the use of planktons as tools for monitoring water quality

Vol. 6(9), pp. 181-193, November 2014 DOI: 10.5897/JTEHS2014.0320 Article Number: C9B3E6549020 ISSN 2006-9820 Copyright © 2014 Author(s) retain the copyright of this article http://www.academicjournals.org/JTEHS

Journal of Toxicology and Environmental Health Sciences

Full Length Research Paper

The use of planktons as tools for monitoring water quality in oil polluted streams of the Niger Delta, Nigeria

Amaeze Nnamdi Henry1* and Onyema Ikenna Charles2

1Ecotoxicology Laboratory, Department of Zoology, University of Lagos, Akoka-Yaba, Lagos, Nigeria. 2Marine Biology Unit, Department of Marine Sciences, University of Lagos, Akoka-Yaba, Lagos, Nigeria.

Received 10 October 2014; Accepted 24 November, 2014

The Niger Delta ecosystems of Nigeria, typically consisting of mangrove swamps and riparian forests, have come under threat in the last six decades as a result of environmental pollution from oil exploration, drilling, refining and transportation. This study examines two Niger Delta streams (Ogba Evie and Otor) to ascertain the extent of hydrocarbon and heavy metal pollution and the status of the biotic communities in them. The physicochemical parameters of surface water samples indicate that dissolved oxygen is significantly lower in Ogba Evie stream which had some of its surface covered with oil films compared to Otor stream. Oil and grease levels were, however, well within the National Environmental Standards and Regulation Enforcement Agency (NESREA) safety limits. Both streams had high concentrations of polycyclic aromatic hydrocarbons (PAHs) and several heavy metals. Overall, the diversity indices point to low phytoplankton and zooplankton species diversity and abundance. Phacus curvicauda Swirenko was the most abundant phytoplankton in the Ogba Evie stream, while Synedra ulna (Nitzsch) Ehrenberg was predominant at the Otor stream. The copepod, Cyclops strenuus Fisher was the most abundant zooplankton common to all sections of both streams. Although, no significant relationship was observed between PAH and plankton abundance, the trend observed in both streams may be a reflection of their present-day pollution rates. Key words: Oil spill, biotic indices, water quality, hydrocarbon pollution, biomonitoring.

INTRODUCTION The global oil industry over the years have become synonymous with spills, especially during drilling operations, accidents involving oil tankers or offshore platforms, incidental release of bunker fuels from ships transportation of crude oils (Dominicis et al., 2011) as well as violent situations (Zodiatis et al., 2011). The environmental and financial costs of large scale oil spills are high (Loureiro et al., 2009), threatening to erase the

economic gains which it accords oil producing countries and equally fuelling a global zeal for alternative energy sources as well. With accidental oil spills accounting for 10 to 15% of global oil spills (European Environmental Agency, 2013 cited in Alves et al., 2014), there is an increasing demand to improve contingency plans and effect monitoring measures particularly in inland and near shore waters.

*Corresponding author. E-mail: [email protected] Tel: +2347066302345.

Author(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution License 4.0 International License

182 J. Toxicol. Environ. Health Sci. Inland waters just like confined marine basins, narrow seaways or interior seas around island groups are particularly susceptible because of their smaller sizes and shorter spill arrival time to their coastline (Alves et al., 2014). Oil spills such as MV Exxon Valdez accident of 1989 in South Alaska which impacted seriously on sensitive aquatic biodiversity presents a classical case of a spill in a relative confined shoreline (Peterson et al., 2003). Recent spill incidents such as Haven tanker in the Mediterranean sea (Coppini et al., 2011), MV Pres-tige and MV Erika oil spills in the North Atlantic Ocean (Tronczynski et al., 2004; Gonzalez et al., 2006) together with those resulting from conflicts around the middle east, continue to bring to the fore environmental health risk which oil industry activities pose to aquatic ecosystems worldwide even in countries with the most sophisticated drilling models and contingency plans.

The Niger Delta region of Nigeria has been under sustained pressure from oil pollution especially inland waters such as creeks, rivers and streams, around exploration sites since the onset of crude oil exploration in the country in 1956 (Celestine, 2003; Tolulope, 2004; Kadafa, 2012). This has rendered numerous water bodies in this area unable to sustain the teeming aquatic life associated with mangrove swamp ecosystems. A number of onshore oil exploration sites in the Niger Delta are located within or around fresh water and brackish mangrove swamps, which have been impacted by oil spill incidents in the region (Luiselli and Akani, 2003). The Niger Delta is the largest mangrove swamp in Africa (Awosika, 1995) and is estimated as the third largest in the world (Powell, 1985; Kadafa, 2012). Its sediment fill is made up of over 12,000 meters of shallow marine sediments and deltaic sediments from the River Niger watershed (Nwilo and Badejo, 2001). This area is said to harbour a vast array of flora and fauna inhabiting both terrestrial, riparian and aquatic ecosystems (Uyigwe and Agho, 2007; Nenibarini, 2004), areas which are often exposed to oil spills from vandalism (Nenibarini, 2004), and exploratory accidents (Ukoli, 2005).

