Pollution

STUDY

CONTAMINATION IN CASCO BAY

Reducing the impacts of current and legacy pollution sources is crucial for both the economy and the health of the estuary and its many communities.

Although Casco Bay remains relatively healthy compared to many East Coast bays, nutrient pollution, primarily from nitrogen, is becoming a growing concern. The Bay is already showing early signs of nutrient overload, such as algae blooms, damage to eelgrass beds, and coastal acidification. With population growth and climate change—leading to warming waters and altered precipitation—these issues are likely to worsen.

Toxic pollution is another significant threat, affecting the Bay’s sediments and the tissues of clams, fish, birds, and marine mammals. Contaminants like heavy metals and organic chemicals pose risks to both aquatic life and human health.

The Bay’s industrial history—including shipyards, tanneries, and textile factories—has left a legacy of toxic chemicals in its sediments and waters. Today, the main source of toxic pollution is nonpoint source pollution, particularly contaminated stormwater runoff. Airborne pollutants from local and distant sources also contribute, depositing toxins in the form of rain or dust.

Despite the widespread presence of toxic chemicals in Casco Bay and its watershed, there is some encouraging news. Over the past two decades, levels of PCBs, dioxins, and many pesticides entering the environment have significantly declined. Since 1991, the levels of most heavy metals, pesticides, tributyltin, polycyclic aromatic hydrocarbons (PCBs), and low molecular weight polycyclic aromatic hydrocarbons (PAHs) in the Bay’s sediments have also decreased.

A CBEP-commissioned report (link below) suggests even more positive news: concentrations of legacy pollutants—such as heavy metals and organic compounds like PAHs and PCBs—are generally on the decline.

CURRENT PROJECTS

Tackling Nutrient Pollution. Nutrient pollution in Casco Bay has been formally recognized by the Legislature as a statewide priority. Casco Bay Estuary Partnership and many partners have been taking action to better understand, convey and reduce the negative impacts of nutrients on Casco Bay.

CBEP and partners are monitoring nutrients around Casco Bay to provide real-time data on nutrient processes. CBEP’s “NuLAB”, a land-based nutrient analyzer, was deployed off the Portland Street Pier in South Portland, and automatically collected nitrate, nitrite and ammonium samples every two hours for two summers. Seeing a likely connection between nitrate/nitrite concentration and rainfall events, CBEP may redeploy the sensor earlier in spring to capture data during heavy rainfall events. All data collected so far is preliminary.

You can see historical buoy data collected by University of Maine’s SEANET (a research network focused on Sustainable Ecological Aquaculture) buoy network here.

Download a report of the Casco Bay Nutrient Council, Nutrient Pollution in Casco Bay, Maine, here.

Download CBEP’s fact sheet, “Nutrient Pollution in Casco Bay,” here.

Next Steps. CBEP and Maine Department of Environmental Protection are jointly convening a Portland Area Nitrogen Criteria Advisory Group that brings together representatives of municipalities, wastewater treatment plant operators, stormwater professionals, environmental groups, government agencies and academic institutions. The Advisory Group will gather information, share perspectives, and provide advice to DEP on how to move forward with establishing nitrogen standards.

For More Information

Contact Curtis Bohlen, CBEP Director, Curtis.Bohlen@maine.edu, (207)780-4306.