In mid-September, the Severn River Association – which claims to be America’s oldest river group - shared some unsettling news. A large dead zone had overtaken a huge stretch of the Severn River between April and August.
After regularly navigating and systematically testing various points throughout the river, the SRA teams identified that the dead zone area of water - with very low oxygen - covered more than five square miles, reaching from just above the Severn River Bridge (Route 50) all the way up to the narrows near Arden-on-the-Severn.
“Excessive nitrogen and phosphorus pollution from human activities cause dead zones, or areas with low amounts of oxygen,” according to the Chesapeake Bay Foundation. “With little or no oxygen, fish, crabs, oysters and other aquatic animals literally suffocate.”
Mackenzie Miller, an SRA summer intern and field investigator from Duquesne University, worked alongside a team of volunteers to collect and review water quality data using a protocol approved by the Chesapeake Monitoring Cooperative, which is a division of the Alliance for the Chesapeake Bay.
In 2018, the region received nearly double the amount of rain than a typical year. The more than 70 inches of precipitation, combined with unrelenting development, overwhelmed waterways like the Severn River with stormwater runoff.
“All of the impervious surfaces around our area are killing the river,” said Tom Guay, SRA secretary. “Clearcutting trees for more homes and townhomes, highways, roads, roofing - it’s flushing everything directly into the river.”
Though not a threat to humans, the conditions can be deadly to fish and crabs if they cannot escape the area. Unresolved, a dead zone can have long-lasting negative impacts on waterways and ecosystems.
While the vast dead zone is disheartening, Guay pointed out that it’s not all bad in the Severn River. Though fish, crabs and oysters won’t inhabit the low-oxygen waters, dark false mussels have thrived.
“Some of our oyster cages were weighing close to 80 pounds,” Guay said. “The little guys have covered the cages and the ropes in a massive scale.”
These tiny shellfish are native to the area and aren’t much larger than a fingernail. In spite of their small size, they can have a big impact as filters for the river.
“These dark false mussels show up and filter the water,” explained Guay. “We’ve seen these all the way up the river, which has contributed to the clarity that we’ve seen this summer, which has led to more grass growth throughout the Severn.”
In my many years of watching the Bay, I've seen several examples where a single species of filter feeder has an exceptionally good year, and seems to be the answer to pollution in one area or another. But my friends in the ecological community could never explain exactly how it happened, and the effects always faded in a subsequent year.
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