A recent study has shown that efforts to reduce the flow of fertilizers, animal waste and other pollutants into the Chesapeake Bay appear to be increasing the health of the bay.
Published in the Nov. 2011 issue of Estuaries and Coasts, this examination was conducted by researchers from Hopkins and the University of Maryland Center for Environmental Science.
According to Rebecca Murphy, the leading research assistant in the study and a doctoral student in the Department of Geography and Environmental Engineering at Hopkins, the team was aiming to develop a database of water quality data in order to analyze the long-term trends of the dead zones, areas of the Bay where plants and animals cannot live. Building off previous research that indicated that the dead zone was not responding to changes in the amounts of nutrients coming into the bay, Murphy and her team created a database to further analyze these prior findings and determine what really is happening.
The team looked at 60 years of data and found that the size of summer oxygen-starved dead zones leveled off in deep channels of the bay during the 1980s and has been declining ever since. In addition, they determined that the duration, or how long the dead zone persists each summer, is closely linked each year to the amount of nutrients entering the bay.
The timing is key because in the 1980s, an intense effort to cut nutrient pollution in the Chesapeake Bay was initiated through the multi-state federal Chesapeake Bay Program. The goal was to restore the water quality and health of the bay.
"I was really excited by these results because they point to improvement in the health of the Chesapeake Bay," Murphy said. "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."
"When we found that the dead zone is indeed responding to a decrease in nutrient loads, it's good news because it means the bay is doing what we expect," Murphy said.
She further explained that if the agriculture industry continues to improve farming practices and decrease the amount of nutrients going into the bay, then the size of the dead zone should become smaller.
Although this has been well known for quite some time, the data did not seem to reflect that. Instead, the data suggested the dead zones were not responding to decreases in nutrient loads at all.
"This study shows that our regional efforts to limit nutrient pollution may be producing results. Continuing nutrient reduction remains critically important for achieving bay restoration goals," Don Boesch, president of the University of Maryland Center for Environmental Science, said.
The Chesapeake Bay is the nation's largest estuary, a body of water where fresh and salt water mix. According to the Chesapeake Bay Program, the bay is about 200 miles long, has about roughly 4,480 square miles of surface area and supports more than 3,600 species of plants, fish and other animals.
However, the health of the bay 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 flow 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, mostly nitrogen and phosphorus, into the Susquehanna River and other waterways that empty into the Chesapeake. There the nutrients promote a large growth of algae.
When the algae die, their remains sink to the bottom of the bay, where they are consumed by bacteria. As they feast 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 large areas of the Chesapeake into dead zones. Hypoxia sometimes results in fish kills.
"By looking at existing data, we have been able to link decreasing hypoxia to a reduction in the nutrient load in the bay," study co-author Michael Kemp, an ecologist with the University of Maryland Center for Environmental Science's Horn Point Laboratory, said. "The overall extent and duration of mid-to-late summer hypoxia are decreasing."
The steady decrease in dead zones coincides with the launch of state and federal efforts to reduce the flow of algae-feeding pollutants into the bay.
For instance, farmers were encouraged to plant natural barriers and to 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.
Despite these efforts, Murphy explains that the greatest reduction of pollutants in the bay have been a result of voluntary agreements between the states and the ETA, which consists of Pennsylvania, Maryland, Virginia, New York, Washington D.C. and a small part of Delaware and West Virginia.
All of the states agreed to decrease pollutants by certain percentages each year. Recently, the ETA has put into works an act called the Total Maximum Daily Load, which sets limits of nitrogen and phosphorus coming into the bay. Although not yet officially established, once passed it will be a federal law to control pollutants in hopes of further improving the reduction of dead zones.
According to Murphy, new efforts like this need to continue to be established.
"What we've seen is a really slight improvement. There needs to be much more reduction of nutrients coming into the bay and a decrease in the amount of sediment," he said.
With more work, Murphy firmly believes there will be more improvement.
The study also examined a trend that shows an early summer spike in dead zones. This observation has troubled many bay watchers because they feared that keeping more nutrients out of the bay was not improving its health. However, the new study found that the early summer jump in dead zones was influenced by climate forces, not by the runoff of pollutants.
Dead zone formation occurs in a phenomenon called stratification. This is when 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.
"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," William P. Ball, a professor of environmental engineering at Hopkins, said.
Ball, a co-author of the new study, is Murphy's doctoral adviser.
"We believe that without those efforts to rein in the pollutants, the dead zone conditions in June and early July would have been even worse," Ball said.
The study was supported by funding from the National Science Foundation and the U.S. Department of Commerce, NOAA. The research was conducted as part of a larger five-year Chesapeake Bay Environmental Observatory project, funded through the Chesapeake Research Consortium, which involves seven institutions.
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