Rivers in Eastern US Becoming Alkaline, Affecting Water Supplies

Decades of data reveals two-thirds of the rivers located in the Eastern United States are now alkaline, and acid rain is likely to blame, according to a new study published in the journal Environmental Science and Technology.

As the first survey of its kind, the report included rivers from Florida to New Hampshire with data covering time spans of 25 to 60 years. The results showed that during this period, two-thirds had become significantly more alkaline and none more acidic.

This is problematic, the researchers explain, since alkalinity is a measure of water's ability to neutralize acid and thus can, in excess, cause ammonia toxicity and algal blooms. As this happens, water quality is compromised and the delicate ecosystems that call these rivers home are thrown into chaos. In addition, increasing alkalinity can harden drinking water, make it more difficult to dispose of wastewater and exacerbate the salinization of fresh water.

And while it may seem counterintuitive, the study's authors believe acid rain, a byproduct of fossil fuel burning, acidic mining runoff and agricultural fertilizers, are to blame as the acid eats away at limestone and other carbonate rocks, causing their alkaline particles to then be picked up by the water.

"It's like rivers on Rolaids," Sujay Kaushal, an associated professor at the University of Maryland, said in statement. "We have some natural antacid in watersheds. In headwater streams, that can be a good thing. But we're also seeing antacid compounds increasing downriver. And those sites are not acidic, and algae and fish can be sensitive to alkalinity changes."

According to Kaushal, while scientists have studied the effects of increased chemical weathering in small mountain streams contaminated by acid runoff, the study is the first to examine the accumulating levels of alkalinity further downstream, including within a number of major rivers such as those that provide water for Washington, DC, Philadelphia, Baltimore, Atlanta.

"This is another example of the widespread impact of human impacts on natural systems which is, I think, increasingly worrisome," said Gene Likens, a co-discoverer who collaborated with Kaushal on the study. "Policymakers and the public think acid rain has gone away, but it has not."