Schutte research explores natural phenomenon contributing to lower ocean oxygen, fishkills

Lower oxygen concentrations in coastal waters, which sometimes occur following storms that wash nitrogen-rich fertilizer and other contaminants into rivers and streams, often trigger fishkills.

Research published by Rowan University's Charles Schutte, Ph.D., posits another theory that could explain low oxygen levels, or hypoxia, that trigger marine die-offs: naturally occurring, below-ground chemicals that leach from aquifers.

Schutte, an assistant professor of Environmental Science in the School of Earth & Environment, said the release of subterranean chemicals into estuaries can exacerbate low oxygen conditions that kill marine life.

"What we're showing is there's this other process that can contribute to hypoxia," said Schutte, a co-author of the paper, "SGD-OD: investigating the potential oxygen demand of submarine groundwater discharge in coastal systems," which ran April 22 in the Nature journal scientific reports. "Separate from runoff and nutrient pollution, the hypoxia isn't being generated by organic matter but by chemicals produced naturally below ground in the sediment."

Schutte's colleagues republished their findings July 26 in The Academic, a publication geared to more mainstream readers under the heading, "Unseen threats: Coastal aquifers and marine hypoxia."

For decades, scientists have known that fertilizer runoff from lawns and agriculture contribute to algal blooms and decreased oxygen in estuaries and other bodies of waters where rivers and streams end, triggering fishkills.

Schutte said the theory posited by the new research does not relieve homeowners and commercial property managers from concerns about downstream effects of fertilizer.

"The thing to be aware of here is, there's this other mechanism for (triggering a loss of) oxygen, and we can't control it," he said. "But we can control the amount of nutrients that we release."

He said the lesson is important not just to property owners but to legislators who set regulations that affect water quality.

"We're making policies designed to prevent hypoxia under the assumption that (nutrient runoff) is the only thing contributing to it," he said. "But the environment is complex and we're still figuring out how it works."

There remain unknowns in natural processes that can contribute to conditions that negatively affect the environment, and the new research suggests they should be considered for policy decisions that can worsen conditions affected by them, Schutte said.

"We grow a lot of corn and turfgrass in this country," he said. "We put a lot of chemicals on the ground and a lot runs off into our storm sewers."

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