Phytoplankton Community of Elechi Creek , Niger Delta , Nigeria-A Nutrient-Polluted Tropical Creek

Problem statement: Elechi creek of the upper bonny estuary in the Nige r D lta contributes to the rivers state fish resources. It is a sink re ceiving organic anthropogenic wastes from Diobu, Ea gle Island and waterfront dwellers of Diobu areas. Fish ing, car washing, bathing, swimming and other human activities are constantly going on within and round this creek. Based on these activities, ther e is urgent need to study the phytoplankton community that supports its fisheries. Approach: The study investigated the phytoplankton composition, diversi ty, abundance and distribution as well as surface water physico-chemical parameters. Phytoplankton an d surface water samples were collected bimonthly from October 2007-March 2008 at high tide f rom five stations according to APHA methods. These were analyzed for temperature, transparency, dissolved oxygen, salinity, alkalinity, chloride an d nutrients. Phytoplankton was identified microscopic ally. Species diversity was calculated using standard indices. Results: A total of 169 species of phytoplankton, based on cell counts, was dominated by diatoms, 33255 counts mL −1 (36%) and blue-green algae, 32909 counts mL −1 (35.7%) were identified. The abundance of phytoplankton dec reased downstream of this creek (1>2>3>4) except in station 5 with the highest phy toplankton abundance (23938 counts mL ). There was slight fluctuation in the measured physico-chemical parameters. The results of this study indicated th characteristic species and distribution of phytopla nkton in Elechi Creek during the dry months. Conclusion/Recommendation: The high level of phosphate above the permissive l imit showed that this creek is hypereutrophic and organic polluted. The high nutrients status favors the high abundance of phytoplankton. The municipal effluents (especial ly raw human and animal faces) discharges must be discontinued. Detergents with low concentration of phosphate are recommended for manufacturing and use. Municipal wastes must be treated and/or re cycled before discharge into this natural aquatic body. Therefore, a continuous environmental surveil lance of this creek is advocated to keep its biological integrity.


INTRODUCTION
The productivity of any water body is determined by the amount of plankton it contains as they are the major primary and secondary producers. Plankton communities serve as a base for the food chain that supports the commercial fisheries [1,2] . According to Wehr and Descy [3] , phytoplankton communities are major producers of organic carbon in large rivers, a food source for planktonic consumers and may represents the primary oxygen source in many low-gradient rivers.
Phytoplankton are of great importance in biomonitoring of pollution. The distribution, abundance, species diversity, species composition of the phytoplankton are used to assess the biological integrity of the water body [1] . Also, they reflect the nutrient status of the environment. They do not have control over their movements thus they cannot escape pollution and this makes them a good indicator of pollution in the environment. Barnes [4] reports that pollution affects plankton distribution, standing crop and chlorophyll concentration. This study was conducted to assess the characteristic phytoplankton species and their distribution in Elechi Creek. Also, it evaluated some surface water physico-chemical parameters.

MATERIALS AND METHODS
Study area: Elechi Creek, South-West of Port Harcourt metropolis, lies between longitude 6°45 11 E and 7°20"N and latitude 4°38"N and 5°5"E. The creek is a tributary of the upper limits of Bonny Estuary and includes its adjoining mangrove Creeks situated near the Eagle Island by the Rivers State University of Science and Technology, Nkpolu, Port Harcourt (Fig. 1). The vegetation is predominantly mangrove.
The low intertidal is dominated mostly by Rhizophora racemosa, R. mangle while the high intertidal is dominated by Avicennia africana, Laguncularia racemosa, Nypa fruticans and Aecrostichum aureum [5] . There are various fishing and transportation activities going on on Elechi Creek. Its vegetation provides logs of wood for domestic and building purposes. The area is also surrounded by numerous waterfront residential houses. The surrounding terrestrial environment is marked by various human activities such as saw milling of timber, free-range pig production, refuse dumping and car washing from Diobu and Eagle Island areas of Port Harcourt. Finally, the study area is a sink for numerous anthropogenic wastes from local industries.
Sampling stations: Samples were collected monthly for three months (October 2007-March 2008) from five sampling stations at high tide namely: (1) Waterfront residential buildings (Upstream), (2) UST brackish water fish pond, (3) A channel from UST female hostel, (4) Right timber market and (5) Left timber market (downstream) (Fig. 1). The six months samples were pooled according to sampling stations.

Sample collections and analyses:
Field and laboratory measurements of some physico-chemical parameters of surface water were taken following standard methods [6] .

Fig. 1: Study area map
Phytoplankton samples were collected by using sterilized, one-liter wide mouth plastic container at each sampling station [7] . The filtered samples were washed into the sterilized collecting bottles and immediately fixed in 4% formalin. Identification and enumeration were done by using leitzuezier binocular microscope and keys by Newell and Newell [8] , Han [9] , Prescott [10] and Kadiri [11] .

Species diversity: From
For Cyanophyceae, station 5 recorded the maximum d 4.86 and station 1 the minimum 2.78. H 1 ranged between 3.06 (station 1) and 3.62 (station 5). The highest d 0.99 for Euglenophyceae was observed in station 1 and the lowest d 0.42 in station 5 while station 1 recorded the maximum H 1 2.09 and station 4 the maximum 1.49. Stations 2 and 3 recorded zero species diversity indices for Chlorophyceae. In other stations, the observed diversity indices were d, 0.61 (station 1) and 1.65 (station 5) and H 1 1.08 (station 1) and 1.76 (station 5). Dinophyceae were absent in stations 1,2 and 3 hence zero species diversity were recorded. Station 5 d 1.56 and H 1 1.41 were higher than d 1.37 and H 1 1.22 of station 4 but an opposite trend was observed for E 1 and D.
Physico-chemical parameters: Temperature variation in relation to station was insignificant (p>0.05) and ranged between 29.0°C (Station 5) and 30.7°C   pH values was maximum 7.2 in station 4 and minimum 6.9 in station 1 (Fig. 4). The highest dissolved oxygen 12.1 mg L −1 was recorded in station 4 and lowest 2.1 mg L −l in station 1. Nitrogen-nitrate ranged between 2.50 mg L −l station 1 and 2.63 mg L −1 (station 3). The highest phosphate level 6.36 mg L −1 was observed in station 1 and the lowest 3.75 mg L −1 in station 3.

