Chesapeake Bay Healing, Dead Zone Shrinking

By Environmental News Service
3 November 2011

BALTIMORE, Maryland, – Efforts to heal Chesapeake Bay are working, finds new research from Johns Hopkins University and the University of Maryland Center for Environmental Science that incorporates 60 years of water quality data.

Reductions in the flow of fertilizers, animal waste and other pollutants into the nation’s largest estuary have reduced the size of oxygen-starved dead zones in the bay, where plants and water animals cannot live, the scientists discovered.

"I was really excited by these results because they point to improvement in the health of the Chesapeake Bay," said lead author Rebecca Murphy, a doctoral student in the Department of Geography and Environmental Engineering at Johns Hopkins. "We now have evidence that cutting back on the nutrient pollutants pouring into the bay can make a difference. I think that’s really significant."

The healing began in the 1980s, when a concerted effort to cut nutrient pollution in the Chesapeake Bay was initiated through the multistate-federal Chesapeake Bay Program. The goal was to restore the water quality and health of the bay.

"This study shows that our regional efforts to limit nutrient pollution may be producing results," said Don Boesch, president of the University of Maryland Center for Environmental Science, who is an expert on dead zones. "Continuing nutrient reduction remains critically important for achieving bay restoration goals."

Yet, this year’s dead zone was larger than usual due to high nutrient pollution levels this year, according to Virginia and Maryland officials. This year the Chesapeake Bay dead zone covered about one-third of the bay, from the Baltimore Harbor to the Potomac River, about 83 miles.

Sunset over Chesapeake Bay (Photo by robinzeggs)

Boesch said this year’s water flow into the bay ranked among the five largest, a result of heavy rains and snow melt mixed with large amounts of the fertilizers nitrogen and phosphorus.

But taking the long view for their study, Johns Hopkins and Maryland researchers retrieved and analyzed bay water quality records from the past 60 years. They determined that the size of the dead zone in mid-to-late summer has decreased steadily since the late 1980s.

They found that the length of time the dead zone persists each summer is closely linked each year to the amount of nutrients entering the bay.

Starting in the 1980s, farmers have been encouraged to plant natural barriers and keep fertilizer out of waterways running into the Chesapeake Bay.

At that time, water treatment plants began to pull more pollutants from their discharges, and air pollution control measures limited the amount of nitrogen from the atmosphere falling on the bay.

"By looking at existing data, we have been able to link decreasing hypoxia to a reduction in the nutrient load in the bay," said study co-author Michael Kemp, an ecologist with the University of Maryland Center for Environmental Science’s Horn Point Laboratory. "The overall extent and duration of mid-to-late summer hypoxia are decreasing."

Another part of the study looked at a trend that has troubled some bay watchers. In recent years, Chesapeake researchers have seen an early summer spike in dead zones. They feared that keeping more nutrients out of the bay was not improving its health.

But the new study found that the early summer jump in dead zones is influenced by climate forces, not by the runoff of pollutants.

In a phenomenon called stratification, fresh water from the rivers entering the bay forms a layer on top of the denser salt water from the ocean. The two layers don’t easily mix, so when air near the surface adds oxygen to the top layer, it does not reach the deeper salt water. Without oxygen at these lower depths, marine animals cannot live, and a dead zone is formed.

"Rebecca discovered that the increase in these early summer dead zones is because of changes in climate forces like wind, sea levels and the salinity of the water. It was not because the efforts to keep pollutants out of the bay were ineffective," said William Ball, a professor of environmental engineering in the Whiting School of Engineering at Johns Hopkins.

Ball, a co-author of the new study, is Murphy’s doctoral advisor. "We believe," he said, "that without those efforts to rein in the pollutants, the dead zone conditions in June and early July would have been even worse."

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