Ecosystem Metabolism in the Columbia River Contrasts with Small Rivers

Metabolism metrics show that conditions in large rivers differ from small rivers.

Image is described in caption.

The Columbia River in Richland, Wash.

[Courtesy Jackie Hager | Pacific Northwest National Laboratory.]

The Science

Large rivers support complex food webs and provide ecosystem services. Despite their importance, metabolism in large rivers is not well-understood because the existing estimation and determination methods apply only to smaller streams. A team of researchers modified existing methods to estimate metabolism for the Hanford Reach of the Columbia River in Washington state. Columbia River metabolism rates, seasonal patterns, the location of metabolism, and the coupling of photosynthesis and respiration all differed from what is typically observed in smaller rivers.

The Impact

Rivers are a major component of the Earth system. The study of river metabolism is key to understanding nutrient dynamics, ecosystem health, and food webs in river ecosystems. Researchers found that metabolism patterns for the Hanford Reach section of the Columbia River differ from those observed in most rivers.

Peak photosynthesis occurred in late summer, as opposed to spring or mid-summer as expected for most other rivers. Photosynthesis rates were primarily influenced by temperature and secondarily influenced by light. Photosynthesis and respiration rates were among the highest measured and the two were strongly connected, indicating little accumulation of algae. Finally, most metabolism occurred in the water column by plankton rather than in sediments.

Conducting more metabolism studies in other large rivers will help determine whether these patterns are typical for large rivers.

Summary

This study focused on understanding ecosystem metabolism in large rivers, an area that has received limited attention compared to small and medium rivers. Large rivers present unique challenges for depth and gas exchange measurements due to their size and large dams.

A team of researchers estimated reach-scale metabolism for the Hanford Reach of the Columbia River in Washington state, a free-flowing stretch with substantial discharge. Researchers used existing, reach-specific hydrologic models to estimate depth and a combination of semi-empirical models and tracer tests to estimate gas exchange.

Metabolism metrics were comparatively high in the Columbia River, with peak values occurring in late summer or early fall. Strong coupling occurred between photosynthesis and respiration. The river exhibited plankton-dominated metabolism driven primarily by temperature and secondarily by light.

These patterns deviate from those typically observed in small and medium rivers and demonstrate that metabolism patterns from smaller rivers may not accurately scale to large rivers.

Principal Investigator

Tim Scheibe
Pacific Northwest National Laboratory
[email protected]

Program Manager

Paul Bayer
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
[email protected]

Funding

This work was partially funded by the River Corridor Science Focus Area (SFA) at the Pacific Northwest National Laboratory, which is operated by Battelle Memorial Institute for the U.S. Department of Energy (DOE) under Contract No. DE-AC05-76RL01830. The SFA is supported by the DOE Biological and Environmental Research program’s Environmental System Science activity.

Related Links

References

​​Roley, S. S., et al. "Coupled Production and Respiration in a Large River Contrasts with Smaller Rivers and Streams." Limnology and Oceanography 68 (11), 2461–75  (2023). https://doi.org/10.1002/lno.12435.