Senior Scientist Beth McGee and Senior Naturalist John Page Williams demonstrate one of the ways scientists measure the Dead Zone. (Credit: Chesapeake Bay Foundation YouTube channel: https://www.youtube.com/user/ChesapeakeBayFound

The Chesapeake Bay can expect bigger oxygen-depleted dead zones than average this summer, and many of the marine creatures that live in its depths will face a tougher struggle to survive.

The forecast comes from the National Oceanic and Atmospheric Administration, which partners with scientists every year to predict areas of hypoxia (low oxygen) and anoxia (no oxygen) in coastal waters that suffocate and kill animal life.

"If you can't breathe, nothing else matters," said Dave Malmquist, spokesman at the Virginia Institute of Marine Science in Gloucester Point. VIMS, associated with the College of William and Mary, partnered with NOAA on its combined hypoxia forecast for the bay and the Gulf of Mexico.

Scientists believe an average of 8.2 cubic kilometers of the bay will experience hypoxia this summer. A VIMS modeling expert said that's enough hypoxic water to cover the entire city of Norfolk to a depth of 108 feet. In an average year, about 6.3 cubic kilometers of the bay turns hypoxic or anoxic, scientists said. That's more than 10 percent of the mainstem bay's total volume of 51 cubic kilometers.

This year's forecast is especially dire for marine organisms that embed on the bottom of the bay or attach to substrate in deep water and can't easily relocate, Malmquist said.

Scientists base their yearly forecast on the amount of nitrogen that enters the bay between January and May from the Susquehanna and Potomac rivers. This year's total was 44,000 metric tons, compared to 36,600 metric tons for the same period last year.

Bay states have worked to reduce the amount of nitrogen and phosphorus entering the polluted estuary from major point sources such as wastewater treatment plants, but experts say a wet spring likely flushed more nitrogen into the system from other sources, such as cropland, and urban and suburban development.

Virginia and other watershed states are under a so-called pollution diet mandated by the U.S. Environmental Protection Agency to reduce nutrients and sediment entering the estuary in a regional effort to restore the bay by 2025. Virginia, Maryland, Delaware, West Virginia, New York, Pennsylvania and the District of Columbia have their individual plans to reach that goal.

The hypoxia forecast dismayed conservationists who are working to restore the bay.

"We're not happy," said Beth McGee, senior scientist with the Chesapeake Bay Foundation. "Although we're making progress reducing pollution, we really need to accelerate our efforts so we're not subject to the vagaries of weather."

A dead zone develops when nitrogen and phosphorus fuel the growth of algae, which can explode into toxic blooms called red tides. As algae decay and sink, bacteria devour dissolved oxygen from the water.

Wind speed and direction also play a role, said Malmquist. Hypoxia is more likely to develop in a water column that has cooler, saltier water on the bottom and warmer, fresher water on top. Wind helps diffuse the water column.

Dead zones have always occurred in nature to an extent, he said, but manmade factors have created conditions that cause them to occur more often and in larger areas.

According to Malmquist and McGee, dead zones could have a big impact this summer on rockfish, or striped bass, a popular and important sport fish in the bay that prefers cooler temperatures. Rockfish could get squeezed between surface water that is too warm and bottom water that suffocates them. Such stressors could also make them more vulnerable to disease.

The bay's iconic blue crabs will also be forced into shallow, inhospitable areas, she said. Blue crabs are already considered depleted in the bay.

"At the bottom of the food chain are the critters that live in the bottom of the bay year-round," McGee said. "And when dead zones occur, they don't have the luxury of moving."

Because the nitrogen loads have already entered the system, experts say there's nothing to be done to stop its effects. But McGee said communities can ramp up efforts to reduce nitrogen and phosphorus loads in future by taking action to reduce runoff, such as creating more green space to absorb and filter nutrients.

In October, scientists will take final oxygen levels and compare them to the forecast models. The data can be used to improve such models in future, Malmquist said, and better understand how to manage limited resources to control nitrogen loads.

NOAA's prediction for the Gulf of Mexico this summer is for an average dead zone ranging from 12,000 square kilometers to 14,785 square kilometers, or roughly the size of the state of Connecticut.

The agency said it used different measurements for the gulf (square kilometers) and the bay (cubic kilometers) because of the shallow nature of large areas of the estuary.

VIMS contributed to the hypoxia forecast for the gulf. The Chesapeake Bay forecast was based on models developed by Donald Scavia of the University of Michigan, Mary Anne Evans at the U.S. Geological Survey and the University of Maryland Center for Environmental Science.

Dietrich can be reached by phone at 757-247-7892.