Last year, the Supreme Court severely limited the federal government’s ability to limit pollution in small waterways that remain dry much of the year and fill only after rain or snowmelt.
Now, a new study finds that these so-called seasonal streams are far more important to the nation’s waterways than is often recognized.
this The study was published Thursday in the journal ScienceAn estimated 55 percent of the water flowing into U.S. rivers can be traced back to millions of seasonal streams that flow periodically. The findings suggest that the Supreme Court ruling rolling back protections for those streams could leave large swaths of water vulnerable to pollution.
“Right now, we manage larger waterways like the Hudson River, but a large portion of that water comes from upstream areas that can no longer be managed,” said Craig Brinkerhoff, a doctoral student at the University of Massachusetts Amherst and leader of the study.
For years, politicians, industry groups and environmentalists have argued over which U.S. waters should be covered by the Clean Water Act, which was passed in 1972 and allows the Environmental Protection Agency to limit water pollution. While there is consensus that the act applies to major rivers and lakes, there is debate over whether federal protections should apply elsewhere, such as nearby wetlands or streams that dry up part of the year.
Environmentalists argue for broad protections, arguing that these other water bodies are important; home builders, some industry groups and conservatives oppose what they see as excessive regulation.
In May 2023, the Supreme Court The motion to limit the scope was passed by a vote of 5 to 4 The majority ruled that the law should apply only to “relatively permanent, stagnant or continuously flowing bodies of water” and wetlands that have a “continuous surface connection” to those waters.
EPA officials said the ruling effectively ends federal protections for 4.9 million miles of rivers that flow only when it rains. Announced in August The guidance of the court will be followed.
Jud Harvey, a senior research hydrologist with the U.S. Geological Survey, said these temporary streams are often overlooked because they look like ordinary dry ditches for much of the year. Wrote a separate review “But when it rains,” he said, “these streams carry a lot of water” that ends up in rivers and lakes.
Mr. Brinkerhoff and his colleagues identified millions of seasonal streams across the country and used detailed models to estimate the amount of water flowing through them.
The study found that in the West, seasonal streams flow an average of only four to 46 days per year, but contribute 79% of downstream river flows. In the contiguous U.S. river basins, seasonal streams contribute an average of about 55% of flows.
Mr. Harvey said he was surprised by the amount of water coming from seasonal streams. “But this was a rigorous and detailed investigation using the best available data in the United States,” he said of the study.
Because of the volume of water flowing through these rivers, whether they are polluted or not is critical, the study noted. Sediment or excess phosphorus from fertilizer runoff from farms can build up in dry waterways until heavy rains carry the pollutants into larger waterways.
Mr. Brinkerhoff said the study did not attempt to quantify exactly how much pollutants flow through the rivers. That is a subject for future research. But he said the rivers have a big impact on water quality.
Even though the EPA is no longer able to regulate pollution in seasonal streams, some states are still trying to do so, said Ciaran Harman, an associate professor of landscape hydrology at Johns Hopkins University who was not involved in the study. For example, farmers can allow grass and other vegetation to grow around seasonal streams to limit erosion and prevent pollutants from flowing into waterways after storms. However, state programs can vary widely, and states often have difficulty coordinating when it comes to water regulation.
Jon Devine, who leads the federal water policy team at the environmental group Natural Resources Defense Council, said that in the past, the EPA has often used new scientific research to update and sometimes expand its water regulation. “Regulators look at whether different water bodies have an impact on downstream water quality and, if so, whether they should be protected,” he said. “Ultimately, it’s a scientific inquiry.”
But Mr. Devine said the EPA’s ability to change those regulations has been greatly weakened after the Supreme Court ruling. “You really need Congress to step in,” he said.
