Effects of stream map resolution on measures of riparian buffer distribution and nutrient retention potential

摘要

Riparian ecosystems are interfacesbetween aquatic and terrestrial environmentsrecognized for their nutrient interception potential in agricultural landscapes. Stream networkmaps from a broad range of map resolutions havebeen employed in watershed studies of riparianareas. However, map resolution may affect important attributes of riparian buffers, such as theconnectivity between source lands and smallstream channels missing in coarse resolutionmaps. We sought to understand the influence ofchanging stream map resolution on measures ofthe river network, near-stream land cover, andjiparian metrics. Our objectives were: (1) toevaluate the influence of stream map resolutionon measures of the stream network, the characterand extent of near-stream zones, and riparianmetrics; (2) to compare patterns of variationamong different physiographic provinces; and (3)to explore how predictions of nutrient retentionpotential might be affected by the resolution of astream map. We found that using fine resolutionstream maps significantly increased our estimatesof stream order, drainage density, and theproportion of watershed area occurring near astream. Increasing stream map resolution reducedthe mean distance to source areas as well as meanbuffer width and increased the frequency of buffergaps. Measures of percent land cover within 100 mof streams were less sensitive to stream mapresolution. Overall, increasing stream map resolution led to reduced estimates of nutrient retention potential in riparian buffers. In somewatersheds, switching from a coarse resolution toa fine resolution stream map completely changedour perception of a stream network from wellbuffered to largely unbuffered. Because previous,broad-scale analyses of riparian buffers usedcoarse-resolution stream maps, those studies mayhave overestimated landscape-level buffer prevalence and effectiveness. We present a case study ofthree watersheds to demonstrate that interactionsamong stream map resolution and land coverpatterns make a dramatic difference in the perceived ability of riparian buffers to ameliorateeffects of agricultural activities across wholewatersheds. Moreover, stream map resolutionaffects inferences about whether retention occursin streams or riparian zones.