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Nitrogen pollution in Casco Bay is coming from land-based sources, says conservation group

City Hall towers over surrounding buildings as the Casco Bay Lines ferry Wabanaki travels out of the harbor, Wednesday morning, June 1, 2022, in Portland, Maine.
Robert F. Bukaty
/
AP
City Hall towers over surrounding buildings as the Casco Bay Lines ferry Wabanaki travels out of the harbor, Wednesday morning, June 1, 2022, in Portland, Maine.

Nitrogen levels in Portland Harbor and Casco Bay indicate that land-based nitrogen sources need to be regulated, according to the Friends of Casco Bay. They said water samples taken during a rainy day resulted in higher nitrogen levels due to storm runoff than those taken during last summer's dry spell. The data are being used to help the state create threshold values of nitrogen for wastewater discharge licensing.

"This is basically a more simplified way to determine which areas along the coast have nitrogen levels that are too high for sustaining sensitive populations, eel grass for example," said Angela Brewer, a Marine Biologist with the Department of Environmental Protection. "So we have developed threshold values that we want to formalize through rulemaking, through policy."

Brewer says the Portland Water District upgraded its facilities to address nitrogen in storm water outflows and reduced the nitrogen load by 72% in the city's East End. The Friends of Casco Bay say South Portland could use a similar upgrade to address nitrogen pollution.