Methods for Removing Nitrate Nitrogen from Agricultural Drainage Waters: A Review and Assessment

摘要

Widespread adoption of conventional surface and subsurface drainage has resulted in increased nitrate losses from agricultural cropland to surface waters. This is due to the drainage water bypassing nutrient removing landscape features (i.e. riparianbuffers and wetlands as it moves from the fields to the stream). A number of approaches have been identified to reduce these nitrate losses including controlled-drainage, routing of drainage water through natural/constructed wetlands and through constructed bioreactors, and in-stream denitrification. Controlled-drainage and infield bioreactors reduce the loss carried off field in drainage discharge, whereas natural /constructed wetlands and in-stream denitrification are post-drainage methods of nitrate reduction. The potential for nitrate reduction with each of these approaches is; approximately 50% for controlled drainage, 37% to 65% for natural/constructed wetlands (with up to an additional 18% if a berm is used in creation of the wetland), 60% to90% for constructed bioreactors, and 1% to 66% for in-stream denitrification. Combinations of these methods would lead to even higher nitrate removal. A combination of controlled-drainage, constructed wetland and in-stream denitrification could possiblyresult in more than 75% nitrate removal prior to release to larger streams or other surface waters reducing water quality degradation.