Riparian Poplar Tree Buffer Impact on Non-point Source Surface Water Contamination: A Paired Agricultural Watershed Study

Principal Investigators
L.A. Licht and J.L. Schnoor, University of Iowa

Abstract

Goals: Objectives are to develop a paired watershed research site sufficiently instrumented to develop a hydrologic, silt, and agricultural chemical movement database; to compile the watershed basin data in a form usable with existing EPA and USDA models to understand the impact of perennial tree buffers on the runoff water quantity and quality from "conventionally" farmed land; to install alternative perennial plant buffer designs to compare plant survival, biomass growth potential, sediment interception, subsurface nitrate movement in near-surface ground water, and herbicide movement from up-gradient application to the stream; to test equipment and tillage practices required by farmers to make this plant production practical; and to develop an education and technology exchange program to explain watershed-scale conservation and cropping concepts to agriculturists, farmers, media, and all ages of students.

Rationale: Tree-buffered riparian corridors can enhance sustainability of agricultural ecosystems and remove a portion of non-point source pollutants. They can provide a tree crop that does not compet e with feed grains.

Approach: Two adjacent agricultural watersheds at Amana, Iowa, have been developed into a field research site, including the in-stream instrumentation required to measure flow and sample at desired intervals. One watersh ed stream is completely buffered using approximately 15,000 trees; the other watershed is unbuffered; annual tillage and cropping occurs up to the stream bank edge. Both watersheds are predominantly cropped with corn and soybeans; oats and hay are a small portion of the field area. Each watershed contains a portion of upland hardwoods.

Status: The concept of planting poplar trees as a perennial row-crop to manage field edges for reducing non-point source pollutants entering a first-order creek has been demonstrated to farmers, agribusiness, government officials, interested citizens, and the media. These watershed buffering concepts were shown to over 20,000 people during the 1993 Farm Progress Show. This demonstration has been called EPA's most successful technology transfer effort. Additionally, other field trips and press conferences have been held. Tours have been given to an agricultural attaché from Egypt, EPA research scientists from Athens Lab, and a press day has been held. A 12-minute video has been produced. In-stream water sampling stations have been monitored to measure water quality parameters. The nitrate nitrogen flow from an unbuffered watershed was consistently above the EPA MCL while the buffered watershed was consistently below the MCL. Ground water in the riparian stream border has been monitored for subsurface flows crossing the border. Tile drainage was the primary source of in-stream nitrate nitrogen. Little nitrate appeared to be added to the stream by base flow after the water flowed through the tree buffer. Buffer plots of grass and different tree varieties have been maintained to test alternative culturing practices. The Universal Soil Loss Equation was used to obtain estimates of relative soil loss potential in each watershed. This project has been completed.

Clients/Users: This research is of interest to those who are responsible for non-point source pollution control including regulators, farmers, and the USDA.

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