A Good Year for the Bay

Delmarva Now, Chesapeake Bay 'dead zones' show big decline: What it means for fish, crabs and economy

The ominously named "dead zones" in the Chesapeake Bay are more than hyperbole and represent potentially millions of dollars lost on industries tied to the Bay, so a report citing improvements is welcome news.

The annual Chesapeake Bay Hypoxia Report for August, released by the Maryland Department of Natural Resources, noted "dissolved oxygen conditions in the Chesapeake Bay mainstem of Maryland and Virginia continued to be much better than average."

The department worked in collaboration with Old Dominion University and looked at results collections during regular, twice-monthly monitoring cruises conducted by research vessels. Throughout the summer, the cruises recorded hypoxic areas of the Bay – water with low enough dissolved oxygen to harm marine life – that have been smaller than those recorded in previous years.

"The better-than-average August dissolved oxygen conditions we are experiencing is not surprising considering the reduced river flows from January through May, as well as less nitrogen carried to the Bay because of nutrient management efforts. Continuing these efforts to reduce nutrient pollution throughout the entire watershed will improve water quality conditions, helping to support all of our aquatic resources," said Tom Parham, director of the Tidewater Ecosystem Assessment at the Maryland Department of Natural Resources.

The hypoxic water volume — waters with less than 2 mg/l oxygen — was 0.31 and 0.72 cubic miles respectively during the early and late August monitoring cruises, compared to early and late August averages of 1.37 and 1.076 cubic miles since 1985.

This year’s data from early August ranks as the smallest volume of hypoxic water volume on record and late August was the eighth smallest volume for their respective time periods.

"We're doing a great deal to reduce the nitrogen phosphates in the watershed. These are the pollutants that are fueling the algae blooms that reduce the oxygen. We got lucky this year in the fact that the rains that deliver those pollutants didn't come until the fall," Meyers said.

Not all nutrients delivered to the Bay are equal. Rain that falls now and later in this year, along with their associated nutrients will largely wash out of the Bay over the course of winter because colder water and less light due to shorter days and lower sun angle will reduce algae's ability to take them up, the second step in the chain of causality leading to the "dead zones." After all these years, it still seems as if the health of the Bay, at least in terms of hypoxia, is largely determined by the weather. We may have slightly reduced the amount of hypoxia at a particular weather scenario by reducing nutrients, but it's still very difficult to detect in the large year to year variation in rainfall.