Settling fluxes and sediment accumulation rates by the combined use of sediment traps and sediment cores in Tema Harbour (Ghana)

Settling fluxes and sediment accumulation rates in coastal Tema Harbour (Ghana) were investigated by the combined analyses of results in sediment traps and sediment cores. Sediment traps were deployed at 5 stations within the Tema Harbour at two sampling depths and were retrieved every two weeks till the end of 12 weeks to estimate the Settling Fluxes (SFs). Four sediment cores from the harbour were analysed for their radioactivity (Be-7, Th-234, Pb-210, Pb-212, Ra-226, K-40 and Cs-137) profiles to quantify Sediment Accumulation Rates (SARs). The sediment cores exhibited variable bulk density profiles, indicating highly dynamic and non-steady sedimentation conditions. Be-7-derived gross-estimates of very recent SARs using the constant flux-constant sedimentation (CF-CS) model were in the range of 2.5-9.0 g.cm(-2).y(-1). These values were much lower than the estimated average SFs (15.2-53.8 g.cm(-2).y(-1)), indicating sediment resuspension plays an important role. On a decadal time scale, conventional Pb-210 sediment dating models did not allow any estimation of SARs in the Tema Harbour. Thus, the Pb-210-based TERESA model was applied to depict a reliable scenario for sedimentation with time-averaged SARs in the range of 1.4-3.0 g.cm(-2).y(-1) and fluxes of matter contributed by the marine inflow and local sources. Sediment accretion rates of 1.7-3 cm.y(-1) were also inferred, which may pose a moderate problem of sustainability for the Tema Harbour. This study reveals how the geochemical behaviour of different radionuclides with Gamma spectrometry in the marine environment can be used to obtain reliable information on the complex dynamics of Suspended Particulate Matter (SPM), even in a very disturbed and anthropic environment as a coastal harbour area where (1) conventional Pb-210-based dating methods fail and (2) the use of sediment traps and Th-234 and Be-7 profiles in sediment cores show serious constraints. (C) 2017 Elsevier B.V. All rights reserved.