Experts from the Maryland Department of Natural Resources report that the 2020 “dead zone” is the second smallest observed in the Maryland portion of the Chesapeake Bay since monitoring began in 1985.
In their 2020 Chesapeake Bay Dead Zone Report Card, researchers from the Virginia Institute of Marine Science also reported that throughout the entire Bay this year’s dead zone was smaller than most recorded in the past 35 years.
Having sufficient oxygen in the water “is a key indicator of Bay health,” said Dr. Bruce Michael, director of resource assessment service of the Maryland Department of Natural Resources. “After two years of extremely high flows and greater than average hypoxia, it is encouraging to see improved oxygen conditions in our bottom waters providing suitable habitat for fish, crabs and oysters.”
The “dead zone” is an area of little to no oxygen that forms in deep Bay waters when excess nutrients, including both nitrogen and phosphorus, enter the water through polluted runoff and feed naturally-occurring algae. This drives the growth of algae blooms, which eventually die and decompose, removing oxygen from the surrounding waters faster than it can be replenished.
This creates low-oxygen – or “hypoxic” – conditions at the bottom of the Bay. Plant and animal life often are unable to survive in this environment.
In the short term, experts believe that several factors, including more average river flows and unseasonably cool temperatures in May and September, contributed to the smaller dead zone.
Over the long term, the continued implementation of nutrient- and sediment-reduction strategies put in place by the six states in the Chesapeake Bay watershed (Delaware, Maryland, New York, Pennsylvania, Virginia and West Virginia) and the District of Columbia are continuing to help reduce pollution in the Bay and limit the size of the dead zone.
Only one out of the eight monitoring cruises showed larger-than-average hypoxic conditions. This occurred in late July as a result of below-average winds and hot temperatures, causing hypoxia to increase considerably, resulting in a large dead zone.
Strong winds from Hurricane Isaias in August helped to mix the waters of the Bay, reducing the dead zone; hypoxia returned in September but quickly dissipated due to cooler temperatures and windy conditions.
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