uriarte M Yackulic CB Lim Y Arce-Nazario JA (2011) Influence of land use onwater quality in a tropical landscape a multi-scale analysis Landsc Ecol 26(8)1151ndash1164 httpsdoiorg101007s10980-011-9642-y

Valiela I Barth-Jensen C Stone T Crusius J Fox S Bartholomew M (2013)Deforestation of watersheds of Panama nutrient retention and export tostreams Biogeochemistry 115(1ndash3)299ndash315 httpsdoiorg101007s10533-013-9836-2

Valiela I Bartholomew M Giblin A Tucker J Harris C Martinetto P Otter M CamiliL Stone T (2014) Watershed deforestation and down-estuary transformationsalter sources transport and export of suspended particles in Panamanianmangrove estuaries Ecosystems 17(1)96ndash111 httpsdoiorg101007s10021-013-9709-5

Valiela I Bowen JL York JK (2001) Mangrove forests one of the worldrsquosthreatened major tropical environments BioScience 51(10)807ndash815 httpsdoiorg1016410006-3568(2001)051[0807MFOOTW]20CO2

Van Ha NT Takizawa S Oguma K Van Phuoc N (2011) Sources and leaching ofmanganese and iron in the Saigon River Basin Vietnam Water Sci Technol63(10)2231ndash2237 httpsdoiorg102166wst2011460

Van Rijn J (2013) Waste treatment in recirculating aquaculture systems AquacEng 5349ndash56 httpsdoiorg101016jaquaeng201211010

Vivier B David F Marchand C Thanh-Nho N Meziane T (2019) Fatty acids C andN dynamics and stable isotope ratios during experimental degradation ofshrimp pond effluents in mangrove water Mar Environ Res 150104751httpsdoiorg101016jmarenvres2019104751

Vuai SA Nakamura K Tokuyama A (2003) Geochemical characteristics of runofffrom acid sulfate soils in the northern area of Okinawa Island JapanGeochem J 37(5)579ndash592 httpsdoiorg102343geochemj37579

Ward ND Krusche AV Sawakuchi HO Brito DC Cunha AC Moura JMS da Silva RYager PL Keil RG Richey JE (2015) The compositional evolution of dissolvedand particulate organic matter along the lower Amazon River-Oacutebidos to theocean Mar Chem 177244ndash256 httpsdoiorg101016jmarchem201506013

Wengrove ME Ballestero TP (2012) Upstream to downstream stormwater qualityin Mayaguumlez Puerto Rico Environ Monit Assess 184(8)5025ndash5034 httpsdoiorg101007s10661-011-2318-x

Wetterstedt JAringM Persson T Aringgren GI (2010) Temperature sensitivity andsubstrate quality in soil organic matter decomposition results of anincubation study with three substrates Glob Chang Biol 16(6)1806ndash1819httpsdoiorg101111j1365-2486200902112x

Wilbers GJ Becker M Nga LT Sebesvari Z Renaud FG (2014) Spatial andtemporal variability of surface water pollution in the Mekong Delta VietnamSci Total Environ 485ndash486653ndash665 httpsdoiorg101016jscitotenv201403049

Williams MR Fisher TR Melack JM (1997) Solute dynamics in soil water andgroundwater in a central Amazon catchment undergoing deforestationBiogeochemistry 38(3)303ndash335 httpsdoiorg101023A1005801303639

Williams MR King KW (2020) Changing rainfall patterns over the Western LakeErie Basin (1975ndash2017) effects on tributary discharge and phosphorus loadWater Resour Res 56(3)e2019WR025985 httpsdoiorg1010292019WR025985

Zhang JZ Huang XL (2011) Effect of temperature and salinity on phosphatesorption on marine sediments Environ Sci Technol 45(16)6831ndash6837 httpsdoiorg101021es200867p

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Ziemann DA Walsh WA Saphore EG Fulton-Bennett K (1992) A survey ofwater quality characteristics of effluent from Hawaiian aquaculturefacilities J World Aquac Soc 23(3)180ndash191 httpsdoiorg101111j1749-73451992tb00767x

Publisherrsquos NoteSpringer Nature remains neutral with regard to jurisdictional claims inpublished maps and institutional affiliations


