Multi-Scale Variations in Streamwater Chemistry and Hydropedological Implications for Hotspot Development

Monday, 15 December 2014: 4:30 PM
Kevin J McGuire1,2, Scott W Bailey3, John P Gannon4, Gene Likens5,6, Donald Buso5, Christian Torgersen7,8 and Winsor Lowe9, (1)Virginia Polytechnic Institute and State University, Virginia Water Resources Research Center, Blacksburg, VA, United States, (2)Virginia Polytechnic Institute and State University, Forest Resources and Environmental Conservation, Blacksburg, VA, United States, (3)USDA Forest Service, North Woodstock, NH, United States, (4)Western Carolina University, Geosciences and Natural Resources, Cullowhee, NC, United States, (5)Cary Institute of Ecosystem Studies, Millbrook, NY, United States, (6)University of Connecticut, Department of Ecology and Evolutionary Biology, Groton, CT, United States, (7)USGS, Forest and Rangeland Ecosystem Science Center, Cascadia Field Station, Seattle, WA, United States, (8)University of Washington Seattle Campus, School of Environmental and Forest Sciences, Seattle, WA, United States, (9)University of Montana, Division of Biological Sciences, Missoula, MT, United States
Headwater streams comprise the vast majority of stream network length in watersheds and affect regional water quality. However, the spatial variation of water quality in headwater regions often remains unknown. In this study, we show that spatial processes differentially affect biogeochemical condition and pattern across a multiple scales in a headwater stream network. Synoptic spatial surveys of streamwater chemistry at both fine grain and broad extent coupled with network-based geostatistical analysis, allowed us to quantify spatial patterns over a range of scales from 1st order ephemeral and intermittent streams to 4th and 5th order perennial streams. In addition, synoptic surveys at a fine spatial grain (50 m) in a small watershed (0.41 km2) showed the same range of chemical variation as its larger basin (36 km2) sampled at coarser grain (100 m). Spatial structure was apparent at either a single scale or at multiple nested scales in the larger basin, suggesting separate processes operating simultaneously within the stream network and surrounding terrestrial landscape. We explored the fine-scale patchiness in stream chemical patterns, with particular emphasis on dissolved organic carbon (DOC), as an example to illustrate hotspot development due to hydropedological variation in a watershed. Hydropedological variations refer to soil morphological differences that directly relate water table regime, flowpaths, and saturation frequency to soil development. Soils have been digitally mapped using topographic and bedrock-related metrics determined from a LiDAR-derived digital elevation model (DEM) and field surveys of bedrock outcropping. Spatial patterns of DOC concentrations were associated with the distribution of soil types and their thresholds to stormflow generation. The hydrologic connection of shallow soils in channel head regions above the stream network where lateral podzols developed appeared to be a source for DOC hotspots in the stream network. Overall, our study highlights the importance of understanding the structural organization within a watershed, particularly hydropedological variation, in assessing controls on the spatial patterns of streamwater chemistry and developing tools for predicting the stream chemical variation in headwater stream networks.