Collaborative stakeholder effort pays off
By Summit Voice
Reducing the flow of fertilizers, animal waste and other pollutants into the Chesapeake Bay appears to be reducing the size of summer dead zones in America’s largest estuary.
Researchers found that dead zones stopped growing in the 1980s, when Chesapeake Bay stakeholders launched a concerted effort to slow the flow of contaminants. The dead zones have been shrinking since then, according to a study by scientists with Johns Hopkins University and the University of Maryland Center for Environmental Science. NOAA tracks the health of the bay at this website.
“I was really excited by these results because they point to improvement in the health of the Chesapeake Bay,” said lead author Rebecca R. 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.”
“This study shows that our regional efforts to limit nutrient pollution may be producing results,” he said. “Continuing nutrient reduction remains critically important for achieving bay restoration goals,” said Don Boesch, president of the University of Maryland Center for Environmental Science.
Chesapeake Bay supports more than 3,600 species of plants, fish and other animals. But the bay’s health deteriorated during much of the 20th century, contributing to a drop in the Chesapeake’s fish and shellfish populations. Environmental experts blamed this largely on a surge of nutrients entering the bay from sources such as farm fertilizer, animal waste, water treatment discharge and atmospheric deposition. Heavy spring rains typically flush these chemicals, primarily nitrogen and phosphorus, into the Susquehanna River and other waterways that empty into the Chesapeake. There, the nutrients promote the prolific growth of algae.
When the algae die, their remains sink to the bottom of the bay, where they are consumed by bacteria. As they dine on algae, the bacteria utilize dissolved oxygen in the water. This leads to a condition called hypoxia, or depletion of oxygen. As this process continues through the spring and summer, the lack of oxygen turns vast stretches of the Chesapeake into dead zones. Hypoxia sometimes results in fish kills.
To find out whether these dead zones are expanding or diminishing, the 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 and that the duration — how long the dead zone persists each summer — is closely linked each year to the amount of nutrients entering the bay.
Starting in the 1980s, farmers were encouraged to plant natural barriers and take other steps to keep fertilizer out of waterways that feed the Chesapeake. Also, water treatment plants began to pull more pollutants from their discharge, and air pollution control measures curbed the movement of nitrogen from the atmosphere into 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 was 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 more dense salt water, which comes from the ocean. The two layers don’t easily mix, so when air near the surface adds oxygen to the top layer, it doesn’t reach the deeper salt water. Without oxygen at these lower depths, marine animals cannot live, and a dead zone is formed.
The study was supported by funding from the National Science Foundation and the U.S. Department of Commerce, NOAA. The research was undertaken as part of a larger five-year Chesapeake Bay Environmental Observatory project, funded through the Chesapeake Research Consortium, which involves seven institutions. Ball serves as lead principal investigator for this project.
Filed under: agriculture, Environment, Summit County news, water, wetlands Tagged: | Chesapeake Bay, Chesapeake Research Consortium, Dead zone (ecology), Johns Hopkins University, Summit County news environment, University of Maryland Center for Environmental Science, wetlands