ABSTRACT In developing countries, lakes being important sources of water supply and fishing are vulnerable to anthropogenic impact, yet knowledge of their trophic state in relation to changes in species composition, and environmental variables, are limited. This study is aimed at assessing the trophic status of lakes by monthly sampling of three lakes located along the floodplain of Cross River, Nigeria between January 2008 and December 2009. Samples were analyzed for water quality parameters, zooplankton and phytoplankton composition and distribution. Results were subjected to community structure analysis using trophic state index, species richness and diversity indexes. Essential primary productivity nutrients, nitrates, sulphates and phosphates were highest in Ejagham Lake, and lowest in Ikot Okpora Lake. Dominant phytoplankton species Oscillatoria lacustria (Cyanophyceae), Cyclotella operculata (Bacilliarophyceae) and zooplankton Keratella tropica, Keratella quadrata, Filinia longiseta, Branchionus anguillaris and Trichocerca pusilla (rotifers) all typical of eutrophic communities were recorded in high densities in Ejagham Lake in both dry and wet seasons while Cladocerans, Bosmina longirostris and Moina micrura and copepods considered indicators of oligotrophy and mesotrophy were recorded in large numbers in Ikot Okpora and Obubra Lakes respectively. Higher values of species richness, Evenness and Shannon-Wiener diversity index for both phytoplankton and zooplankton, were recorded in Ejagham Lake during the dry season than wet. Also values of the Trophic state index were generally highest at the Ejagham Lake in the savanna region of the floodplain and lowest at Ikot Okpora in the forest region of the floodplain. Forest region is therefore a limiting factor in the productivity of lakes in the tropics.
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nullB. Offem, E. Ayotunde, G. Ikpi, F. Ada and S. Ochang, "Plankton- Based Assessment of the Trophic State of Three Tropical Lakes," Journal of Environmental Protection, Vol. 2 No. 3, 2011, pp. 304-315. doi: 10.4236/jep.2011.23034.
 S. Kroeger, E. Fensin, K. Lynch and M. V. Borgh, “United State Water Programs That Use Algae as Biological Assessment Tool,” Technical Guidance Document: EPA 007-841, 1999.
 D. F. Westlake, “The Functioning of the Freshwater Ecosystem,” International Biological Programme, Cambridge University Press, London, Vol. 122, 2003, pp. 423-442.
 A. Payne, “Ecology of Tropical Lakes and Rivers,” John Wiley and Sons, New York, 1986.
 G. M. Sechi and A. Sulis, “Multi-Reservoir System Optimization Using Chlorophyll-A Trophic Indexes,” Water Resources Managemnet, Vol. 21, No. 5, 2007, pp. 849-860. doi:10.1007/s11269-006-9114-3
 L. H?kanson and V. V. Boulion, “Regularities in Primary Production, Secchi Depth and Fish Yield and a New System to Define Trophic and Humic State Indices for Lake Ecosystems,” International Review Hydrobiology, Vol. 86, 2001, pp. 23-62.
 R. E. Carlson and J. Simpson, “A Coordinator’s Guide to Volunteer Lake Monitoring Methods,” North American Lake Management Society, USA, 1996.
 L. Sifa and X. Senlin, “Culture and Capture of Fish in Chinese Reservoirs,” IDRC, Ottawa, Canada, 1995.
 D. G. Frey, “Wisconsin: Birge-Juday era,” In D. G. Frey Ed., Limnology in North America, The University of Wisconsin Press, Madison, 1963.
 S. D. Peckham, J. W. Chipman, T. M. Lillesand and S. I. Dodson, “Alternate Stable States and the Shape of the Lake Trophic Distribution,” Hydrobiologia, Vol. 571, No. 1, 2006, pp. 401-407. doi:10.1007/s10750-006-0221-1
 I. C. Duggan, J. D. Green and R. J. Shiel, “Distribution of Rotifers in North Island, New Zealand, and Their Potential Use as Bioindicators of Lake Trophic State,” Hydrobiologia, Vol. 446-447, No. 1, 2003, pp. 155-157.
 S. Guess, D. Albrecht, H. J. Krambeck, D. C. Mueller-Navarra and H. Mumm, “Impact of Weather on Lake Ecosystem, Assessed by Cyclo-Stationary MCCA of Long-Term Observations,” Ecology, Vol. 81, No. 6, 2003, pp. 1720-1730.
 K. O. Coyle and A. I. Pinchuk, “Climate-Related Differences in Zooplankton Density and Growth on the Inner Shelf of the South-Eastern Bering Sea,” Progress in Oceanography, Vol. 55, No. 1-2, 2002, pp. 177-179.
