Water Resources Research Act Program

Details for Project ID 2013SD226B

Evaluating the Nitrate-Removal Effectiveness of Denitrifying Bioreactors (part 2)

Institute: South Dakota
Year Established: 2013 Start Date: 2013-03-01 End Date: 2014-02-28
Total Federal Funds: $20,526 Total Non-Federal Funds: $43,374

Principal Investigators: Jeppe Kjaersgaard, Christopher Hay, Todd Trooien

Abstract: Emergent problems caused by intensive agriculture include nutrient contamination of local drinking water supplies and hypoxic conditions in aquatic environments. Combined with the increased need for food production to feed the world’s growing population there is a need to reconcile the increased need for agricultural production with a more effective and sustainable protection of the environment. Subsurface (tile) drainage on agricultural land with poor natural drainage allows timelier field operation and contributes to improved crop yields. While properly designed and installed subsurface drainage typically reduces field sediment and phosphorus losses compared to surface runoff, studies show that subsurface drainage increases the movement of nitrate-nitrogen from the field to surface waters. Following several years with high commodity and land prizes and above-average precipitation (with 2012 being an exception) eastern South Dakota continues to experience a rapid growth in tile drained acres. Nitrogen is an essential plant nutrient, but in aquatic ecosystems excess nitrogen leads to eutrophication and hypoxic conditions. Non-point source pollution from tiled farmlands in the Midwest contributes 90 % of the nitrate-N nitrogen delivered to the Gulf of Mexico causing the annual hypoxic zone (USEPA, 2007). In South Dakota, where the majority of the lakes are eutrophic or hypereutrophic and impacted by non-point source nutrient export from agricultural land (SD DENR, 2006), there remains an urgent need to implement conservation practices that allow tile drainage to support agricultural production while still effectively reducing tile-drained nutrient exports from these agricultural uplands to streams and lakes. While improved management of nitrogen fertilizer and animal manure is one important method for reducing nitrate losses, it is often not enough. To reach water quality goals for nitrate, additional edge-of-field (sometimes also referred to as end-of-pipe methods) treatment technologies is often needed. One of these technologies, termed denitrifying bioreactors, have been found to be an effective technology for reducing nitrate concentrations in tile drain water. Bioreactors utilize biological denitrification to reduce nitrate to inert dinitrogen gas (N2). This requires suitable bacteria, a carbon source, and anoxic (oxygen-free) conditions. Bioreactors are typically designed as an excavated trench filled with a carbon source, typically woodchips. The drainage water from the field is routed into the reactor from the drainage pipe at one end, and collected in a pipe at the other end and discharged into the surface water system. However, bioreactors for treatment of drainage water are still an emerging technology, and their utility for nutrient and water conservation in South Dakota is currently not documented. There is a need to demonstrate and evaluate the utility, efficiency, design criteria and cost of bioreactors in South Dakota in order to give agricultural producers, water managers, resource conservationists and policy-makers confidence in using the bioreactors to removed nitrate from tile drain water.