easy and inexpensive to measure and it is a generally used biological measure of phytoplankton biomass and
relatively few measurements are needed to get reliable mean value [5]. Carlson’s Trophic State Index (TSI) classification [6] can be used to provide a single trophic criterion for the purpose of classifying and ranking water bodies in complex multi-wetland systems. Secchi depth is a much debated and used variable in lake management. Secchi disk transparency is a standard indicator of water clarity, which is strongly correlated with biomass and annual productivity of suspended algae. This is also closely related to the amount of sandy clay, detritus and organic and inorganic suspended and dissolved matter in water [7].
The use of zooplankton community structure as indi-cator of the wellbeing of water body dates back to 1879- 1910 [8]. Zooplankton is an important component of the trophic food webs of lakes because of its particular posi-tion at the crossroads of carbon and energy flows from the lower levels of food chains to fish. Zooplankton biomass which is part of secondary production of lakes is bottom-up regulated by the availability of bacteria and phytoplankton as food and top-down controlled by pre-dation from fish etc. [9]. The composition of zooplank-ton especially in relation to filter feeders depends on the quality of nutrient supply. So some zooplankton species (mainly rotifers, branchiopods and copepods) could be used as indicators of lakes trophic status [10] because their composition is affected by any of the several envi-ronmental parameters e.g. pH or alkalinity and salinity and other biological parameters [11-13]. Zooplankton abundance is usually closely related to phytoplankton concentration and species composition and increases with increasing nutrients concentrations [14].
Biodiversity is also one of the promising ecological criteria that could be added to lake monitoring pro-grammes. Plankton richness within lakes appears to be largely controlled by factors related to productivity, wa-ter quality and fish predation levels. Diversity indices, such as Shannon-Weaner index appeared to detect sig-nificant differences in the structure of the communities.
Around the world several researches have been carried out using phytoplankton and zooplankton to investigate pollution [15-19] because they are relatively easy to identify, particularly when community sensitivity can be detected based on plankton body sizes or gross taxo-nomic classifications. Eastern Nigerian lakes in particu-lar being important sources of water for drinking, fishing and domestic use are vulnerable to anthropogenic impact, yet there is limited water quality data [20,21]. This is the first-ever baseline study of the condition of the nation’s akes in eastern Nigeria using statistically valid approach. It will help the government of the region implement lake
monitoring and assessment programs, establish a base-line for lake condition that can be used for future trend assessment. It is focused on studying plankton diversity and evaluating trophic status of some wetlands of East-ern Nigeria for the first time.
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