Seasonal variations of water physico-chemistry, heavy metal concentrations and ecological abundance and biodiversity of fish from two Lagoon streams

Abstract

Background The fluctuation trends of ecological parameters and the biodiversity of aquatic living resources in freshwater environments are influenced majorly by anthropogenic activities. However, little or no study has been reported on the influence of natural events particularly seasons, on water physico-chemistry, heavy metal concentrations and their impacts on the ecological assemblages of fish in interlinked lagoon systems. The present study was carried out to estimate the influence of seasonal variations on the physico-chemical parameters, heavy metal concentration of water and biodiversity, and richness of fish from two lagoons with a view to ascertaining the significance of seasons on aquatic ecosystems and their resources. Methods The sampling lasted 12 months (from December 2021 to November 2022), during which both dry and rainy seasons were experienced. Samples of water and fish were collected twice per month. Water quality analysis was done using BOYD titration and APHA standard methods. The heavy metal contents were determined using the atomic absorption spectrophotometer. Diversity indices were computed using Microsoft Excel 2015. Results There were inconsistencies in the results obtained, and as a result, statistical differences (P < 0.05) were observed. Most of the water parameters were at their highest during the dry season. High heavy metal concentrations, particularly Cd, Pb, Zn, and Fe at (P < 0.05), were recorded during the dry season. A total of 920 and 953 individual fish from 22 and 26 families were obtained from Lekki Lagoon during the dry and wet seasons, respectively. In the Lagos Lagoon, a total of 1299 and 1772 individual fish, which belong to 24 and 25 families, were collected during the dry and rainy seasons, respectively. The best diversity indices, such as Shannon Weiner, Simpson's dominant index, Margalef, Menhinick, and the evenness index, were obtained during the rainy season. Conclusion Our results suggested that variation in seasons strongly influenced water quality parameters and heavy metal concentrations, as well as fish species biodiversity in the study areas. Hence, seasonal patterns in relation to aquatic ecosystems should be taken into account when making long-term policies for the sustainability of fisheries resources.