In today’s Academic Minute, Dr. Sujay Kaushal of the University of Maryland reveals how acid rain has made rivers and streams less acidic.
Sujay Kaushal is an associate professor of geology at the University of Maryland where his research focuses on the ecology and biogeochemistry of watersheds and aquatic ecosystems. Primarily through long-term studies, his lab had conducted research projects concerning: land use and climate impacts on water resources, urban watershed restoration, long-term trends in stream chemistry, and human-impacted biogeochemical cycles. He earned his Ph.D. at the University of Colorado.
Dr. Sujay Kaushal – Acid Rain and Alkaline Rivers
Acid rain and other unintended side effects of human activities are changing the basic chemistry of many rivers in the Eastern U.S., with potentially major consequences for urban water supplies and aquatic ecosystems.
We analyzed long-term records of alkalinity trends in 97 streams and rivers from Florida to New Hampshire. Alkalinity is a measure of water’s ability to neutralize acid. Over time spans of 25 to 60 years, two-thirds of the rivers had become significantly more alkaline. Increased river alkalinization can contribute to ammonia toxicity, algal blooms, water hardness, and increased salinization of fresh water.
Paradoxically, higher acid levels in rain, soil and water, caused by human activity, are one of the major triggers for these changes in river chemistry, in addition to acidic mining runoff and agricultural activities. Acid rain can speed up the dissolving of surfaces that are naturally high in alkaline minerals. In a process known as chemical weathering, acid eats away at limestone, other carbonate rocks, and even concrete structures, dissolving alkaline particles that wash off into streams and rivers.
We found that alkalinity has risen over the past several decades in rivers that provide water for Washington, D.C., Philadelphia, Baltimore, Atlanta, and other major cities. Also affected are rivers that flow into water bodies already harmed by excess algae growth, such as the Chesapeake Bay.
Areas of the Eastern U.S. are underlain by porous, alkaline limestone and other carbonate rocks, making the region more prone to river alkalinization. In fact, river alkalinization has increased the fastest in areas underlain by carbonate rocks, at high elevations, and where acid rain or acid mine drainage is greatest. The large regional scale of river alkalinization was unexpected, and there are still many questions regarding rates, drivers, and impacts. Alkalinization is another example of widespread human impacts on rivers.