A study of heavy metals and radionuclides in Scottish freshwater loch sediments

• Main Author: Bryant, Charlotte L.
• Published: University of Edinburgh 1993
• Subjects: 551.9
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.642163

Heavy metals (Fe, Mn, Pb, Zn, Cu, Cd, Co and Ni) and radionuclides <SUP>210</SUP>Pb, <SUP>134</SUP>Cs and <SUP>137</SUP>Cs were studied in the sediments of Scottish freshwater lochs (acidified Round Loch of Glenhead, oligotrophic/mesotrophic Loch Lomond, eutrophic Loch Leven and Balgavies Loch and Loch Coire nan Arr in the remote north-west) to compare metal behaviour and associations in the different systems. Metal concentrations were determined in acid digested and sequentially extracted sediment and sediment porewaters. Radionuclide concentrations were measured to investigate sedimentation processes. Redox cycling of Fe and Mn was important in all the lochs. In Balgavies Loch, porewater data for Fe and Mn were related to redox conditions at the time of sampling, whereas the solid phase concentrations were still changing in response to recent water column stratification. The association of Fe with organic matter was additionally important in surface sediment of Round Loch and Loch Coire nan Arr. Mn behaviour in Round Loch was also influenced by surface water acidification via post-depositional leaching of Mn from the sediment and/or a pH-related decrease in the efficiency of Mn sedimentation, resulting in increasing Mn concentration with depth. Post-depositional mobility of Pb was not evident, despite the association of Pb with Fe oxides/hydroxides in sediments from all the lochs. This was supported by low, or non-detectable, porewater Pb concentrations and little change with depth in the relative concentrations of Pb in each fraction. Zn was generally more labile than Pb and, in Loch Coire nan Arr and Balgavies Loch, redox related release of Zn from the sediment and short-range mobility was apparent. In Round Loch, Zn concentrations, decreasing sharply towards the sediment surface, were explained by historical trends in pollutant Zn deposition to the loch, as well as a pH-related decrease in the efficiency of Zn deposition to the sediment.