Riparian land-use impacts on stream and gully bank soil and phosphorus losses with an emphasis on grazing practices

Abstract

The tall-grass prairies, wetlands and forests that dominated the Iowa landscape have been replaced by annual row-crops and grass pastures that occupy more than 90 % of the landscape today. Because of these changes water reaches the streams and gullies much faster and has led to incised streams and an extensive growth of gully networks. Stream and gully banks are major contributors of the nonpoint source sediment and phosphorus. Reducing these pollutants is a priority to maintain healthy streams. The objective of this study was to compare stream and gully bank soil and phosphorus looses under different land-use practices in three Iowa regions. The hypothesis was that stream and gully bank erosion would decrease in the following order: annual row-cropped fields, continuous pastures, rotational pastures, intensive rotational pastures, pastures with cattle excluded from the stream, grass filters and riparian forest buffers. In rotational and intensive rotational grazing the pastures are divided into paddocks. One paddock is grazed at a time while the others are rested. To estimate soil losses for each treatment, erosion pins were used for stream and gully bank rates and all the severe eroding site heights and lengths were measured. Estimating soil total phosphorus concentrations from the stream and gully bank faces allowed us to estimate phosphorus losses. In addition phosphorus concentrations in riparian, stream bed and loafing areas of all treatments were measures. Riparian forest buffers, grass filters and pastures with the cattle excluded from the stream had the lowest soil and phosphorus losses from stream and bank erosion. Row-cropped fields had high soil and phosphorus losses that were similar to the continuous pastures. There are