Systematics in the size structure of prairie pothole lakes through drought and deluge

This study examines the response of a complex lake-wetland system to variations in climate. The focus is on the lakes and wetlands of the Prairie Coteau, which is part of the larger Prairie Pothole Region of the Central Plains of North America. Information on lake size was enumerated from satellite images and aerial photos and yielded power law relationships for different hydrological conditions. Of particular interest is a recent drought and deluge sequence, 1988-1992 and 1993-1998. Results showed that lake sizes followed well-defined power laws that changed intra-annually and interannually as a function of climate. The power laws for spring seasons in 1987, 1990, 1992, 1997, and 2002 have a relatively constant slope. However, slopes changed with time within each year. These lines produced from Landsat images and aerial photos describe a systematic variation in sizes for lakes ranging in area from 100 m(2) to more than 30,000 m(2). This tendency for lake size to follow a power law coupled with area measurement from aerial photos taken on 29 July 1939 provides a basis for reconstructing the distribution of pothole lakes in summer 1939, near the end of the Dust Bowl drought. The study shows that the areas of smaller lakes are profoundly affected seasonally by the spring snowmelt and evaporation. The areas of larger lakes are influenced more slowly by longer-term periods of drought and deluge.