The fresh water in America’s lakes is increasingly turning greenish- brown—which has negative consequences for water quality, fish and the aquatic food chain.
Lakes in the continental United States are progressively becoming “murkier,” according to a research paper co-authored by Dr. Dina Leech and recently published in Limnology and Oceanography. Leech, associate professor of biology at Longwood, is the lead author of the research, which reveals that from 2007-12, the dominant lake type in the U.S. shifted from clear blue to greenish brown and murky. Approximately 45 percent of lakes were blue in 2007, but by 2012 that figure had decreased to only about 28 percent. In those same five years, murky lakes increased from 23 percent to 35 percent.
“Blue lakes typically are those that do not show evidence of nutrient pollution or elevated organic matter while murky lakes have high levels of both,” Leech said. “A shift toward murkiness is a management concern because murky lakes tend to have more algae, including potentially harmful cyanobacteria. And with poor quality food at the base of the food web, over time murky lakes may not be able to support a healthy fishery.”
Leech’s research was published in Limnology and Oceanography’s special research newsletter, which highlights selected submissions that have been judged on their originality and intellectual contribution to the fields of limnology and oceanography. Limnology and Oceanography is a journal published on behalf of the Association for the Sciences of Limnology and Oceanography. The journal’s unifying theme is the understanding of aquatic systems.
Using data from the Environmental Protection Agency’s National Lakes Assessment Program, Leech and the other researchers demonstrate that many lakes across the U.S. are increasing in both total phosphorus and dissolved organic matter concentration. The results emphasize that many lakes are simultaneously “greening” and “browning,” with potentially negative consequences for water quality and food web structure. The findings show that murky lakes significantly increased in the Northern Appalachian, Southern Plains and Xeric ecoregions.
The research suggests that more work needs to be done to reduce nutrient and/or organic matter runoff, particularly from agricultural areas. There also may be links to climate change—for example, changes in precipitation patterns that influence runoff—although these are harder to pinpoint.