Estuary Ecosystem Spotlight: Great Bay

Posted on November 9, 2016


Guest post by Jeff Barnum | Great Bay-Piscataqua Waterkeeper for the Conservation Law Foundation

Great Bay, in coastal New Hampshire, is one of only 28 ecosystems in the U.S. to be designated as an ‘estuary of national significance,’ so we are spotlighting one of the challenges the bay is facing: loss of eelgrass. Jeff Barnum took SSC staff members out on the water for a guided tour of Great Bay earlier this year to see and discuss areas of concern.



At the heart of the Great Bay ecosystem is eelgrass—a sub-tidal, flowering plant that provides essential habitat for fish and crustaceans, produces oxygen, and protects water quality, and that even sequesters carbon more effectively than trees and other plants on the landscape. Most people will never even see live eelgrass.

It is no secret that the Great Bay estuary and the Piscataqua River have been losing eelgrass for the last two decades. The ten miles between Great Bay’s Adams Point in Durham and the naval shipyard on Seavey Island are essentially devoid of eelgrass. Every so often, a new bed will appear here or there, giving us hope, last a season or two, and then disappear. The losses are attributed to nitrogen pollution from a variety of sources. The weight of evidence connects the excessive nitrogen discharged from sewage treatment plants to the demise of eelgrass. Fortunately, communities all around the Great Bay estuary are responding.

great-bay-estuary-mapNew sewage treatment plants in Newmarket and Exeter are underway.  Rochester and Dover have made changes to their plants and have reduced nitrogen discharges. And Portsmouth has committed to completing construction of a new plant by the end of 2019. Nitrogen also comes from fertilizers—mostly our lawns— as well as animal waste, atmospheric deposition from the vehicles we drive, power plants, and septic systems—all of it delivered by precipitation and stormwater.

Photo: Seacoast Science Center
This research buoy records a variety of water quality parameters in Great Bay: salinity, pH, dissolved oxygen, temperature, and more.

The most recent report shows a slight gain in eelgrass acres, compared to the previous year, but that minor gain does not offset the previous year’s loss. Moreover, acreage alone is not the best indicator of eelgrass health where it still exists. The real indicator is biomass—the density and dry weight of eelgrass meadows. In 1996, all of the eelgrass in Great Bay proper was estimated to weigh 1630 tons. That number is now estimated to be just 348 tons— almost 80% of the essential habitat, oxygen production, its ability to sequester carbon, and anchor sediment has evaporated.

To learn more about the challenges and successes happening in Great Bay, please visit Great Bay Waterkeeper blog.

greatbaytour_waterkeeperdrivesboatJeff Barnum is the Great Bay-Piscataqua Waterkeeper for the Conservation Law Foundation, working to address water quality issues throughout the Great Bay estuary. Jeff comes to the position with great knowledge of the estuary, having served as president for the Coastal Conservation Association of NH, where he focused on the health of New Hampshire’s estuarine ecosystems. As a recreational fisherman who has fished Great Bay and the Piscataqua River, Jeff has witnessed, first-hand, negative changes in the estuary caused by water pollution.


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CLOSED today.

Seacoast Science Center is closed today due to inclement weather.