Groundwater and surface-water interactions of two lakes in North Dakota are related to climatic variations over the past 50 years. Moon Lake (46E 51'N, 98E 09'W) and Coldwater Lake (46E 01'N, 99E 05'W), located approximately 100 km apart, have reacted quite differently to climatic changes over the last 2000 years. Salinity reconstructions show that about 1200 A.D. Coldwater Lake became more saline, and Moon Lake became fresher (Fritz, 2000). Because strong regional climatic variations are unlikely to exist over such a short distance, the variance is hypothesized to result from differences in groundwater flow patterns.

Through installation of piezometers around the catchments of both lakes and analysis of the regional and local groundwater flow patterns, it was concluded that neither Moon Lake or Coldwater Lake are groundwater recharge areas at present.

To identify how these lakes change relative to local climate variation, Geographic Information System (GIS) processes were applied to aerial photographs obtained for both lakes over the past 50 years, to calculate the surface area and volume changes over time. These data were then compared to corresponding measurements of annual precipitation, conductivity, local groundwater-levels, and Palmer Drought Index values. These analyses indicate that the main component of the water budget for both lakes comes from local precipitation.