DISCUSSION
The high phytoplankton species composition, diversity and abundance recorded for the entire study were more than the values reported for studies in other waters of Bonny Estuary and Niger Delta. This indicates that these phytoplankton will support commercial fisheries in this creek [1,2] . This might be attributed to the high nutrients status (phosphate, nitrate and sulphate). This creek receives enormous quantities of anthropogenic wastes (domestic and industries) such as raw human and animal faces from its surroundings.
These wastes increase the nutrients capabilities of this creek. The present observation might be attributed to environmental influence like high temperature, low pH, transparency and dissolved oxygen. Phosphorus stimulates phytoplankton (algae) growth. According to Frankovick et al. [12] , the epiphytic diatom assemblage of the Florida Bay Estuary was structured by nutrient availability particularly phosphorus . Phosphate might have structured the phytoplankton community of Elechi Creek. High temperature enhances photosynthesis and this is expected during the dry months. High phytoplankton growths lead to high photosynthetic activities thus enough food for organisms in higher trophic levels and for these algae. In addition, photosynthetic activities of the algae are usually higher during the dry months hence the present observation. Some of these algae are expected to die and decay. The decomposed matter will invariably increase the nutrients of this creek. The low pH makes nutrients (such as phosphate and nitrate) available to the primary producers.
The high abundance of phytoplankton in station 5 might be attributed to the large amounts of domestic and industrial wastes containing high level of phosphates from the Diobu and Eagle Island areas. The Diobu area of Port Harcourt is densely populated. The waterfront areas lack sanitary facilities.
The dominance of diatoms and blue-green algae indicate that Elechi Creek is polluted. Ruivo [13] states that natural unpolluted environments are characterized by balanced biological conditions and contains a great diversity of plants and animals life's with no one species dominating. The difference in the community structure despite the dominance by diatoms is mainly due to the importance assumed by Cyanophyceae, Chlorophyceae and Euglenophyceae in the phytoplankton community. However, the distribution of diatoms reflects the average ecological conditions of this aquatic environment [14] . Dinoflagellates were the least abundant and this might be attributed to their inefficiency to compete for nutrients [15,16] .
The maximum number of diatoms species in station 5 might probably due to immense municipal wastes from the surroundings. The recorded dominant species could be as a result of high phosphate concentration and organic pollutants in these wastes. These species have been implicated with organic pollution. The same reason for highest number of diatom species in station 5 might be given for bluegreen algae species in station 5. Anabaena spiroides had also been implicated with organic pollution [17] . The presence of dominant Euglena species further indicates organic pollution. However, the presence of Ceratium furcas in stations 4 and 5 also shows organic pollution in Elechi Creek. Dominant species might indicate that these species love nutrients-rich environment. The presence of all these indicator phytoplankton species serves as a warning to the rise in nutrient capabilities of Elechi Creek. It is possible that diatoms and blue-green algae possess resilient ability to withstand organic pollution. Organic pollution eliminates the enemies of the more tolerant species which in turn increase in numbers.
The observed spatial variations of the phytoplankton might be attributed to the varied physico-chemical parameters. The recorded high temperature and low transparency favored the high abundance of phytoplankton. This is expected in tropical water bodies and fell within the acceptable range [18] . The present range of transparency is characteristic of brackish environment [18] . The recorded salinity, chloride and alkalinity were suitable for phytoplankton growths. The recorded salinity shows brackish environment. Salinity is one of the major factors influencing algae zonation and distribution within estuaries, both in terms of range of values and rate of changes [12] . It might be responsible for the observed variations of phytoplankton in this creek.
One of the factors that is likely to play an important role in determining community productive levels is nutrients availability; nitrogen, phosphate and sulphate [12] . No station showed absence of nitrogen (nitrate-nitrogen) or phosphate (phosphate-phosphorus) but the concentrations seem limiting hence the varied diatoms density. This emphasizes the influence and significant role of nutrients in phytoplankton productivity in the stations. The phosphate level recorded was higher than the permissible concentrations in natural aquatic bodies (0.10 mg L −1 ) [19] . This might be attributed to the raw human and animal faces. The high sulphate concentration is characteristic of brackish water [18] . However, the high nutrients levels (phosphate, sulphate and nitrogen-nitrate) enhanced the growths of phytoplankton.
It could reasonably be concluded that Elechi Creek is hypereutrophic and organic polluted. The high nutrients status favors the high abundance of phytoplankton. The municipal effluents (especially raw human and animal faces) discharges must be discouraged or discontinued. Detergents with low concentration of phosphate are recommended for manufacturing and use. Municipal wastes must be treated and/or recycled before discharge into this natural aquatic body. Therefore, a continuous environmental surveillance of this creek is advocated to keep its biological integrity.

CONCLUSION
The high abundance of phytoplankton in Elechi Creek can support fisheries but its nutrients availability especially phosphate of Elechi Creek is very high. This high phosphate level indicates that this creek is under stress. Its biological integrity may completely be destroyed if remedial and surveillance measures are not promptly taken by the Rivers State government.