Submitted to: American Geophysical Union
Publication Type: Abstract only
Publication Acceptance Date: 9/16/2011
Publication Date: 12/5/2011
Citation: Buda, A.R., Kleinman, P.J.A., Bryant, R.B., Schmidt, J.P., Drohan, P.J., Folmar, G.J., Dewalle, D.R. 2011. Fragipan controls on nitrogen loss by surface and subsurface flow pathways in an upland agricultural watershed [abstract]. American Geophysical Union. Paper No. B11C-0510. Interpretive Summary: An interpretive summary is not required.
Technical Abstract: Improved understanding of nutrient transport by surface and subsurface flow pathways is critical to protecting water quality in agricultural watersheds. We sought to compare nitrogen loss in overland and subsurface flow on two opposing hillslopes (north versus south facing), each with contrasting soils. The experimental hillslopes are located within FD-36, a 39.5 ha agricultural watershed in the Valley and Ridge physiographic region of central Pennsylvania. A total of six storm events were monitored from September to December of 2010 using small hillslope trenches (1 m wide × 3 m long × 1.5 m deep) constructed to route, measure, and sample subsurface flow from major soil horizons (bottom of A horizon, center of argillic or cambic horizon, top of fragipan or top of parent bedrock) as well as overland flow. On each hillslope, one trench was located at the shoulder position in well-drained residual soils, while the second trench was situated at the footslope position in poorly drained fragipan soils. Preliminary results show that the six storms at the residual soil sampling sites generated small volumes of runoff (1,200 L) that was mainly a mixture of overland flow and shallow lateral subsurface flow draining the A horizon (88%). These flows had high concentrations of total nitrogen (8.7 to 30.3 mg per L), but produced relatively small nitrogen losses. In contrast, much larger volumes of runoff (15,000 L) were generated at the fragipan location over the course of the six events. Here, the majority of runoff was subsurface flow, with most of the water emanating from the gutter that drained the top of the fragipan surface (73%). Nitrogen concentrations in runoff from the fragipan sites were dilute in comparison to runoff from the residual soil sites (1.0 to 6.4 mg per L), but the large runoff volumes led to substantially higher nitrogen losses. The overall patterns in this study demonstrate the importance of subsurface flow from fragipan soils as a controlling variable on nitrogen loss from agricultural watersheds.