Suchergebnisse

Catchments with minimal disturbance usually have low dissolved inorganic nitrogen (DIN) export, but disturbances and anthropogenic inputs result in elevated DIN concentration and export and eutrophication of downstream ecosystems. We studied streams in the southern Appalachian Mountains, USA, an area dominated by hardwood deciduous forest but with areas of valley agriculture and increasing residential development. We collected weekly grab samples and storm samples from nine small catchments and three river sites. Most discharge occurred at baseflow, with baseflow indices ranging from 69% to 95%. We identified three seasonal patterns of baseflow DIN concentration. Streams in mostly forested catchments had low DIN with bimodal peaks, and summer peaks were greater than winter peaks. Streams with more agriculture and development also had bimodal peaks; however, winter peaks were the highest. In streams draining catchments with more residential development, DIN concentration had a single peak, greatest in winter and lowest in summer. Three methods for estimating DIN export produced consistent results. Annual DIN export ranged from less than 200 g ha(-1) year(-1) for the less disturbed catchments to over 2,000 g ha(-1) year(-1) in the catchments with the least forest area. Land cover was a strong predictor of DIN concentration but less significant for predicting DIN export. The two forested reference catchments appeared supply limited, the most residential catchment appeared transport limited, and export for the other catchments was significantly related to discharge. In all streams, baseflow DIN export exceeded stormflow export. Morphological and climatological variation among watersheds created complexities unexplainable by land cover. Nevertheless, regression models developed using land cover data from the small catchments reasonably predicted concentration and export for receiving rivers. Our results illustrate the complexity of mechanisms involved in DIN export in a region with a mosaic of climate, geology, topography, soils, vegetation, and past and present land use. ; U.S. Forest ServiceUnited States Department of Agriculture (USDA)United States Forest Service; National Science FoundationNational Science Foundation (NSF) [DEB0823293] ; U.S. Forest Service; National Science Foundation, Grant/Award Number: DEB0823293 ; Public domain authored by a U.S. government employee

Water and land resource management planning benefits greatly from accurate prediction and understanding of the spatial distribution of wetness. The topographic wetness index (TWI) was conceived to predict relative surface wetness, and thus hydrologic responsiveness, across a watershed based on the assumption that shallow slope-parallel flow is a major driver of the movement and distribution of soil water. The index has been extensively used in modeling of landscape characteristics responsive to wetness, and some studies have shown the TWI performs well in landscapes where interflow is a dominant process. However, groundwater flow dominates the hydrology of low-slope landscapes with high subsurface conductivities, and the TWI assumptions are not likely to perform well in such environments. For groundwater dominated systems, we propose a hybrid wetness index (Wetness Index based on Landscape position and Topography, WILT) that inversely weights the upslope contributing area by the distance to the nearest surface water feature and the depth to groundwater. When explicit depth to groundwater data are not available, height above and separation from surface water features can act as surrogates for proximity to groundwater. The resulting WILT map provides a more realistic spatial distribution of relative wetness across a low-slope Coastal Plain landscape as demonstrated by improved prediction of hydric soils, depth to groundwater, nitrogen and carbon concentrations in the A horizon of the soil profile, and sensitivity to DEM scale. ; Department of Energy-Bioenergy Technologies Office and Savannah River Operations Office through the U.S. Forest Service Savannah River under Interagency Agreement [DE-AI09-00SR22188] ; This research was implemented as part of large-scale collaborative investigation of dominant hydrologic processes within small watersheds of the Sandhills of South Carolina within the Savannah River Site (SRS). SRS is a National Environmental Research Park. Support was provided by the Department of Energy-Bioenergy Technologies Office and Savannah River Operations Office through the U.S. Forest Service Savannah River under Interagency Agreement DE-AI09-00SR22188. ; Public domain authored by a U.S. government employee

The water-quality effects of low-density rural land-use activities are understudied but important because of large rural land coverage. We review and synthesize spatially extensive studies of oligotrophic mountain streams in the rural Southern Appalachian Mountains, concluding that rural land-use activities significantly degrade water quality through altered and mostly enhanced landscape-stream connections, despite high forest retention. Some connections (insolation, organic inputs, root-channel interactions, stream-field connectivity, individual landowner discharges) are controlled by near-stream land-use activities, whereas others (reduced nitrogen uptake and cycling, enhanced biological nitrogen fixation, nutrient subsidy, runoff from compacted soils, road runoff delivery) are controlled by basin-wide land use. These connections merge to alter basal resources and shift fish, salamander, and invertebrate assemblages toward species tolerant of higher turbidity and summer temperatures and those more competitive in mesotrophic systems. Rural water quality problems could be mitigated substantially with well-known best management practices, raising socioecological governance questions about best management practice adoption. ; National Science Foundation through the LTER program [DEB-1637522] ; Published version ; Thomas Prebyl created the land cover map. The Coweeta LTER and Coweeta Hydrologic Laboratory technicians, students, and investigators who worked on the synthesized projects are too numerous to name, but we thank all of them for their help. Jason Meador and Kelder Monar from Mainspring Conservation Trust provided input about their conservation programs, such as Shade Your Stream. Fred Benfield, John Maerz, Cathy Pringle, and Paul Bolstad helped conceptualize and frame this synthesis. This work was supported by multiple grants from the National Science Foundation through the LTER program, the last of which was grant no. DEB-1637522. ; Public domain authored by a U.S. government employee