Effects of Global Climate Warming on Water Quality Characteristics and Fish Habitats in Lakes of the Contiguous USA Xing Fang Ph.D., P.E., D.WRE, Associate Professor Department of Civil Engineering Auburn University Auburn, Alabama 36849, USA

Acknowledgements Thanks for NIER’s invitation and arrangement on attending the international seminar. Thanks for the support from US EPA to conduct research projects on the topic presented here.

Presentation Outline: Model overview (MINLAKE96) Database for model simulation Impacts on water temperature characteristics Impacts on snow and ice cover characteristics Impacts on dissolved oxygen characteristics Impacts on fish habitats in lakes Conclusions

1. Model Overview - MINLAKE96 MINLAKE96 uses a mixed-layer approach to simulate water temperature and dissolved oxygen distribution day by day. It is a one- dimensional model. It simulates water temperature and dissolved oxygen in open water season and ice cover period. The model can be run continuously for number of years with algorithm to model ice formation date, snow accumulation and melting, ice growth and decay, and ice melting date.

Schematic of a stratified lake with a 10 m sediment layer showing heat transfer components and water/sediment temperature profiles in the open water season and during the ice cover period Water Temperature Modeling

Dissolved Oxygen Modeling

Check one- dimensional assumption using DO and temperature measurements in Fish Lake (Minnesota)

Year-round lake model development and applications

Simulated and observed water temperature profiles in winter period for Thrush Lake, MN

Simulated and observed snow and ice thickness in winter period for Thrush Lake, MN

Model Performance  Quantitative error measurements (between measured and simulated values in 9 lakes) of the model are  Standard errors between simulated and observed ice thickness and snow depths for three lakes (128 data points over 8 years) are 0.07 m and 0.12 m, respectively.  Nine lakes are Fish Lake, Cedar Lake, Lake George, Lake Orchard, Lake Riley, Square Lake, Thrush Lake, Lake Wabasso, and Lake Waconia with total of 5,976 data pairs. Error ParameterTemperature ( o C)DO (mg/l) Standard error of estimate1.43 (0.5 for winter)1.93 R2R

2. Modeling Database: Regional Lake Designation

Frequency distributions of lake surface area, maximum depth, and Secchi depths for 3002 Minnesota Lakes.

Past climate data – 209 weather stations from 1961 to 1979 (air temperature, dew point temperature, wind speed, solar radiation, sunshine percentage, rainfall and snowfall. Future climate scenario – The second generation Canadian Climate Centre Global Circulation Model (3.75 o x 3.75 o ), apply for monthly increments or ratios.

Projected air temperature increase due to climate warming

Past ( ) and projected 2xCO 2 climate scenarios (monthly averages) at Duluth, MN.

3. Impacts on Snow and Ice Cover Characteristics Parameters studied: frequency of occurrence and duration of ice cover, dates of ice-in (freeze-over) and ice-out (melting), maximum ice and snow thickness.

Simulated earliest ice-out date under past (1962 – 1979) and future (2xCO 2 ) climate scenario

Simulated annual cumulative days of ice cover on small, medium- depth lakes under past climate conditions Projected difference of annual cumulative days of ice cover on small, medium- depth lakes

4. Impacts on Water Temperature Characteristics Parameters studied: maximum and minimum surface and bottom water temperatures,.

Strongly dependent on geographic location More or less independent of lake types

Regional Lake Types for Contiguous USA Study

Simulated maximum bottom water temperature under the past climate conditions

Simulated maximum temperature difference between lake surface and bottom

Simulated change or difference (GCM- Past) on seasonal stratification ratio (during open water season) for deep medium lakes

5. Impacts on Dissolved Oxygen Characteristics Parameters studied: minimum surface and hypolimnetic DO during open water season and ice cover period, number of dates and percent lake volume with anoxic conditions.

Simulated average dissolved oxygen (mg/l) isopleths for a shallow eutrophic lake (10 km 2 ) near Duluth, MN under past and future climate scenario winter fish kill

 DO criteria for three fish guilds: cold-water and cool- water fish mg/l; and warm-water fish mg/l A schematic distribution of survival and growth of fish in a seasonally stratified lake 6. Impacts on Fish Habitats in Lakes

GuildLower good- growth temperature LGGT, ( o C) Upper good- growth temperature UGGT, ( o C) Upper lethal temperature LT, ( o C) Optimum temperature OT, ( o C) Dissolved Oxygen DO, (mg/l) Cold-water 1 Mean Range 9.0 ( ) 18.5 ( ) 23.4 ( ) 15.3 ( ) 3.0 Cool-water 2 Mean Range 16.3 ( ) 28.2 ( ) 30.4 ( ) 25.1 ( ) 3.0 Warmwater 3 Mean Range 19.7 ( ) 32.3 ( ) 34.5 ( ) 29.2 ( ) 2.5 Thermal and dissolved oxygen criteria for cold-, cool- and warm-water fish guilds 1 Cold-water species: brook trout, brown trout, chinook salmon, chum salmon, coho salmon, mountain whitefish, pink salmon, and rainbow trout.

Simulated depth- time contour for shallow large eutrophic lake near Duluth, MN

Simulated depth- time contour for cool- water fish in medium- depth medium- size trophic lake

Fish Habitat Model Validation Simulated fish habitats were compared with fish observations in 3002 Minnesota lakes. Simulated fish habitats agree with observations in all medium and deep lakes, small and medium- size shallow oligotrophic lakes for cold-, cool-, and warm-water fish guilds. Winterkill was simulated to occur in shall eutrophic and mesotrophic lakes. Sensitivity analysis shows that a lower DO limit (<0.5 mg/l) produced better agreement with the fish observation database than higher limits.

Distribution of number of lake types with suitable fish habitat for cold- water fish at 209 locations in the contiguous USA

Distribution of number of lake types with suitable fish habitat for cool- water fish at 209 locations in the contiguous USA Winterkill Summerkill

Distribution of number of lake types with suitable fish habitat for warm- water fish at 209 locations in the contiguous USA

Conclusion Remarks Simulated water quality and ice cover characteristics were related to lake geometric and trophic characteristics and to geographic location. The 2xCO 2 climate scenario is projected to increase lake surface temperatures by up to 5.2 o C when CCC GCM projects an increase of mean annual air temperature up to 6.7 o C. The duration of seasonal summer stratification is projected to be up to 66 days longer under a 2xCO 2 climate scenario, and this leads to longer period of anoxic hypolimnetic conditions that will result various negative environmental and ecological impacts in lakes.

Conclusion Remarks Projected climate warming has strong impact on ecological conditions in ice-covered lakes, e.g., later ice formation, earlier ice-out, and short ice cover period (shorten up to 90 days). Climate warming is projected to reduce the number of locations in the contiguous U.S. where lakes have suitable cold- and cool-water fish habitat, by up to 45% and 30%, respectively. Summerkill under the projected 2xCO 2 CCC climate scenario is projected to have a significant negative influence on cold-water fish in northern lakes and cool-water fish in southern lakes of the contiguous U.S., where suitable habitat existed under historical conditions.

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