These are the findings of a U.S. Geological Survey report published today. Researchers from the USGS Western Ecological Research Center and the USGS California Water Science Center surveyed the elevation, water levels, sediment and vegetation at 12 marshes near Petaluma River, San Pablo Bay, Napa River and South San Francisco Bay.

Using a new computer model, they found that 95 percent (4,798 acres) of these 12 marshes will be inundated by 2100 under a four-foot sea-level rise scenario — losing their vegetation and being converted into tidal mudflat habitats.

“Future inhabitants of the Bay Area shoreline will see a very different set of wetlands and wildlife, according to our model,” says USGS ecologist and study author Karen Thorne. “Losing marshes means losing the wild birds and animal species that depend on them, and we also lose the natural infrastructure that marshes serve as — as buffers against extreme tides and floods.”

The study sites represent about 12 percent of the remaining marshes in San Francisco Bay overall. Results of the study are published in USGS Open-File Report 2013-1081, and videos of the sea level rise scenarios for the study sites can be viewed at the project website: www.werc.usgs.gov/SFBaySLR.

Researchers painstakingly surveyed the marshes using sophisticated “RTK GPS” instruments (see Tech Tidbit, below) — which are capable of measuring elevation within a two-centimeter (0.78 inch) resolution.  With this ability, researchers not only mapped the marsh topography, but they mapped the layout of the marsh plants as well — a previously unavailable, yet crucial dataset.

Marsh plants offer nesting grounds and daily high-tide refuges for native wildlife, including endangered species like the salt marsh harvest mouse (Reithrodontomys raviventris) and California clapper rail (Rallus longirostrus obsoletus).

Animations, graphs and data from the San Francisco Bay sea level rise study.

Alternate Futures?

The report has implications for habitat restoration efforts for San Francisco Bay’s national wildlife refuges. And the implications of the study are not necessarily bleak.

“San Francisco Bay is home to one of the world’s most vibrant centers of society and commerce, but it also means that our remaining marshes are often fenced in by urban barriers, and there’s little high ground left for marsh plants to naturally spread and adapt to rising seas,” says Don Brubaker, manager of the San Pablo Bay National Wildlife Refuge. “But if there are other things we can do to help our existing marshes become more resilient to future changes and give migratory birds and endangered wildlife more habitat and time to adapt to sea level rise effects, then we might be able to keep pace with sea-level rise.”

“This new report actually underscores the need to restore more marshes to San Francisco Bay,” says Eric Mruz, refuge manager at the Don Edwards San Francisco Bay National Wildlife Refuge, also one of the sites of the South Bay Salt Pond Restoration Project. “The study is based on current conditions. But if we change that equation, and have more acres of marshes and healthier marshes on hand to begin with, then maybe we’ll have a different outcome 100 years from now.”

The salt marsh harvest mouse (Reithrodontomys raviventris) is an endangered species dependent on San Francisco Bay marshes. Image Credit: USGS

Thorne and colleagues are currently applying the same research methods to forecast the impacts of sea level rise on marshes in San Diego, Orange, Ventura, San Luis Obispo and Humboldt counties, as well as marshes in Oregon and Washington states.

This research was made possible by the support of the USGS National Climate Change and Wildlife Science Center, with additional support from the U.S. Fish and Wildlife Service Inventory and Monitoring and Science Applications Program and the Department of Interior’s California Landscape Conservation Cooperative.

Local cooperators in San Francisco Bay include USFWS, NOAA, National Estuarine Research Reserve System, California Department of Fish and Wildlife, California State Parks, East Bay Regional Parks, City of Oakland and San Francisco International Airport.

Tech Tidbit: What is an RTK GPS?

RTK GPS stands for “real-time kinematic global positioning system”. However, unlike GPS units commonly used by consumers, RTK GPS systems require a “base unit” in addition to the measuring unit (the tall pole device held by the USGS technician in the photo). In urban areas like San Francisco Bay, local cell phone tower networks can sometimes function as the base unit.

A USGS researcher surveying marsh topography using a RTK GPS measuring unit. Image Credit: Kevin Buffington/USGS Western Ecological Research Center

The system then measures the relative difference in positions between the base unit and the measuring unit.

