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Nitrogen discharges from municipal sewage treatment plants increased only slightly in 2013 from the previous year, and the state remains on track to meet its nitrogen reduction goals for 2014, the state Council on Environmental Quality said in its recently updated report.
About 4,000 tons of nitrogen flowed into Long Island Sound and rivers that discharge into the Sound from 80 municipal treatment plants in 2013, down from 7,500 tons a decade ago. State and town investments in plant upgrades enabled the plants to remove more nitrogen, which acts as a fertilizer spurring excessive algae and aquatic plant growth. As the algae and plants decompose, bacteria flourish that consume large quantities of oxygen, leading to hypoxic conditions in the Sound that harm fish and other marine life. In the summer of 2013, only a small portion of western Long Island Sound experienced hypoxia, said Karl Wagener, executive director of the council.
The slightly higher nitrogen levels in 2013 were attributed to cooler and wetter weather last summer, "not any backsliding," and the long-term trend remains positive, Wagener said.
"This is an infrastructure issue," he said Wednesday. "Connecticut and municipal taxpayers have paid a fair amount for treatment plant upgrades, and they should be pleased to see that it's working. The investment needs to continue."
Nitrogen discharged from treatment plants totaled 4,002 tons in 2013, compared to 3,934 tons in 2012, said Mark Parker, environmental analyst with the state Department of Energy and Environmental Protection. The main reason for the slight increase was that the bacteria that remove nitrogen in the treatment plants didn't work as efficiently in 2013 compared to 2012, when the weather was warmer and drier.
Denise Ruzicka, director of water planning and standards at DEEP, said Tuesday that much of the success at reducing nitrogen from treatment plants is due to plant upgrades and the nitrogen trading program. The program allows plants not meeting state goals for nitrogen levels to purchase credits from other plants that exceed goals.
"It's worked really well for some of the smaller plants," she said. "The bigger plants are more efficient at taking out more nitrogen, and in the end, Long Island Sound doesn't care where the nitrogen is being removed."
Connecticut contributes about one-third of the nitrogen pollution in Long Island Sound, with the remainder coming from New York state. In 2001, the Environmental Protection Agency approved a plan for the two states to reduce total nitrogen. Connecticut is on track to meet the goals of the plan, but New York state is behind, the council noted in its report. Ruzicka said upgrades to New York City sewage treatment plants that are expected to be completed in the next two years are expected to have a major impact.
As a result of lower nitrogen levels, Long Island Sound can support more shore birds, fish, shellfish and other marine life, and more beaches are free of excessive algae and plant growth, Ruzicka said.
Progress will continue with additional nitrogen removal projects being designed for sewage treatment plants in Norwich, Farmington and Rocky Hill, she added. Projects currently under construction include the Mattabasset District plant in Cromwell, the Greater New Haven Plant, the Metropolitan District plant in Hartford and the Manchester and Plymouth plants.
Wagener said one of the main challenges to further reducing nitrogen in the Sound is to address runoff polluted from roads, lawn and agricultural fertilizers and other "non-point" sources.