THE APPLICATION OF A COUPLED WATER-BALANCE SALINITY MODEL TO EVALUATE THE SENSITIVITY OF A LAKE DOMINATED BY GROUNDWATER TO CLIMATIC VARIABILITY

A dynamic hydrologic model, specifically designed to assess lake-groundwater systems, has been used to provide insight into the effects of climatic variability on Wabamun Lake and its watershed, in Alberta, Canada. This lake is typical of many lakes in the prairies of Canada or western plains of the United States in that groundwater exhibits a dominant role in the hydrologic balance of the lake. Sensitivity analyses indicate that small changes in temperature (1-2-degrees-C rise) or precipitation (5-10% decline) throughout the watershed, may significantly impact upon the quality of the lake water and the availability of groundwater resources. Specifically, a long-term temperature rise that increases evaporation, or a decrease in precipitation, will reduce the amount of water available to recharge the groundwater-flow regime. Groundwater storage in the watershed will further decline due to continued discharge to the lake. The effect of climatic variability on the quantity of water in Wabamun Lake (as reflected by its surface elevation) is relatively small. However, the salinity of the lake will increase dramatically, due to: (1) the loss of surface runoff and direct precipitation, which act to dilute the salinity: (2) increased evaporation, which concentrates the salts left in the lake water; (3) reduced surface discharge from the lake as its surface elevation falls below the elevation of the outlet, which removes dissolved mass from the lake.