More brown waters a healthy sign: study
More murky streams and lakes in northern countries are a good sign, a study to be published Thursday says.
The dissolved organic compounds (DOC) that turn water brown show that pollutants like acid rain are declining, the authors said.
"As acidity and pollutant concentrations in the soil fall, carbon becomes more soluble, which means more of it moves into our lakes and rivers and more can be exported to the oceans," U.S. Environmental Protection Agency researcher John Stoddard said in a release Wednesday.
"In some ways, we're seeing waters returning to their natural, pre-industrial, state," he said.
There is a huge amount of carbon stored in soil, and over the past two decades,it has been dissolving and turning lakes and rivers brown, said Don Monteith ofthe Environmental Change Research Centreat University College London.
Researchers have blamed phenomena fromglobal warming to changes inland use as the cause.
But using data from 522 remote sites in six countries —including Canada —gathered between 1990 and 2004, the researchers concluded that declines in sulphur pollution and sea salt (in coastal areas) accounted for the change.
Therelative change in DOC "was strongly and inversely related" to changes in both sulphate concentration (from acid rain) and chloride concentration (from sea salt), the study said. Declining acid rain was the most important factor.
The authors also said their work breaks the link some researchers have suggested between browning water and global warming.
"Although CO2 concentrations are increasing globally, they cannot simultaneously explain both the upward and downward trends in DOC we observe in different regions," the study said.
Atlantic Canada was alone in reporting lower DOC levels among the areas studied. Increased sea-salt deposits explain that result, the authors said.
The study used data gathered by national monitoring programs inBritain, the United States,Canada, Norway, Sweden and Finland.
The researchers began with data from1990 because sulphur depositions had begun to fall by then, after many countriesbegan to control acid rain.
There weresmall average increases in DOC in the northeastern U.S., Ontario and Quebec and northern Nordic regions, anda large average increase in the southern Nordic region.
The study isin the Nov. 22 edition of the journal Nature.