Since the first discovery of oil by Shell in 1956, approximately 1.5 million tons of oil has been spilled within the Niger Delta over several decades, most of which only was partially cleaned or not cleaned at all (Onuoha, 2008; Kadafa, 2012). The problem of spills in Nigeria is worrisome given the frequency of reported and unreported oil spills (Odu, 1989; NDES, 1998) and the persistence of pollution effects several years after spills (Jackson et al., 1989; Teal et al., 1992; Otitoloju et al., 2007). Recent major oil spills reported in Nigeria include the 1998 Mobil Oil spills, the 2001 Shell Ogbodo and Ogoni oil spills, the Exxon Mobil Oil Spill in 2010 and the Shell Bonga field oil spill in 2011. These were documented in local and international media but there is still a paucity of scientific publications on environmental impacts (Luiselli and Akani, 2003). Although, efforts are often made to mitigate effects, clean up processes are often slow due to bureaucracy, conflict of interests among regulatory

organizations, improper contingency plans, and general apathy of oil companies towards the process.

Oil pollution releases polyaromatic hydrocarbons (Olajire et al., 2005) and heavy metals into the environment (Osuji and Onajake, 2004), substances that have been considered as capable of bioaccumulation, causing toxic effects and disrupting aquatic ecosystems (Otitoloju and Don-Pedro, 2002, 2004; Obire et al., 2003; Jack et al., 2005; Ibiene et al., 2011). The Nigerian coastline is also dotted with the sale and transfer of refined petroleum products, with numerous illegal refineries often releasing some form of refined crude oil into the environment. Hudson et al. (1977) reported that processed oils were more toxic to microbial populations in controlled ecosystem pollution experiments, resulting in the inhibition of heterotrophic uptake and minerali-zation of D-glucose-11C. An oil spill impact, similarly to any other ecological disaster, is often catastrophic at the outset but quickly dissipates in the short term as biodegradation and natural physicochemical processes set in. In a study investigating the impact of oil spill in an estuary, Lytle (1975) reported drastic changes in diversity and numbers of fish population coupled with initial reductions in zooplankton populations and phytoplankton boom. Therefore, the effects of oil spill in ecosystems remains poorly understood and rather controversial. This therefore implies that there is need for more ecosystem based studies particularly in the Nigerian Niger Delta where spills have become common place. MATERIALS AND METHODS Description of sampling sites Sampling was conducted in two streams (Otor and Ogba Evie), which are located in Isoko South Local government areas of Delta State, Niger Delta (Figure 1). Both streams are close to oil exploration sites; the Ogba Evie stream runs along an active well head, whereas the Otor stream runs beside an old abandoned well head. Both streams are shallow and short and experience seasonal flooding at the height of the rainy season. Sampling design Sampling was carried out once in the two streams during the rainy season of 2011. Samples were collected in two sites- upstream and downstream of both water bodies. Sampling in the dry season was hampered by civil unrest around the study communities. At each sampling site, water and sediments were obtained for chemical and biological assessments. Sampling operations Surface water sampling: Water samples from both streams were collected using 250 ml amber glass bottles for hydrocarbon analysis and 1 litre plastic kegs for heavy metals and physico-chemical analysis. In each instance, sampling was repeated three times and water pulled into a composite to represent a sampling location. Samples for heavy metal assessment were initially fixed with few drops of concentrated HNO3 and all samples were stored at 4°C

Amaeze and Onyema 183

Figure 1. Sampling sites in the Ogba Evie and Otor streams, Niger Delta, Nigeria.

prior to analysis with 48 h post collection. Sediment sampling: Both water bodies were shallow and it was possible to collect bottom sediment with a hand trowel at locations where surface water samples were collected and the samples were wrapped in aluminum foils. The trowel was washed with clean water before its use to sample at other locations to minimize cross contamination. Sampling of phytoplankton and zooplankton: At each study site, water samples (1000 ml) were also collected with the Ruthner water sampler from subsurface water (approximately 15 to 20 cm below surface) and filtered. It was then fixed with approximately 5 ml of 4% formalin solution before transferring to the laboratory for plankton analysis. Fish Sampling: Fishing exercise was conducted using locally fabricated baited hook and lines to determine the fin fish species present in both water bodies. Analysis of samples Physicochemical characteristics: The physicochemical analysis of water samples were conducted using standard methods (APHA, 1998) and calibrated probes. The pH, electrical conductivity (EC) and total dissolved solid (TDS) were measured with Metler Toledo (Model In lab 730), and dissolved oxygen (DO) was determined in situ using a Jenway DO meter. Turbidity was determined using

HACH DR 2000 direct spectrophotometer method 8237 and then estimated against deionized water as blank at 450 nm. Total suspended solids (TSS), turbidity, nitrate (NO3-N), phosphate (PO4

3- -P) and sulphate (SO42-) were determined using HACH DR

2000 equipments. Acidity, alkalinity, chloride ion (Cl-) and biological oxygen demand (BOD) were analyzed volumetrically (APHA, 1998). Water samples were incubated in the dark for 5 days at 20°C in BOD bottles so as to determine the BOD in mg/l. Chemical oxygen demand (COD) were analyzed by Winkler's titrimetry method (APHA, 1998). Heavy metals analysis: The concentration of heavy metals in water and sediment samples were analyzed by Alpha-4 cathodeon atomic absorption spectrophotometer (AAS) by comparing their relative absorbance to those of mixed metal elements standards (Sigma Aldrich) (APHA 1998). The water samples were first filtered and digested using IM HNO3. The sediment samples were earlier air dried under a ceiling fan, ground in ceramics mortar and sieved using 200 µm diameter sieve to homogenize the particles followed by digestion (Don-Pedro et al., 2004). All glass wares for heavy metal analysis were subjected to prior cleaning by acid wash. Assessment of polycyclic aromatic hydrocarbons: PAHs were analyzed using a gas chromatography mass spectrometer (GC-MS). Water and sediment extraction were carried out using dichloromethane and n-hexane, followed by analysis using the ASTMD 2887-93 and US EPA 1664 methods (ASTM 1997). The samples were subsequently analysed on already calibrated Agilent 4890D gas chromatography/ flame ionization detector (Doherty and

184 J. Toxicol. Environ. Health Sci.

Table 1. Physicochemical characteristics of surface water from the Ogba Evie and Otor streams.

