Geochronology and historical deposition of trace metals in three tropical estuaries in the Gulf of Guinea. (5th August 2016)

• Record Type: Journal Article
• Authors: Mahu, Edem; Nyarko, Elvis; Hulme, Samuel; Swarzenski, Peter; Asiedu, Daniel K.; Coale, Kenneth H.
• Is Part Of: Estuarine, coastal and shelf science. Volume 177(2016)
• Page Start: 31
• Page End: 40
• Publication Date: 2016-08-05
• Subjects: 210Pb -- 137Cs -- Trace metals -- Sediment cores -- Estuaries -- Ghana; Estuarine oceanography -- Periodicals; Coasts -- Periodicals; Estuarine biology -- Periodicals; Seashore biology -- Periodicals; Coasts; Estuarine biology; Estuarine oceanography; Seashore biology; Periodicals; 551.461805
• DOI: 10.1016/j.ecss.2016.05.007
• Languages: English
• ISSNs: 0272-7714

Abstract

Abstract: The depositional histories of trace metals (Pb, Cu, and Zn) in sediment cores from three Ghanaian estuaries were reconstructed using radioisotope-derived ( 210 Pb and 137 Cs) geochronologies. A core collected from each of the Amisa, Sakumo II and Volta estuaries was analyzed for trace metals and radionuclides. Lead-210 and 137 Cs dating via gamma spectroscopy, and trace metal analysis via inductively coupled plasma mass spectrometry (ICP-MS) were used in deriving sedimentation rates, geochronologies and accumulation trends of trace metals. The sedimentation rates in all three estuaries (in the range of 0.54–0.83 cm yr −1 ) were greater than the predicted sea level rise (∼0.33 cm yr −1 ) for the Accra Coast of Ghana. The 210 Pb depositional rates of 6.83 dpm cm −2 y −1, 2.74 dpm cm −2 y −1 and 1.75 dpm cm −2 y −1 estimated for the Amisa, Sakumo II and Volta estuaries, respectively, are higher than those recorded in other latitudes. Trace metal analysis revealed differences in the concentrations of Cu, Pb and Zn between deeper and surficial layers of each core to be in the range of 10–20%, which is well within the natural variations attributed to geochemical factors. Relative to the Amisa and Volta estuaries, the temporal profiles of Al-normalized metal concentrations and estimated fluxes suggest anthropogenic processes augmented the natural fluxes of trace metals, particularly Zn into the Sakumo II estuary during the last 7 years. Highlights: We dated sediment cores from three Ghanaian estuaries for the first time using 210 Pb and 137 Cs chronologies. Estimated sedimentation rates were greater than the predicted sea level rise rate on the Accra Ghana Coast. Anthropogenic processes augmented the natural fluxes of trace metals into the Sakumo II estuary during the last seven years. Natural processes accounted for more than 90% of the total flux of metals into the three estuaries.