Abstract

Introduction

Logging

Pastures and ranches

Agriculture

Wildfire and intentional burning

Aquaculture

Urbanization

Conclusions and future research

Abbreviations

Acknowledgements

Authorsrsquo contributions

Funding

Availability of data and materials

Declarations

Ethics approval and consent to participate

Consent for publication

Competing interests

References

Publisherrsquos Note

IntroductionPrimary forests have been globally cut down with in-creasing human populations and expanding commercialland use in particular tropical forests have been lost fas-ter than those in other climate regions during the pastseveral decades (Gibbs et al 2010 Miettinen et al 2011Achard et al 2014 Rosa et al 2016) As a result for ex-ample the eastern lowlands of Sumatra and the peat-lands of Borneo lost approximately half of their peatswamps for conversion to industrial plantations from2000 to 2010 (Miettinen et al 2011) and the BrazilianAmazon lost 15 of the primary forest by 2010 (Maiaand Schons 2020) Not only inland forests but alsocoastal forests have been cut down quickly Tropicalcoasts and estuaries are often bordered by mangrove for-ests but it was estimated that 35 of global mangroveswere already lost from 1980 to 2000 (Valiela et al 2001)although recently the rate seems to be declining (Friesset al 2019) At the global level the gross loss of tropicalforests has been estimated to be 8 million ha per yearfrom 1990 to 2010 (05 annually Achard et al 2014)These deforested lands have been replaced with com-mercial lands for various purposes agricultural fields(eg rice soybeans and oil palm) aquaculture ponds orranching and poultry farms depending on the demandsof the region (Chen et al 2013 Richards and Friess2016)Generally tropical forests and their soil have higher

carbon (C) and nitrogen (N) stocks than those in otherclimate regions because of active photosynthesis andbiological N fixation throughout the year (Clevelandet al 1999 Jobbaacutegy and Jackson 2000 Hedin et al 2009Cloern et al 2014) Organic litter is fragmented into dis-solved and particulate organic matter (DOM and POMrespectively) and is mineralized into carbon dioxide(CO2) by bacteria faster in the tropics because of warmertemperatures (Wetterstedt et al 2010) When precipita-tion and throughfall pass through forest soils the con-centration of dissolved organic carbon (DOC) in the soilsolution gradually declines with soil depth because DOCtends to be adsorbed to soil particles (McDowell 1998)Because of organic matter decomposition the ammo-nium (NH4

+) concentration is relatively high in the sur-face soil but is gradually oxidized into nitrate (NO3

minus) assoil water moves downstream as groundwater (McDow-ell et al 1995 McDowell 1998) Phosphate (PO4

3minus) isalso regenerated from organic matter decompositionbut PO4

3minus tends to be adsorbed to soil and does not per-colate deeply into groundwater (McDowell et al 1995McDowell 1998) Thus stream waters surrounded bytropical primary forest and its downstream river and es-tuarine waters are usually enriched with dissolved inor-ganic carbon (DIC) and NO3

minus (McDowell 1998Miyajima et al 2009 Brookshire et al 2012 Noriega and

Araujo 2014) DIC and N exports from undisturbedtropical watersheds are generally higher than those fromtemperate watersheds because of the higher stock of or-ganic matter and active bacterial mineralization in theforest (Hedin et al 2009 Sarma et al 2011 Abril et al2014) However along with the disappearance of tropicalprimary forests less organic matter is produced on landand more organic matter is discharged downstream byincreased erosion which results in a reduction in thestock of soil organic C and N (Brown and Lugo 1990Brouwer and Riezebos 1998 Don et al 2011 Drakeet al 2019 Hattori et al 2019) Therefore the impact ofdeforestation on downstream limnological processes isexpected to be greater in tropical regions than in otherclimate regionsConversely artificial nutrient loading such as the ap-

plication of fertilizers increases with human land useafter deforestation because many human activities in-volve the use of nutrients (Downing et al 1999) In agri-culture more than half of applied fertilizers are oftennot recovered by plants but can accumulate in soilsvolatilize to the atmosphere or leach from the land toambient streams and rivers through groundwater or sur-face water runoff (Rocha et al 2019) The impact of fer-tilizers may remain in the soil even after several decades(Sebilo et al 2013) The fluxes of total N (TN) or NO3

minus

in rivers are correlated with population densities in thewatershed and TN fluxes have increased by 2- to 20-fold in temperate rivers since industrialization (Howarthet al 1996) although the trend is specific to the catch-ment and is also highly affected by climatic drivers suchas hydrology and temperature (Argerich et al 2013)The discharge of total phosphorus (TP) and PO4

