tule (Scirpus acutus) and other dominant and subdominant marsh species. The tule marshes followed the courses of the Sacramento River bottomland and extended along the San Joaquin River through the Central Valley. Extensive levees on the delta eventually excluded tides and floodwaters from 90 percent of the delta, vastly changing its physical character, vegetation, and fauna.
Changes in the bay-delta are well documented in Nichols et al. (1986). Nineteenth-century hydraulic mining in the Sacramento-San Joaquin drainages deposited tens of millions of cubic meters of earth and rock in the bay, reducing its depth, and changing its shape and circulatory patterns. Combined with the loss of marshes and the reduction in freshwater inflow to less than 40 percent of historic totals, deleterious changes detected in planktonic abundances had repercussions throughout the aquatic food web.
Dams above the delta have cut off anadromous fish from their spawning grounds, and alterations in freshwater flow regimes and salinity have contributed to the demise of bay fisheries. These problems have been compounded by massive discharges of agricultural wastewater, much of it containing toxic elements, such as selenium, leached from the soil, along with sulfate and nitrate from fertilizers and soil amendments. Untreated urban runoff, containing substantial quantities of oil and grease, and spills of industrial chemicals add further to the stresses being placed on the estuary.
Damage to aquatic life from untreated discharges was first documented in the early 1950s, about the time municipalities around the bay began giving their sewage primary treatment (San Francisco Estuary Project, 1990). Secondary treatment of sewage began in the mid-1960s, along with the consolidation and relocation of discharges to deeper water (San Francisco Estuary Project, 1990). Effluent discharge standards were tightened as a result of the state's Porter-Cologne Water Quality Act of 1969 and the federal Clean Water Act of 1977. Today 37 percent of the publicly owned treatment works perform tertiary treatment on waste streams, and the remainder deliver secondary treatment (San Francisco Estuary Project, 1990). Over the past 30 years, more than $3 billion has been spent on improvements in wastewater treatment or discharge (Condit, cited in San Francisco Estuary Project, 1990).
Numerous wetland restoration projects have been conducted on San Francisco Bay (Berger, 1990) and on the West Coast (Josselyn and Buchholz, 1984). For a comparison of natural and restored eastern coastal marshes with respect to fish and wildlife habitat value, see Roberts (1989).