lecture 3 fw habitats_2 slides
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LSM3254 Ecology of Aquatic Environments
Freshwater habitats
Darren Yeo
Dept of Biological Sciences
Objectives
To learn about:
Selected freshwater habitats and associated limnologicalconcepts
Freshwater habitats in Singapore
Scope
Watershed
Lentic habitat lakes, swamps
Lotic habitat streams
Freshwater habitats in Singapore
References:Dodson, S. 2005.Introduction to Limnology. McGraw-HillChapters 2, 11
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Watershed
Area of land that supplieswater to a lake or stream
= Area of land drainedbya lake or stream
Also known as catchmentor drainage
Note: Surface watershed maynot necessarily correspondwith groundwater watershed
Lentic environments
Standing water bodies
Lake
Large body of water, depth>3m, area >1-10 ha
Often shows thermalstratification
Pond Small body of water, area
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Lakes
The majority of freshwater resides in just a few large lakesCan you name them?
~60% of the worlds fresh water in three areas
Lake parameters
Lake morphometrics
Shape, area, volume
Shore length (=perimeter)
Varies with shoreline development
E.g., for given area,
- More elongate, with rough, folded shoreline longer shore length
- More circular, with smooth, simple shoreline shorter shore length
Measured shore length of lake
Index of shoreline development of lake= ------------------------------------------------------------
Shore length of a circular lake with same area
Minimum index value = 1
Higher index value!increased shoreline development
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Water budget: lake inputs and outputs
Residence time: amount of time water spends in lake (yr)= Lake volume/discharge rate
Discharge rate: rate of water output from lake (m3yr-1)
Flushing rate: rate of lake volume output (yr-1)= 1 / residence time
Lake parameters
6%+18% 12%
Lowest salinity,
nutrients,
productivity,
biodiversity
Highest salinity,
nutrients,
productivity,
biodiversity
Lake position (expressed as lake order)determines water input/output of lake
!influences chemical and biological characteristicsof lake
Seepage lakes: no surface inlets; ground water only (2, 1)
Drainage lakes: have surface outlets (1, 1, 2, 3)
Lake position in landscape
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Vertical stratification in lakes: Thermal, oxygen, light,biological, primary production
Thermal stratification: vertical pattern of temperature differencesalong a depth gradient
Water column divided into layers that resist mixing above 4 deg C: warmer water floats on top of cooler water
below 4 deg C: cooler water floats on top of warmer water
at 4 deg C: max density water sinks to lake bottom
Mixingof the water column - breakdown of stratification Wind-driven
Ecologically important
Oxygenation of bottom waters
Replenish nutrients in surface waters
Stratified lakes - oxygenation/temp regulation of upper layers
Vertical temperature profile
Graph of lake depth vs temperature
Depth plotted on y axis (vertical)
More diagrammatic representation
Fundamental to limnological
understanding
Thermal stratification gives rise to
other forms of stratification
(chemical, light, biological)
Vertical temperature profile
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Vertical temperature profile
Summer stratification Epilimnion
Warm, bright, less dense upper layer
Oxygen rich!higher concentration of fauna
Wind-driven mixing (within the layer)
Metalimnion
Transition zone
Includes thermocline where temperaturechanges most rapidly with depth
Hypolimnion
Cool, dark, denser lower layer Oxygen-poor!lower concentration of fauna
Winter stratification Very weak stratifiction
Reverse of summer
Cooler epilimnion
Warmer hypolimnion
Mixing prevented by ice cover
Isothermal lake Spring, autumn
No temperature change with depth
No layers
Mixed
Vertical temperature profile
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Winter
- Ice cover
-Reverse of summer stratification
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Cooler epilimnion floating on warmer hypolimnion
-Stratified lake
Autumn
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Epilimnion cools
-Cool water sinks
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Lake mixes
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Breakdown of
stratification
!Isothermal lake
Summer
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Epilimnion warms further, mixes
-Hypolimnion remains cool but is deeper,
i.e. thermocline descends
Annual pattern
on temperate
zone lake
Late spring
-Lake warms further
-Warmer epilimnion
floating on cooler
hypolimnion
!Stratified lake
Early spring
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Ice melts-Lake warms slightly
-Lake mixes
!Isothermal lake
Factors affecting thermal stratification
