The California Bay Delta

The California Bay Delta is a regional ecosystem that spans nearly 61,000 square miles, composing over 42% of California’s land area, and encompasses the Central Valley, the Sacramento-San Joaquin Delta, and greater San Francisco Bay. 

A map of the Bay Delta ecosystem.

Produced by the California Department of Water Resources

Humans and wildlife alike depend on the Bay Delta, whether it be for drinking water, produce, or crucial habitat. The Bay Delta serves as both a storage and delivery system for California water, providing exports to users in the Bay Area, Central Valley, and Southern California. Over two-thirds of Californians rely on the Delta for their drinking water (Austin). Islands in the delta are also used for farming, with its fertile soil supporting one of the most productive agricultural regions in the world. The Delta is a popular recreation area, with activities such as boating and common across the area. Finally, the Delta serves as a crucial habitat for the state’s faunas, with over eighty percent of the state’s commercial fishery species living in and migrating through the Delta and a vast diversity of birds relying on the ecosystem’s wetland areas (Austin).

An overhead view of the Bay Delta ecosystem; a maze of 
waterways that wind through farmland and natural habitat areas
Photo by: Chris Austin

Prior to the occurrence of the California Gold Rush in the early 1850’s, the Bay Delta was one of the 
richest ecosystems in the state, home to a wide abundance and diversity of game animals and birds, including the bears, beavers, elk, and the California valley quail. The Delta was largely a sea-level swamp, composed of wetlands and a network of waterways. As settlers moved into the region, however, they drained the wetlands and constructed levees to create new farmland, causing a major alteration in the region’s habitat. More than 75% of the estimated 242,000 acres of the Delta’s highly productive native tidal marshes and mudflats has been converted to a variety of urban and industrial uses, altering trophic dynamics and food webs (From Sierra to Sea). Overharvesting, pollution, introduction of exotic species, and habitat degradation have also contributed to the ecosystem’s deterioration. 

Projected 2010–2099 changes in annual mean values of nine environmental indicators based on two scenarios compared to modeled and observed values during the 1970–1999 period.
Source: Cloern, Projected Evolution of California's San Francisco Bay-Delta-River System

Human impact on the Bay Delta has also manifested itself in the ecosystem’s declining fish population. Though the watershed once supported enormous populations of fish such as salmon, commercial harvesting since the Gold Rush caused the Bay to be “systematically overfished with nets of such small mesh that probably the Bay does not contain one-twentieth the number of fish that it did twenty years ago” (Jordan). Declining stocks of fish forced fish canneries to shut down beginning in 1882, and by 1916 most had gone out of business. Though limits have been established for all harvested species of fish in California, many commercial fisheries continue to shift from species to species as stocks of each fish become overfished and unprofitable. 

A graphic display of how the rise in sea levels has

transformed the Bay Delta over the past 15,000 years.
Source: From Sierra to the Sea

The introduction of exotic species to the Delta ecosystem has proved disastrous for native species. Due to the dissatisfaction of the region’s early settlers with the native fishes, foreign species of fish – such as the American shad and brook trout – were released into the region’s waters. The Asiatic clam, for example, was introduced to the Bay in 1986, spread rapidly throughout the region, and is believed to have caused the disappearance of the summer phytoplankton bloom and declines in species of zooplankton, which depend on the phytoplankton for food. For species such as the Delta smelt, exotic species influence the abundance and composition of food supply, predators, and competitors in ways not completely known to scientists. Exotic species have also entered the Bay Delta’s waters unintentionally, largely through hulls of boats entering the ecosystem from outside waters.

Providing California with agricultural and recreational uses, wildlife habitat, infrastructure pathways, and water supply services for over 20 million Californians, the future of the Bay Delta is of vital importance. However, serious ecological problems continue to affect the ecosystem. Toxic substances, including arsenic, mercury, and ammonia, adversely affect the water supply of the region, and continued overgrazing and bad forestry practices threaten to cause increased sedimentation and erosion. The increased introduction of exotic species, as shown by Figure III-B below, threatens to disturb the habitat for native plants and animals. Without a serious rehabilitation of the Delta ecosystem, an increasing number of fish and wildlife animals are sure to become extinct. 