Parameters Ogba evie stream Otor stream

Nesrea limit I II II II

Temp. °C 30.0 29.3 32.6 32.7 <40 pH 5.74 6.21 6.5 5.3 6.5-8.5 EC (µS/cm) 83 944 146 2612 NS D.O (mg/l) 3.26 4.56 11.0 11.3 4 Cl- (mg/l) 1.24 120 44 140 350 SO3

2- (mg/l) 0.80 88 36 104 500 CN- (mg/l) ND ND ND ND NS H2S (mg/l) 0.22 0.24 0.34 0.12 NS PO4-P (mg/l) 0.28 0.33 0.41 0.26 5 NO3-N (mg/l) 0.24 0.18 0.31 0.18 20 Oil and grease (mg/l) 1.20 0.16 0.32 0.14 10 TSS (mg/l) 120 29 28 52 30 TDS (mg/l) 40 471 72 1305 2000 Turb.(NTU) 250 34 34 79 10

ND Not Detected Otitoloju, 2012). Plankton and fish species assessment Plankton samples were allowed to settle in the lab for at least 48 h and concentrated to 20 ml. For each settled sample, 5 drops of well mixed sample was investigated. On each occasion, one drop of sample (0.1 ml) was thoroughly investigated using the drop count method (Onyema, 2007). The mount was thoroughly investigated and counts were made per species and recorded using a Carl Zeiss monocular microscope. An average of 5 outcomes of this procedure was carried out per sample and averaged. The species identification were done using various texts (Smith 1950; Hendey, 1958; Wimpenny, 1966; Nwankwo, 2004; Rosowski, 2003). The fishes observed in the field were identified in situ and confirmed in the laboratory using a field guide to Nigerian freshwater fisheries (Olaosebikan and Raji, 1998). Statistical analysis The relationship between key chemical characteristics of the surface water samples and the plantktonic communities were determined using independent sample t test (SPSS 16). The plankton species diversity were estimated using different indices including (Shannon and Wiener, 1963; Margalef, 1951; Ogbeibu, 2005). RESULTS Physical and chemical characteristics of the water and sediment samples The results from the physicochemical analysis indicated that conditions at both streams were typical of the tropics, with surface temperatures of about 30°C in both Ogba

Evie and Otor streams (Table 1). The surface water pH was within NESREA (National Environmental Standards and Regulations Enforcement Agency) limit in both streams with values ranging from 5.74 to 6.21 and 5.3 to 6.5 at Ogba Evie and Otor, respectively. Conductivity, chloride ions, sulphates and total dissolved solids (TDS) were generally lower downstream and higher values were generally measured in the Otor stream. Also, DO was higher at Otor with values of at least 11.0 mg/l while Ogba Evie had values lower than the NESREA limit of 4.0 mg/l in the upstream location. The concentrations of hydrogen sulphide (H2S), total phosphates (PO4-P) and nitrates (NO3-N) in both streams remained <1.0 mg/l across sampling sites. Oil and grease levels were higher in water samples from the Ogba Evie stream but values were significantly lower (P<0.05) than the NESREA limit of 10 mg/l. The oil and grease levels as well as total suspended solids (TSS) and turbidity were highest at the upstream site in Ogba Evie (Table 1). Assessment of the sediment samples indicated that the oil and grease levels were relatively stable across sampling sites in both streams. The organic matter parameters (NO3-N, PO4-P and SO3

2-) were generally high and stable across sampling sites in both streams (Table 2). The chloride concentrations and the electrical conductivity were also stable across the sites (Figure 2).

The chemical assessment of the surface water and sediment samples from both streams indicate widespread pollution with aliphatic and polycyclic aromatic hydro-carbons as well as considerable levels of heavy metals (Table 3). Upstream sites had slightly higher aliphatic hydrocarbon concentrations than the downstream sites (P>0.05). In the Otor stream, total aromatic hydrocarbons (TAH) concentrations in the sediments were 11 and 10


Table 2. Physicochemical parameters sediment samples from the Ogba Evie and Otor streams.

Streams Oil and grease

(mg/l) NO3-N (mg/l)

PO4-P (mg/l)

SO32-

(mg/l) Chloride

(mg/l) Conductivity

(µS/cm)

Ogba Evie

I 4.46 29.21 53.22 67.31 19.22 1.17 II 3.36 27.54 48.26 66.21 20.21 1.18

Otor I 4.28 32.55 45.44 66.24 18.54 1.46 II 5.46 28.55 52.33 64.21 18.24 1.12

Table 3. Chemical characteristics of surface water (mg/l) and sediment samples (mg/kg) from the Ogba Evie and Otor streams.