 A. Hobaek, M. Manca and T. Anderson, “Factors Influencing Species Richness Lacustrine Zooplankton,” Acta Oecologica, Vol. 23, No. 3, 2002, pp. 155-165.
 G. Balvay, “Evolution du Zooplacton du Leman,” Campagne 1999, Rapp. Comm. int. prot. Eaux. Leman conte pollut (CIPEL), 2000.
 M. G. Nogueira, “Phytoplankton Composition, Dominance and Abundance as Indicators of Environmental Compartmentalization in Jurumirim Reservoir (Paranapanema River), S?o Paulo, Brazil,” Hydrobiologia, Vol. 431, No. 2-3, 2000, pp. 115-128.
 C. C. Figueredo and A. Giani, “Seasonal Variation in the Diversity and Species Richness of Phytoplankton in a Tropical Eutrophic Reservoir,” Hydrobiologia, Vol. 445, No. 3, 2001, pp. 165-174. doi:10.1023/A:1017513731393
 C. S. Pedrozo and O. Rocha, “Zooplankton and Water Quality of Lakes of the Northern Coast of Rio Grande Do Sul State, Brazil,” Acta Limnologica Brasiliensia, Vol. 17, No. 4, 2005, pp. 445-459.
 E. I. L. Silva, “Ecology of Phytoplankton in Tropical Waters: Introduction to the Topic and Ecosystem Changes from Sri Lanka,” Asian Journal of Water Environmental Pollution, Vol. 4, No. 1, 2005, pp. 25-35.
 D. Zorka, V. Mitrovic-Tutundzic, Z. Markovic and I. Zivic, “Monitoring Water Quality Using Zooplankton Organisms as Bioindicators at the Dubica Fish Farm, Serbia,” Archives of Biological Sciences, Vol. 58, No. 4, 2006, pp. 245-248. doi:10.2298/ABS0604245D
 B. O. Offem and E. O. Ayotunde, “Toxicity of Lead to Freshwater Invertebrates. Waterfleas; Daphnia magna and Cyclop sp ) in Fish Ponds in a Tropical Floodplain,” Water Air Soil Pollution, Vol. 192, No. 1-4, 2008, pp. 39-46. doi:10.1007/s11270-008-9632-0
 B. O. Offem, Y. Akegbejo-Samsons, I. T. Omoniyi and G. U. Ikpi, “Dynamics of the Limnological Features and Diversity of Zooplankton Populations of the Cross River System SE Nigeria,” Knowledge and Management of Aquatic Ecosystems, Vol. 393, No. 2, 2009, pp. 2-19.
 U. I. Enin, “The Artisanal Shrimp Fishery of the Outer Cross River Estuary, Nigeria,” Ph. D. Thesis, University of Calabar, Calabar, 1994.
 H. I. Golterman, “Methods for chemical analysis of freshwater,” International Biological Programme, Handbook & Oxford, Blackwell Scientific Publications, Oxford, 1969.
 American Public Health Association (APHA), “Standard Methods for the Examination of Water and Waste Water,” 20th eds, Washington D.C., 1998.
 G. W. Prescott, “Algae of the Western Great Lakes Area,” Brown Publishers, Dubuque, Iowa, 1951.
 W. T. Edmondson, “Fresh Water Biology,” 2nd Edition, John Wiley & Sons Inc., New York, 1959.
 D. M. John, B. A. Whitton and A. J. Brook, “The Freshwater Algal Flora of the British Isles: An Identification Guide to Freshwater and Terrestrial Algae,” 1st Edition, Cambridge University Press, UK, 2002.
 R. A. Vollenweider, “A Manual on Methods for Measuring Primary Production in Aquatic Environments,” 2nd Edition, Blackwell Scientific Publications, Oxford, 1974.
 C. E. Boyd, “Water Quality in Warm Water Fish Ponds,” Auburn University Publishers, Alabama, 1981.
 M. O. Kadiri, “Seasonal Changes in the Phytoplankton Biomass of Shallow Tropical Reservoir, Nigeria,” Journal of Botany, Vol. 6, 1988, pp. 167-173.
 E. C. Kemdirim, “Checklist of Phytoplankton of Shedam Reservoir in Plateau State, Nigeria,” Journal of Aquatic Sciences, Vol. 16, 2001, pp. 61-66.
 E. R. Akpan and J. O. Offem, “Seasonal Variation in the Water Quality of Cross River, Nigeria,” Hydrobiologia, Vol. 26, No. 2, 1993, pp. 95-98.
