Rivers and streams in the U.S. have seen better days, but it’s not all bad. That was the message from the U.S. Environmental Protection Agency when explaining the findings of a new study.
The EPA’s newly released draft of the National River and Streams Assessment showed that biological conditions in many rivers and streams are significantly damaged. However, the nation’s rivers did improve in some categories when compared with a 2004 study on wadeable streams.
About 55 percent of streams have poor conditions for biology based on surveys of benthic macroinvertebrates and algae. Another 21 percent are in good condition.
Macroinvertebrate species loss was also covered in the study. About 17 percent of streams lacked more than 50 percent of their expected species, compared with reference sites. However, almost 40 percent of streams retained more than 90 percent of their wildlife.
Still, the damage to wildlife is significant, said Ellen Tarquinio, EPA environmental protection specialist and one of the study’s main coordinators. “There’s a large portion of our stream miles that have lost a significant percent of their taxa,” she said.
The new assessment shows a total of 40 percent of the nation’s rivers have excessive phosphorus levels. That’s a 19 percent increase from the 2004 study.
“Total phosphorus is really the most widespread stressor across the United States,” said Tarquinio.
Some positive trends also appeared from the data, which was collected and analyzed by hundreds of scientists and technicians across the country. While negative impact from phosphorus rose, poor health ratings for nitrogen decreased in the nation’s waters compared with the 2004 study.
The study also found improved habitat conditions. Human disturbance decreased by 12 percent and in-stream fish habitat conditions improved by 17 percent compared to 2004.
Human health indicators were also analyzed to gain a national portrait of recreational health of rivers and streams. The study showed through fish filet analysis that 13,000 miles of rivers had fish with mercury levels exceeding safe thresholds.
Another 9 percent of river miles had enterococci bacteria exceeding human health thresholds. Tarquinio said the study did not include measurements of E. coli because of time limitations.
The study’s statistical design compared 1,942 sample sites and 234 reference sites to draw general trends about the lower 48 states’ riparian waterways. Samples were taken from 2008 to 2009 and analyzed and interpreted into the newly released draft.
Streams were sampled based on a stratified random selection. “We tried to make sure we were sampling some of the small systems and some of the large systems,” Tarquinio said.
Each waterway sampled was only visited once for the study during the course of a day. Sampling followed standard protocols to ensure consistent data collection practices, Tarquinio said.
Tarquinio said the study focuses purely on correlation. “The survey does not look at causes,” she said. “The survey looks at relationships between biological conditions and indicators.”
The report is out now as a draft and open to comments from the public. The public comment period will close on May 9. Click here to read the full study.
Upcoming related studies by the EPA include the second national lakes assessment and first ever assessments of the coasts and wetlands.
Top image credit: Eric Vance/U.S. EPA