Parameters

Ogba Evie Otor

Surface water Sediment Surface water Sediment

I II I II I II I II

Ʃ Aliphatic hydrocarbons (TAH) 40.61 37.78 29.89 29.14 29.89 29.14 343.61 301.83 Ʃ 16 EPA PAH 6.32 10.38 40.21 37.93 40.21 37.93 133.35 174.38 Phenol 0.55 1.24 1.83 ND 1.83 ND 3.48 4.56 Ba 1.34 2.12 1.80 1.60 1.80 1.60 102 111 Cr ND ND ND ND ND ND 5.48 6.21 Cu ND ND ND ND ND ND 3.67 6.56 Fe 0.08 0.04 0.02 0.06 0.02 0.06 12890 11234 Mn 0.02 0.01 0.03 0.04 0.03 0.04 120 130 Ni 0.05 0.07 0.06 0.08 0.06 0.08 7.56 7.33 Pb 0.70 1.10 0.92 1.09 0.92 1.09 5.67 6.88 V 0.04 0.05 0.04 0.05 0.04 0.05 5.88 6.32 Zn 0.02 ND ND ND ND ND 36.58 38.54

Not detected (ND) times higher than those in the surface water samples for the upstream and downstream areas, respectively. PAH and TAH concentrations were significantly higher in sediments than in water samples. The Otor stream also had higher PAH values than Ogba Evie, particularly in sediments. Phenol was also measured in the surface water samples, and Otor stream sediments also had higher levels. Overall, Otor stream sediments also had higher heavy metal levels than those of Ogba Evie in both upstream and downstream sites (P<0.05), with chromium (Cr) and copper (Cu) occurring exclusively in its sediment samples (Table 3). Iron (Fe) had the highest concentrations in both streams. The recorded values were several thousand folds higher in sediments when compared to the surface water. The physical appearance of Ogba Evie stream was indicative of recent oil pollution (Figure 2a) compared to Otor stream (Figure 2a). Phytoplankton and Zooplankton communities in both streams

The checklist of phytoplankton taxa at the upstream and downstream sites of both streams is provided in Table 4.

Three divisions of phytoplanktons including Bacillariophycta, Cyanophyta and Euglemophta were recorded at Ogba Evie stream. Euglenophyta was the most dominant taxa (Figure 3a). The Euglenales, Phacus curvicauda was the most abundant species. At Otor stream, only division Cyanophyta and Bacillariophyta were recorded in the water samples (Table 4) with the Bacillariophycae being significantly higher (P<0.05) in population (Figure 3b). Synedra ulna was the most abundant phytoplankton in Otor stream. The plankton species diversity assessment indicates that the species number and variety at Ogba Evie stream did not show a consistent trend. However, both upstream and downstream sites had similar dominance index values. The Otor stream, however, shows a clear distinction between the upstream and downstream sites, with the latter sites indicating a richer diversity (Table 4). The zooplankton taxa identified in both sampling sites of the streams are presented in Table 5. They include rotifers, branchiopods, calanoid and cyclopod copepods and copepods larvae. The dominant zooplankton group in both streams were the cyclopoid copepod - Cyclops strenus (Figure 4a and b). The species diversity indices indicate that the upstream sampling sites in both streams


Figure 2a. Oil sheen over an upstream section of the Ogba Evie stream.

Figure 2b. A section of the Otor stream.

had higher zooplankton species in number and variety.

The upstream sites also had higher equitability index of 1.00 each and had more uniform distribution of species compared to the downstream sites. The structure of the zooplankton communities as described by the Simpson's Dominance Index indicates that the downstream site of the Ogba Evie stream with value 0.17, has no clear dominant species compared to its upstream site. In the Otor stream, there was no clear difference in the dominance structure in both sites (Table 5). Although, there was no significant relationship (P>0.05) between the chemical characteristics of the surface water (TAH, PAH) and the number planktons observed. The Ogba Evie stream, showing lower levels of TAH and PAH, recorded higher levels of both phytoplankton and zooplankton populations (Figure 5).

Fish species assessment Results from fish species assessment indicated that both streams were poor on fish species. Hemichromis faciatus was the only species detected at Otor stream while at Ogba Eivie, the African lung fish Protopterus sp. breeding sites were identified. DISCUSSION Oil spills during crude oil exploration and production activities is inevitable (Otitoloju, 2005). Therefore, surrounding land and water bodies are in constant threat of the resulting damaging effects. The findings from this paper indicate some level of hydrocarbon pollution in


Table 4. Phytoplankton species (No of cells M-1-1) in water samples obtained from the Ogba Evie and Otor streams.

