Abstract
Denitrifying bioreactors are an agricultural best management practice developed in the midwestern United States to treat agricultural drainage water enriched with nitrate‐nitrogen (NO3N). The practice is spreading rapidly to agricultural regions with poor water quality due to nutrient enrichment. This makes it imperative to track bioreactor NO3‐N reduction efficiency as this practice gets deployed to new regions. This study evaluated the application and performance of denitrifying bioreactors in the humid subtropical coastal plain environment of the Chesapeake Bay catchment to provide data about regionally specific NO3‐N reduction efficiencies. NO3‐N samples were taken before and after treatment at three denitrifying bioreactors, in addition to other nutrients (orthophosphate‐phosphorus, PO4‐P; ammonium‐nitrogen, NH4‐N; total nitrogen, TN; total phosphorus, TP) and water quality parameters (dissolved oxygen, DO; oxidation reduction potential, ORP; pH; specific conductance, SPC). Total removal ranged drastically between bioreactors from 10 to 133 kg N, with removal efficiencies of 9.0% to 62% and N removal rates of 0.21 to 5.36 g N removed per m3 of bioreactor per day. As the first bioreactor study in the humid subtropical coastal plain, this data provides positive proof of concept that denitrifying bioreactor is another tool for reducing N loads in agricultural tile drainage in this region.
Highlights
Denitrifying bioreactors are a new agricultural best management practice (BMP) developed for the treatment of agricultural drainage water over-enriched with nitrate-nitrogen (NO3 -N)
Complete nitrate removal was consistently achieved for the drainage water that was treated in the Ridgely Farm bioreactor (>96% bioreactor load reduction; Table 2; Figure 3c)
Nitrate-nitrogen removal was achieved at all bioreactors in all monitoring periods, with an overall average removal efficiency of 24%
Summary
Denitrifying bioreactors are a new agricultural best management practice (BMP) developed for the treatment of agricultural drainage water over-enriched with nitrate-nitrogen (NO3 -N). The practice was pioneered in humid continental climates of the midwestern United States of America [1]. The application of this practice has been adopted by other locations around the world, which have artificial drainage (drainage tile or ditches) and problems associated with nutrient enrichment in receiving waterbodies [1,2]. With the expansion of this innovative practice to new locations and climates, it is imperative that rigorous monitoring and engineering assessment are completed to determine if this agricultural BMP can be applied practically and achieve the desired NO3 -N reduction to help reduce impacts from agricultural nitrogen pollution on local waterways. While agricultural drainage improvements are essential for row-crop farming on the Delmarva Peninsula, widespread, Water 2017, 9, 112; doi:10.3390/w9020112 www.mdpi.com/journal/water
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