3minus hasalso been increasing with wastewater discharge artificialdrainage systems and erosion (Nieminen et al 2017Williams and King 2020) Because tropical regions oftenexperience more rainfall than other climate regionsmore N and phosphorus (P) might be discharged withwater from tropical landsThe impacts of land-use change on downstream

aquatic processes have mainly been studied in temperateregions and some reviews are available (Howarth et al2011 Statham 2012 Bauer et al 2013) However re-views of the impacts on tropical regions are scarce(Downing et al 1999 Camara et al 2019 Thomaz et al2020) even though the impacts are expected to be dif-ferent from those seen in other climate regions as intro-duced above To summarize our present understandingof changing tropical aquatic processes the present art-icle reviews the impacts of various tropical land-usechanges on the water properties and biogeochemical cy-cles in adjacent streams rivers and estuaries We fo-cused on six major land-use changes (1) logging ofprimary forests (2) pasture including ranching (3)

Tanaka et al Ecological Processes (2021) 1040 of 21











Sources






+ DOCdarr DOCDON




Ling et al (2016)




























+










minus NH4+ PO4





rarr TDN NH4+


Neill et al (2001)





uarr SS NH4+ PO4

3minus


Deegan et al (2011)








3minus

darr NO3minus NH4

+ DINDIP

















+ and K+









minus











Sources









rarr NO3minus



minus PO43minus



rarr NO3minus



3minus








3minus




minus NH4+

rarr DON PO43minus

darr DO

Silva et al (2011)




rarr PO43minus

darr DO















Sources



Malmer (1996)


+

rarr PO43minus

Malmer (2004)



minus NH4+ TP PO4



uarr TNrarr SS TP






+







3minusChl ararr NO3

minus NO2minus




Vivier et al (2019)


+Anh et al (2010)


minus NH4+ Chl a


3minus

Islam et al (2004)






PO43minus

Molnar et al (2013)


Thomas et al (2010)


darr NO3minus NO2

minus

uarrdarr PO43minus






NO3minus and NO2











+















minus











Hua (2017)


rarr pHdarr DO



darr DO NO3minus

Kozaki et al (2016)



Hoang et al (2018)








3minus CODrarr NO3

minus NO2minus

darr DO







uarr NH4+ PO4

3minus

rarr NO3minus

darr DO



minus TP PO43minus



rarr SS NO3minus

darr DO



darr DO NO3minus

Silva et al (2012)



3minus BODdarr DO








+PP DOP PO4

3minus

rarr pHdarr DO



minus NH4+




Silva et al (2013)







3minus

darr DO NO3minus

















Declarations








































































































































































































































































Abstract

Introduction

Logging


Agriculture


Aquaculture

Urbanization


Abbreviations

Acknowledgements


Funding


Declarations



Competing interests

References












Sources






+ DOCdarr DOCDON




Ling et al (2016)




























+










minus NH4+ PO4





rarr TDN NH4+


Neill et al (2001)





uarr SS NH4+ PO4

3minus


Deegan et al (2011)








3minus

darr NO3minus NH4

+ DINDIP

















+ and K+









minus











Sources









rarr NO3minus



minus PO43minus



rarr NO3minus



3minus








3minus




minus NH4+

rarr DON PO43minus

darr DO

Silva et al (2011)




rarr PO43minus

darr DO















Sources



Malmer (1996)


+

rarr PO43minus

Malmer (2004)



minus NH4+ TP PO4



uarr TNrarr SS TP






+







3minusChl ararr NO3

minus NO2minus




Vivier et al (2019)


+Anh et al (2010)


minus NH4+ Chl a


3minus

Islam et al (2004)






PO43minus

Molnar et al (2013)


Thomas et al (2010)


darr NO3minus NO2

minus

uarrdarr PO43minus






NO3minus and NO2











+















minus











Hua (2017)


rarr pHdarr DO



darr DO NO3minus

Kozaki et al (2016)



Hoang et al (2018)








3minus CODrarr NO3

minus NO2minus

darr DO







uarr NH4+ PO4

3minus

rarr NO3minus

darr DO



minus TP PO43minus



rarr SS NO3minus

darr DO



darr DO NO3minus

Silva et al (2012)



3minus BODdarr DO








+PP DOP PO4

3minus

rarr pHdarr DO



minus NH4+




Silva et al (2013)







3minus

darr DO NO3minus

















Declarations








































































































































































































































































Abstract

Introduction

Logging


Agriculture


Aquaculture

Urbanization


Abbreviations

Acknowledgements


Funding


Declarations



Competing interests

References






















+










minus NH4+ PO4





rarr TDN NH4+


Neill et al (2001)





uarr SS NH4+ PO4

3minus


Deegan et al (2011)








3minus

darr NO3minus NH4

+ DINDIP

















+ and K+









minus











Sources









rarr NO3minus



minus PO43minus



rarr NO3minus



3minus








3minus




minus NH4+

rarr DON PO43minus

darr DO

Silva et al (2011)




rarr PO43minus

darr DO















Sources



Malmer (1996)