Sampling stations Ogba Evie Otor

I 11 I 11

Phytoplankton Taxa Division – Bacillariophyta

- - - -

Class-Bacillariophyceae - - - - Order I – Centrales - - - - Aulacoseira granulata Ehrenberg (Ralfs) - - - 5 Aulacoseira granulata var. angstissima Muller - - - 10 Order II – Pennales - - - - Pinnularia major (Kutzing) Rabenh - 5 - - Pinnularia gibba Ehrenberg - 10 - - Synedra ulna (Nitzsch) Ehrenberg - - - 40 Synedra ulna var. biceps Ehrenberg - - - 25 Synedra sp. 20 - - - Division – Cyanophyta - - - - Class – Cyanophyceae - - - - Order – Hormogonales - - - - Nostoc sp. 5 - - - Lynbgya martensiana Meneghini - - 5 10 Oscillatoria limnosa Agardh - - - 5 Division – Euglenopohyta - - - - Class – Euglenophyceae - - - - Order – Euglenales - - - - Euglena acus Ehrenberg sp. 30 10 - - Trachelomonas hispida (Perry) Stein 10 5 - - Phacus curvicauda Swirenko 40 15 - - Phacus acuminatus Stokes 5 10 - - Phacus sp. 25 - - - Total species diversity (S) 8 6 1 6 Total abundance (N) 135 55 5 95 Log of Species diversity (Log S) 0.90 0.78 0.00 0.78 Log of abundance (Log N) 2.13 1.74 0.70 1.98 Shannon-Wiener Index (Hs) 0.79 0.75 0.00 0.65 Menhinick Index (D) 0.69 0.81 0.45 0.62 Margalef Index (d) 1.43 1.25 0.00 1.10 Equitability Index (j) 0.88 0.96 0.00 0.84 Simpson’s Dominance Index (C) 0.19 0.19 1.00 0.27

both streams resulting from recent and past oil drilling. The fact that the Otor stream abandoned well head still had substantial amount of hydrocarbons nearby should imply that these compounds are retained in the environ-ment for long periods. The higher concentrations of aliphatic and polycyclic aromatic hydrocarbons recorded in sediments of the Otor stream could therefore be linked to longer and more substantive historic contamination compared to the Ogba Evie. The lower levels of PAH in surface water of the Ogba Evie may be linked to its sloppy course which gives it a higher flow rate compared to Otor. Despite these results, a significant level of heavy metal pollution was absent in both streams. The chemical

properties of the surface water samples in both streams did not indicate any significant deviation from local standards. However, lower DO levels at Ogba Evie could be linked to its close proximity to an active exploration site. The oil films over most of the surface of a shallow and slow flowing stream such as Ogba Evie, coupled with activities of hydrocarbon degrading microrganisms which actively use up available oxygen would results in depletion of the DO levels over time. Continuous spill from oil drilling activities at the active well head, coupled with the low rate of surface water refreshment would imply that the depleting oxygen content of the water would not be balanced fast enough, leading to changes in


020

4060

80

Bacillariophyta

Cyanophyta

Euglenopohyta

Percentage abundance (%) Figure 3a. Relative abundance of the phytoplankton community in the Ogba Evie stream.

020

4060

80

Bacillariophyta

Cyanophyta

Percentage abundance (%) Figure 3b. Relative abundance of the phytoplankton community in the Otor stream.

biotic composition of such a water body. Although, sampling was done in the rainy season, a period characterized by high and frequent rainfall in this region, large scale spills prevents speedy surface water renewal. This may be further compounded by drifts of debris and decomposing leaves along surface runoffs into the stream. Large forest canopies, and trees with broad leaves, also limit the rate at which rain reaches the ground and water bodies.

The investigation of the plankton species variety and abundance was also conducted to draw key ecological process conclusion which would be useful for future biomonitoring efforts. Bott et al. (1978) reported in their study involving three crude oils that various benthic algal

communities exhibit differential responses of growth inhibition and enhancement. This indicates that a blanked assessment of plankton number is less important than the species observed when assessing the pollution rates of an aquatic ecosystem. Given their simple nature and their ability to respond to changes in water quality, plankton microalgae qualify as suitable bioindicators (Onyema, 2007).

The plankton species observed in this study were higher in number and diversity at the Ogba Evie stream, which had significantly lower total PAH levels than the Otor stream. However, no significant relationship could be interpreted between plankton abundance and hydrocarbons in the two streams. Nwankwo and Akinsoji


05

1015

20

Rotiferan egg

Copepod nauplius larvae

Diaphnia sp

Bosmina sp

Microcyclops sp.

Cyclops strenus Fisher

Cyclops sp.

Percentage abundance (%) Figure 4a. Relative abundance of the zooplankton in the Ogba Evie stream.

020

4060

Microcyclops sp.

Cyclops sp.

Cyclops strenus Fisher

Percentage abundance (%) Figure 4a. Relative abundance of zooplankton in the Otor stream.

(1989), Nwankwo (2004) and Onyema and Nwankwo (2006, 2009) have categorized a number of species as suitable bio-diagnostics tools for pollution monitoring. In the present study, with respect to the phytoplankton communities, species indicating some form of nutrient enrichment and organic pollution were evident in both streams. The sediments in both streams appeared to store up nutrients (phosphates, nitrates and sulphates), releasing them by gradual suspension into the water column. However, the presence and exclusivity of species belonging to the order Euglena, such as Euglena acus, Trachelomonas hispida, Phacus curvicauda and Panaeolus acuminatus to the Ogba Evie stream, which runs adjacently to active well head, is an indication of

very high nutrient levels and organic pollution as indicated by Onyema (2013). The absence of these indicative species in the Otor stream, which runs beside an abandoned well head, indicate low to moderate nutrient and organic pollution - despite the presence of some species such as Aulacoseira granulata, Synedra ulna var. biceps, Lynbgya martensiana and Oscillatoria limnosa. Such an observation strengthens the importance of Euglenophyceae (Euglena) in the Ogba Evie stream as a diagnostic flagelate to monitor pollution resulting from crude oil spills.

