Responses of Nonpoint Source Pollution to Flow-Impediment Structure in Surface-Drained Row Crops

Pierce, S., Poganski, B., Kroger, R., Prevost, D., Ramirez-Avila, J. J., Pierce, T., Flora, C., & Brinson, A. (2013). Responses of Nonpoint Source Pollution to Flow-Impediment Structure in Surface-Drained Row Crops. AWRA 2013 Spring Specialty Conference- Agricultural Hydrology and Water Quality. St. Louis, MO.

This study monitors movement of water, total suspended solids (TSS), and nutrients in three intermittently flowing agricultural ditches in surface-drained rowcrop fields. Data were collected several months preceding and following the implementation of controlled drainage practices including riser boards, slotted pipes, and low-grade weirs. Water samples were collected both during and after high discharge events via grab sampling and different automated techniques. Concentrations of ammonia and dissolved inorganic phosphorus (DIP) showed relatively little variation compared with nitrate, total inorganic phosphorus (TIP), and TSS. TIP and TSS were significantly higher during high discharge events, with TIP concentrations of 10 ppm not uncommon. After storm flows receded, TIP concentrations were around 1 ppm, only slightly higher than DIP concentrations. Although nitrate concentrations varied from less than 1 ppm to over 15 ppm, it was not clear if nitrate was following a similar pattern of being flushed through the system during storms. Preliminary analyses of hydrographs from high precipitation events (not weighted by precipitation rate or duration) indicate that installation of controlled drainage increased time to peak (p < 0.001), which was likely related to concurrent decreases in storm flow TIP concentrations (p&#8804;0.001). With regard to nitrate, only one of the two ditches in which controlled drainage was implemented demonstrated a significant decrease in storm flow concentrations. Results indicate that impediment structures placed in concentrated flow paths of surface-drained agriculture can serve to decrease effluent concentrations of particulate-bound nutrients within the first year of implementation. These data will be used to estimate nitrate and TIP load efflux relative to fertilizer application rates in order to gauge the overall effectiveness of these structures for retention of nonpoint source pollutants.