Processes Controlling the Source, Movement, and Release of Soil Phosphorus in Midwestern Streams from Pasture and Crop Land.

There is a growing body of evidence that much of the phosphorus delivered to the Mississippi River from agricultural landscapes originates from stream bed and bank erosion. This erosion seems largely the result of the combined actions of altered watershed hydrology, sediment accretion from historic erosion of uplands, and riparian land management. To effectively target soil conservation and water management practices that reduce P loading to waterways, identification and quantification of key processes controlling the release and transport of P in Midwestern streams is critical.

Based on preliminary studies, a detailed three-year assessment of stream bank and sediment-derived P contribution was initiated in 2014. Specific objectives of the study include: quantify annual flux of sediment-bound P from channel erosion; quantify annual flux of soluble P; determine how adsorption/desorption and precipitation/dissolution processes regulate P mobility; and estimate the net contributions of channel, groundwater, and overland flow sources of P loads.

The study focuses on Walnut Creek, a perennial, warm-water stream that drains a 5218 hectare, agriculturally-dominated watershed in Jasper County, Iowa. The Walnut Creek watershed is unique in that it provides an opportunity to investigate P sourcing and transport in the contexts of both intensive agriculture and large-scale landscape restoration (10% of the watershed has been restored to native tallgrass prairie). An additional asset of the study is the fact that Walnut Creek has a near-continuous record of water quality monitoring dating back to 1995.