The few zooplankton taxa reported in this study may be an indicative of the stressed nature of both streams. With only two genera of zooplankton recorded, the Otor


Figure 5. The key chemical characteristics of the surface water and plankton abundance in both streams indicated a trend but overall differences were not significant (P>0.05).

stream may represent the future state of the Ogba Evie when the oil drilling ceases on its margins. These assumptions are, however, speculative because the relative zooplankton species variety in both stream could also historically predate oil exploration in the area. This view is in line with the findings of Varela et al. (2006), who investigated the Chlorophyll, primary production, zooplankton biomass and the species composition of phytoplankton and zooplankton in 2003, after the prestige shipwreck off the Spanish coast. The authors found no significant differences in the structure of the planktonic communities during the productive seasons. The fewer zooplankton species at the Otor stream (which is seemingly under recovery) do not conform to Otitoloju et al. (2007) data, who reported early signs of recovery few months after an oil spill and fire outbreak in a mangrove ecosystem. Thus, other environmental factors

local to each water body may play important roles in the recovery process.

The basic structure of ecological pyramids implies that primary producers with higher biomass bear the weight of the pyramid, thus determining the fate of the consumers at the apex. It is apparent that apart from water quality, the quality and availability of food invariably affect the fish species a water body can support, thus the unitary number of species observed in both streams. Tilapia species are commonly referred to as invasive, exploring waters far from their origin and thriving in stressed conditions over thresholds which native fishes can tolerate (Lowe et al., 2000; Zambrano et al., 2006). The Otor stream had evidence of lung fish nests which may be an indicative of a thriving population of the African Protopterus sp. This fish is common to creeks and swamps in Nigeria and being air breathers, are able to


Table 5. Species composition and abundance of zooplankton (No of cells M-1-1) in water samples taken from the Ogba Evie and Otor streams.

Sampling stations

Ogba Evie Otor

I II I II

Phytoplankton taxa Phylum- crustacea

- - - -

Class- copepoda - - - - Order - cyclopoida - - - Cyclops strenus fisher 5 15 5 10 Cyclops sp. 5 5 5 - Microcyclops sp. - 10 - 5 Order: cladocera - - - - Bosmina sp - 15 - Diaphnia sp - 5 - - Juvenile stages - - - - Copepod nauplius larvae - 10 - - Rotiferan egg - 5 - - Total species diversity (S) 2 7 2 2 Total abundance (N) 10 65 10 15 Log of species diversity (Log S) 0.30 0.85 0.30 0.30 Log of abundance (Log N) 1.00 1.81 1.00 1.18 Shannon-wiener index (Hs) 0.30 0.80 0.30 0.28 Menhinick index (D) 0.63 0.87 0.63 0.52 Margalef index (d) 0.43 1.44 0.43 0.37 Equitability index (j) 1.00 0.95 1.00 0.92 Simpson's dominance index (C) 0.50 0.17 0.50 0.56

thrive in hypoxic and microaerophylic waters propping out their head at intervals to breathe in air. CONCLUSION The results from this study reaffirm the polluting effects of crude oil in the Niger Delta region of Nigeria. The low plankton diversity are indicative of important changes from normal 'background' values, particularly in the Ogba Evie stream - running adjacent to an active oil production site. The fact that the second stream, Otor, runs beside a well head that has been decommissioned for about a decade allows for some form of comparison and a prediction of the future status of Ogba Evie stream and similar water bodies in the region. The relevance of phytoplankton as a bio-diagnostic tool in aquatic ecosystems monitoring is reemphasized in this work. As a corollary, we stress the need for constant auditing of oil industry activities in Nigeria in order to encourage better practices centred on preserving the environment of the Niger Delta. In view of the conflicts which pollution resulting from oil exploratory activities generate espe-cially regarding impacts on the Niger Delta ecosystems, this study supports conscious monitoring efforts on the part of the oil companies which is based on their understanding of the potential impacts of spills rather

than as response to regulatory actions. Conflict of interest There is no conflict of interest regarding this article. REFERENCES Alves TM, Kokinou E, Zodiatis G (2014). A three-step model to assess

shoreline and offshore susceptibility to oil spills: The South Aegean (Crete) as an analogue for confined marine basins. 8 Mar. Pollut. 6 (1-2):443-457.

American Public Health Association (APHA) (1998). Standard methods for examination of water and waste water (20th Edition). New York: American Public Health Association.

American Society for Testing and Materials (ASTM) (1997). Method D2887-93, Test Method for boiling range distribution of petroleum fractions by gas chromatography. In: Annual Book of ASTM Standards. Philadelphia: American Society for Testing and Materials 05. p. 27

Awosika LF (1995). Impacts of global climate change and sea level rise on coastal resources and energy development in Nigeria. In: Umolu, JC, (ed). Global Climate Change: Impact on Energy Development. DAMTECH Nigeria Limited, Nigeria.

Bott TL, Rogenmuser K, Thome P (1978). Effects of No.2 Fuel Oil, Nigerian Crude Oil, and used crankcase oil on benthic algal communities. J. Environ. Sci. Health. Part 13 (10):751-799.

Celestine A (2003). Hydrocarbon Exploitation, Environmental Degradation and Poverty: The Niger Delta Experience. Diffuse Pollution Conference, Dublin.

192 J. Toxicol. Environ. Health Sci. Coppini G, De Dominicis M, Zodiatis G, Lardner R, Pinardi N, Santoleri

R, Colella S, Bignami F, Hayes DR, Soloviev D, Georgiou G, Kallos G (2011). Hindcast of oil-spill pollution during the Lebanon crisis in the Eastern Mediterranean. Mar. Pollut. Bull. 62:140-153.

