Effects of Climate Change on San Francisco Bay-Delta Wetlands Featured in San Francisco Estuary and Watershed Science Papers

Two papers were featured in a special issue of San Francisco Estuary and Watershed Science (SFEWS) on regional perspectives on tidal marsh restoration and anticipated consequences of climate change in the San Francisco Bay-Delta.

“Climate Change and San Francisco Bay-Delta Tidal Wetlands” shows that climate change will likely have “significant global impacts” on tidal wetland ecosystems. “In addition to responses to changes in CO2, temperature, and precipitation that all biotic communities will experience, tidal marshes also will experience shifts in salinity and sea level,” the paper from Thomas Parker, John Callaway, and others said.

In the San Francisco Bay-Delta, the areas most likely to be affected-brackish and freshwater tidal wetlands-are also the sites with the majority of endemic plant species and the greater biodiversity and productivity. “Effects on the San Francisco Bay-Delta estuary are complex and difficult to predict, but a few things are clear,” the paper said. “Biodiversity of the tidal wetland system in the San Francisco Bay-Delta region will decline, with subsequent effects on ecosystem functioning and services. Altered plant production, physiological tolerances, and shifts in rates of mortality will modify wetland plant communities in ways not yet predictable. Tidal wetlands are especially sensitive to processes that climate change will alter.”

Another paper, “Tidal Wetland Restoration in San Francisco Bay: History and Current Issues,” also by Callaway and Parker explores the state of knowledge about wetland restoration around San Francisco Bay. Wetland projects are becoming larger and more complex requiring more sophisticated planning. “Although approximately 90 percent of bay tidal wetlands have been lost, current interest in restoring tidal wetlands in the region is great, with opportunities for large-scale projects that will substantially increase the present area within the bay,” the paper says.

The paper further goes on to say that the greatest future challenge for tidal wetland restoration will be climate change. “While specific effects are unpredictable, some general trends are extremely likely: (1) there will be seasonal shifts in estuarine salinities, with higher concentrations during the growing season resulting from reductions in snowmelt and shifts in the timing of watershed runoff; and (2) rates of sea-level rise will increase over the next century, although the magnitude of change is not certain. Changes in both salinity and inundation will have large-scale effects on tidal wetlands in the bay. Increases in salinity during the growing season are likely to cause more salt-tolerant species to migrate up the estuary over the long term. Tidal wetlands can keep pace with some increases in sea-level rise through increased mineral and organic matter accumulation; however, large-scale increases in sea-level rise are likely to lead to wetland loss.”

SFEWS is an open access, peer-reviewed, academic journal that publishes research about the science and resource management of San Francisco Bay, the Sacramento-San Joaquin River Delta, and the upstream watersheds. The journal is published jointly by the Delta Stewardship Council and the University of California at Davis John Muir Institute of the Environment. To read the special issue, click here. To read the current issue, click here.