NITRATE REMEDIATION CAPACITY OF AGRICULTURAL DRAIN TILE DIVERSION INTO RIPARIAN BUFFER ZONE

Nitrate pollution from agricultural runoff is a growing societal and ecological burden. Nitrate is transported by runoff from agriculturally active land to lake, stream, and near-shore waters resulting in degraded water quality. Agricultural runoff in the Midwest is often carried by subsurface drain tile directly into streams, thus bypassing riparian buffer zones known to remediate nitrate polluted runoff. This study seeks to understand how the redirection of drain tile into a riparian buffer zone via perforated subsurface pipes affects nitrate (NO3-N) concentration. The leading question of this study is “Does redirection of agricultural runoff into a riparian buffer zone significantly reduce NO3-N concentration, and what factors may be responsible for a reduction in NO3-N?” We hypothesize 1) NO3-N concentration will be significantly lower in the riparian buffer zone when compared to source. 2) NO3-N reduction will vary seasonally. Source samples are collected directly from the diversion box, and riparian buffer zone samples are collected from wells located between the perforated diversion pipes. Samples are analyzed for NO3-N concentration using a DIONEX ICS-1100 ion chromatography system. Results for the first year of data collection show riparian buffer zone water to have a significantly lower NO3-N concentration than source water (p<0.0001). Riparian buffer zone mean NO3-N concentration is 2.56mg/L and source mean NO3-N concentration is 11.63mg/L. Conservative tracer chloride shows the role of dilution to be minimal. Mean NO3-N reduction by season is as follows: Spring=6.8mg/L, Summer=15.1mg/L, Fall=2.7mg/L, and Winter=8.2mg/L. The reduction in NO3-N is likely a combination of denitrification and plant assimilation. The greatest reduction in NO3-N occurs during summer and suggests plant assimilation is a substantial factor. These data provide evidence for a riparian buffer zone diversion system remedial capacity.