A novel method using sedimentary metals and GIS for measuring anthropogenic change in coastal lake environments

A new method using sedimentary metals and geographic information system as indicators for assessing temporal and spatial anthropogenic change in estuaries has been applied to a large coastal lake (Lake Macquarie) in New South Wales, Australia. Two vintages of data (1975 and 2003) on surficial sediment metal (Cd, Cu, Pb and Zn) concentrations combined with Pb-210 core profiles were used to determine past changes in sediment quality and to predict possible future relaxation rates for the entire lake area in response to change in anthropogenic pressure. Sediment cores showed distinct vertical profiles; sedimentation rates in the northern part of the lake were consistent (14 mm year(-1)) over the 55-year period investigated. Surficial metal concentrations were highest in the 1975 sediment than in the 2003 samples, with the northern part of Lake Macquarie having much greater metal concentrations than the rest of the lake. Past and future declining sedimentary metal concentrations in the northern part of the lake were expected due to the closure of a nearby Pb-Zn smelter; however, possible increases in Cu in the south of the lake to the year 2020 were surprising. The new method presented in this study can assist estuary managers by providing data on past, present and future conditions, which are essential in making informed decisions for the improvement of estuarine systems.