PNNL PROJECT OVERVIEW
Land-surface fluxes and the surface energy budget can be significantly influenced by subsurface processes. Soil moisture variability is a critical driver of soil biogeochemical and plant physiological processes, affecting the partitioning of the surface energy balance and variability in trace gas fluxes. However, it remains unclear how groundwater-surface water exchange affects the availability of soil water, solutes, and nutrients which, in turn, influence land-surface fluxes. To quantify the impacts of ground water-surface water interaction on land atmosphere exchange, a micrometeorological field campaign is being undertaken to measure the surface energy budget and CO2 fluxes by deploying eddy covariance systems over four different ecosystems along the Columbia River. The ecosystems range from upland shrub-steppe to riparian, and are characterized by a distinct geographical gradient in groundwater availability and variability in ecosystem structure and functioning. We are using these data to investigate how the surface energy budget and CO2 fluxes vary among the four different ecosystems. These data will be used to improve the integrated land surface-subsurface model being developed at PNNL.
The main goal in this study is to understand how groundwater availability affects ecosystem-atmosphere interaction in the Columbia River subsurface interaction zone (SIZ) over multiple time scales ranging from diurnal to seasonal and interannual such that uncertainty in estimating reach-scale carbon budget with an integrated land surface-subsurface model can be assessed. To address this goal, we are conducting our research within the Columbia River subsurface interaction zone (SIZ), as defined by the PNNL SFA. The SIZ is a subsurface domain of variable dimensions and temporal extent where groundwater and surface water mix in response to water cycle dynamics. Our study sites are located within the domain corresponding to the Hanford Reach, an 80-km stretch of the Columbia River that defines the north and east boundaries of the U.S. Department of Energy (DOE) Hanford Site. Specifically, we are making eddy covariance flux measurements of energy, water, and CO2 within the Columbia River SIZ in three sites with different groundwater accessibility by plants. The objective of the existing subcontract is to study the influence of soil moisture variability as a result of ground water-surface water interactions and environmental variables on the surface energy budget and CO2 fluxes over ecosystems with strong gradients in groundwater and subsurface processes.
300 Area flux site (Main tower - PNNL 300 Area Tower)
Vegetation is comprised primary of invasive weedy species, including cheatgrass and Russian thistle. Shrub species include antelope bitterbrush, big sagebrush, and green rabbitbrush (needs updates from PNNL).
100-H Area Site 1 (Second tower)
This site is located in a low land area with shallow ground water tables and subject to seasonal inundation. Vegetation is comprised primarily of native reed canarygrass, Washington State Class C noxious weed, purple loosestrife, Washington State Class B noxious weed (needs updates from PNNL).
100-H Area Site 2 (Third tower)
Vegetation is comprised primary of invasive weedy species, including cheatgrass and Russian thistle (needs updates from PNNL).