Time of year, location: affect annual/daily variation inenvironmental temperature
Lake depth: shallow vs deep lakes
Fetch:
Uninterrupted distance travelled by wind across lake !mixing of lake
But correlated with depth !stratification intact!deeper mixing ofepilimnion only (rather than whole lake)!pushes hypolimniondeeper
Topography: geographic features shielding lake from wind
Solutes: increased density!resist mixing
Vertical temperature profile
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Lake classification based on stratification/mixing patterns
Dimictic: biannual mixing (spring, autumn) and stratification (summer, winter)
Monomictic: annual mixing (autumn to spring) and stratification (summer only)
Amictic: no mixing
Polymictic: frequent, sometimes daily, mixing (afternoon through night) fromstorms and strong winds and stratification (mornings as sun rises) seen inmany shallow tropical lakes
Meromictic chemically stratified due to high solute concentration
Monimolimnion (dense, deep, non-mixing layer of salts)
Demarcated by pycnocline, depth with greatest density change (associated withchemocline- depth with most rapid [solute] change)
May stillbe thermally stratified above monimolimnion
Vertical temperature profile
Vertical oxygen profile
Vertical oxygen profileaffected by
Thermal stratification
Biological activity
Lake classification based on patterns of oxygenconcentration:
Orthograde
Spring, low production lakes, lower biological activity
Epilimnion (warmer, lower O2solubility) lower [O2]
Hypolimnion (cooler, higher O2solubility) higher [O2]
Clinograde
Summer, productive lakes, higher biological activity
Epilimnion (warmer, light, photosynthesis) higher [O2]
Hypolimnion (cooler, dark, decomposition) lower [O2]
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Vertical oxygen profile
Heterograde
Just below thermocline!peak [O2] (oxygen anomaly)
Low production lakes!deep light penetration Growth of hypolimnion algae (Algal plate)
Vertical light profile
Euphotic zone Upper layer with sufficient light for net primary production by
algae
From surface (100% light penetration) to 1% surface light
penetration depth
Compensation zone Just enough light for photosynthesis to support algae only
Net primary production = 0
Aphotic zone Insufficient light for photosynthesis to support growth
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Vertical light profile
Log
Light penetration Estimated using Secchi disk
Affected by:
Suspended particles (e.g.,phytoplankton, sediment)
Dissolved pigments (e.g.,tannins)
Depth/differentialabsorbance of colours(wavelengths) by water
Most strongly absorbed: IR,red, UV
Least absorbed: blue,green (most reflected)
Biological vertical profiles
Examples
Algae (phytoplankton) affected by light penetration
Bacteria and zoobenthos (bottom-dwelling
invertebrates) vertical profiles in the sediment
affected by [O2]
Zooplankton and fishes affected by physical (e.g.,
[O2]) and biological factors (e.g., predation)
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Diel Vertical Migration (DVM)
Daily pattern observed in zooplankton (small pelagic
animals)
Diurnal migration to deeper waters avoid predation from
visual predators
Depth limited by [O2]
Nocturnal migration to shallow waters faster growth and
reproduction
Also observed in larval fishes
Biological vertical profiles
Primary production vertical profiles
Net primary production (NPP): Energy in lakeecosystem (from photosynthesis) excludingmetabolic requirements (for respiration) of algaeand plants
Highest NPP surface waters (epilimnion) inagricultural and urban watersheds
Higher temperature
High light
High inorganic nutrients
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Primary production vertical profiles
Lake classification based on primary production
Eutrophic lake: High 1 production
Nutrient-rich
Abundant phytoplankton
Poor light penetration!turbid water due to phytoplankton
Photic zone!upper epilimnion Oxygen depleted (anoxic) hypolimnion
Oligotrophic lake: Low 1 production
Nutrient-poor
Low in phytoplankton Good light penetration!clear water
Photic zone!epilimnion to hypolimnion
Well oxygenated hypolimnion
Primary production vertical profiles
Lake classification based on primary production
Mesotrophic lake: Intermediate 1 production
Intermediate nutrient availability - between oligotrophic to eutrophicconditions
Dystrophic lake: Very low 1 production
Nutrient-poor abundant predacious plants
Low in phytoplankton
Low light penetration!dark water dissolved organic pigments
Oxygen depleted!anoxic hypolimnion
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Lake types and origins
Glacial lakes
Glaciation - a major processat higher latitudes
Deposited sediments(glacial till)!moraines,alluvial dams
Deposited icebergs!kettle ponds
Depressions/basins plunge basins, glacialscouring, proglacial lakes
