On the Physico-chemistry and Nutrient Profile in the Lagos Harbour

Abstract

Physico-chemical and nutrient distribution control lagoon biological productivity, however, focus has been on studies on surface and bottom distribution with little on the vertical profiling of nutrients. Yet it is important to validate physico-chemical properties with nutrients to successfully determine the biological variability and trend of the Lagos harbour. Here, the study was carried out during the rainy season in the months of August, September and October 2014 at surface, 2.6 m and 5.2 m depth to demonstrate quantitatively that variability of nutrients within the Lagos harbour is correlated with physic chemical parameters and depth. Water temperature (°C), pH, Conductivity (µS/cm} and salinity (‰) were measured in-situ. Dissolved oxygen, alkalinity, calcium and magnesium concentration were determined in the laboratory by titremetry, while chloride, sulphate, silicate, nitrate, nitrite and phosphate were determined by colorimetry. The result shows that temperature (23-27°C), pH (7.91-8.68) and dissolved oxygen (6.37-11.20 mg/l) were relatively constant as a result of mixing and the relatively shallow water. Conductivity and salinity were seen to increase down the depth across the months studied. The month of September had the highest physico-chemical and nutrient concentrations reflecting impact of decomposition of introduced macrophytes and high tides. Though nutrient variability as a function of depth was shown to have no significant difference p>0.05, variations down the depth in the months studied were attributed to factors such as tidal influence, chemical precipitation and decomposition. The result indicated that the dynamic in physical and chemical processes are probably the main variables that determine the instantaneous distribution of nutrients. However, subsequent studies are recommended in deeper areas of the harbour to understand and provide information on biological productivity of Lagoons.