NITRATE REDUCTION THROUGH TILE DRAIN REDIRECTION TO A RIPARIAN BUFFER ZONE AT A LOW ORDER STREAM IN CENTRAL ILLINOIS

In areas dominated by agricultural land use, excess nitrate is one of the leading contributors to water pollution. Tile drains, installed to drain crop root zones, decouple farm water from interacting with subsurface soil and instead transport and discharge the nitrate-rich water into a nearby stream. Due to the risks elevated levels of nitrate pose to humans (methemaoglobinemia) and the ecosystem (hypoxia and eutrophication), the following project investigates a method of reducing nitrate concentrations from tile water in-situ. A tile draining a 60acre farm in central Illinois was redirected to discharge its contents into the subsurface of an herbaceous riparian buffer zone (RBZ) located between the farm and a stream. A transect of nested wells is installed across the riparian buffer intersecting the redirected tiles. These wells are used to observe the change in the chemistry of the tile water as it migrates through the RBZ, interacting with the subsurface. A chemical and biochemical analysis of the study site is performed to determine suitability for nitrate removal. As a reference, another transect of wells is installed away from any tile contact and its water observed. In-situ dissolved oxygen, temperature, and conductivity were noted every two weeks using a YSI probe. Prior to redirecting tile water into the RBZ, chemical analysis of the RBZ water showed low concentrations of NO₃^--N (≤5mg/L) with the exception of one nest of well. The conditions necessary for the reduction/removal of nitrate, such as low levels of dissolved oxygen and adequate organic matter, were present. The NO₃^--N concentrations appear to be the lowest once diversion begun. Concentrations measured in the diversion box leading to the riparian buffer is around 22mg/L. Once this water has entered the riparian buffer however, the highest concentration registered was lower than 5mg/L indicating a significant nitrate reduction/removal.