Fossil chironomids as indicators of water quality changes in south-central Ontario and Qu'Appelle Valley (Saskatchewan) Lakes

Subfossil chironomid assemblages were examined from sediment cores from Qu'Appelle Valley (Saskatchewan) lakes to determine how water quality has changed since European settlement in the region, and to determine the relative influence of climate, urban and rural factors on variations in chironomid assemblages. Results indicated that these lakes were naturally productive; however, water quality has declined in the 20th century due to anthropogenic disturbances. Results suggest that sewage inputs from the cities of Regina and Moose Jaw severely impacted water quality in downstream lakes, and that these impacts lessened in successive lake basins further downstream. Variance partitioning analysis (VPA) indicates that, during the period ∼1920–1993, climate-related factors were more important than urban or rural factors in explaining variations in subfossil assemblages. Chironomid communities may be more influenced by climate, compared to algal communities, due to their longer life cycle.; Ordination (Redundancy Analysis (RDA), Canonical Correspondence Analysis (CCA)) of chironomid head capsule assemblages from surface sediments of 59 south-central Ontario (Canada) shield lakes suggested that deepwater oxygen conditions were the most important explanatory environmental variable. Variance parititioning using partially constrained RDAs and CCAs indicates that the variation explained by oxygen conditions was significant (p < 0.05) and partially independent from the variation explained by trophic status and take depth. Inference model statistics (e.g. correlation between observed and inferred values, root mean squared error of prediction) suggest that subfossil chironomids can be used to develop robust and reliable quantitative oxygen inference models.; Application of an end-of-summer, volume-weighted, hypolimnetic oxygen (avg[VWHO]) inference model to surface and bottom chironomid assemblages from south-central Ontario lakes indicated that current hypolimnetic oxygen conditions were similar in most lakes to pre-industrial conditions. Present-day hypolimnetic oxygen was higher, however, in shallow takes with managed hydrological regimes and increased lake levels due to dam construction. Present-day hypolimnetic oxygen levels are generally lower in lakes with natural hydrological regimes, suggesting a possible impact of recent climate change, however the patterns of change are subtle.