SATURATED RIPARIAN BUFFERS: A MANAGEMENT PRACTICE TO REDUCE NITRATE CONCENTRATIONS IN SURFACE WATERS

In the U.S. Midwest, where fertile soils with high water retention are prevalent, the installation of tile drainage networks have become a common practice to drain excess soil water. Designed to enhance plant growth and increases crop productivity, tile drainage networks, coupled with the use of inorganic fertilizers, have significant implications on water quality, contributing to eutrophication, leading to harmful algal blooms, and resulting in hypoxic conditions in surface water bodies. To mitigate nutrient exports to surface water bodies, edge-of-field practices have been introduced. One notable practice is the saturated riparian buffer (SRB), which utilizes a diversion system to redirect tile drainage water from an agricultural field into a riparian buffer rather than directly discharging into a stream. As a best management practice, SRBs have been shown to reduce nitrate loads delivered to surface water by increasing the travel time of nutrient rich waters through soils and exposing the nutrients to soil processes. Data collected over eight years (2015-2023) at the study site were analyzed to examine the effectiveness of the SRB in the removal of nitrate. This work summarizes the impact of tile flow on nitrate concentrations within the SRB, identifies the mechanisms responsible for nitrate removal, explores the consistency of nitrate as nitrogen (NO₃-N) concentrations across seasons, and assesses whether nitrate accumulates in the SRB over time (year-to-year). During tile flow events, there was an increase in NO₃-N concentrations within the SRB, underscoring the direct influence of tile waters on the groundwater. In the absence of flow, the concentration of NO₃-N in the groundwater continued to increase for up to two weeks and declined after three weeks. The SRB removed NO₃-N through denitrification and plant uptake. Seasonal and diurnal changes in NO₃-N concentration existed, with the highest concentrations observed in the Spring when the tile was actively flowing. On a year-to-year basis, NO₃-N concentration within the SRB remained stable, indicating that there was not a long-term accumulation within SRB.

KEYWORDS: Nitrate, Tile water, Agricultural practice, Groundwater, Saturated Riparian Buffer.