19 Hydrogeology and Water Resources: Long-Term Sustainability and Management

Tuesday, 14 March 2023
8:00 AM - 9:40 AM
Room 108

EFFECTIVENESS OF SATURATED RIPARIAN BUFFERS: A CASE STUDY IN CENTRAL ILLINOIS

Paper number: 19-5
Program: Theme Sessions
Time: 9:20 AM – 9:40 AM

Authors

Abstract

In the U.S. Midwest, agriculture is a principal use of the land. Successful cultivation of corn and soybean depends upon a balance of nutrients and water. However, the application of excess nitrogen (N) fertilizers coupled with tile-drainage systems contribute to eutrophication and hypoxic conditions in surface water. To abate these conditions, the U.S. EPA established a goal to decrease N loading by 45% in the Mississippi River by 2035. One proposed best-management practice is the implementation of a saturated riparian buffer (SRB). To assess their utility, an SRB was installed in a restored prairie, diverting the tile-water into the vadose zone rather than directly discharging into a stream. The tile-system drains an upgradient field that grows corn and soybeans. This work summarizes nearly seven years of research and provides a conceptual model of the SRB. As the water table rises in response to precipitation, the diversion system directs water to the soil beginning late winter (late-February) until late spring (early June). The tile-waters are rich in nitrate, greater than 10 mg/L nitrate as nitrogen (NO3-N), while NO3-N concentrations of background water are below 1 mg/L. Travel times from the diversion system to the stream are variable but are greater than 30 days. Along the flow paths, NO3-N concentrations decrease. While the mixing of tile-waters and groundwater will produce diluted water, a mixing-model indicates dilution is not the sole mechanism for the decrease in NO3-N concentration. The mixing model reveals losses of NO3-N exceeding 30%. Analysis of δ18O-NO3- and δ15N-NO3- highlight a denitrification signature among the waters traveling away from the diversion system. Measured rates of denitrification were low, less than 1.4 mg NO3-N/h/g. During the growing season, plant uptake by riparian vegetation results in the minimum NO3-N concentrations in groundwater occurring in the afternoon, between 1300 to 1800, and the maximum concentrations measured at night, from 0000 to 0600. Decomposition of the vegetation increases NO3-N concentrations and generates organic carbon within the vadose zone. The vegetation is interpreted as a seasonal sink for NO3-N. While a single system is not the basis of review, the reduction of NO3-N by 30% indicates the use of SRBs may help to achieve the 45% reduction goal.

Geological Society of America Abstracts with Programs. Vol. 55, No. 1

doi: 10.1130/abs/2023SC-385209

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