Assessment of surface-water acidification using diatoms as paleoecological indicators in low-alkalinity lakes in Nova Scotia, Canada with a focus on lakes in Kejimkujik and Cape Breton Highlands National Parks

Environmental changes in low-alkalinity Nova Scotia lakes related to deposition of anthropogenic-sourced strong acids were tracked using diatoms as paleoecological indicators. As all Nova Scotia study lakes have pH = ∼7.0, a diatom-environment calibration set was constructed from 494 study lakes in northeastern North America to better study diatom autecology and describe the range of environmental conditions present in these regions. Of the three inference models tested on this dataset, maximum likelihood best described changes in diatom-assemblages and provided more accurate diatom-based reconstructions of environmental changes. Of the five Nova Scotia study regions, lakes in Kejimkujik National Park, an area of high sulphate deposition, have been most impacted by anthropogenic acidification (mean change in pH = -0.4) due to low background pH values (mean pre-industrial pH = 5.8). Timing of the onset of acidification in Kejimkujik National Park was between ∼1920 and ∼1940 depending on lake sensitivity. Other high deposition areas (i.e. Bridgewater and Yarmouth) had higher background pH values (mean pre-industrial pH = 6.2 and 6.3, respectively) and were less affected by strong acid inputs. Lakes in Cape Breton Highlands National Park, also an area with low lakewater pre-industrial pH values (mean = 5.8), were not affected by acidic deposition (mean pH change = -0.1) as they are located in an area of relatively low sulphate deposition.