The importance of catchment slope to soil water N and C concentrations in riparian zones: implications for riparian buffer width

摘要

Buffer zones are an important component of forest-management strategies and are thought to reduce the impact of nutrients released after harvesting on water quality. Conceptually, steep slopes have shorter water residence times than shallow slopes, have a reduced capacity to moderate water quality, and therefore, require wider buffers. Carbon and N concentrations in riparian zone shallow soil water at 30 cm depth and lake water were measured on shallow and steep slopes at the Esker Lakes Research Area in northeastern Ontario to determine if nutrient concentrations were correlated to catchment terrain attributes. Field measured slope, slope class obtained from a triangular irregular network model, and upslope contributing area and topographic index calculated from a digital elevation model were calculated for each sampling location. Modeled terrain properties, including those currently used during forest-management planning, were not significantly correlated with soil water N and C concentrations, whereas only dissolved organic carbon levels were significantly greater on field measured steep slopes. Forest species composition and soil N levels were positively correlated with soil water N concentrations. These results from the undisturbed boreal ecosystem highlight the potential limitation of using only catchment slope as a tool for prescribing riparian buffers during harvesting when considering terrestrial nutrient export.