Spatial distribution of suspended particulate matter (SPM) in Mtwapa creek and Funzi Bay - Kenya

Abstract

Surface water concentrations of inorganic nutrients and suspended particulate matter (SPM) components were examined and compared between Mtwapa and Shirazi creeks in Kenya. This was aimed at assesing the ecological situation of the two creeks and determine the influence of sewage discharge. The results obtained were further compared with those from Ramisi, an estuarine system. Mtwapa recorded higher nutrient, chlorophyll a and phytoplankton carbon concentrations than Shirazi. The two creeks also recorded different phytoplankton stocks and groups. Dinoflagellates dominated Mtwapa in the stations within the vicinity of sewage discharge points whereas Shirazi was dominated by pennate and centric diatoms, though at lower concentrations. Shirazi recorded the highest particulate organic carbon (POC) / phytoplankton carbon ratio. The Ramisi estuarine stations were characterised by high concentrations of dry weight (DW), centric diatoms, phytoplankton carbon, detritus and POC. Cluster analysis revealed three main clusters; the first cluster of pure estuarine stations, a second cluster comprised of stations from Mtwapa and Shirazi and a third cluster of two Mtwapa stations which were located within the vicinity of sewage discharge points. A PCA sites scatter plot produced similar clusters. A PCA species-sites biplot showed that stations in the first cluster were characterised by high concentrations of phytoplankton carbon, centric diatoms, DW, POC and detritus, 'species' which were highly correlated with axis 2; stations in the second cluster were characterised by high concentrations of POC / phytoplankton carbon ratio whereas stations in the third cluster were characterised by high concentrations of dinoflagellates, a 'species' which was highly correlated with axis 1. The three systems however had detritus as the main POC component contributing above 60% of the total POC.