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The ciscoCoregonus artediis the most common coldwater stenothermal fish in Minnesota lakes. To project its chances of survival under future warmer climate conditions, an oxythermal habitat variable, i.e., the water temperature at 3 mg/L of dissolved oxygen in stratified lakes (TDO3) was calculated from simulated daily temperature and DO profiles in 30 lake types under past (1962–2008) climate conditions and two future climate scenarios. The mean daily TDO3 values over a 31-d fixed benchmark period were calculated for each of the simulated years and then averaged over the simulation period for each lake type. The multiyear average TDO3 was used to identify cisco refuge lakes in Minnesota. Six hundred twenty known cisco lakes in Minnesota were divided into three groups, tier 1 refuge lakes having the most suitable habitat for ciscoes, tier 2 refuge lakes having suitable habitat for ciscoes, and tier 3 or nonrefuge lakes supporting ciscoes only at a reduced probability of occurrence. The multiyear average TDO3s for tier 1, 2, and 3 lakes were ≤11°C, 11–17°C, and >17°C, respectively. Projected increases in the multiyear average TDO3 under the two future climate scenarios averaged 2.6°C to 2.9°C. About one-third of the 620 lakes that are known to have cisco populations were projected to maintain viable cisco habitat under the two future climate scenarios. These lakes have a Secchi depth greater than 2.3 m (mesotrophic and oligotrophic lakes) and are seasonally stratified. Received November 9, 2011; accepted July 13, 2012 [ABSTRACT FROM PUBLISHER]

A deterministic, process-oriented, dynamic and one-dimensional year-round lake water quality model, MINLAKE2010, was developed for water temperature (T) and dissolved oxygen (DO) simulations to study impacts of climate warming on lake water quality and cisco fish habitat. The DO model is able to simulate metalimnetic oxygen maxima in vertical DO profiles of oligotrophic lakes. The model was calibrated with profile data from the 28 study lakes in Minnesota; two-thirds of them are deep mesotrophic/oligotrophic lakes that support cisco, a coldwater fish species. The average standard error of estimate against measured data was 1.47 °C for T and 1.50 mg/L for DO. Oxythermal habitat parameter TDO3 (T at DO = 3 mg/L) was determined from simulated daily T and DO profiles under past and future climate scenarios in the 28 study lakes. Average annual maximum TDO3 (TDO3AM) for the 28 study lakes is projected to increase on the average of 3.2 °C under the MIROC 3.2 future scenario, while the occurrence day of TDO3AM is not much different under past and future climate scenarios. Both physical processes (mixing characteristics related to lake geometry ratio) and trophic status control temperature and DO characteristics and then affect cisco habitat in a lake. [ABSTRACT FROM AUTHOR]

Fish habitat in lakes is strongly constrained by water temperature (T) and available dissolved oxygen (DO). With climate warming both of these water quality parameters will change. A fish habitat simulation model was developed to calculate an oxythermal habitat variable, TDO3, i.e. water temperature at 3mg/L of DO, from simulated daily T and DO profiles and used to determine potential refuge lakes for lake herring or cisco (Coregonus artedi) in Minnesota. Daily T and DO profiles were simulated using a deterministic, unsteady, one-dimensional (vertical) year-round lake water quality model (MINLAKE2010) that was developed specifically for transparent deep lakes. Profiles for thirty Minnesota cisco lakes were simulated with the MINLAKE2010 model using recorded (1961–2008) weather data or projected future climate scenarios (CGCM 3.1 and MIROC 3.2) as model input. The average of daily TDO3 values (called ATDO3VB) over a 31-day sliding or variable benchmark period (VB), was first calculated from daily TDO3 values. The annual maximum of ATDO3VB was retained for each simulated lake and year, and the average of 47 ATDO3VB values (called AvgATD3VB) obtained for the 1962–2008 simulation period was compared to oxythermal stress criteria for cisco determined from the analysis of field data. Isopleths of AvgATD3VB were interpolated for the 30 simulated lakes on a plot of Secchi depth vs. lake geometry ratio used as indicators of trophic state and summer mixing conditions, respectively. Marking the 620 Minnesota lakes with identified cisco populations on the plot of AvgATD3VB allowed to partition the 620 lakes into the three tiers depending on where they fell between the isopleths: lakes with AvgATD3VB ≤11°C (Tier 1 lakes) were selected to be most suitable for cisco; lakes with 11°CVB ≤17°C (Tier 2 lakes) had suitable habitat for cisco; and non-refuge lakes with AvgATD3VB >17°C (Tier 3 lakes) would support cisco only at a reduced probability of occurrence or not at all. About 160 existing cisco lakes were thus projected to be suitable refuge lakes (Tier 1 plus Tier 2) under the two future climate scenarios. The remaining lakes were projected to loose their cisco supporting ability. The methodology to identify the refuge lakes was applied to a cisco kill that occurred in 18 cisco lakes in Minnesota in the hot summer of 2006, and was able to identify the majority of these lakes as non-refuge lakes. [Copyright &y& Elsevier]