Nutrient and Phytoplankton Dynamics along the Ocean Road Sewage Discharge Channel, Dar es Salaam, Tanzania

Abstract

Ocean Road shoreline is situated close to Dar es Salaam largest fish market and is subjected to sewage discharge. In this study, temporal and spatial variations of physicochemical parameters and phytoplankton were studied in five stations along the Ocean Road Coast. Phytoplankton composition, temperature, dissolved oxygen (DO), salinity, water clarity, pH, and dissolved inorganic nutrients (DIN) including nitrite, nitrate, and phosphate were measured. Results revealed that DIN were significantly higher in the station close to the discharge point than other stations ( P < 0.0001 ). There were no significant temporal variations in DIN except nitrate that was significantly higher during Northeast Monsoon than Southeast Monsoon ( P < 0.001 ). Other environmental parameters showed no significant differences except clarity, conductivity, and DO. Occurrence of potential harmful species such as Trichodesmium, Microcystis, and Pseudo-nitzschia was observed. The phytoplankton biomass (chlorophyll a ) ranged from 3.2 to 56.5 mg m −3 and 18 to 113 mg m −3 for Mjimwema (MJ) and Ocean Road (OR) stations, respectively. There was significant difference ( P = 0.0033 ) in chlorophyll a among the stations being higher in OR II. The phytoplankton biomass was positively correlated with nutrient concentration in all stations except OR I. This study suggests an alarming level of DIN at OR that may alter phytoplankton biomass, abundance, and composition.