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Saving D.C. Rivers

Courtesy of Stephen MacAvoy

Courtesy of Stephen MacAvoy

Stephen MacAvoy can tell you a lot about the D.C. sewer system, but perhaps not for the reasons you might think. “We have an interesting feature here in Washington—combined sewage outflow,” he says. “When there’s a heavy storm, the system gets overloaded, and runoff and sewage water bypass the overloaded water treatment system and get dumped into our rivers.”

MacAvoy, an environmental science professor, studies nutrient movement in aquatic systems, specifically in urban waters. His most recent research involves studying the water chemistry of the Anacostia River. It’s not a happy river, he says. “After looking at it, my team and I discovered that the calcium, magnesium, and sodium concentrations are very high, which is a little odd.” 

At first, they thought the high concentration of these elements was due to road salting. But because the levels didn’t fluctuate seasonally, they ruled that out. 

Then the team came up with another idea: perhaps the high ion concentrations in the Anacostia were caused by acidic rain and its interaction with concrete hardscape near the river. The concrete is loaded with limestone. When acidic rainwater hits it, the concrete neutralizes the rainwater, which causes the concrete to dissolve and wash into the river. 

“Our findings suggest that human beings have created so much of an artificial conglomerate rock and put it in such a small area that we’ve changed the chemistry of the water,” he says. “We see the elevated calcium, magnesium, and sodium that won’t go away and just gets washed downstream. It’s a permanent feature of this changed landscape.” 

The new chemistry of the water may not seem particularly detrimental, but aquatic animals face potentially insurmountable challenges. “Any creature needs to regulate its ion balance,” says MacAvoy. “If you’d been drinking freshwater all your life and the water suddenly started getting saltier, you’d have a major problem. These poor animals in the Anacostia have no choice but to drink the water.” 

This problem doesn’t just affect aquatic life, says MacAvoy. “D.C. wants to make the Anacostia fishable and swimmable in the next 18 years,” he says. “Cleaning the river is becoming a serious priority.” 

MacAvoy isn’t just concerned about the Anacostia; the state of other D.C. water systems requires a call to action. While they’re not looking at the Potomac River in this study, he notes that other studies have indicated that there are high levels of estrogen in the Potomac, which is causing male fish to develop eggs. “Washington gets its drinking water from the Potomac,” he says. “That’s definitely a concern.” 

Despite the problems that local waterways are facing, MacAvoy is heartened by the city’s interest in becoming a greener, more environmentally sound place. “People want to live in nice, clean cities—and on top of that, it’s good PR,” he says. “There’s a tax reason to do it too. Property is more valuable when it’s greener. There’s a growing realization that we are making significant changes to the landscape and that something needs to be done about it.”