BELLINGHAM - To the non-scientist, it looks obvious: The decline in marine life at the bottom of Bellingham Bay is what we would expect in a bay used as a dump for industrial waste, human sewage, garbage and polluted stormwater over many decades.
But marine researchers say it's not that simple.
Valerie Partridge, one of the authors of a recent Washington Department of Ecology study of Bellingham Bay sediment quality, said she doesn't feel she has evidence beyond a reasonable doubt to convict man-made pollution in this case.
"We certainly can't rule it out, nor can we rule out that there are natural factors at work," Partridge said. "We certainly have our suspicions, but as scientists we can't make that certain link, with the type of information that we have available to us."
The Department of Ecology's latest study is based on an extensive survey of bay sediments and the creatures that live in them. The survey tests found "unusually low" numbers of clams, snails, sea stars, crabs, shrimp and other sea life, according to an Ecology press release. The surveys also found that organisms least sensitive to pollutants were the most abundant, while the most sensitive organisms were scarce.
But the health of the life forms in the sediment did not correlate perfectly with areas of chemical contamination. While marine life populations did not change much between 2006 and the most recent study in 2010, there was a dramatic decline between 1997 and 2006. Why?
Because there is a lack of thorough data for earlier periods, it's hard to say, Partridge said. Her examination of the sketchy information that is available for earlier decades does indicate that some marine life populations have dramatic ups and downs that may be driven by natural processes such as cyclical changes in seawater temperature: the El Nino phenomenon and the Pacific decadal oscillation, for example.
"It's possible that this is just part of a large natural swing that we don't have enough information to understand," Partridge said.
It is also possible that marine life is being harmed by chemicals not on the list of things that scientists have been testing for. While the current Ecology tests included 263 chemicals ranging from industrial toxins like metals and PCBs to chemicals found in drugs and cosmetics, Partridge noted that there are about 80,000 chemicals in the human race's chemistry set.
One factor not included in the latest batch of Ecology tests is dissolved oxygen levels. That is being studied by Jude Apple, a marine scientist at Western Washington University's Shannon Point Marine Center.
Apple sees some indications that reduced oxygen levels in bay water, combined with chemical pollutants, may help explain the downturn in marine life.
Reduced oxygen levels are also causing problems in Lake Whatcom, but for a different reason. In the lake, Apple said, phosphorus-laden runoff triggers the growth of algae and bacteria that deplete the oxygen. In the bay, the triggering pollutants are nitrogen compounds from fertilizers, manure and other man-made sources.
But Apple also notes that natural processes have a big impact on the bay's oxygen levels. Marine waters flowing in from the Pacific Ocean have naturally higher levels of nitrogen nutrients.
Apple's research shows reduced dissolved oxygen levels as a potential issue in deeper areas of the bay, and areas east of Portage Island and south of the Nooksack River mouth. The river seems to be a significant contributor to the bay's load of nitrogen-based nutrients after heavy rainfall, when manure and other pollutants move down the river. Apple said he hasn't identified low oxygen levels as an issue in shallower areas on the eastern side of the bay.
Climate change also affects oxygen levels, which in turn affect ocean acidity now believed to be harming shellfish and other organisms. Warmer water contains less oxygen and becomes more acidic, Apple said.
Apple and the Department of Ecology researchers have been comparing notes in hope of shedding more light on the bay's problems.
Lucy McInerney, Ecology's manager for Bellingham Bay cleanup, said the latest research on bay marine life problems won't affect cleanup projects now underway. McInerney noted that the cleanup strategies being carried out by the Port of Bellingham are getting detailed scrutiny from her agency to make sure they are good enough to prevent contact between marine life and toxins. In the years ahead, areas where that contact is occurring will be cleaned up, McInerney said.
"The exposure to harmful levels of contamination will be eliminated by the cleanups," McInerney said.
WWU's Apple remarked that it is not simple for people and marine life to share the bay.
"We need food and we need commerce," Apple said. "We also need water quality. Keeping all that in balance is really challenging."