Soil indicators of agricultural impacts on northern prairie wetlands: Cottonwood lake research area, north Dakota, USA

Potential damage to wetlands by land-use practices has prompted a need for relatively inexpensive, reliable indicators in monitoring ecological conditions. In this study, soil classification and the following soil tests, sodium bicarbonate-extractable P, nitrate (NO3−), organic matter (OM), pH, clectrical conductivity (EC), and137Cs distribution, were used to compare four wetlands surrounded by cultivated land or grassland. Cumulic A horizons greater than 60-cm thick were found covering the wet meadow zone of the wetland surrounded by cultivated land. No cumulic A horizons were observed in wet meadow zones adjacent to grassland. Laboratory analyses of surface (0–15 cm) soil showed that the wetland surrounded by cultivated land had P cencentrations 2.5 to 6 times higher in the wet meadow and shallow marsh zones than did the other wetlands. In the wetland surrounded by cultivated land, the dominant soil separate in the wet meadow was silt, while sand was the dominant soil separate in the wet meadow zone in the other three wetlands. Phosphorus, OM, and NO3− concentrations in wet meadow subsoils (15–60 cm) were higher in the wetland surrounded by cultivated land than in the wetlands surrounded by grasslands. Cesium-137 activities were about 3 to 6 times greater in surface (0–15 cm) soils collected from upland grassy slopes compared to cultivated slopes. Soil morphology,137Cs, P, and OM data indicate higher sedimentation and fertilization rates in wetlands next to cultivated fields.