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Report: Sacramento Delta 'No Longer a Delta'

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In the Delta | Photo: Lisa Padilla/Flickr/Creative Commons License

A new report on the decline of the Sacramento-San Joaquin Delta says that development over the last 160 years has drastically changed how the state's largest wetland area functions. "A Delta Transformed," put together by the San Francisco Estuary Institute with funding from the California Department of Fish and Wildlife, compares historical conditions in the 1,200-square mile estuary with those of the present day.

And though it's no secret that the Delta has been radically transformed for agriculture, urban development, and water supply, the report's conclusions are nonetheless startling. The most common habitat in the historic Delta has been almost eradicated, and the most basic ecological functions of the Delta have been engineered out of existence.

"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," said Bay-Delta expert Carl Wilcox of CDFW.

The study's authors measured changes in a number of different habitat types over 160 years of Delta history. The Delta's grasslands and open water have increased in extent since the Gold Rush era, but the nine other historic habitat types studied have declined drastically. The Delta's oak savannas and vegetated dunes have been essentially eradicated. There were more than 2,500 acres of dunes in the Delta in the 19th Century; there are four acres remaining today. The historic Delta held just under 80 square miles of oak woodlands; all of them are now gone.

But probably the single largest change in Delta habitat is the decline in what the report calls "freshwater emergent wetlands," a term of art meaning areas of standing water with plants "emerging" from beneath the surface. A typical example would be the vast tangled tracts of tule marshes that once thrived in the delta, but cattail stands and similar vegetated marshes also qualify.

In the mid-1800s, there were nearly 750 square miles of freshwater emergent wetlands in the delta, a nearly unbroken landscape stretching across the heart of the Central Valley one and a half times the size of Los Angeles, After 160 years of draining, filling, and dredging, just 16.4 square miles of that habitat remains: a 98 percent decline.

The report, which was released on Tuesday, shows similar declines in seasonal wetlands like vernal pools, in wet meadows, and in riparian forests.

Direct conversion of habitat for farming and urban development is a major reason for the declines in habitat, but the other main way in which we've changed the Delta may well have been even more destructive. The Delta is now a vital link in the state's water transport system. Its former network of open waterways that once mixed seawater and runoff from the Sierra Nevada, Cascades, and Coast Ranges is now a web of engineered canals designed to shunt water from the northern end of the state to San Joaquin Valley farms and southern cities.

That has spelled disaster for salmon and other fish who have evolved under the operating assumption that rivers flow downstream to the ocean; the Delta's engineered waterways often flow away from the Bay and the Pacific. It also means that the annual floods that built the historic Delta's soils no longer spread nutrient-rich sediment across the landscape.

The result is an ecosystem suffering from loss of fertility, fragmentation of habitat, decline in wildlife populations, and incursions by invasive species, says the report.

In a press statement, CDFW said that it plans to use the report as a guide for identifying which parts of the Delta landscape should be restored in order to better provide habitat for wildlife in the future.

But that bit of optimism aside, it's hard to shake the feeling of finality in the report's summation of changes in the Delta:

The historical Delta Is gone. The defining characteristic of the historical Delta was its extensive wetland landscape, formed over time as floodwaters met the tides. Modern land management has increasingly disconnected floodwaters from the wetlands by widening and deepening channels, diking and draining wetlands for agriculture, and building levees for flood protection. The consequences of this disconnection include a nearly complete loss of Delta wetlands, along with the processes that sustain them, and a dramatic altering of the remaining aquatic habitats. The Delta has become more susceptible to invasive species, and the consequences of those invasions are magnified as a result of habitat loss and alteration. The ecological impacts of these transformations have been dire; the Delta food web has collapsed, wildlife populations have been drastically reduced in size, and the resilience of many remaining populations has been impaired.

It's hard to come up with a way to see that glass as "half full."

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