Report reveals dramatic changes to Delta ecosystem
October 28, 2014
• Historical investigation may help researchers with restoration planning
• “The Delta no longer functions as a delta”
“Extensive tidal wetlands and large tidal channels are seen at the central core of the Delta. Riparian forest extends downstream into the tidal Delta along the natural levees of the Sacramento River, and to a certain extent on the San Joaquin and Mokelumne rivers. To the north and south, tidal wetlands grade into non-tidal perennial wetlands. At the upland edge, an array of seasonal wetlands, grasslands, and oak savannas and woodlands occupy positions along the alluvial fans of the rivers and streams that enter the valley.”
That pastoral description is of the California Delta, also known as the Sacramento-San Joaquin Delta.
Not of the Delta today, but of the Delta before it was modified by man.
It helps lead off a recent study produced by the San Francisco Estuary Institute-Aquatic Science Center and funded by the California Department of Fish and Wildlife (CDFW) that identifies the dramatic ecological transformation of the Delta over the past 150 years.
“The most visible changes between the historical and modern habitat type mapping are the dominance of agriculture, increase in open water, and expansion of urban landscapes. The dearth of freshwater emergent wetland and edge habitat types has vastly changed the functioning of the modern Delta with respect to life-history support for wildlife (defined as both plants and animals),” the report says.
Developed by a group of scientists and resource managers, “A Delta Transformed” explains the relationship between specific landscape features and ecological functions, and compares historic conditions with the present.
It identifies the restoration framework needed to design landscapes that will support native wildlife and hold up to the threats presented by climate change and invasive species.
The complete report can be downloaded at the link at the end of this story.
“The Delta no longer functions as a delta and is now a network of deep, engineered channels with declining abundances of native wildlife, particularly fish species, and increasing numbers of invasive species,” says Carl Wilcox, CDFW policy advisor to the director for the Bay-Delta. “This critical report contributes a missing dimension to Delta planning by providing a landscape-scale perspective that illustrates how restoration in the Delta should be implemented to support native habitat and species.”
Presently, the Delta estuary – the largest estuary on the west coast of the Western Hemisphere -- is in a highly altered condition and struggling, the report says.
Study participants identified a variety of landscape changes in the Delta that have impacted its ecological function over the years. These primary changes include loss of connectivity among habitat, degradation of habitat quality and loss of complexity. The knowledge gained from this project will be used to identify specific elements of the landscape that can be restored to meet the needs of native species.
But changes will be difficult at best, the report suggests.
“The major physical changes to the system, as well as the impacts from invasive species, water diversions, and other stressors, make it difficult to envision how Delta ecosystems could work successfully in the future,” it says in conclusion.
The Sacramento-San Joaquin Delta is home to more than 750 native species and supplies water to more than 25 million Californians as well as 3 million acres of farmland.