NITRATE TRANSPORT IN THE UNSATURATED ZONE

Abundance of nitrate in the soil is a basic issue in agricultural land-use regions, which can lead to pollution and eutrophication of surface water bodies. The study focuses on the role of a riparian buffer zone (RBZ) to remove nitrate from the groundwater infiltrated from agricultural activities. The study area is herbaceous RBZ located in central Illinois (40.614382ºN, -89.023542ºW), which lies between a stream and a farm located upgradient. The RBZ has been outfitted with an agricultural runoff treatment system that diverts the tile drainage into the subsurface of the RBZ rather than discharging into the stream. The unsaturated zone of the RBZ allows tile discharge to infiltrate into the unconfined aquifer where it then moves to the stream. The main objective of this research is to understand the role of plants in the transport and fate of nitrate in the unsaturated.

As runoff infiltrates into the subsurface, the nitrate gets converted into nitrogen by microbial activities within the top organic layer before it percolates downwards hence reducing the nitrate level with depth. The chemical analysis of nitrate concentration in subsurface waters in the RBZ showed low concentrations (≤ 5mg/l) with a mean of 0.62 mg/l. Nitrate levels currently are higher within the stream and wells located northeast of the study site and areas where the diversion tiles are located. However, nitrate levels for wells located close to the RBZ are relatively low and tend to decrease along the flow path away from the diversion tiles. This shows that nitrate is significantly reduced once it enters the RBZ and this is probably happening due to denitrification by microbial activity and plant uptake occurring within the study site. This indicates the RBZ is working effectively to remove nitrate from the subsurface.