Groundwater Hydrology and Quality in Drained Wetlands of the Des Moines Lobe in Iowa

Abstract

The prairie pothole region covers 700,000 km2 of North America and once contained millions of pothole wetlands but agricultural drainage was used to convert many these wetlands to agriculture. Termed “drained wetlands” in this study, groundwater hydrology and quality beneath these pothole depressions is poorly understood. In this study we characterized water table levels and nutrient concentrations at eight drained wetland sites in Iowa. During the 2011 to 2014 study period that ranged from drought to above-normal rainfall, water table levels exhibited a clear seasonal pattern, rapidly increasing in the spring with rainfall and decreasing in the late summer due to evapotranspiration (ET) and lateral flow to subsurface drainage tiles. The average water table depth ranged from approximately 90 to 130 cm near the typical tile depth in Iowa (120 cm). Results suggest that ponding observed at the farmed pothole depressions is rarely due to groundwater rise. High concentrations of NO3-N and PO4-P were present in shallow groundwater beneath the drained wetlands, averaging 16.7 and 0.4 mg l−1, respectively. Overall, both groundwater hydrology and quality of drained wetlands appear to be dominated by the agricultural land use.