San Joaquin River delta's biggest enemy hard to pinpoint

Alex Breitler in Recordnet.com (Stockton, California): There are more than 40 potential causes for the [San Joaquin River] Delta's decline, scientists said Friday, but ranking them in order is just too difficult "We're not in a position now - we may be in a position later - to say it's these three stressors that are causing 90 percent of the problem, or one stressor causing 45 percent of the problem," said Richard Norgaard, chair of the Delta Independent Science Board, a panel of 10 experts established by California's sweeping water reform in 2009.

"At the present state of knowledge, we just think there's a lot of interacting stressors," Norgaard told the Delta Stewardship Council on Friday. Scientists say many causes may be contributing to the decline of the Delta:

Global causes: Climate change (sea level rise, changes in water flows, higher temperatures and changes in ocean conditions); earthquakes; population growth; state economy.

Historic causes: Habitat loss; mercury from the Gold Rush accumulating in fish; toxic selenium runoff from farms; sinking Delta islands; artificial levees that may break, causing flooding; upstream dams that cut off breeding areas for salmon; agricultural subsidies; development, zoning and building codes; invasive species.

Current causes: Water withdrawals upstream of the Delta, in the Delta and outside of the Delta; fish sucked into export pumps; nutrients from farm runoff and city wastewater treatment plants; pesticides; metals that enter the water from farms, cities and industry; channel dredging; illegal harvest of threatened species; hatcheries that alter the genetic makeup of fish.

Anticipated causes: Landscape changes; urban expansion; land use along streams feeding the Delta; people's lifestyle decisions on where and how they live….

The San Francisco Bay Area, home to the San Joaquin River Delta, via NASA