Existing dataset suggests lakes in agricultural watersheds are warming faster than urban or forested lakes

Abstract

Lake temperatures are important drivers of ecological and ecosystem processes, including influencing organism physiology and biogeochemical rates. Over the past several decades, lake surface temperatures have warmed due to increases in air temperatures driven by anthropogenic climate change. Similarly, increases in surface temperatures have contributed to stronger water column stratification, which also affects oxygen dynamics, nutrient cycling, and organism habitat availability. To date, we know relatively little about how land use impacts lake temperatures. We hypothesized a greater proportion of urban land use within the watershed may increase warming in lakes and lead to increased strength of stratification through time relative to other land use types, as urban heat islands and warmer runoff would contribute to greater warming. We explored trends in lake surface temperatures and stratification strength using a long-term dataset of widely distributed lakes. Contrary to our expectations, we did not observe greater warming in urban lakes; however, we did see higher rates of warming with greater agricultural land use in the watershed. We did not observe any patterns between land use and stratification strength, but stratification strength increased through the time series across lakes. Our results suggest greater warming is an important consideration for projecting the ecological implications for land use change and agricultural expansion. Our assessment of a multi-continental set of lakes also highlights the need to emphasize long-term data collection in human-impacted systems.