ABSTRACT

The hydrobiological characteristics of the Imo River Estuary in Nigeria as well as the land cover dynamics of it’s surrounding wetlands, were investigated. Selected physico-chemical parameters (Temperature, DO, BOD, Conductivity, Nitrates and Nitrites, Salinity, Phosphates, TSS, pH, TDS, Transparency, NH_4, Pb, Zn, Cu and Cd) and the biological parameters which includes phytoplankton, zooplankton and fish species were analysed to determine the present condition of the water body and how it affects fish catch, abundance and diversity. Based on these findings, land cover change was analysed to ascertain any changes in the intergrity of the estuary within a thirty years span, to  detect any perturbations that could have affected the intergrity of the river. Samples were collected bi-monthly between April 2015 and March 2016, covering the dry and wet seasons of the year at 3 stations namely, Kalibiama, Opobo and Queenstown.. Variations observed in the physicochemical parameters were affected more in the seasonal scale than the spatial, as Pb, PO₄, and TSS were the only parameters significantly different at p≤0.05 between the stations.  The water quality of the estuary was examined by comparing means of parameters to Federal Environmental Protection Agency, Federal Ministry of Environment and World Health Organisation’s acceptable standards. Parameters that exceeded regulatory units were cadmium, lead and nickel against FMENV standards of 0.33, 0.05 and 0.5mg/l respectively, suggesting a slightly chemically polluted environment. A total of 2,738 individuals from 4 phyla (Bacillariophyta, Chlorophyta, Euglenophyta and Cyanophyta) were recorded for phytoplankton. Shannon  diversity index were used to determine abundance and diversity of plankton and fish. The diversity results showed values which suggests a slightly polluted ecosystem. The correlation of the plankton and environmental parameters indicated that phytoplankton correlated both positively and negatively with parameters such as TDS (P<0.003), salinity(P<0.002), cadium(p<0.038), zooplankton(P<0.048), pH( p<0.006), conductivity(P<0.003) and negatively with  BOD at (P<0.032). A total of 1950 individuals in 22 fish species consisting of 13 families were collected during the study period from artisanal fisheries landings. The Carrangids and Clupeids made up the dominant fisheries of the estuary. A Remote Sensing analysis of the study area within a period of thirty years, 1986, 2000 and 2016 showed that the mangrove ecosysytem had been depleted by 17% to crop and grassland within this period, the implication of this is an increase in silt sediment and nutrient load from run off into the river by the nearby crop and grassland. Also an increase in the human settlements was witnesed at 3.4% total area (723.456 hectares) causing increased waste discharges into the river. It is recommended that constant policy regulation and compliance checks should be carried out on coastal wetlands to reduce degradation.