Evaluation of a nontidal riparian wetland as a naturally occurring decontamination zone
The potential harmful effects of agricultural chemicals on human health and the Chesapeake Bay have led to the need to identify economical practices that limit the chemicals impact on surface and ground water contamination. The agricultural practices of the Atlantic Coastal Plain in Virginia have resulted in many bottom land areas of forests and wetlands being left uncultivated, while the upland areas are being utilized for intensive agriculture that may act as a source of chemicals in the environment. The capacity of a riparian wetland to act as a buffer zone between an intensively managed agricultural field, located in Westmoreland Co., Virginia, and a riparian stream that borders the field was investigated in this study.
The ground-water chemistry was evaluated using water samples from ground-water wells and the stream. Seventeen ground-water wells were installed and three surface-water sample locations were stablished. Samples were collected bi-weekly for an 18 month period. Samples were analyzed for nutrient and pesticide constituents. A tracer study was used, unsuccessfully, to determine flowrates at the study site. A ground-water model was used to estimate flowrates at the study site using measured site characteristics. Pesticides were not detected in samples. Results from this study revealed that the elevated levels of nitrate in ground-water, resulting from fertilizer application, were reduced by 48% by the riparian zone, from an average level of 9.0 mg/l in the agricultural field to an average level of 4.68 mg/l in the stream. Reductions of nitrate were as great as 57% between ground-water samples from the agricultural field and ground-water samples from the riparian wetlands.
The reduction in nitrate concentration was less than has previously been reported by other investigators, primarily due to differences in site characteristics. This study demonstrates the role that buffer zones along streams may play in reducing the influence of agricultural fertilizers on surface waters and the need to manage riparian forests as a beneficial part of the agroecosystem. The data collected from this study will aid in the proper design and implementation of riparian forest corridors as decontamination zones.