Dry season physicochemical characteristics of a tropical meso-tidal estuary: cross river estuary, southeast nigeria

Abstract

The Cross River estuary is a tide-dominated coastal plain estuary which empties into the Atlantic Ocean at the Bight of Biafra, Gulf of Guinea. It receives fresh water from major tributaries including Calabar, Great Kwa, Akpa-Yafe, Mbo and Little Kwa rivers; and plays a significant role in anthropogenic activities such as fishing exploitation and commerce. This research focuses on the assessment data from the hydrodynamic variability of the Cross River estuary. Data from April 2017 to March 2018 were generated from monitoring tidal current velocity in the estuary as well as the tidal variations under spring and neap tidal conditions. The result shows that the average current velocity in the water column was 0.85 m/s during flood tides and 0.96 m/s during ebb tides. Residual currents were observed to be seaward, with ebb dominance. In-situ measurements of physicochemical parameters including dissolved oxygen, temperature, pH, salinity, density and transparency were recorded at 55 geo-referenced sampling stations throughout the estuary in the dry season month of January, 2018. Further to this, salinity, temperature and pH varied from 0 – 20 ppt; 27.9-31.4°C; 5.4-8.4 respectively, and in increased seaward direction. The relationship between physicochemical parameters were interpreted using Pearson’s Correlation Matrix. Here, salinity showed significant correlations (p<0.05) with pH while density showed significant correlations with temperature, salinity and pH (add reasons). This research study reveals that changes in tidal cycles and current velocity are important factors contributing to the observed variations in physicochemical properties of the Cross River estuary and thus, useful for effective monitoring of the estuary and similar meso-tidal systems.