LANDSCAPE HYDROGEOLOGY AND ITS INFLUENCE ON PATTERNS OF GROUNDWATER FLUX AND NITRATE REMOVAL EFFICIENCY IN RIPARIAN BUFFERS

摘要

This study uses data from 46 riparian sites to examine the influence of landscape hydrogeology on patterns of groundwater flux and the buffer width required for effective nitrate removal in humid temperate agricultural regions. There is a considerable imbalance in the research focus on different hydrogeologic settings. More than 40% of the buffers are located in landscapes with surficial sand aquifers, whereas few buffers have been studied in glacial till and weathered bedrock landscapes which cover large areas. Annual groundwater fluxes for 29 of these sites ranged from 20L/m/day for buffers on flat sand plains and uplands with fine-textured deposits to 50-1,200L/m/day for many sites with upland sand aquifers. Despite a similar range of water fluxes, buffers in gently to moderately sloping landscapes with 4m depths of sand sediments reached a 90% removal efficiency within 30-60m while sites with 4m depths required a 150-200m width. The width for 90% efficiency in buffers with loamy sand and sandy loam sediments also increased from 10-20m with 4m sediment depths to 50-100m for 4m depths. Limited data for buffers with fine-textured sediments suggest that 90% of the nitrate flux was often depleted in a 10-20m width. Groundwater flux did not have a significant relationship with nitrate removal percent per meter buffer width because of the variation in efficiency that occurred in buffers with similar fluxes in different hydrogeologic settings.