Watershed Dynamics and Evolution Science Focus Area Theme 1: Dynamic Headwaters
Authors
Alexander Johs1* (johsa@ornl.gov), Elizabeth Herndon1, Matthew Berens1, Xin Gu1, Xiangping Yin1, Mircea Podar1, Melissa Cregger1, Moses Adebayo2, Christopher McNabb3, Kamini Singha2, Holly Barnard3, Lydia Zeglin4, Eric M. Pierce1
Institutions
1Oak Ridge National Laboratory, Oak Ridge, TN; 2Colorado School of Mines, Golden, CO; 3University of Colorado–Boulder, CO; 4Kansas State University, Manhattan, KS
URLs
Abstract
Non-perennial streams that periodically cease to flow constitute a large portion of global stream networks; however, their contributions to watershed function and downstream hydro-biogeochemistry remain unclear. Theme 1 in the Watershed Dynamics and Evolution Science Focus Area evaluates the ecohydrology, biogeochemistry, and microbiology of nonperennial streams (dynamic headwaters). The team characterizes processes that control the quantity and composition of water and solutes that are transported from upland catchments into the stream network. The goal is to understand how variable streambed saturation drives hydro-biogeochemical processes that influence downstream metabolism. Here, researchers examine flow patterns and concentrations of carbon species, other nutrients, and trace metals in non-perennial tributaries across different types of land cover to evaluate contributions from weathering and potential anthropogenic sources. Data obtained on the frequency and duration of flow in nonperennial streams will be used to improve representation of nonperennial streams in watershed-scale models. Researchers are also intensively monitoring two nonperennial streams draining contrasting urban and forested areas to study how surface-groundwater interactions, plant water use, redox biogeochemistry, and microbial communities respond to variable flow. The redox-sensitive metals iron and manganese are known to regulate the solubility, transport, and transformation of organic matter and micronutrients, such as trace metals. Under no-flow conditions, iron and manganese metal precipitates can accumulate in disconnected pools along the stream channel. During high-discharge events, the mobilization of particles and colloids may contribute significantly to the export of nutrients and trace metals from uplands. The field and laboratory studies performed will resolve how colloid and particle dynamics influence (micro)nutrient levels across saturation and redox gradients generated through intermittent flow.