Source: From Sierra to the Sea

 In September of 1992, the California Legislature declared that the state had a duty to preserve and protect the resources of the California Delta and passed the Delta Protection Act. The Act established the Delta Protection Commission, which was given the task of guiding the conservation and enhancement of the Delta’s natural resources. In order to achieve this task, the Act defined a Primary Zone within the ecosystem, for which the Commission was responsible for preparing a land use and resource management plan which met the goal to "protect, maintain, and where possible, enhance and restore the overall quality of the Delta environment, including but not limited to agriculture, wildlife habitat, and recreational activities” (Delta Protection Commission). In 2009, the Delta Stewardship Council was also formed, charged with protecting the Delta’s critical role as a water supply for millions of Californians and its unique ecosystem. Though these acts have had limited success, the ecosystem remains at critical risk of losing species and habitat. 

Despite the ruined state of the California Delta, steps can be taken to improve the environmental status of the ecosystem. In August 2012, the Environmental Protection Agency (EPA) published a Bay Delta Action Plan, highlighting seven priority activities they believed would help restore the Bay Delta estuary. These recommendations included, among others, the strengthening of selenium water quality criteria, the prevention of pesticide pollution, and the restoration of aquatic habitats. However, as the EPA itself admits, even the successful implementation of these suggestions would not be enough to completely resolve the environmental crisis facing the Delta, and any comprehensive solution would have to address the many issues facing the Bay Delta ecosystem.

In addition to the EPA’s Action Plan, several lines of action have been proposed by multiple entities to help improve human impacts on the ecosystem. Though the release of toxins into the Delta waters is difficult to control due to the multiple sources of origin, the reduction of inputs of toxicants from regional agriculture and urban areas would drastically improve the condition of the Delta’s water. To prevent the spread of invasive species carried on boat hulls, mandatory boat inspections should be implemented on all boats sailing into the Bay Delta. This will, in turn, help to restore endangered species of fish such as the smelt, which was listed as threatened under the Endangered Species Act in 1993. Finally, stricter limits on fishing can be imposed to prevent fisheries from simply varying the species of fish they deplete each year.

Works Cited 

Austin, Chris, and Gary Pitzer. "Aquafornia Exclusive: Why the Delta Matters to Every Californian." Aquafornia. N.p., 3 Sept. 2007. Web. 26 Nov. 2012. <http://www.aquafornia.com/archives/588/>.

"Bay Delta Action Plan." EPA. Environmental Protection Agency, Web. 21 Nov. 2012. <http://www.epa.gov/sfbay-delta/actionplan.html>.

Bennett, William A. San Francisco Estuary and Watershed Science (2005): Eschlolarship. Web. 20 Nov. 2012. <http://escholarship.org/uc/item/0725n5vk>.

Cloern JE, Knowles N, Brown LR, Cayan D, Dettinger MD, et al. (2011) Projected Evolution of California's San Francisco Bay-Delta-River System in a Century of Climate Change. PLoS ONE 6(9): e24465. doi:10.1371/journal.pone.0024465

 

Draft Land Use and Resource Management Plan for the Primary Zone of the Delta. Publication. 2009. Print.

Delta Protection Commission. State of California, Web. 22 Nov. 2012. <http://www.delta.ca.gov/>.

From the Sierra to the Sea: The Ecological History of the San Francisco Bay-Delta Watershed. Rep. San Francisco: Bay Institute, 2003. Print.

Jordan, D. S. 1887. The Fisheries of the Pacific Coast. Part XVI in G. B. Goode, ed. The Fisheries and Fishery Industries of the United States. Section II, U.S. Commission of Fish and Fisheries. Government Printing Office, Washington, D.C.

Moyle, Peter B., and William A. Bennett. The Future of the Delta Ecosystem and Its Fish. Rep: Public Policy Institute of California, 2008. Print.