Chesapeake Bay dead zone smaller than in recent years
"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 (80%).
In June 2020, researchers from the Chesapeake Bay Program, the University of Maryland Center for Environmental Science, University of Michigan and U.S. Geological Survey forecasted that the Bay would see a slightly smaller than average dead zone this year, due to reduced spring rainfall and less nutrient-rich runoff flowing into the Bay from the watershed.
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 decrease pollution in the Bay and reduce the size of the dead zone.
Hypoxic and anoxic regions—areas with little to no oxygen, respectively—are caused by excess nutrient pollution entering the Bay. One way in which nutrients can enter the Bay is through its tributaries in the watershed that drain into it. Higher river flows bring increased amounts of nutrient pollution into the Bay. The previous two years have seen above-average river flows, with 2019 setting a record high. According to the U.S. Geological Survey, the current year (measured from October 1, 2019—September 30, 2020) has been normal, with flows entering the Bay at an average of 77,665 cubic feet per second, which is slightly below the long-term average of 79,000 cubic feet per second.
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 the hottest temperatures ever recorded in Maryland, 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. This year’s dead zone started later and ended earlier than it has in the past several years. Additionally, no anoxic areas were noted in the mainstem of the Bay this year. . ."