Assessment of short term changes in hyporheic zone organic carbon character in response to re-inundation
EMSL Project ID
49897
Abstract
Understanding processes that govern organic carbon (OC) oxidation is paramount in achieving PNNL’s Subsurface Biogeochemical Research Science Focus Area’s goal of (i) transforming fundamental understanding of the hydrobiogeochemical function of dynamic river corridor ecosystems and (ii) developing a predictive watershed modeling framework encapsulating river corridor processes. The SFA’s focus on the hydrobiogeochemical influences of variable river stage (e.g., desaturation and re-inundation) is of chief importance, as more than 90% of water discharge in the United States experiences variable river stages due to dam operations and seasonal patterns in discharge (e.g., snowmelt). The Columbia River experiences variable discharge at sub-daily to seasonal scales (due to dam operations and seasonal snow melt patterns) that generate dynamic desaturation/re-inundation cycles. As such, the Hanford 300A along the Columbia River provides optimal field conditions for investigating the mechanisms by which re-inundation influences riverine ecosystem processes.
Large riverine corridors such as the Columbia River are considered non-reactive hydrologic pipes for the transport of OC, nutrients, and contaminants, despite the recognition that up to 96% of respiration within riverine ecosystems occurs in nearshore zones. A critical knowledge gap is the influence of variable discharge on hyporheic biogeochemistry that strongly influences the fate of organic matter, nutrients, and contaminants transported through watersheds. We predict that variable discharge causes spatially structured hydrologic histories (e.g., time since last inundation) in the nearshore environment. Biogeochemical and microbial community responses to hydrologic shifts (e.g., from desaturated to saturated conditions) likely depend on these hydrologic histories, but processes that govern how history influences future responses have not been fully elucidated. We also predict that variable discharge should lead to spatiotemporal variation in the chemical character of OC delivered to the hyporheic zone, but the processes governing these shifts are unclear.
Importantly, there is a need to incorporate knowledge on OC character into new modeling frameworks that explicitly represent mechanisms governing OC metabolism and follow-on biogeochemical consequences. In current reactive transport modeling, OC reaction networks are conceptualized using a few lumped carbon pools that do not fully reflect the characteristics of distinct carbon sources. Even when accounting for an expanded carbon reaction network, the models are hypothetical because experimental measurements of OC character are often insufficient. Therefore, resolving OC oxidation at a molecular level is foundational to a predictive understanding of hyporheic zone biogeochemical function and, in turn, process-based watershed models.
We request EMSL’s ultra high-resolution mass spectrometry capabilities to assess preferential use of OC in response to rapid re-inundation. Specifically, we request the use of EMSL’s 12T Fourier Transform Ion Cyclotron Mass Spectrometer (FTICR-MS) to characterize 24 in-hand aqueous samples. The results will constitute key preliminary results to be presented at the SFA’s program review by the U.S. Department of Energy on April 27-28, 2017. The impact of OC character on river corridor function is a critical part of our proposed science plan, and these results will strengthen PNNL’s demonstrated capabilities in OC character analysis, facilitating a successful review.
Project Details
Project type
Limited Scope
Start Date
2017-04-07
End Date
2017-06-07
Status
Closed
Released Data Link
Team
Principal Investigator
Co-Investigator(s)
Team Members