2012-11-15 / News

How does flushing a toilet affect ecosystem of Narragansett Bay?

Scientist says 65 percent of bay’s nitrogen from sewage

Dr. Jason Krumholz of the National Oceanic and Atmospheric Administration gave a lecture Tuesday titled “The Grand Experiment” at the University of Rhode Island’s Coastal Institute. The scientist, who works at the NOAA’s Northeast Fisheries Science Center, addressed the impact of upgrades to the state’s wastewater treatment facilities on Narragansett Bay.

Krumholz took the title of his lecture from the late Scott Nixon, a professor from the URI Graduate School of Oceanography who died earlier this year. Nixon called the use of advanced wastewater treatment to reduce nitrogen loads to Narragansett Bay a grand experiment.

Krumholz earned his Ph.D. from URI earlier this year. His lecture was designed to make people think about what happens after they flush – a subject that he readily admits most people don’t spend much time talking about – and what it means to the ecology of Narragansett Bay. In short, Krumholz said, the resultant sewage ends up in the bay after passing through wastewater-treatment facilities.

This process contributes a great deal of nitrogen to the water. When this nitrogen becomes excessive, it can have a significantly negative impact on the bay’s ecosystem. Among the problems created by the nitrogen overload are reduced water clarity, hypoxia, which is a process where oxygen in the water is depleted and reduces the ability of fish to use habitat in the bay, and even fish kills.

Krumholz used a series of charts and graphs to depict the scientifi c findings that were the basis of his lecture. Although he said at the outset that for the purposes of the talk he would not be addressing man-made climate change as a factor in the transformations occurring in the bay, he acknowledged that there is little doubt that climate change is playing an important role in those changes.

According to Krumholz, Rhode Island has already spent millions of dollars to improve wastewatertreatment facilities, and last week voters approved an additional expenditure of $20 million for this purpose. The goal is to remove more nitrogen from the sewage. The upgrades began in 2005, and Krumholz has been tracking the changes to the bay as a result of the upgrades.

“The one-sentence answer is that we do think that we see some improvements, but it’s too early to tell for sure, because Mother Nature is very variable,” Krumholz said. “But the next few years will be key to developing our understanding on this topic.”

Krumholz said that the subject is an important one because the bay is around everybody in Rhode Island, providing recreational opportunities, jobs and tourism. Research from other ecosystems has shown that once they get degraded, they don’t always recover well. He added that it is much easier to protect a mostly healthy ecosystem than to restore a damaged one.

“Sometimes we have to make an investment in our future to make sure that this resource will continue to provide those services for future generations,” Krumholz said.

There are 28 wastewater-treatment plants in the state, most of them in Upper Narragansett Bay. The largest are at Bucklin Point and Fields Point in the Providence area, where nutrient overload is far more pronounced than it is in the lower-bay area that includes Jamestown. Sewage accounts for 65 percent of nitrogen in the bay, while the remainder is the result of urban runoff and storm water.

A number of factors go into the creation of nutrient overload in the bay. At the center of it all is the simple phytoplankton, a microscopic plant that inhabits the upper sunlit levels of almost all oceans and bodies of fresh water. It feeds on the nutrients that exist in the bay. The phytoplankton only live for two days, and when the organisms die they fall to the bottom of the bay, consuming oxygen and creating a hypoxic state.

A reduction of nutrients like nitrogen and phosphorous will result in less primary production of phytoplankton, which means less settling organic manner resulting in less oxygen loss and therefore less hypoxia. The state Department of Environmental Management has set a goal of a 50 percent reduction in nitrogen loading by 2014, and according the Krumholz, that target appears to have been nearly reached.

Despite what seems to be positive findings, there is no definitive proof that the situation in the bay is improving, although levels of phosphorous are markedly lower, largely as a result of the removal of detergents from wastewater. There will have to be several more years of study before the determination with regard to nitrogen can be made with any certainty.

The first upgrades to the treatment plants came online in 2005, and more time is needed to study their effectiveness. It appears that things are moving in the right direction, he said, but the effects of climate change and other factors indicate that more study is needed.

“I guess my takeaway message is that we can no longer view sewage as a flush-and-forget issue,” Krumholz said. “We have dumped sewage into the bay for over 100 years now, and we have to take the time to educate ourselves about how our actions influence the ecosystem around us.”

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