De Dominicis M, Pinardi N, Zodiatis G, Lardner R (2011). Advanced marine oil spill modelling for short term forecasting and applications to the Mediterranean Sea Geophysical Research Abstracts Vol. 13, EGU2011-6187, 2011 EGU General Assembly 2011.

Doherty VF, Otitoloju AA (2012). Monitoring of soil and ground water contamination following a pipeline explosion and petroleum products spillage in Ijegun, Lagos, Nigeria. Environ Monit Assess. doi: 10. 1007/s10661-02-2858-8.

Gonzalez JJ, Viñas L, Franco MA, Fumega J, Soriano JA, Grueiro G, Muniategui S, López-Mahía P, Prada D, Bayona JM, Alzaga R, Albalgés J (2006). Spatial and temporal distribution of dissolved/dispersed aromatic hydrocarbons in seawater in the area affected by the prestige oil spill. Mar. Pollut. Bull. 53:250-259.

Hendey NI (1958). Marine diatoms from West African Ports. J. R. Microsc. Soc. III. 77:28-88.

Hodson RE, Azam F, Lee RF (1977). Effects of Four Oils on Marine Bacterial Populations: Controlled Ecosystem Pollution Experiment. B. Mar. Sci. 27 (1):119-126.

Ibiene AA, Orji FA, Orji-Nwosu EC (2011). Microbial population dynamics in crude oil polluted soils in the Niger DeltJack IR, Fakarurhobo GK, Igwe FU, Okorosaye-Orubite K (2005). Determination of total hydrocarbons levels in some marine organisms from some towns within Rivers State of Nigeria. J. Appl. Sci. Environ. Manag. 9 (3):59-61.

Jackson JBC, Cubit JD, Keller BD, Batista V, Burns K, Caffey HM, Cadwell RL, Garrity SD, Getter CD, Gonzalez C, Guzman HM, Kaufmann KW, Knap AH, Levings SC, Marshall MJ, Steger R, Thompson RC Weil E (1989). Ecological Effects of a Major Oil Spill on Panamanian Coastal Marine Communities. Science, New Series. 243 (4887):37-44.

Kadafa AA (2012a). Oil Exploration and Spillage in the Niger Delta of Nigeria. Civil Environ.Res. 2 (3):38- 51.

Kadafa AA (2012b). Environmental Impacts of Oil Exploration and Exploitation in the Niger Delta of Nigeria. GJSFR H: Environ. Earth Sci.12 (3):19-22.

Loureiro ML, Loomis JB, Vázquez MX (2009). Economic valuation of environmental damages due to the prestige oil spill in Spain. Environ. Resour. Econ. 44 (4):537-553.

Lowe S, Browne M, Boudjelas S, De Poorter M (2000). 100 of the World’s Worst Invasive Alien Species A selection from the Global Invasive Species Database. Published by The Invasive Species Specialist Group (ISSG) a specialist group of the Species Survival Commission (SSC) of the World Conservation Union (IUCN). 12pp.

Luiselli L, Akani GC (2003). An indirect assessment of the effects of oil pollution on the diversity and functioning of turtle communities in the Niger Delta, Nigeria. Ani. Biodivers. Conserv. 26 (1):57-65.

Lytle SJ (1975). Fate And Effects Of Crude Oil On An Estuarine Pond. International Oil Spill Conference Proceedings. 1: 595-600.

Margalef R (1951). Diversidad de espicces en las comunidades naturales, Publ. Inst. Biol. Apl. (Barcelona). 9:5-27.

NESREA National Environmental Regulations. (2011). Surface and Groundwater quality. National Environmental Standards and Regulations Enforcement Agency, S.I. pp: 22.

Niger Delta Environmental Survey (NDES) (1998). Environment and Socio–economic Characteristics. Vol 1. Niger Delta Environnemental

Survey, Port Harcourt. Nwankwo, D.I. (2004a). A Practical Guide to the study of algae. JAS

Publishers, Lagos. Nigeria. 84 pp. Nwankwo DI (2004b). The Microalgae: Our indispensable allies in

aquatic monitoring and biodiversity sustainability. University of Lagos Press. Inaugural lecture series. 44 pp.

Nwankwo DI, Akinsoji A (1989). The Benthic Algal Community of a Sawdust Deposition Site in Lagos Lagoon. Int. J. Ecol. Environmental Sci. 15:197-204.

Nwilo PC, Badejo OT (2001). Impacts of Oil spill along the Nigerian Coast. Proceedings of the 1st International Congress on Petroleum Contaminated Soils, Sediments and Water, (PCSSW’ 01), Imperial College, London. pp:27-39.

Obire O, Tamuno DC, Wemedo SA (2003). Physico-Chemical quality of

Elechi creek in port Harcourt. Nigeria. J. Appl. Sci. Environ. Manage. 9:79-84.

Odu CTI, Nwboshi LC, Fagade SO, Awani PE (1989). Final Report on Post–Impact Study of SPDC "8" Nun River Delivery Line Spillage. Report to Shell Petroleum Developmental Company, Port Harcourt.

Ogbeibu AE (2005). Biostatistics: A practical approach to research and data handling. Mindex Publishing Company limited, Benin City, Nigeria.

