Ice cover and thermal regime in a dimictic seepage lake under climate change

ABSTRACT

Changes in water temperature and ice cover are important for controlling the biogeochemical and food-web processes of dimictic lakes in temperate regions. To investigate these changes, we applied a 1-dimensional hydrodynamic lake-ice model to Crystal Lake, a 20  m deep, dimictic seepage lake in northern Wisconsin, USA, to a period of 23 years (1989–2011). The model, DYRESM-WQ-I, incorporates the evolution of blue ice, white ice, and snow cover; time-varying ice and snow albedo; and 2-way coupling across the ice–water interface by incorporating components of previous ice models embedded in the hydrodynamic component of the DYRESM-WQ model. A new element of the current model is time-varying sediment heat fluxes, important to under-ice water temperatures in shallow lakes. Simulations closely reproduce the observed annual stratification regime and ice phenology with standard errors in temperature of 0.7 °C; total difference of 10–20% in ice thickness compared with measured values; and standard errors of 0.9 d for ice-on and 1.55 d for ice-off. Under a likely future climate scenario involving changes in air temperature forecasted to occur by the middle of this century (2055), results suggest an average reduction in mean ice cover thickness of about 0.18  m and an increase in surface mixed-layer temperature of up to 3.5 °C over summer. In addition, water levels decreased by 5.1  m over the simulation period, mostly in response to greater evaporation from higher surface water temperature in summer. The results have important implications for seepage lakes in temperate regions, where projected changes in precipitation with climate warming will not compensate for increased evaporation from the lake surface and the likely alteration in groundwater flows.

KEYWORDS:

• climate change
• dimictic lakes
• ice cover
• seepage lakes
• thermal regime
• water levels

Acknowledgements

Data for the model were compiled from the North Temperate Lakes Long-Term Ecological Research Project database. The project is funded by the US National Science Foundation Long-Term Ecological Research Program and University of Wisconsin Water Resources Institute USGS 104(B) Research Grant Project and the University of Western Australia Gledden Study Leave Award. We especially thank Yi-Fang Hsieh, Brett Wallace, and John Patterson for assistance with development of the ice model, and John Magnuson and the late Tom Frost of the Center for Limnology for their support and valuable discussions and comments during the early preparation of this manuscript. Paulette Homant from the Wisconsin Department of Natural Resources who provided information on groundwater characteristics of Crystal Lake is also acknowledged. We thank the Associate Editor and 2 anonymous reviewers for providing helpful comments to greatly improve the quality of this paper.

ORCID

David P. Hamilton http://orcid.org/0000-0002-9341-8777

Madeline R. Magee http://orcid.org/0000-0002-2741-2262

Chin H. Wu http://orcid.org/0000-0001-8393-1940