ABSTRACT
Edge-of-field practices such as denitrifying woodchip bioreactors can be used to improve the water quality of agricultural effluents. This study evaluated the effectiveness of four field-scale woodchip bioreactors in removing nitratenitrogen (nitrate-N) from subsurface drainage in eastern South Dakota. Four woodchip bioreactors were installed and monitored between 2014 and 2016 near Arlington, Baltic, Hartford, and Montrose, South Dakota. Results showed that reduction in nitrate-N concentration for the four bioreactors ranged from 7 % to 100 %, corresponding to removal rates of 5 to 27 g N/m3/day for the four bioreactors during the study period. Average Nitrate-N load reduction in the four bioreactors studied ranged from 39 % to 89 % during the study period. Reduction of nitrate-N in the four bioreactors decreased, on average, by 30 % when temperature dropped below 12 °C during the study period. Flow rate and hydraulic retention time (HRT) also influenced nitrate-N removal in the bioreactors as samples collected immediately following rainfall events showed high nitrate-N load removal compared to samples collected later after the rainfall events during the study period.
Subject(s)
Denitrification , Nitrogen , Nitrates , South Dakota , Bioreactors , Nitrogen OxidesABSTRACT
The verification of remotely sensed estimates of surface variables is essential for any remote sensing study. The objective of this study was to compare leaf area index (LAI), surface temperature (Ts), and actual evapotranspiration (ETa), estimated using the remote sensing-based METRIC model and in situ measurements collected at the satellite overpass time. The study was carried out at a commercial corn field in eastern South Dakota. Six clear-sky images from Landsat 7 and Landsat 8 (Path 29, Row 29) were processed and used for the assessment. LAI and Ts were measured in situ, and ETa was estimated using an atmometer and independent crop coefficients. The results revealed good agreement between the variables measured in situ and estimated by the METRIC model. LAI showed r2 = 0.76, and RMSE = 0.59 m2 m-2, the Ts comparison had an agreement of r2 = 0.87 and RMSE 1.24 °C, and ETa presented r2 = 0.89 and RMSE = 0.71 mm day-1.
ABSTRACT
Agricultural subsurface drainage has been recognized as an important pathway for phosphorus transport from soils to surface waters. Reactive permeable filters are a promising technology to remove phosphate from subsurface drainage. Three natural minerals (limestone, zeolite, and calcite) and five industrial by-products (steel slag, iron filings, and three recycled steel by-products) were evaluated for phosphate removal from subsurface drainage using batch adsorption experiments. Phosphate adsorption onto these materials was characterized by Langmuir isotherm and second-order kinetic models. The adsorption capacities increased by factors of 1.2-2.5 when temperature was increased from 5°C to 30°C. Industrial by-products exhibited phosphate adsorption capacities that were one order of magnitude higher than natural minerals. Medium-sized steel chips exhibited high phosphate adsorption capacities (1.64-3.38â mg/g) across different temperatures, pH values, organic matter concentrations, and real drainage water matrixes. The strong chemical bonds between phosphate and steel by-products prevented the release of adsorbed phosphate back to the solution. The steel by-product filter can be paired with a woodchip bioreactor for nitrate and phosphate removal. It is suggested that the phosphate filter be connected to a woodchip bioreactor after the startup phase to minimize the impact of dissolved organic matter on phosphate adsorption. The results of this study suggest that the low-cost steel by-products examined could be used as effective adsorption media for phosphate removal from subsurface drainage.
