HYDROLOGY OF PRAIRIE POTHOLE WETLANDS DURING DROUGHT AND DELUGE - A 17-YEAR STUDY OF THE COTTONWOOD LAKE WETLAND COMPLEX IN NORTH-DAKOTA INTHE PERSPECTIVE OF LONGER TERM MEASURED AND PROXY HYDROLOGICAL RECORDS

From 1988 to 1992 the north-central plains of North America had a drou ght that was followed by a wet period that continues to the present (1 997). Data on the hydrology of the Cottonwood Lake area (CWLA) collect ed for nearly 10 years before, and during, the recent dry and wet peri ods indicate that some prairie pothole wetlands served only a recharge function under all climate conditions. Transpiration from groundwater around the perimeter of groundwater discharge wetlands drew water fro m the wetlands by the end of summer, even during very wet years. Long- term records of a climate index (Palmer Drought Severity Index), strea m discharge (Pembina River), and lake level (Devils Lake) were used to put the 17-year CWLA record into a longer term perspective. In additi on, proxy records of climate determined from fossils in the sediments of Devils Lake were also used. These data indicate that the drought of 1988-92 may have been the second worst of the 20th century, but that droughts of that magnitude, and worse, were common during the past 500 years. In contrast, the present wet period may be the wettest it has been during the past 130 years, or possibly the past 500 years.