Date of Award
Master of Science
Agricultural and Biosystems Engineering
Agricultural and Biosystems Engineering; Civil Engineering
Michelle L. Soupir
The Upper Midwestern United States is extensively tile drained and drainage provides a preferential pathway for nutrient losses from cropland. Phosphorus (P) in subsurface drainage is the focus of current research on agricultural nutrient losses, however, the effects of best management practice (BMP) implementation on drainage phosphorus losses is unclear. Phosphorus and suspended solids losses were monitored at five sites — two streams, two tile drain outlets, and a grassed waterway — located in three paired subwatersheds of Iowa’s Black Hawk Lake watershed. Subwatersheds ranged in size from 221.23-822.49 hectares and BMP implementation ranged from 22.5-87.5% of the subwatershed area. Specific water quality analytes examined include total phosphorus (TP), dissolved reactive phosphorus (DRP), total suspended solids (TSS), and volatile suspended solids (VSS). The results from the study reveal that drainage analyte losses can equal or exceed those of surface waters. Precipitation events accounted for the majority of analyte losses at each of the subwatersheds. An analysis of intra-event samples from the five monitoring sites showed that flow is the driving factor of event analyte concentrations. Results from the paired watersheds indicate that BMP implementation has a positive impact on P and suspended solids losses in both surface and drainage waters. This study also evaluated the performance of the new drainage phosphorus and sediment loss model, SoilIceDB, at the small catchment scale as well as its applicability to cropland outside of Scandinavia. Preliminary results suggest that with more extensive calibration, the model will be able to acceptably simulate drainage flow and DRP losses. Establishing relationships between BMP implementation and P losses and a successful model will assist water quality improvement projects and could identify areas for remediation and BMP implementation.
Brendel, Conrad, "Evaluation of subsurface drainage on phosphorus losses and application of the SoilIceDB model in the Black Hawk Lake Watershed, Iowa" (2017). Graduate Theses and Dissertations. 16273.