Refuge Lake Reclassification in 620 Minnesota Cisco Lakes under Future Climate Scenarios

Cisco (Coregonus artedi) is the most common coldwater stenothermal fish in Minnesota lakes. Water temperature (T) and dissolved oxygen (DO) in lakes are important controls of fish growth and reproduction and likely change with future climate warming. Built upon a previous study, this study uses a modified method to identify which of 620 cisco lakes in Minnesota can still support cisco populations under future climate and therefore be classified as cisco refuge lakes. The previous study used oxythermal stress parameter TDO3, the temperature at DO of 3 mg/L, simulated only from deep virtual lakes to classify 620 cisco lakes. Using four categories of virtual but representative cisco lakes in modified method, a one-dimensional water quality model MINLAKE2012 was used to simulate daily T and DO profiles in 82 virtual lakes under the past (1961–2008) and two future climate scenarios. A multiyear average of 31-day largest TDO3 over variable benchmark (VB) periods, AvgATDO3VB, was calculated from simulated T and DO profiles using FishHabitat2013. Contour plots of AvgATDO3VB for four categories of virtual lakes were then developed to reclassify 620 cisco lakes into Tier 1 (AvgATDO3VB < 11 °C) or Tier 2 refuge lakes, and Tier 3 non-refuge lakes (AvgATDO3VB > 17 °C). About 20% of 620 cisco lakes are projected to be refuge lakes under future climate scenarios, which is a more accurate projection (improving the prediction accuracy by ~6.5% from the previous study) since AvgATDO3VB was found to vary by lake categories