A September 18 Sustainable City Network article reports that a recently published study shows that acid rain and acidic runoff from mines and farms is actually causing many waterways on the East Coast of the United States, including in the Maryland region, to become more alkaline.  Besides negatively affecting a waterway’s flora and fauna, high alkalinity can increase water infrastructure and desalinization costs.  The study was based on a survey of 97 streams and rivers along the East Coast and found that over the last 25 to 60 years, two-thirds have had significant increases in alkalinity.  From the article:

Human activities are changing the water chemistry of many streams and rivers in the Eastern U.S., with consequences for water supplies and aquatic life, so reports a new study in the journal Environmental Science and Technology.  …

Alkalinity is a measure of water’s ability to neutralize acid. In excess, it can cause ammonia toxicity and algal blooms, altering water quality and harming aquatic life. Increasing alkalinity hardens drinking water, causing pipe scaling and costly infrastructure problems. And, perhaps most alarming, it exacerbates the salinization of fresh water.

In what may seem like a paradox, human activities that create acid conditions are driving the problem. This is because acid rain, acidic mining waste, and agricultural fertilizers speed the breakdown of limestone, other carbonate rocks, and even concrete and cement. The result: alkaline particles are washed off of the landscape and into streams and rivers.

The survey found watershed geology was the strongest predictor of river alkalinization, with rivers receiving water from porous, limestone, and other carbonate rocks being more alkaline. Topography and pollution were also triggers. The most rapid rates of alkalinization were at high elevation sites that were chronically exposed to acid pollution.

Among the rivers impacted by higher alkalinity are those that provide water for Washington, D.C., Philadelphia, Baltimore, Atlanta, and other major cities, the researchers reported. This is due, in part, to acid rain exposure, urbanization, and the extent of land covered by concrete.