Last year, the Supreme Court severely limited the federal government’s ability to limit pollution in creeks that stay dry most of the year and fill up only after rainfall or snowmelt.
Now, a new study finds that these so-called ephemeral rivers are far more important to the nation’s waterways than is often thought.
The study, published Thursday in the journal Science, estimates that 55 percent of the water flowing out of U.S. river basins can be traced to millions of ephemeral streams that flow periodically. The findings suggest that Supreme Court rulings that remove protections from these streams could leave large swathes of water vulnerable to pollution.
“Currently, we regulate larger waterways like the Hudson River, but a large portion of that water comes from Upstream from a place that can no longer be regulated.
For years, politicians, industry groups and environmentalists have debated which U.S. waters should be subject to the Clean Water Act. While there is agreement that the law applies to major rivers and lakes, there is controversy over whether federal protections should apply elsewhere, such as nearby wetlands or streams that dry out part of the year.
Environmentalists favor broad protections, arguing these other bodies of water are important; homebuilders, some industry groups and conservatives oppose what they see as overregulation.
In May 2023, the Supreme Court limited the scope of the Clean Water Act in a 5-4 vote, with the majority ruling that the law should apply only to “bodies of water that are relatively permanent, stationary, or continuously flowing” and wetlands that are “connected to those waters.” Continuous surface connection”.
EPA officials said the ruling effectively ended federal protections for 4.9 million miles of streams that flow only when it rains, and the agency announced in August it would follow the court’s guidance.
Jud Harvey, a senior research hydrologist at the U.S. Geological Survey who wrote a separate commentary for the study, said these temporary streams are often overlooked because they flow during much of the year. Time seems like an inconspicuous dry ditch. “But when it rains,” he said, “these streams carry a lot of water” that eventually flows into rivers and lakes.
Brinkerhoff and his colleagues identified millions of ephemeral streams across the country and used detailed models to estimate the amount of water flowing through them.
The study found that in the West, ephemeral rivers flow only an average of 4 to 46 days per year but contribute 79% of downstream river flows. On average, ephemeral rivers contribute approximately 55% of river basin flows in the contiguous United States.
Mr Harvey said he was surprised by the amount of water coming from the ephemeral stream. “But this was a rigorous and detailed investigation, using the best data available in the United States,” he said of the study.
The study noted that because large amounts of water flow through these streams, it is important whether they are contaminated. Sediments or excess phosphorus from fertilizer runoff from farms can accumulate in dry waterways until a heavy rainstorm picks up the contaminants and washes them into larger waterways.
Mr. Brinkerhoff said the study did not attempt to quantify how much pollutants actually passed through the streams. This is a topic for future research. But, he said, these streams have a big impact on water quality.
Even though the EPA can no longer regulate pollution in ephemeral rivers, some states are still trying to do so, said Ciaran Harman, associate professor of landscape hydrology at Johns Hopkins University who was not involved in the study. For example, farmers can let grass and other vegetation grow around ephemeral streams to limit erosion and prevent pollutants from ending up in waterways after storms. However, state plans can vary widely, and it is often difficult for states to coordinate on water regulations.
In the past, the EPA has often used new scientific research to update and sometimes expand the scope of water regulations, said Jon Devine, who leads the federal water policy team at the Natural Resources Defense Council. . “Regulators will look at whether different water bodies have an impact on downstream water quality and, if so, whether they should be protected,” he said. “Ultimately, this is a scientific inquiry.”
But Devine said the EPA’s ability to change those regulations has been significantly curtailed since the Supreme Court’s ruling. “You do need Congress to step in,” he said.
