By Dr. Robert Thorson
Living in a coastal region with beautiful hills and valleys, very few residents of southern New England focus their outdoor attention on lakes. But more attention is needed, if only because lakes are an important part of our national freshwater resource.
A major boost to that crucial focus is being provided by the National Lakes Assessment, a four-year project now being released by the U.S. Environmental Protection Agency. For the first time ever, the tens of thousands of small lakes that buffer our nation’s plumbing system finally got the funding they deserved from an agency devoted largely to saltwater shores, wetlands, streams and freshwater seas (the Great Lakes).
The assessment began a few years ago when Congress asked the EPA about the status of America’s small lakes. The answer was effectively: “We don’t know.” In response, the agency went to work creating the first statistically robust sampling of our nation’s lakes – all 123,439 within the contiguous United States. Restricting analysis to water bodies that were fresh, 10 acres (four hectares) or larger in surface area, more than one meter deep and having more than 1,000 square meters of open water, and ignoring the many lakes that couldn’t be easily sampled, scientists from every state used that federal money to check out the present status of American lakes.
All in all, 1,028 lakes were visited during the summer of 2007 to obtain a stratified random sample that could be used to characterize all American lakes in the target population, and to differentiate them into nine different eco-regions. Preliminary results were released at the 22nd annual National Lakes Conference in Chicago, which I attended in April. Here are a few key points that caught my attention.
Through excavation and dam construction, humans are responsible for creating more lakes than Mother Nature. Nationwide, 59 percent of lakes are artificial reservoirs. In the Southern Appalachians eco-region, this number rises to 100 percent. In contrast, 97 percent of lakes in the Upper Midwest eco-region are naturally formed glacial lakes.
In New England, there are also thousands of natural lakes that were intentionally augmented in some way by human activity.
Humans have greatly compromised the shoreline conditions of lakes. On a carefully constructed scale of 0 to 1 – from no disturbance to complete disturbance – most regions have an index between 0.4 and 0.7.
Enterococci bacteria are indicators from you know where: the intestinal tracts and feces of humans and warm-blooded animals. When the count is high, which it is in about 20 percent of the sampled lakes, swimmers often get the “runs,” or worse, gastroenteritis.
Water transparency? Dropping a special disk into the water and observing when it can’t be seen is one way to measure lake quality, especially when it’s impaired by the growth of algae and other phytoplankton. On a national basis, most lakes fall in the “eutrophic” range, with Secchi disk visibility less than six feet. The good news is that lakes in the northern Appalachian ecoregion are normally as clear as those in the Western mountains.
When a nutrient-polluted lake develops a bloom of blue-green algae, it can become poisoned by microsystins. These are liver toxins that when sufficiently concentrated can also cause allergic reactions to the skin and respiratory system. The good news is that very few lakes exceed the level of medical concern. The bad news is that 32 percent of lakes had detectable levels of these toxins.
Though the national summary for more general statements is not yet complete, the scientists I spoke to are certain of one thing: For the sake of habitat quality, water supply, recreational use and human health, the nation must commit itself to slowing, if not reversing, the creeping damage to our lakes.
Between June 29 and June 15, I will be providing first-hand accounts of lake water quality, and the human stories behind the successes and failures, on my new blog: “Walden to Wobegon: Blogging Kettles from Maine to Montana” at http://www.waldentowobegon.blogspot.com.