Trace element distribution and pollution status of surface sediments in lakes impacted by volcanic activity

Abstract

Purpose: The main objective of the study was to assess the environmental quality status of the sediments of eleven Patagonian lakes regarding the concentrations of five trace elements, evaluating the influence of volcanic activity and water and sediment parameters on element concentration and distribution. Materials and methods: Surface sediment samples from 11 lakes were collected at different depths for granulometric analysis, organic matter (OM) contents, and determination of As, Br, Cr, Hg, Ni, and Zn concentrations. Physicochemical variables of the water column were also measured. The quality of the sediments and the potential ecological risks were assessed by comparing the concentrations of elements with local and global geochemical background values and with consensus-based sediment quality guidelines and through the calculation of environmental quality indices (enrichment factor and index of geo-accumulation). Results and discussion: A higher proportion of sand with a lower %OM characterized the surface sediments in lakes close to the volcanic complex (PCCVC), while a higher proportion of silt–clay with a higher %OM was found in sediments from lakes furthest from the PCCVC, consistent with the expected gradient of volcanic ash size deposited in the lakes. The presence of volcanic ashes in sediments seems to dilute trace element concentrations of samples, having sediment samples from lakes near the PCCVC lower concentrations of Br, Cr, and Ni than the furthest lakes. Environmental quality indices indicated minimal to moderate enrichment/contamination in sediments from deep lakes near the PCCVC and significant to high enrichment/contamination in sediments from lakes far from the volcano and in the shallower lakes. The concentrations of As, Cr, and Ni in six of the 11 sampled lakes are at levels considered harmful for sediment-dwelling organisms according to north hemisphere guidelines. Conclusions: Despite being in a protected area, the sediments of some Patagonian lakes have concentrations of potentially toxic elements at levels that may cause pollution and be of risk to the aquatic biota, with the volcanic ashes acting to dilute this effect.