Watershed Dynamics and Evolution Science Focus Area Theme 2: Stream Corridor Processes
Authors
Scott C. Brooks1* (brookssc@ornl.gov), Erin R. Hotchkiss2, Eric Pierce1
Institutions
1Oak Ridge National Laboratory, Oak Ridge, TN; 2Virginia Polytechnic Institute and State University, Blacksburg, VA
URLs
Abstract
Theme 2 of the Watershed Dynamics and Evolution (WaDE) science focus area characterizes stream corridor processes at the reach scale using a combination of field experiments, laboratory mesocosm studies, and modeling. Mid-order streams are reactive conveyors that receive, process, and transport carbon, nutrients, and other solutes from upstream and the surrounding uplands. Nevertheless, they are noticeably underrepresented in the research literature so quantitative understanding of their roles in watershed function is lacking. Specific questions and hypotheses address (1) Quantifying the contributions of water column gross primary production (GPP) and ecosystem respiration (ER) to net ecosystem production (NEP) across gradients in land cover, (2) Elucidating the effects of organic matter burial in the stream benthos on aerobic versus anaerobic metabolism, and (3) Assessing the resistance and resilience of reach-scale GPP and ER to disruption by transient high flow events.
The team has established three long-term observation stations that span dominant land-cover categories within the first research watershed. Using a combination of manual sampling across a range of flow conditions and continuous water quality data collected with multiparameter sondes, researchers are analyzing element and nutrient yield across the watershed. When normalized to sub-watershed area, DOC flux is comparable among sites with marginal seasonal differences. Concentration versus discharge curves suggest allochthonous sources of organic carbon enter the stream during rain-driven floods. Nutrient spiraling analysis shows uptake lengths for nitrate, ammonium, and phosphate are long (on the order of kilometers), consistent with chronically high nutrient concentrations characteristic of urban-influenced streams. Overall, there is net removal of nitrate and phosphate and net release of ammonium. Initial estimates of dissimilarity among sites using the multivariate time series indicate (1) dissimilarity changes with time in response to watershed-wide controls, and (2) in periods of constant dissimilarity, the contribution of individual variables to dissimilarity estimates changes with time.