RTK GPS offers very high resolution within 2 cm for elevation measurement — the span of a U.S. nickel coin and easily the difference in height between low-growing and taller-growing plant species. And the horizontal x- and y-axis positions can be closer to 1 cm or less in resolution.

There are other technical differences, but in essence RTK GPS systems have excellent applications for land surveys, especially where a high-precision instrument is needed to discern elevation changes in areas with very little slope — much like the marsh vegetation and elevation surveys required of this USGS project.

Forests, grasslands and shrublands in the West sequester nearly 100 million tons of carbon each year, an amount equivalent to counterbalancing the emissions of about 83 million passenger cars a year in the United States, according to a new USGS report.

Carbon that is absorbed or “sequestered” through natural processes reduces the amount of carbon dioxide in the atmosphere.

While the study showed that western ecosystems are a strong carbon sink now, the region could experience a decline in storage potential between now and 2050, depending on future changes in land-use, climate and wildfires. Future carbon stocks are inextricably linked to these drivers because as ecosystems, forests or agricultural lands are converted for other uses, their ability to capture and store carbon is affected.

From the Rocky Mountains to the Pacific Coastal Waters

The area USGS studied extends from the Rocky Mountains to the Pacific coastal waters, and totals just over 1 million square miles. The major ecosystems evaluated were terrestrial — forests, wetlands, agricultural lands, and shrublands and grasslands — and aquatic — rivers, lakes, estuaries and coastal waters. It includes well-known ecosystems, such as the Rocky Mountains and the Sierra Nevada Mountains, the Mojave and Sonoran deserts, the Pacific Northwest forests and the vast grasslands and shrublands of the Great Basin.

Western Forests Stored the Most Carbon

While the western ecosystems varied widely in their potential for storing carbon now and in the future, forests are by far the largest carbon-storing pools, accounting for about 70 percent of the carbon stored recently in the West.

• Forests cover 28 percent of the land areas of West, contain the most carbon per unit area, and have the second-highest rate of sequestration of ecosystem types.
• Wetlands cover less than 1 percent of the West and had the highest rate of sequestration of all ecosystem types, but because they cover only such a small percentage of land, the amount of carbon they sequester is far less significant than other ecosystem types.
• Grasslands and shrublands cover nearly 60 percent of the West and contain 23 percent of the region’s carbon stored recently.
• Agricultural lands cover about 6 percent of the land areas of the West and contain 4.5 percent of the carbon stored recently.

Significant Greenhouse Gas Emission Sources in Western Ecosystems

Wildland fires in western ecosystems generated significant amounts of greenhouse gas emissions, with such emissions equivalent to 13 percent of the estimated rate of the recent annual carbon sequestration by western terrestrial ecosystems. This amount could increase up to 31 percent in the future.

Water bodies in the West emitted even more CO₂ than fires. Emissions from water bodies are equivalent to more than 30 percent of the recent annual carbon sequestration rate of terrestrial ecosystems in the West.  Basically, the more interaction with the atmosphere, the more CO₂ is released.  So, in fast-moving waters, where the water is churned up, there is a greater loss of CO₂ to the atmosphere.

Land-Use, Land-Cover, and Carbon Stocks

Future changes in the ability of western ecosystems to sequester carbon will depend on future changes in land-use, climate, and wildfires.  Future carbon stocks are tied to these drivers because as ecosystems, forests or agricultural lands are converted for other uses, their ability to capture and store carbon is affected.  Land use by people causes a significant loss of carbon from ecosystems. Specific examples are forest harvesting (nearly 13 million tons of carbon per year) and agricultural harvesting (more than 20 million tons of carbon per year).

To Read More:

Blog on the Report by David Hayes, Deputy Secretary of the Department of the Interior

Department of the Interior News Release on the New Report

The report: Baseline and Projected Carbon Storage and Greenhouse Gas Fluxes in the Ecosystems of the Western United States.

Coastal wetlands worldwide may disappear.

Many coastal wetlands worldwide including several on the U.S. Atlantic coast may be more sensitive than previously thought to climate change and sea-level rise in the this century.

Find out more