Annapolis, Md. — The Chesapeake Bay’s oxygen-starved “dead zone” was smaller than average last summer, meaning a larger area of the estuary was available for many types of aquatic life.
Monitoring and analyses by both the Maryland Department of Natural Resources and Virginia Institute of Marine Science found that the Chesapeake had the 10th smallest area impacted by low-oxygen, or hypoxic, water since baywide monitoring began in 1985.
Areas of hypoxic water are created in large part by excess amounts of nutrients that fuel algae blooms in the bay. When there is more algae than aquatic organisms can consume, the excess sinks to the bottom and decomposes in a process that removes oxygen from the water.
That means less oxygen for fish, shellfish and other creatures.
Nutrient-control efforts have reduced the amount of nitrogen and phosphorus entering the Bay, but this year’s improvement was also driven by lower-than-average river flows. Less precipitation and lower river flows drive fewer nutrients off the land and into the Chesapeake.
Monitoring by the U.S. Geological Survey shows that average river flows into the bay during the past year were 73,000 cubic feet per second, slightly less than the average of 79,000 cfs.
Scientists say conditions would likely have been better except that a portion of the oxygen improvements are being offset by gradually warming temperatures. That makes the job of reducing hypoxic water more difficult, because warmer water holds less oxygen than cool water.
“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 be occurring due to warming atmospheric temperatures,” said Marjy Friedrichs, a research professor at the Virginia Institute of Marine Science.
Beth McGee, director of science and agricultural policy with the Chesapeake Bay Foundation, agreed that the better-than-average dead zone showed that nutrient reduction efforts were working.