Quantification of the Effectiveness of Agricultural Riparian Buffers to Protect Stream Health in Maryland's Coastal Plain and Piedmont Regions

Abstract

This research quantified the effectiveness of agricultural riparian buffers to protect stream health in Maryland's Coastal Plain and Piedmont physiographic regions. Easily-obtainable data were used to develop scientific guidance for buffer management strategies. Three data sets were used: the 1998 University of Maryland Agricultural Buffer Survey, the 1996 Smithsonian Environmental Research Center Water Quality Survey, and the 1995-1997 Maryland Biological Stream Survey. Collectively, these data were used to represent baseflow water quality and landscape conditions in agricultural catchments. A set of landscape characteristics describing the agricultural riparian landscape was developed, from which a classification system for agricultural riparian landscapes was developed. The Agricultural Riparian Classification System can identify a subset of sites for targeted research. Additionally, the distribution of agricultural riparian buffers was characterized. Although over 70% of sites were buffered, because the statewide average buffer width was approximately 49 meters, almost 50% of buffers could not be detected by remotely sensed data with a resolution of 30 meters. Models were developed to predict measures of stream health at a site. Buffers acted differently on instream nitrate concentration, fish IBI (FIBI), benthic IBI (BIBI), and instream physical habitat (PHI). All models indicated that nitrate source terms overshadowed any on-site buffer effects and that Confined Animal Feeding Operations and pastures acted as point sources, overwhelming non-point-source effects. Therefore, livestock best managements practices are critical for the reduction of nitrate to streams. Fish IBI, benthic IBI and physical habitat index (PHI) in the Piedmont region were unaffected by buffer presence, but benthic IBI and PHI in the Coastal Plain were affected by buffer presence, type and width. Regression tree modeling was able to delineate a range of minimum effective buffer width between 22-38 meters. All measures of stream health in Piedmont systems were controlled by hydrology and geomorphology. Therefore, insofar as buffers can mediate hydrologic effects on flow conditions in a stream, they may indirectly affect FIBI, and BIBI and PHI in Piedmont systems. Use of fish IBI to measure success of buffer installation or restoration would give false results.