Assessment of Sediment and Benthic Macrofauna Distribution at Dar es Salaam Harbour Channel

Abstract

Sediment and macrobenthic fauna distribution at Dar es Salaam harbour channel were investigated to attest the influence of sediment grain size distribution and total organic carbon contents on benthic macrofauna dominance and diversity. Sampling campaign was conducted from January to April, 2019 in 25 sampling stations along the channel. Sediment grain sizes ranged between 0.7405 and 0.00273 mm with an average of 0.0804 mm classified as medium silt. Sediment distribution showed an onshore-offshore pattern consisting of fine dark clay-silt sediments in the southern part of the harbour close to Mwalimu Nyerere Bridge, medium (sandy) at the harbour and coarse sandy offshore. Five classes of macrofauna were identified with sedentary Polychaetes (Diopatra cuprea) found in tubes and free forms being dominant in most of the sediment types, however more abundant in clay-silt. High species diversity index values were encountered in sediments with medium total organic carbon (TOC) and sediment grain sizes (sand-silt). Apparently, low species similarity indices were observed in all sediment type indicating significant dissimilarities in species composition among sediment grain sizes. Thus, the distribution of benthic macrofauna species along Dar es Salaam harbour channel is strongly influenced by the sediment grain sizes and organic carbon contents in sediments.

Heavy Metal Contamination and Potential Ecological Risks in Surface Sediments along Dar es Salaam Harbour Channel

“…The concentrations of Ni were below all the recommended environmental quality targets, despite the fact that Ni and Pb are among the elements found in petroleum products, lubricants and marine diesel oil (Mihale 2017(Mihale , 2019. This indicated that low Ni was due to low carbon content in sediments to complex more Ni (Mrutu et al 2013, Silva et al 2019.However, the overall trend of heavy metal distribution was decreasing offshore, a trend similar to that observed by Mrutu et al (2013), Mihale (2017), andSilva et al (2019), associated with the changes in sediment grain size from clay-silt to sandy-pebble offshore (Mwakisunga et al 2020).…”