Quantifying the Water Quality Benefits of Riparian Buffers in the Cache River Watershed

Abstract

In agricultural watersheds across the U.S. and world, many woody and herbaceous species of riparian vegetation have proven to be effective filters of nutrients and sediment. Over the past decade, we have investigated the water quality impacts of giant cane (Arundinaria gigantea (Walt.) Muhl.) riparian buffers in the Cache River watershed. Giant cane is a native bamboo-like grass species that once thrived in southern Illinois and has received considerable attention from federal and state agencies for reestablishment into its native range. A series of three field-scale studies evaluated giant cane’s ability to attenuate sediment and nutrients in surface runoff and groundwater. The initial study monitored nutrient and sediment concentrations in surface runoff and groundwater in Cypress Creek watershed, while two subsequent studies focused on groundwater quality and added riparian buffer plots along Big Creek and Cache River. Overland flow collectors and groundwater monitoring wells were used to collect water samples at fixed distances from the edge of three agricultural fields (i.e., 0m, 1.5m, 3m, 6m, 9m, and 12m). Results showed significant nutrient and sediment reductions within the first 3m of the giant cane buffers, whereas equivalent reductions were observed at ~6m in adjacent forested buffers. Nutrient reductions in overland flow in the cane buffer were 80%, 80%, and 68% for phosphate, dissolved ammonium, and dissolved nitrate, respectively. Further, sediment (97%) and groundwater nitrate concentrations (90%) were significantly reduced in the initial 3m of the cane buffers. Microbial denitrification was likely the most important groundwater nitrate loss mechanism, given the relatively deep ground water depths (\u3e 2 m) at the study sites. High stem density and infiltration rates promoted deposition of sediment and sediment-bound nutrients in the first 1.5 to 3 meters of the buffers. Currently, a paired watershed experiment is being conducted on SIUC farms properties to quantify the water quality benefits of giant cane and deciduous forest buffers in row-crop agricultural watersheds with no artificial drainage. Further, a giant cane nursery has been established to help provide propagules for future restoration efforts