Are Minnesota lakes warming? And if so when?

Casey Schoenbeck

Sentinel lakes coordinator, Minnesota Department of Natural Resources

Abstract

Water temperature affects most lake biological, chemical, and physical processes, making it an important metric for the long-term monitoring of lake ecosystems.  Beginning in 2008, the Sentinel Lake Program, with the help of MNDNR Fisheries Areas, placed continuous water temperature loggers, either singly or as a logger chain, in the 25 Sentinel Lakes.  We used these data to explore water temperature trends using several analyses.  First, we looked at the monthly mean temperature of the shallowest temperature loggers to see if monthly means have changed across years. Second, we looked at how annual growing degree days (GDD) patterns have changed across years for each lake and ecoregion.  We found that water temperature trends are different depending on the month.  There is a high degree of natural, annual variability in water temperature data making it difficult to elucidate trends. Increasing water temperature trends were stronger in June than other months which could influence multiple lake processes such as lake stratification, life-history of organisms, autochthonous production, and dissolved oxygen depletion rates.  In this seminar we will explore the changes we are observing in Minnesota’s lakes and discuss how this may impact these systems and the biological communities that rely on them.