Abstract

Iron (Fe) has been found to play a significant role in the surface waters biogeochemical cycles of some macronutrients responsible for eutrophication. Thus, the need to assess the cause of increasing concentration of Fe in the eutrophication of the economically important Lagos coastal waters. Top and bottom water samples were obtained from ten (10) study stations along the Lagos coastal water system, spanning Lagos Central to Lagos East, between November 2019 and March 2020. Physicochemical parameters including pH, Dissolved Oxygen (DO), Oxidation-Reduction Potential (ORP), Total Dissolved Solids (TDS), Turbidity and Salinity were measured in-situ while iron concentrations were determined by spectrophotometric method. The data showed average pH, DO, ORP, TDS, turbidity and salinity of 7.56 ± 0.24; 11.99 ± 2.58 mg L^-1; 52.25 ± 42.01 mV; 9.45 ± 2.92 g L^-1; 54.92 ± 21.91 NTU and 10.13 ± 2.76 ppt respectively while average Fe concentration was 0.67 ± 0.32 mg L^-1 for both top and bottom water layer. The locations with elevated concentrations of Fe, mainly driven by anthropogenic inputs from the catchments of the study locations, showed negative ORP values which was indicative of high microbial activities. Increasing Fe concentration and presence of other micronutrients suggest that inputs of minerogenic matter will continue to be a major composite in the sustenance of eutrophication in the waters.  

Keywords: Iron; Eutrophication; Microbial Activities; Micronutrients.