A survey of alkalinity trends in 97 streams and rivers from Florida to New Hampshire, ranging from small headwater streams to some of the nation's largest rivers, showed a significant increase in alkalinity over the past 25 to 60 years in two-thirds of them, the Cary Institute of Ecosystem Studies in Millbrook, N.Y., reported Monday.
Excess alkalinity can cause ammonia toxicity and algal blooms, altering water quality and harming aquatic life, the researchers said.
It also hardens drinking water, causing pipe scaling and costly infrastructure problems, they said.
Rivers providing water for Washington, Philadelphia, Baltimore, Atlanta and other major cities were among those with increased alkalinity.
Alkaline rivers are flowing into water bodies already harmed by excess algae, such as the Chesapeake Bay, exacerbating algal blooms that are toxic to fish, oysters and crabs, the researchers said.
Paradoxically, they said, it's human activities that create acid conditions that are driving the problem, as acid rain, acidic mining waste and agricultural fertilizers speed the breakdown of limestone, concrete and cement, creating alkaline particles that are washed off of the landscape and into streams and rivers.
"Acid rain has led to increased outputs of alkalinity from watersheds and contributed to long-term, increasing trends in our rivers," institute director Gene Likens said. "And this is twenty years after federal regulations were enacted to reduce the airborne pollutants that cause acid rain.
"Policymakers and the public think that the acid rain problem has gone away, but it has not."