Olaosebikan BD, Raji A (1998). Field Guide to Nigerian Freshwater Fisheries. Federal College of Freshwater Fisheries Technology, New Bussa, Niger State, Nigeria.

Onuoha FC (2008). Oil Pipeline Sabotage in Nigeria: Dimensions, Actors and Implications for National Security L/C. ASR:17 (3).

Onyema IC (2013) Phytoplankton Bio-indicators of Water Quality Situations in the Iyagbe Lagoon, South-Western Nigeria. actaSATECH. 4(2):93-107.

Onyema IC (2007). Mudflat microalgae of a tropical bay in Lagos, Nigeria. AJMBES. 9 (4):877-883.

Onyema IC, Nwankwo DI (2006) The epipelic assemblage of a polluted estuarine creek in Lagos, Nigeria. Pollution Res. 25 (3):459-468.

Onyema IC, Nwankwo DI (2009) Chlorophyll a dynamics and environmental factors in a tropical estuarine lagoon. AA.1 (1):18- 30.

Osuji LC, Onojake CM (2004). Trace Heavy Metals Associated with Crude Oil: A Case Study of Ebocha-8 Oil-Spill-Polluted Site in Niger Delta, Nigeria. Chem. Biodivers. 1 (11): 1708-1715.

Otitoloju AA, Don-Pedro KN (2004). Integrated laboratory and field assessments of heavy metals accumulation in edible periwinkle, Tympanotonus fuscatus var radula (L.) Ecotox. Environ. Safe. 57: 354-362.

Otitoloju AA (2005). Crude Oil plus Dispersant: Always a boon or bane? Ecotox Environ. Safe., 60:198-202

Otitoloju AA, Don-Pedro KN (2002). Bioaccumulation of heavy metals (Zn, Pb, Cu and Cd) by Tympanotonus fuscatus var radula (L.) exposed to sublethal concentrations of the test metal compounds in laboratory bioassays. WAJAE 3:17-29.

Otitoloju AA., Junaid KA, Are T (2007). Recovery assessment of a refined-oil impacted and fire ravaged mangrove ecosystem. Environ. Monit. Assess. 127:353-362.

Peterson CH, Rice SD, Short JW, Esler D, Bodkin JL, Ballachey BE, Irons DR (2003). Long-term ecosystem response to the Exxon Valdez oil spill. Science. 302:2082–2086.

Powell CB, White SA, Ibiebele DO, Bara M, Dut KB, Isoun M, Oteogbu FU (1985). Oshika Oil Spill Environmental Impact; effect on Aquatic biology. Paper presented at NNPC/FMHE International Seminar on petroleum industry and the Nigerian Environment 11 – 13 Nov. 1985, Kaduna, Nigeria. pp. 168-178.

Rosowski JR (2003). Photosynthetic Euglenoids. In: Freshwater Algae of North America. Ecology and Classification, Wehr, JD, Sheath RG (Eds). Academic Press, New York. pp 383-422.

Shannon CE, Weiner W (1963). The mathematical theory of communication. Urban University Illinois Press.

Smith GM (1950). The fresh-water algae of the United States. McGraw-Hill, London.719pp.

Teal JM, Farrington JW, Burns KA, Stegeman JJ, Tripp BW, Woodin B, Phinney C (1992). The West Falmouth oil spill after 20 years: Fate of fuel oil compounds and effects on animals. Mar. Pollut. Bull. 24 (12): 607-614.

Tolulope AO (2004). Oil Exploration and Environmental Degradation: the Nigerian Experience. International Society for Environmental Information Science. Int. Information Arch. 2:387-393.

Tronczynski J, Munschy C, Héas-Moisan K, Guiot N, Truquet I, Olivier N, Men S, Furant A (2004). Contamination of the Bay of Biscay by polycyclic aromatic hydrocarbons (PAHs) following the T/V “Erika” oil spill. Aquat. Living Res. 17:243-259.

Ukoli MK (2005). Environmental Factors in the Management of the Oil and Gas Industry in Nigeria. www.cenbank.org

Uyigue E, Agho M (2007). Coping with Climate Change and Environmental Degradation in the Niger Delta of Southern Nigeria. Community Research and Development Centre Nigeria (CREDC).

Varela M, Bode A, Lorenzo J, Álvarez-Ossorio MT, Miranda A, Patrocinio T, Anadón R, Viesca L, Rodríguez N, Valdés L, Cabal J,

Urrutia A, García-Soto C, Rodríguez M, Álvarez-Salgado XA, Groom, S (2006).The effect of the “Prestige” oil spill on the plankton of the N–NW Spanish coast. Mar. Pollut. Bull. 53 (5–7):272-286.

Wimpenny RS (1966). The plankton of the sea. Faber and Faber Limited, London. 426pp.

Zambrano L, Martínez-Meyer E, Menezes N, Peterson, AT (2006).Invasive potential of common carp (Cyprinus carpio) and Nile tilapia (Oreochromis niloticus) in American freshwater systems. Can. J. Fish. Aquat. Sci. 63 (9 ):1903-1910.

Amaeze and Onyema 193 Zodiatis G, Larder R, Nikolaidis A, Stylianou S, Panayidou X, Hayes D

(2011). The use of MyOcean products in the CYCOFOS- LEV Decision Support System. MyOcean User Workshop. Area 1: Marine Safety. Stockholm, 7- 8 April 2011. 13pp.

the use of planktons as tools for monitoring water quality

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