Lake types and origins
Non-glacial lakes Oxbow lakes(billabongs, bayous)
erosion/sedimentation along streammeanders
Sinkholes dissolved limestone in karst
areas
Frost polygons thawed permafrost
Beaver ponds biological activity
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Lake types and origins
Crater lakes volcanicactivity
Rift lakes tectonicactivity along fault lines
Lake Pinatubo Lake Toba
Lake Baikal Lake Poso African Rift Lakes
Lakes types and origins
Inland, shallow wetlands
Coastal wetlands - part brackish
Tonle Sap
Chilka Lake
Lake Songkhla
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Natural lakes in
tropical SE Asia- Inland, shallow wetlands
- Coastal wetlands: part brackish
- Volcanic and tectonic lakes
Tasik Bera (Malaysia)
Tonle Sap (Cambodia)
Inle Lake (Myanmar)
Lake Songkhla (Thailand)
Lake Toba (Sumatra)
Lake Poso (Sulawesi)
Lake Pinatubo (Luzon)
Lake development Lakes have finite life spans
Gradually become shallower
Lakes!wetlands
Key process: sedimentation particles dropped bymoving water
Inorganic sediment (e.g., clay,silt, sand, etc.) in drainage lakes
Basins often deeper thanwater depth
Lake Baikal: 1741m water +>3000m of sediment
Organic sediment (e.g., peat
compressed, very slowlydecomposing plant material)
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Artificial Lakes
Reservoirs
Artificial pond or lake Created by construction of
a dam or barrage across a
Valley
Depression
River mouth
River basin
Morphology and hydrologydistinct from natural ponds
or lakes
Artificial Lakes
Reservoirs Often characterised by
dendriticshorelines
Different from natural lakes
TasikTemenggor
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Swamps
Wetland
Soil saturated with
water
Shallow standing water
(up to 1m depth)
Extensively vegetated
Grasses marsh or bog
Trees - swamp
Tasik Chini
Okeefenokee
Swamps Lentic environment
Low-lying area relative to surrounding topography
Water table at or close to the surface; prone to flooding
Substratum includes spongy, slowly rotting vegetation
Extensive root mats and macrophytes
Regulates water flow and quality - functions like a giant,landscape level sponge
Absorbs and holds excess water during rainy periods flood control
Slow release of trapped water during dry period maintain water flow
Natural filter for polluted runoff traps/absorbs pollutants and nutrients
Important habitat
E.g., Singapores Nee Soon Swamp Forest
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Lotic environments
Running or flowing waters(cf. lentic - standing waters)
Rivers
Streams (creek, crick, branch,rivulet, trace, brook )
Springs
Estuary
Stream parameters
Stream morphometrics Velocity: rate of downstream
movement
Gradient: decrease in elevationover fixed distance
Cross-sectional area ~0.5 x (greatest depth x width)
Discharge: volume of watercarried per unit time
Velocity x Cross-sectional area
High discharge:
Spates: Small pulses
Floods: major peaks
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Stream order
Streams classified based on position in landscape
Assignment of stream order based on joining of two
streams of previous order
First Order:
permanent stream
originating from
ground water; no
other streams joining
Second Order:
Joining of two first
order streams
Third Order: Joining
of two second order
streams
Joining of a lower order
stream does not raise
the order of the stream
River Continuum Hypothesis
Low order streams
Heavily shaded; allochthonous input
coarse particulate organic matter (CPOM)e.g., falling leaves
Shredders(that break up CPOM) dominate
Intermediate order streams
More open; autochthonousinputaquatic algae and
plantsand allochthonous inputfine particulate organic
matter (FPOM)from upstream Scrapers/grazersand filter feeders/collectorsdominate
High order streams
Open; allochthonousinput
FPOM (photosynthesis
inhibited by turbid water)Filter feeders/collectors
dominate
Predicting downstream characteristics of temperatestreams
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References Singapore freshwater habitats
Corner EJH, 1978. The Freshwater Swamp-forest of South Johore and Singapore. BotanicGardens, Parks and Recreation Department, Singapore. 266 pp.
Johnson DS, 1973. Freshwater life. p. 103-127. In: Chuang, S. H. (ed.).Animal Life and Nature inSingapore.Singapore University Press. xiv + 302 pp.
Lim KKP, Ng PKL, 1990.A Guide to the Freshwater Fishes of Singapore.Singapore Science
Centre, Singapore. 160 pp.
Ng PKL, 1991.A Guide to the Freshwater Life in Singapore. Singapore Science Centre,Singapore. 162 pp.
Ng PKL, Lim KKP, 1999. The diversity and conservation status of fishes in the nature reserves of
Singapore. Proceedings of the Nature Reserves Survey Seminar (1997). Gardens Bulletin,
Singapore, 49: 245265.
Tan HTW, Chou LM, Yeo DCJ, Ng PKL, 2010. The Natural Heritage of Singapore, 3rd Edition.
