Spatio-temporal accumulation patterns of trace metals in sediments of a large plateau lake (Erhai) in Southwest China and their relationship with human activities over the past century

Lake sediments are important archives of environmental changes and human activities, but the influences of human processes and lake spatial heterogeneity on the sedimentation of trace metals are still poorly understood. Based on 16 sediment cores from Lake Erhai (249 km2), trace metals (including As and Hg) contamination over the past century and the spatial heterogeneity and their response to the in-lake and in-watershed factors were explored. The elements were divided into two groups by cluster analysis: group I included As, Cd, Hg and Pb, and group II included Al, Fe, Ti, Cr, Cu, Ni and Zn. The element concentrations were generally stable in the low section of the cores, and started to increase since the 1980s for elements in group I, while element concentrations in group II generally decreased since the 1990s. Enrichment factor analyses identified group I elements as typical pollutants, and suggested that contamination started from the 1980s and reached maximum in the 2000s. Regional atmospheric deposition from ore mining and smelting was the main source, and anthropogenic As and Cd were also affected by watershed industrial discharges. Multi-core analyses indicated that spatial distributions and accumulation of As, Cd, Hg and Pb in the cores were affected by both human activities and sediment supply. Different from metal contamination pattern in surface sediments, high anthropogenic metal fluxes appeared in the central lake areas due to more sediment accumulation. Our study highlighted that reliable estimation of whole-lake pollutant inventories strongly relied on comprehensive analyses of multiple sediment cores and legacy input from the catchment.