The Chesapeake Bay dead zone—an area of low oxygen that forms in deep Bay waters when excess nutrients enter through polluted runoff and feed naturally-occurring algae—was the 10th smallest since 1985 according to experts from the Maryland Department of Natural Resources and the Virginia Institute of Marine Science.
“It is always welcome news to see improved Chesapeake Bay dissolved oxygen conditions that are so vital for the health of fish, crabs, oysters and other aquatic life,” remarked Mark Trice, water quality informatics program manager with the Maryland Department of Natural Resources.
Hypoxic, or low-oxygen, conditions form when nitrogen, phosphorus and sediment pollution enter waterways in greater amounts than the ecosystem can handle. It causes naturally-occurring algae to grow and bloom in large quantities and then die off. When the algae blooms decompose, they remove oxygen from the surrounding water faster than it can be replenished. It can suffocate the marine life that live in that region and cause others to seek new habitat.
Each year, the Maryland Department of Natural Resources and Old Dominion University conduct water quality monitoring cruises from May—October to measure the amount of hypoxia in the Bay. Results from these cruises can be found on Maryland’s Eyes on the Bay and Virginia’s VECOS websites, respectively.
In addition, the Virginia Institute of Marine Science and Anchor QEA use a sophisticated computer model, combined with local weather information, to estimate how much nitrogen and phosphorus enters the Bay from its surrounding watershed. This information produces daily, real-time estimates of the dead zone size throughout the summer. These forecasts, along with other daily estimates of environmental conditions throughout the Bay, are available to view on the Chesapeake Bay Environmental Forecast System.
Weather conditions are primarily responsible for dictating how large the annual dead zone will be, and how long it will last, into the fall. In June, experts predicted that the 2022 dead zone would be 13% smaller than those in the past, due to less winter and spring precipitation. Lower amounts of precipitation bring about smaller river flows, meaning lower amounts of nitrogen, phosphorus and sediment pollutants entering the Bay. The U.S. Geological Survey reported that the 2022 water year (measured from October 1, 2021—September 30, 2022) had river flows entering the Chesapeake at an average of 73,000 cubic feet per second, which is below the long-term average of 79,000 cubic feet per second.
Hypoxia appeared later than normal this year—in June—due to cool and windy conditions in the spring. The dead zone was more typical in size until mid-August due to moderate river flows, temperatures and winds throughout the region. It was still observed in mid-September, but cooler temperatures and stronger winds in the early fall caused it to disappear soon after. In fact, the Virginia Institute of Marine Science model found that the 2022 dead zone duration was likely 95% shorter than any since 1985.
Actions taken throughout the watershed also play a significant role in the size and duration of the annual dead zone. Despite the size and strength of springtime river flows, conservation practices installed by farmers, nonprofits, local governments and state agencies help manage the amount of nitrogen, phosphorus and sediment pollutants flowing into the Bay and causing hypoxic conditions.
Dr. Marjy Friedrichs, research professor at the Virginia Institute of Marine Science concludes, “it is now clear that actions taken by the Chesapeake Bay Program partnership to reduce nutrient pollution are offsetting the increases in hypoxia that would otherwise by occurring due to warming atmospheric temperatures.”