Winter Droughts Reduce Summer Carbon Capture on California’s Coast

The Science

Tidal wetlands have high plant productivity and high soil carbon storage. These characteristics make wetlands naturally helpful for combating climate change; they remove carbon dioxide (CO₂) from the atmosphere and trap it underground. A team of researchers collected 4 years of continuous high-frequency measurements of CO₂ exchange in a brackish tidal marsh and investigated ecosystem responses to wet and dry years. Tidal channel salinity was the best predictor of plant productivity changes from year to year with no measurable impact on ecosystem respiration (CO₂ release to the atmosphere). When salinity levels doubled, net removal of CO₂ decreased by up to 30%.

The Impact

As tolerant as brackish marsh communities are to variable salinities, plant productivity and respiration models must account for drought conditions and subsequent impacts on water salinity to avoid overpredicting brackish tidal wetland carbon sequestration. These data improve the ability to model and forecast carbon flux responses to hydrologic changes at this critical land-sea interface. Meteorological drought in California’s winter months leads to hydrological drought in summer months and concomitant increases in coastal ecosystem salinity. Accounting for water quality leads to better model forecasts of greenhouse gas fluxes and climate mitigation potential of tidal wetlands.

Summary

These research findings highlight the value of continuous data for capturing strong climate drivers at multiple timescales. The Peatland Ecosystem Photosynthesis Respiration and Methane Transport (PEPRMT) model can represent key drivers when data is available to support those calibrations. Model-data fusion occurring within this project across multiple U.S. tidal marshes is identifying necessary key constituents for constraining coastal carbon and methane fluxes to air, water, and soil. Continued measurements of atmospheric fluxes (AmeriFlux site US-Srr), water quality, and hydrologic fluxes at the Rush Ranch National Estuarine Research Reserve make this the longest continuously monitored U.S. tidal wetland for coupled high-frequency carbon fluxes. With accelerated sea level rise and increasing western U.S. drought frequency and intensity, Rush Ranch and other brackish wetlands along the Pacific coast are likely to experience profound increases in salinity over the next decade and through operations that control water flows from land to ocean, compromising their ability to mitigate climate change.

Principal Investigator

Lisamarie Windham-Myers
U.S. Geological Survey, Water Resources Mission Area
[email protected]

Co-Principal Investigator

Patty Oikawa
California State University–East Bay
[email protected]

Program Manager

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

Funding

This research is supported by the U.S. Department of Energy’s (DOE) Biological and Environmental Research (BER) program, U.S. Geological Survey (USGS) LandCarbon program, USGS California Water Science Center, and AmeriFlux network. The DOE Environmental System Science (ESS) Award #89243021SSC000081 to the USGS California Water Science Center is a subaward of the DOE ESS project (DE-SC0022185) led by California State University–East Bay.

Related Links

• Rush Ranch AmeriFlux Data

References