The impacts of whole-lake acidification and eutrophication on the accumulation of lead in sediments from manipulated lakes in the Experimental Lakes Area (IISD-ELA).

Acidification and eutrophication are common limnological stressors impacting many water bodies across the globe. While the negative impacts of these stressors on limnetic communities are generally known, their influence on the accumulation of specific sediment constituents, such as metals, remains unclear. Benefitting from past research and long-term monitoring, lakes at the International Institute for Sustainable Development - Experimental Lakes Area (IISD-ELA) in northwestern Ontario, Canada are invaluable to understand the extent to which these two common lake stressors can influence the accumulation of metals in lacustrine sediment. To address these issues, sediment cores were retrieved from six lakes: four were subjected to past experimental acidification or eutrophication and two were reference lakes. Focusing on elemental lead (Pb), a metal known to have accumulated in lake sediments worldwide and generally exhibiting a relatively small fraction of terrigenous input, we assessed the hypothesis that greater accumulation of Pb would be observed in lakes subjected to eutrophication, while the reverse was expected for lakes subjected to acidification experiments. Our analyses support this hypothesis, whereby relatively low enrichment was recorded in sediments deposited in the acidified lake during the manipulation era. On the other hand, eutrophied lakes demonstrated a strong enrichment in Pb during experimental manipulation. When investigating the mechanisms behind these divergent responses, we found epilimnetic dissolved organic carbon (DOC) and conductivity were associated with a relative increase in Pb accumulation in sediments. Acidic pH is also expected to mediate these responses by decreasing epilimnetic DOC concentrations leading to reduced Pb accumulation in the sediment.