Survey Paddy Levee System. (Credit: Southeast Missouri State University)
By moving toward no-till conservation strategies to reduce sediment loads in waterways around their land, farmers have had to rely more on fertilizers to provide the nutrients needed for growing crops. This shift has contributed to another problem: the rise of nitrate concentrations in freshwater systems and nearby soils.
Approaching the issue is difficult, because it bears out through a region’s hydrology, including its soil type, morphology and weather patterns. But there are researchers working to come up with treatments to minimize, and even eliminate, the high concentrations.
Some of these pioneering minds hail from Southeast Missouri State University, where scientists have come up with a new subsurface drainage and irrigation system that aims to clean up the water as well as improve soil health. In a recent pilot period spanning the spring of 2015, the system proved its worth by filtering out high nitrate levels. If used elsewhere, such as in the Midwest or U.S. West where water issues are a priority, its creators say that it could help make sure that used water is returned to streams cleaner than when it was first withdrawn.
The system is fairly straightforward and was built by students taking classes in the university’s David M. Barton Agriculture Research Center. Its design uses a paddy levee system on a 100-acre field that receives pumped water from a creek nearby. Water that doesn’t get absorbed by plants on the surface filters through the soil and enters a subsurface drainage system that directs it to a bioreactor underground. The chamber is filled with two-inch wood chips and helps to filter nitrates that got into the water from the creek and soil.
Once inside the bioreactor, researchers at the university say that bacteria on the wood chips converts the nitrates to nitrogen gas, a form that is inert and found commonly in Earth’s atmosphere. The water is then returned to the creek.
During the 2015 growing season, students at the agriculture research center used automated samplers to gather water from the inflow and outflow of the denitrification bioreactors used. Samples, also taken from the bioreactors themselves, were gathered using pre-cleaned plastic bottles. Waters going in and out of the biochambers were sampled every week, while those within the reactors were sampled daily.
The samples were analyzed in a lab for a host of things, including nitrates, ammonium and phosphorus, pH, conductivity and dissolved organic carbon, among others. The creek’s water level was also monitored with a U.S. Class A Rain Gauge.
Taking all of the data together, Southeast Missouri State investigators found that the drainage and irrigation system they devised does a very good job of reducing nitrate levels. Scientists say they registered significant decreases in the concentrations going back into the creek and a local aquifer.
With those results in hand, the researchers plan to run through the experiment again beginning in December 2015. This will help them to assess some of the seasonal differences between their results.
In addition, the scientists are planning future studies into the issue of nitrate concentrations relating to the effects of water flow; how the bioreactor’s internal conditions affect levels; and how carbon sources support denitrification.
The project is part of a pilot program with the U.S. Department of Agriculture-Agriculture Research Service to pump nutrient-impacted water from Williams Creek in Cape Girardeau, Missouri, onto fields, cleanse the drained water and return it to the creek.
Top image: Survey Paddy Levee System. (Credit: Southeast Missouri State University)