+

rarr PO43minus

Malmer (2004)



minus NH4+ TP PO4



uarr TNrarr SS TP






+







3minusChl ararr NO3

minus NO2minus




Vivier et al (2019)


+Anh et al (2010)


minus NH4+ Chl a


3minus

Islam et al (2004)






PO43minus

Molnar et al (2013)


Thomas et al (2010)


darr NO3minus NO2

minus

uarrdarr PO43minus






NO3minus and NO2











+















minus











Hua (2017)


rarr pHdarr DO



darr DO NO3minus

Kozaki et al (2016)



Hoang et al (2018)








3minus CODrarr NO3

minus NO2minus

darr DO







uarr NH4+ PO4

3minus

rarr NO3minus

darr DO



minus TP PO43minus



rarr SS NO3minus

darr DO



darr DO NO3minus

Silva et al (2012)



3minus BODdarr DO








+PP DOP PO4

3minus

rarr pHdarr DO



minus NH4+




Silva et al (2013)







3minus

darr DO NO3minus

















Declarations








































































































































































































































































Abstract

Introduction

Logging


Agriculture


Aquaculture

Urbanization


Abbreviations

Acknowledgements


Funding


Declarations



Competing interests

References














+ and K+









minus











Sources









rarr NO3minus



minus PO43minus



rarr NO3minus



3minus








3minus




minus NH4+

rarr DON PO43minus

darr DO

Silva et al (2011)




rarr PO43minus

darr DO















Sources



Malmer (1996)


+

rarr PO43minus

Malmer (2004)



minus NH4+ TP PO4



uarr TNrarr SS TP






+







3minusChl ararr NO3

minus NO2minus




Vivier et al (2019)


+Anh et al (2010)


minus NH4+ Chl a


3minus

Islam et al (2004)






PO43minus

Molnar et al (2013)


Thomas et al (2010)


darr NO3minus NO2

minus

uarrdarr PO43minus






NO3minus and NO2











+















minus











Hua (2017)


rarr pHdarr DO



darr DO NO3minus

Kozaki et al (2016)



Hoang et al (2018)








3minus CODrarr NO3

minus NO2minus

darr DO







uarr NH4+ PO4

3minus

rarr NO3minus

darr DO



minus TP PO43minus



rarr SS NO3minus

darr DO



darr DO NO3minus

Silva et al (2012)



3minus BODdarr DO








+PP DOP PO4

3minus

rarr pHdarr DO



minus NH4+




Silva et al (2013)







3minus

darr DO NO3minus

















Declarations








































































































































































































































































Abstract

Introduction

Logging


Agriculture


Aquaculture

Urbanization


Abbreviations

Acknowledgements


Funding


Declarations



Competing interests

References






Sources









rarr NO3minus



minus PO43minus



rarr NO3minus



3minus








3minus




minus NH4+

rarr DON PO43minus

darr DO

Silva et al (2011)




rarr PO43minus

darr DO















Sources



Malmer (1996)


+

rarr PO43minus

Malmer (2004)



minus NH4+ TP PO4



uarr TNrarr SS TP






+







3minusChl ararr NO3

minus NO2minus




Vivier et al (2019)


+Anh et al (2010)


minus NH4+ Chl a


3minus

Islam et al (2004)






PO43minus

Molnar et al (2013)


Thomas et al (2010)


darr NO3minus NO2

minus

uarrdarr PO43minus






NO3minus and NO2











+















minus











Hua (2017)


rarr pHdarr DO



darr DO NO3minus

Kozaki et al (2016)



Hoang et al (2018)








3minus CODrarr NO3

minus NO2minus

darr DO







uarr NH4+ PO4

3minus

rarr NO3minus

darr DO



minus TP PO43minus



rarr SS NO3minus

darr DO



darr DO NO3minus

Silva et al (2012)



3minus BODdarr DO








+PP DOP PO4

3minus

rarr pHdarr DO



minus NH4+




Silva et al (2013)







3minus

darr DO NO3minus

















Declarations








































































































































































































































































Abstract

Introduction

Logging


Agriculture


Aquaculture

Urbanization


Abbreviations

Acknowledgements


Funding


Declarations



Competing interests

References












Sources



Malmer (1996)


+

rarr PO43minus

Malmer (2004)



minus NH4+ TP PO4



uarr TNrarr SS TP






+







3minusChl ararr NO3

minus NO2minus




Vivier et al (2019)


+Anh et al (2010)


minus NH4+ Chl a


3minus

Islam et al (2004)






PO43minus

Molnar et al (2013)


