10:13 a.m., March 31, 2010----The Delaware Estuary was so unhealthy in the 1940s that in some areas it completely lacked oxygen and was largely void of aquatic life in the summer. Its low oxygen levels and the production of hydrogen sulfide turned white ships grey, and its severe rotten egg odor even threatened its use as a port.

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The estuary today, by comparison, is a much healthier place. In fact, new research published by Jonathan Sharp, University of Delaware professor of oceanography, in the March issue of the journal Limnology and Oceanography documents that the Delaware Estuary has seen one of the most dramatic improvements of water quality of any river worldwide.

The research, based on about 100 years of data on oxygen levels, also paints one of the most complete pictures of an estuary's demise and recovery available. Not only did Sharp analyze data from his own research sampling, which he's done multiple times each year since 1978, he also looked at Delaware River Basin Commission's water monitoring stations going back to 1967. Less consistent data from other sources such as the Philadelphia Water Department and anecdotal sources such as newspaper articles provided perspective on the earlier years.

Together this information shows an estuary that for decades was pumped with municipal and industrial wastes, including raw sewage put directly into the river. The sewage caused outbreaks of disease such as typhoid fever. In addition, oxygen-consuming bacteria in the water, fed by copious organic matter in sewage and other human-created contaminants, caused large declines in the amount of oxygen in the estuary.

In one of the paper's anecdotal examples, Sharp explains that the estuary used to support the largest shad spawning area of the whole east coast. The numbers plummeted in the early 1900s, however.

“The waters were so depleted of oxygen that the shad couldn't hold their breath long enough to swim up stream,” said Sharp, a faculty member in UD's College of Earth, Ocean, and Environment.

By World War II, the estuary was so unhealthy that certain areas completely lacked oxygen in the summer.

The tide began to turn in 1970 when the Environmental Protection Agency was formed and major grants financed upgrades to sewage treatment plants.

“That's when the real change took place,” Sharp said. “because so much of that oxygen depletion in the Philadelphia area was due to sewage that was inadequately treated.”

As regulations for sewage treatment plants and industrial discharges have resulted in water quality improvements, Sharp said, natural resource managers have tended to turn their attention to other areas.

“There has been a lot of interest recently that nutrients coming into the water are stimulating excess algal production,” he said.

Increased nutrient concentrations fuel overgrowths of oxygen-robbing algae.

“One of the things I was trying to do here is to point it out that it's not quite so simple as a lot of people are treating it,” he said.

In his paper, Sharp suggests that while addressing nutrient loading is important, resource managers should not make that their only focus. Many other factors, such as habitat alteration and destruction, and other contaminants, directly and indirectly influence oxygen concentrations in the Delaware estuary.

Sharp explained further that today the estuary experiences no lack of oxygen in the summer. The recovery, he said, is reason to fully consider any changes that could affect the estuary.

“With the tremendous improvement in water quality, this is more reason to be cautious about anything that could impair the water quality such as the dredging to deepen the channel,” he said.

For more details on this research, read the full article on the Limnology and Oceanography March issue Web page.

Article by Elizabeth Boyle