Surface sediment elemental compositions of 167 Canadian lakes show widespread exceedance of quality guidelines for metals

Sediments form a key part of lake ecosystems and play important roles in biological and chemical processes. Yet in the most lake-rich country in the world, Canada, there was no standardized portrait of lake sediment elemental compositions and knowledge was lacking about how frequently field data exceeded sediment quality guidelines. To address these gaps and generate a more comprehensive understanding of large-scale spatial patterns in surface sediment geochemistry, we undertook an analysis of 167 lakes sampled by the NSERC Canadian Lake Pulse Network. We analyzed sediment elemental compositions and identified three geographic regions with distinct sediment geochemistry by applying a cascade multivariate regression tree analysis (cMRT). Of these regions, sediments in eastern Canada had relatively high concentrations of metals, while central Canada and southwestern Ontario lakes had relatively high concentrations of detrital elements. Urbanization was correlated with elevated sediment metal concentrations whereas agricultural and pastoral activities were correlated with elevated concentrations of detrital elements. Comparisons between sites with low and high levels of anthropogenic land use indicated limited differences in sediment elemental compositions. However, 70 % of all sites exceeded the guidelines for at least one of the six potentially toxic elements with published sediment quality guidelines that we examined. Since these guidelines were designed to be conservative, we recommend the development of regional sediment quality guidelines for implementation across Canada.