Thomas et al (2010)


darr NO3minus NO2

minus

uarrdarr PO43minus






NO3minus and NO2











+















minus











Hua (2017)


rarr pHdarr DO



darr DO NO3minus

Kozaki et al (2016)



Hoang et al (2018)








3minus CODrarr NO3

minus NO2minus

darr DO







uarr NH4+ PO4

3minus

rarr NO3minus

darr DO



minus TP PO43minus



rarr SS NO3minus

darr DO



darr DO NO3minus

Silva et al (2012)



3minus BODdarr DO








+PP DOP PO4

3minus

rarr pHdarr DO



minus NH4+




Silva et al (2013)







3minus

darr DO NO3minus

















Declarations








































































































































































































































































Abstract

Introduction

Logging


Agriculture


Aquaculture

Urbanization


Abbreviations

Acknowledgements


Funding


Declarations



Competing interests

References





+







3minusChl ararr NO3

minus NO2minus




Vivier et al (2019)


+Anh et al (2010)


minus NH4+ Chl a


3minus

Islam et al (2004)






PO43minus

Molnar et al (2013)


Thomas et al (2010)


darr NO3minus NO2

minus

uarrdarr PO43minus






NO3minus and NO2











+















minus











Hua (2017)


rarr pHdarr DO



darr DO NO3minus

Kozaki et al (2016)



Hoang et al (2018)








3minus CODrarr NO3

minus NO2minus

darr DO







uarr NH4+ PO4

3minus

rarr NO3minus

darr DO



minus TP PO43minus



rarr SS NO3minus

darr DO



darr DO NO3minus

Silva et al (2012)



3minus BODdarr DO








+PP DOP PO4

3minus

rarr pHdarr DO



minus NH4+




Silva et al (2013)







3minus

darr DO NO3minus

















Declarations








































































































































































































































































Abstract

Introduction

Logging


Agriculture


Aquaculture

Urbanization


Abbreviations

Acknowledgements


Funding


Declarations



Competing interests

References





NO3minus and NO2











+















minus











Hua (2017)


rarr pHdarr DO



darr DO NO3minus

Kozaki et al (2016)



Hoang et al (2018)








3minus CODrarr NO3

minus NO2minus

darr DO







uarr NH4+ PO4

3minus

rarr NO3minus

darr DO



minus TP PO43minus



rarr SS NO3minus

darr DO



darr DO NO3minus

Silva et al (2012)



3minus BODdarr DO








+PP DOP PO4

3minus

rarr pHdarr DO



minus NH4+




Silva et al (2013)







3minus

darr DO NO3minus

















Declarations








































































































































































































































































Abstract

Introduction

Logging


Agriculture


Aquaculture

Urbanization


Abbreviations

Acknowledgements


Funding


Declarations



Competing interests

References







minus











Hua (2017)


rarr pHdarr DO



darr DO NO3minus

Kozaki et al (2016)



Hoang et al (2018)








3minus CODrarr NO3

minus NO2minus

darr DO







uarr NH4+ PO4

3minus

rarr NO3minus

darr DO



minus TP PO43minus



rarr SS NO3minus

darr DO



darr DO NO3minus

Silva et al (2012)



3minus BODdarr DO








+PP DOP PO4

3minus

rarr pHdarr DO



minus NH4+




Silva et al (2013)







3minus

darr DO NO3minus

















Declarations








































































































































































































































































Abstract

Introduction

Logging


Agriculture


Aquaculture

Urbanization


Abbreviations

Acknowledgements


Funding


Declarations



Competing interests

References





Hua (2017)


rarr pHdarr DO



darr DO NO3minus

Kozaki et al (2016)



Hoang et al (2018)








3minus CODrarr NO3

minus NO2minus

darr DO







uarr NH4+ PO4

3minus

rarr NO3minus

darr DO



minus TP PO43minus



rarr SS NO3minus

darr DO



darr DO NO3minus

Silva et al (2012)



3minus BODdarr DO








+PP DOP PO4

3minus

rarr pHdarr DO



minus NH4+




Silva et al (2013)







3minus

darr DO NO3minus

















Declarations








































































































































































































































































Abstract

Introduction

Logging


Agriculture


Aquaculture

Urbanization


Abbreviations

Acknowledgements


Funding


Declarations



Competing interests

References
















Declarations








































































































































































































































































Abstract

Introduction

Logging


Agriculture


Aquaculture

Urbanization


Abbreviations

Acknowledgements


Funding


Declarations



Competing interests

References




















































































































































































































































Abstract

Introduction

Logging


Agriculture


Aquaculture

Urbanization


Abbreviations

Acknowledgements


Funding


Declarations



Competing interests

References


the impact of tropical land-use change on downstream

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