Patterns and trends in lake concentrations of dissolved organic carbon in a landscape recovering from environmental degradation and widespread acidification

Abstract

Concentrations of dissolved organic carbon (DOC) have increased in lakes throughout North America and Europe over the last three decades. Recovery from acid deposition and climate change have both been postulated as the primary mechanisms for the increase in DOC. To provide a clearer insight into the mechanisms responsible for increasing DOC we evaluated changes in lake and peat porewater chemistry collected in an area of approximately 33,000 km2 surrounding Sudbury, Ontario, a region undergoing dramatic recovery from acidic deposition. DOC concentrations varied considerably among the 44 lakes and over time (samples annually from 1981 to 2018), but the Sens Slope value showed a strong increase in lake DOC concentration over time, at 0.05 mg/ L y-1 (p < 0.001) that was related to increasing pH [0.03 units y-1, p < 0.001] and decreasing lake SO4 concentration [-0.24 mg/ L y-1; p < 0.001 …