PNNL

The Pacific Northwest National Laboratory (PNNL) River Corridor Scientific Focus Area (RC-SFA) works to transform understanding of spatial and temporal dynamics in river corridor hydro-biogeochemical functions from molecular to watershed and multi-basin scales. We leverage numerous AI-based methods to generate otherwise unattainable knowledge that is used to improve the nation’s capacity to predict impacts of perturbations on river corridor function.  

Project successes

As a collective, RC-SFA progress has been expansive. For example, we revealed 1) how wildfire effects mechanistically cascade from terrestrial to in-stream dynamics , 2) demonstrated that nearly all stream ecosystem respiration across environments can be from sediment-associated respiration (ERsed) driven by benthic primary producers, 3) found that dissolved organic matter (DOM) chemistry is the most important driver of batch-scale ERsed across the contiguous United States (CONUS), 4) discovered CONUS-wide transferable patterns linking watershed physical properties to DOM chemistry and microbial community gene expression, and 5) showed that hydrologic exchange flows (HEFs) dominate not only reach-scale ERsed across basins but also ERsed allometry. Research during FY 2025–2028 builds on this progress (Fig. 1). 

Current priorities

The Earth system is increasingly impacted by perturbations that directly and indirectly result from human activity. Watershed systems are a foundational unit of Earth’s land surface; how these systems will respond to perturbations over the coming decades is highly uncertain. This uncertainty needs to be reduced to enable effective decisions in support of the Department of Energy’s mission. In the long-term, the RC-SFA will meet this need by delivering predictive understanding of how perturbations impact watershed hydro-biogeochemistry (HBGC) across the hillslope-to-stream continuum. We work to reveal how perturbations interact with each other and with other environmental features to influence the movement of water and transformations of organic matter in connected surface and subsurface components of watersheds (Fig. 2). We focus on wildfire and drying of streams as two interacting perturbations that are highly dynamic in frequency, duration, and severity and that have highly uncertain impacts on watershed HBGC that are relevant across most of Earth’s land surface (Fig. 3). Given the domestic and global relevance of these perturbations, we need clarity on how they jointly impact watershed HBGC. Otherwise, we risk increasingly uncertain predictions for water availability in terms of both quantity and usability, especially across domestic land surface systems. The RC-SFA will protect against this risk through a novel focus on interactions between wildfire and variable inundation across environmentally divergent basins of the CONUS. 

How we do science is as important as the hypotheses we test and the methods we use. We value team science built on a foundation of a respectful, secure, and safe environment. To achieve transferable and mutually beneficial science outcomes, we use ICON (integrated, coordinated, open, networked) science principles to guide design and implementation of our research. We merge model-experiment (ModEx) iteration, intensive place-based research aimed at deep mechanistic understanding (using the YRB testbed), and widely distributed efforts across the CONUS aimed at transferability (in collaboration with the WHONDRS consortium) (Fig. 4). In this hypothesis-centered approach, conceptual and mechanistic understanding guide model development, model predictions guide data generation, and interpretation of generated data guide further model development.

Long-term vision

We will progressively deliver new understanding, model advances, and benchmark data to improve predictive confidence for future states of the Earth system, with an emphasis on mechanistically understanding how perturbations affect HBGC across the hillslope-to-stream continuum.

Near-term objective

Reveal how wildfires and environmental features jointly influence hydrologic connectivity from hillslopes to streams, variable inundation dynamics in stream networks, and subsequent biogeochemical dynamics (Fig. 5). For our near-term objective, we are working to resolve knowledge gaps about interactions among physical, chemical, and biological mechanisms—from molecular to watershed scales—that connect perturbations to hydro-biogeochemical responses. In turn, we are quantifying the influences of wildfire, variable inundation, and molecular-scale properties of organic matter (OM) chemistry and microbes. These influences are quantified as changes to water availability through space and time and the spatiotemporal scaling of ERsed across watersheds.

Overarching science questions

1. ST-1A: Across YRB watersheds in south-central Washington State, how do precipitation, temperature, vegetation, subsurface hydrogeology, and wildfires control hydrologic connectivity and flow intermittency?
2. ST-1B: How are wildfire impacts on stream OM chemistry mediated by the relative influence of subsurface pathways to the transport and transformation of DOM?
3. ST-2A: Across YRB and CONUS watersheds, how do variable inundation and pyrogenic OM (PyOM) interactively influence ERsed via changes to microbial communities and OM chemistry? 
4. ST-2B: Across YRB reaches, what is the optimal combination of flow path, flow velocity, inundation history, and sediment texture that maximizes ERsed post-inundation? 
5. ST-3A: Across YRB watersheds, to what degree do variable inundation, wildfire, and molecular properties individually and interactively influence ERsed scaling dynamics, in context of constraints imposed by HEFs? 
6. ST-3B: Across CONUS watersheds with divergent biophysical conditions, to what degree do the primary drivers of ERsed allometry change and are there systematic shifts in the primary drivers across the arid-to-mesic continuum? 

Acknowledgments

This research is supported by the U.S. Department of Energy (DOE), Office of Science, Biological and Environmental Research (BER) Earth Systems Science (ESS) program.