Paleolimnology and Environmental Change

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The proposed research will contribute to advancing our understanding of the impacts of acidic deposition, climate change and their interactions on lakes. My research program is on paleolimnology and long-term environmental change in lakes and rivers. Paleolimnology is the interdisciplinary science that uses the physical, chemical, and biological information preserved in lake sediments to understand how lakes change over time. Long-term perspectives are essential to understand environmental change. In the 1980s, lake sediment cores from Adirondack lakes showed that the timing and rate of lake acidification was strongly associated with acidic deposition, and that between 25-35% of Adirondack lakes acidified since pre-industrial times. These conclusions supported the 1990 amendment of the Clean Air Act, and reductions in SO2 and NOX emissions continued, resulting in the `chemical' recovery of many Adirondack lakes. Recent increases in water colour (related to dissolved organic carbon, DOC) has been associated with recovery, but could also be related to recent warming and higher rainfall. Biological recovery following chemical recovery is complex because in any individual lake, there are many possible drivers related to both regional and local factors. This study uses lake sediments from groups of morphologically similar lakes, all with undisturbed catchments and lakes, in both the Adirondacks and northwest Ontario. Both regions have experienced recent warming and general increases in precipitation. However, northwest Ontario has not experienced high loads of acidic precipitation, whereas the sulphate deposition in the Adirondack reached over >30 kg/ha/year in the 1970s, before decreasing by over 80% by 2020. The goal of this study is to understand how changes in algal (pigments, diatoms, and scaled chrysophytes) and invertebrate (cladocerans and chironomids) assemblages, since pre-industrial times in both regions, are related to patterns in S and N deposition, spectrally inferred patterns of DOC from the sediment cores, and changes in temperature and precipitation.  This paleolimnological study will be based on biological changes in a priori defined groups of lakes sampled at a sub-decadal resolution since pre-industrial times. Two distinct groups of Adirondack lakes include: a) lakes that were chronically acidic in the late 1980s; and b) Adirondack lakes with a higher pH that did not acidify but may have experienced changes in algal and invertebrate assemblages associated with decreases in DOC linked to the acidic deposition. Lakes in northwest Ontario will be the final group, providing for biological changes associated with changes in climate, and smaller changes in DOC and acidic deposition; a varved sediment record will provide information on algal seasonality, and a higher resolution record of change for northwest Ontario. Understanding the major environmental drivers of biological changes is important for effective lake management.