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

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 ( ). There were no significant temporal variations in DIN except nitrate that was significantly higher during Northeast Monsoon than Southeast Monsoon ( ). 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 ( ) 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. 1. Introduction Aquatic ecosystems around the world mostly have been heavily impacted by waste discharges from human activities, including point sources of urban, residential and industrial pollution, and nonpoint sources of agricultural pollution which alters the nutrient contents of the coastal waters. Traditionally, pathways of nutrient influx to the coastal water bodies were considered mainly surface river runoff and waste water discharges [1, 2]. Increase in anthropogenic inputs has led to severe eutrophication problems, inducing an enhancement of phytoplankton primary production in many coastal areas [3, 4]. In addition to increasing primary production, nutrients dynamics have inevitable effects on the taxonomic composition of phytoplankton communities [4]. It is known that there is a large difference between coastal ecosystems in the magnitude and character of responses of phytoplankton biomass or primary production to anthropogenic inputs (e.g., [5, 6]). It is also known that seasonal succession of phytoplankton can be controlled by a combination of physical, chemical, and biological variables [7]. However, Reynolds [5] reported that nutrient is the