Chesapeake Bay gets good news: Dead zones shrank this year
By DAVE RESS DAILY PRESS | NOV 03, 2020 AT 7:50 AM
A crab rest beneath the water as a dead fish floats by in Hampton's Indian Creek Tuesday morning September 15, 2020. Officials have said an algae bloom is responsible for a fish kill in Hampton’s Indian Creek. (Jonathon Gruenke/Daily Press)
Chesapeake Bay dead zones were a lot smaller this summer than in recent years, the Virginia Institute of Marine Science says.
The Bay — and especially the crabs, fish and shellfish that suffocate in the low-oxygen, “hypoxic” water of a dead zone — benefited from a cooler spring and fall, brisk summer winds and continued efforts to cut runoff, VIMS said.
The total amount of hypoxia waters in 2020, at 525 cubic kilometer-days. was the lowest in the past five years. It was one-third less than that the 776 cubic-kilometer days experienced during 2019. This year’s dead zone season lasted 95 days, well below the 136 days recorded in 2019.
Dead zones form when nitrogen, mostly from fertilizers and wastewater, flowing into the Bay fields algae blooms.
When these short-lived blooms die, and sink, they feed rapidly-growing populations of bacteria, which consume oxygen from the bottom waters.
Since hot weather encourages algae, and calm winds make mean little mixing of oxygen-rich surface waters with low-oxygen depths, summer is a bad time for dead zones. Dead zones peaked this year on July 22 — hitting a total of 11.2 cubic kilometers, enough to fill nearly 4.5 million Olympic-sized swimming pools — before August winds from the remnants of Hurricane Isaias mixed in enough oxygen to cut dead zones of 4.2 cubic kilometers.
“Even despite long-term warming temperatures, hypoxia is decreasing due to nutrient reductions—a testament to the fact that management actions to curb nutrient pollution are working,” said Marjy Friedrichs, a Virginia Institute of Marine Science professor who works on the annual report.
She said runoff was slightly lower than average early in the year, because of a small decline in rainfall — which was much lower than in 2018 and 2019.
Unusually cool temperatures in May and September also discouraged algae blooms.
“When we look at the long-term trend and take transient weather conditions and summer storms into account, we’re generally seeing lower volumes of hypoxic water in recent years. This is due to the success of management actions that have been reducing nutrient runoff into the Bay,” she said.
Separately, Maryland’s Department of Natural Resources reported that the 2020 dead zone is the second smallest observed in the Maryland portion of the Chesapeake Bay since monitoring began in 1985.
“A smaller dead zone means more areas for oysters, crabs, and fish, to thrive in the Bay. This is good news,” said Beth McGee, the Chesapeake Bay Foundation’s director of science.
“This year’s small dead zone is another positive sign that watershed-wide Chesapeake Bay cleanup efforts are working,” she said.