Dead zones increased dramatically in U.S. waters over the past 50 years, threatening ecosystems and fisheries nationwide, according to a sweeping report Friday by the federal Office of Science and Technology Policy.
The multiagency assessment said that incidents of hypoxia — a condition in which oxygen levels drop so low that fish and other animals are stressed or killed — have risen nearly 30-fold since 1960 due in part to man-made pollutants.
It called for renewed efforts to reduce water pollutants that lead to low levels of dissolved oxygen and improve strategies to protect marine food sources.
A dead zone in San Diego Bay, first documented in the 1980s, was part of the analysis. Scientists have used it for years as an example of an oxygen-starved area where runoff from cities contributes to hypoxic conditions.
“There are reasons to worry about San Diego Bay, but hypoxia hasn’t been studied as rigorously here as it has in other places like the Chesapeake Bay, where it is a much bigger problem,” said Brian Hentschel, a biology professor at San Diego State University who studies bottom-dwelling organisms such as worms, clams and shrimps.
He hopes Friday’s national assessment spurs more funding for local research that tracks dissolved oxygen and related factors across San Diego Bay over time.
“That report should trigger some alarm bells because it’s pretty clear that the human impacts that create hypoxic conditions have been increasing,” Hentschel said. “More detailed data now will make it easier 15 or 20 years from now to know how the bay is changing.”
Dead zones were detected in nearly half of the 647 waterways assessed. On the West Coast, federal researchers found a sixfold increase in the number of dead zones over the past 20 years, with 37 areas now suffering from low oxygen. A region off the coast of Oregon and Washington has become the second-largest seasonal hypoxic region in the United States and third largest in the world.
Friday’s report said work to study and control pollutants are advancing but management efforts to stem the tide of hypoxia “have not made significant headway” in part due to increased development and population growth in coastal watersheds.
“If current practices are continued, the expansion of hypoxia in coastal waters will continue and increase in severity, leading to further impacts on marine habitats, living resources, economies, and coastal communities,” the report’s authors said.