Using multi-proxy measures of lake sediments to identify environmental changes in protected watersheds of British Columbia, Canada

Abstract

Paleolimnology uses lake sediments to recognize environmental trends through time. This is useful in watersheds with a knowledge gap of historical environmental conditions or missing perspectives of long-term ecosystem responses. Cameron Lake sediments were used to identify historical trends of Didymosphenia geminata valves in a mat-prone watershed. The lake core represented approximately 600 years of sediment accumulation and findings demonstrated that D. geminata was a historical member of the riverine diatom community. Though in low abundance in older sediment, valve concentrations increased in the early 1900s and peaked at ~1990s, coinciding with observations of mats. Geochemical proxy measures were then analyzed to explore if watershed disturbance was a driver of environmental conditions favouring D. geminata mat formation. No clear geochemical trends were identified, thus watershed disturbance was not associated with D. geminata proliferation in the ~600 year record. Cultus Lake has experienced urbanization, resulting in cultural eutrophication. Over the past century, water quality metrics suggested a decline in hypolimnetic oxygen, however there is a lack of temporal knowledge on the biological responses to eutrophication. Cultus Lake sediments were analyzed for temporal trends in benthic invertebrate assemblages. Chironomid assemblages shifted from taxa associated with oligotrophic, high oxygen conditions to an assemblage indicative of low oxygen conditions. This shift began in the 1920s, coinciding with forestry and agricultural activities. A recent assemblage shift in the 1970s indicated that the assemblage is now dominated by generalist taxa. Findings suggest the benthic environment of Cultus Lake has less oxygen availability in recent decades. This temporal information can be used in future lake management and recovery plans for species of concern at Cultus Lake.