Delta Stressors are Interactive, Complex

Delta Independent Science Board Releases Stressors Report

No one stressor, or group of stressors in the California Delta, is the most important, according to the Delta Independent Science Board (Delta ISB). “The stressors are interactive and complex,” said Richard Norgaard, Delta ISB Chair. “[Ranking stressors] is going to be a judgment call on the political side and on the scientific side. The importance of the objectives will tell us about the importance of the stressors.”

The Delta ISB recently released its report evaluating multiple stressors in the Sacramento-San Joaquin Delta (Delta) as requested by some members of the California Legislature and the Delta Stewardship Council. They had requested a report helping them understand which stressors to deal with first.

“There are no scientifically objective, agreed upon methods for ranking stressors,” said Norgaard, who served as spokesperson for the Delta ISB in summarizing the report, to the Delta Stewardship Council during its January meeting. “Stressors and the objectives we are trying to reach have to be thought about together. The state of the methodology is not complete and this is a worldwide problem. The Delta is better studied than most areas,” Norgaard added, “but there is only now beginning to be some unity in the methods being used, and so we’re very much in a situation where we need to combine our judgments and work together.”

In preparation for its report to the Stewardship Council, the Delta ISB held a two-day workshop Jan. 12-13 to identify alternative classifications of stressors and ways of evaluating their relative importance, considering the interactions of multiple stressors. In advance of the workshop, board members evaluated other environmental management programs around the world and summarized how they were tackling the problem of ranking stressors. The Delta ISB then prepared a draft report which was posted publicly, and followed up with a separate teleconference among the members Jan. 24 to finalize the draft.

“The Council needs to make sure that the [Delta] Plan makes as tight a connection as possible between the objectives we’re trying to reach and the stressors affecting the ecosystem that are making it complicated or difficult to reach those objectives,” Norgaard said. “Part of the scientific process is making those connections and the Delta ISB will be insisting that those connections be as tight as possible.”

Norgaard added that the Delta ISB did not find any single stressor or combination of stressors that could be a direct cause of Delta problems, for example, the POD (Pelagic Organism Decline). “At the present state of knowledge we think there are a lot of interactive stressors,” he said.

He explained that scientists characterize stressors as specific effects of drivers. “It’s sometimes helpful to think about drivers, which are creating stressors and stressors which are all driven by a big driver,” Norgaard said, “so climate change we can think of as a big driver, but then it creates all kinds of different stressors from warmer temperatures to changes in precipitation to sea level rise. All of those are stressors, but the driver is climate change.”

Norgaard discussed models of ecosystems. One issue with ecological models is the whole problem of the system changing over time. “Can you actually say that ‘if we reduce this stressor that the system will go back to where the system was before?’ Sometimes it will, and sometimes it won’t,” Norgaard said. “And when it won’t, it’s because you’ve just got a new system now…This is adaptive environmental management, and the strength of the Delta Plan is really going to be rooted in the strength of the adaptive environmental management plan-how tightly we set that up is really critical to how we manage stressors over time, because these stressors will be changing over time.”

The Delta ISB’s report organized stressors into four categories: global stressors, legacy stressors, anticipated stressors and current stressors.

  • Global stressors are those that have to be adapted to, like climate change and population growth.

  • Legacy stressors are human-caused actions, such as the continuing effects of sediment and mercury discharge from the gold mining era. Management actions can reduce their effects.

  • Anticipated stressors are stressors that can be anticipated and will result from present or future activities (i.e., continued pollution). Management actions can prevent, reduce, or provide for adaptation.

  • Current stressors are ongoing activities like water management practices, agricultural practices and waste discharges that can be changed or steps taken to reduce their effects on the Delta, or both.

“The important thing about legacy stressors,” Norgaard said, “is that generally these are things that we wish we hadn’t done or wish we’d done better.”

In its report, the Delta ISB said, “Decision-makers need to plan management in the context of the directional changes that are occurring in the Delta as well as the potential for catastrophic change if Delta levees fail. Decision-makers need to be looking 30-50 years into the future as they develop policy.”

Council members complimented the Delta ISB on the report. “You’ve convinced me it’s even more complex than I thought it was,” said Hank Nordhoff, “and exceedingly difficult to model.” Council Chair Phil Isenberg called the final comment in the report “very valuable:” “Expect surprises.”