Pearson Prentice Hall. 323 pp.
Turner IM, Boo CM, Wong YK, Chew PT, Ibrahim A, 1996. Freshwater swamp forest in
Singapore, with particular reference to that found around the Nee Soon firing ranges. Gardens
Bulletin, Singapore,48: 129157.
Yeo DCJ, Wang LK, Lim KKP (eds.), 2010. Private Lives: An Expos of Singapores Freshwaters.
Raffles Museum of Biodiversity Research. 258 pp.
Ng PKL, Corlett RT, Tan HTW (eds.), 2011. Singapore Biodiversity: An Encyclopedia of the
Natural Environment and Sustainable Development. Editions Didier Millet.
Freshwater habitats in Singapore
Up to two-thirds or more of Singapores land area iswater catchment
Much of Singapores original freshwater habitats lost ormodified
High biodiversity - including rare and endangeredspecies
Singapores freshwater habitats can be broadly classifiedinto three categories: Natural
Urban (artificial or modified) Ephemeral
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Classification of habitats in Singapore
Natural habitats
Tend to be refuges for native aquaticspecies
Tree-country forest streams (primary,secondary forest)
Freshwater swamp
Urban habitats (artificial of modified)
Artificial or modified ecosystems
Tend to have more exotic species Open-country rural streams
Concrete canals, drains
Reservoirs (inland, coastal)
Park/garden/landscape ponds
Ephemeral habitats
In natural areas, e.g., pools, temporarystreams in forests
In artificial areas, e.g., marshland?
Natural freshwater ecosystems
Rivers and streamsAbsence of large rivers
Original large natural freshwater ecosystems - small rivers e.g., Sungei Kranji, Sungei Seletar, Sungei Kallang, Singapore River
But now almost all drowned or heavily modified
Absence of native large river species
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Natural freshwater ecosystems
Forest streams
Primary/secondary rain-forests
Bukit Timah and Central Catchment NatureReserves
Mostly flowing into inland reservoirs
Few, if any, torrent streams
Natural/unmodified environmentalconditions
Shallow (
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Natural freshwater ecosystems
Nee Soon Swamp Forest (contd)
Natural/unmodified environmental conditions
Slow-flowing streams draining into shallow, oftenflooded, valleys
Saturated, waterlogged soils - unstable and anaerobicsubstratum
Plants with some similar adaptations to mangrove plants
stilt or prop roots
breathing roots (pneumatophores)
Clear, stained (by tannins from decaying vegetation),soft, acidic (typically 28 deg C
Little any leaf litter or woody debris
Algae and macrophytes
Different environmental conditions (cf.forest streams) Open, deeper, less acidic waters
Few robust, adaptable native aquaticspecies
More exotic species better adapted to
modified conditions. E.g.,
Small species
Species associated with higher pH andtemperature waters
Guppy (Poecilia reticulata)
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Name that reservoir
Bedok
Jurong Lake
KranjiLower Peirce
Lower Seletar
MacRitchie
MarinaMurai
Pandan
Poyan
PunggolSarimbun
Serangoon
Tekong
TengehUpper Peirce
Upper Seletar
Artificial/modified freshwater ecosystems
Reservoirs
17 reservoirs for domestic/industrial use
Artificial equivalents of natural lentic habitats (i.e. lakes),which are absent
Damming natural river drainages or river basins Protected and Urban/Unprotected catchments
Inland reservoirs and coastal (estuarine) reservoirs
Inland reservoirs dams at headwaters/upper reaches
Coastal (estuarine) reservoirs barrages at river mouth or acrosscommon basin
Take years to flush out salt water
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Artificial/modified freshwater ecosystems
Different environmental conditions (cf. foreststreams)
Open, deeper, less acidic, sluggish to standing waters
Few robust, adaptable native aquatic species
More exotic species better adapted to modified conditions.E.g.,
Large river/lentic species
Species associated with higher pH and temperature waters
Artificial/modified freshwater
ecosystems
Ponds Small, mostly isolated in parks, golf courses and
disused granite quarries
Canals
Heavily modified rivers/streams, especially thoseflowing through urban areas
Canalisation - straightening, deepening, widening,and cementing of the banks and substrates
Canalised for: Flood control
Mosquito control
Exposed to urban runoff and pollution
Harsh, exposed environmental conditions Warm, hard, often polluted, shallow waters
Bare concrete substratum
Frequent and severe flash flooding
Few robust, adaptable natives
More exotic species. E.g., Species associated with hard, high pH and temperature
waters