 A. E. Magurran, “Ecological Diversity and Its Measurement,” Cambridge University Press, Cambridge, 1988.
 J. H. Zar, “Biostatistical Analysis,” Pretice-Hall International, London, 1984.
 J. A. Downing and E. Mccauley, “The Nitrogen: Phosphorus Relationship in Lakes,” Limnology Oceangraphy, Vol. 37, 1992. pp. 936-977.
 B. Moss, J. Madgwick and G. Phillips, “A Guide to the Restoration of Nutrients-Enrich Shallow Lakes,” W. W. Hawes, Suffolk, 1997.
 J. Padisak and C. S. Reynolds, “Selection of Phytoplankton Associations in Lake Balaton, Hungary in Response to Eutrophication and Restoration Measures, with Special Reference to the Cyanoprokaryotes,” Hydrobiologia, Vol. 384, 1998, pp. 41-53. doi:10.1023/A:1003255529403
 M. P. Stoyneva, “Steady-State Phytoplankton Assemblage in Shallow Bulgarian Wetlands,” Hydrobiologia, Vol. 502, No. 1-3, 2003, pp. 169-177.
 C. Berger and H. E. Sweers, “Ijsselmeer and Its Phytoplankton with Special Attention to the Suitability of the Lake as a Habitat for Oscillatoria Agardhii Gom,” Journal of Plankton Research, Vol. 10, No. 4, 1988, pp. 579-586. doi:10.1093/plankt/10.4.579
 D. I. Nwankwo, K. Onyema and T. A. Adesah, “A Survey of Harmful Algae in Coastal Waters of South Western Nigeria,” Journal of Nigerian Environmental Society, Vol. 1, No. 2, 2003, pp. 241-246.
 J. Hall, J. B. Catharine and W. Carolyn, “Environmental Gradient and Zooplankton Distribution, in a Shallow, Tidal Lake,” Archives of Hydrobiologia, Vol. 154, No. 3, 2002, pp. 485-490.
 A. Karabin, “Pelagic Zooplankton (Rotatoria and Crustacea) Variation in the Process of Lake Eutrophication. II. Modifying Effect of Biotic Agents,” Polish Journal of Ecology, Vol. 33, No. 4, 1985b, pp. 567-589.
 S. Sendacz, E. Kubo and M. A. Cestarolli, “Limnologia de Reservatios do Estado do Sao Paulo, Brasil, VIII Zooplankton,” Boletim do Instituto de Saúde, Vol. 12, 1985, pp. 145-176
 A. Swierzoski, M. Godlewska and T. Poltorak, “The Relationship between the Spatial Distribution of Fish, Zooplankton and Other Environmental Parameters in the Solina Reservoir, Poland,” Aquatic Living Resources, Vol. 13, 2000, pp. 373-387.
 C. J. Krebs, “Ecology: The Experimental Analysis of Distribution and Abundance,” Harper Intel, Lectual Edition, New York, 1996.
 Z. Kajak, “Ecological Characteristics of Lakes in North-Eastern Poland Versus Their Trophic Gradient,” Polish Journal of Ecology, Vol. 31, 1983, pp. 495-510.
 K. Irvine, M. T. Bales, B. Moss, J. H. Stanfield and D. Snook, “Trophic Relations in Hickling Broad - a Shallow and Brackish Eutrophic Lake,” Verhandlungen des Internationalen Verein Limnologie, Vol. 24, 1990, pp. 576-587.
 A. G. Rogozin, “Specific Structural Features of Zooplankton in Lakes Differing in Trophic Status: Species Population,” Ekologia, Moscow, Vol. 6, 2000, pp. 438-455.
 M. J. Behrenfeld and E. Boss, “Beam Attenuation and Chlorophyll Concentration as Alternative Optical Indices of Phytoplankton Biomass,” Journal of Marine Research, Vol. 64, 2006, pp. 431-451.
 G. Almazan and C. E. Boyd, “An Evaluation of Secchi Disk Visibility for Estimating Plankton Density in Fish Ponds,” Hydrobiologia, Vol. 61, No. 3, 1978, pp. 601-608. doi:10.1007/BF00044446
 U. A. D. Jayasinghe, U. S. Amarasinghe and S. S. De Silva, “Trophic classification of non-perennial reservoirs utilized for the development of culture-based fisheries, Sri Lanka,” International Review of Hydrobiology, Vol. 90, No. 2, 2005, pp. 209-222.
 F. Dominique, G. Hans, L. Malgorzata, C. Lawrence and K. Andoline, “Integrated Water Resource Management for Important Deep European Lakes and their Catchment Areas,” Eurolakes, Vol. 36, 2003, pp. 56-67.