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May-June 2010

Effects of Nitrogen on Seagrass: Results from a Comparative Study

Eelgrass in Lagoon Pond, MA (photo courtesy of Giancarlo Cicchetti)

Excess nitrogen from human activities contributes greatly to cultural eutrophication in estuaries. One symptom of excess nitrogen in shallow embayments is the loss of seagrass habitat. Seagrass habitat provides important ecological services including fish and shellfish nursery and refuge, shore-bird feeding grounds, nutrient and carbon cycling, sediment stabilization, and increased biodiversity in tropical and temperate regions throughout the world. Because seagrasses are so sensitive to anthropogenic pressures and have a global distribution, they are excellent biological sentinels for assessments of estuarine condition.

As part of a larger project to evaluate multiple effects of nitrogen loading on shallow coastal embayments in southern New England, scientists at EPA’s Atlantic Ecology Division have shown how spatial extent of eelgrass (Zostera marina, the common seagrass in New England) varies as a function of nitrogen loading.

EPA scientists applied an empirical watershed model, previously verified in coastal bays of Cape Cod, MA to estimate nitrogen loading rates for 74 small- to medium-sized embayment-type estuaries along the CT, RI and MA coasts. These calculated rates were compared with airplane-derived photographic data of eelgrass areal extent from the same estuaries, revealing a pattern between eelgrass extent and nitrogen loading. When nitrogen loading rates exceed 50 kg N ha-1 yr-1, eelgrass extent declines markedly, with eelgrass generally absent when levels exceed 100 kg N ha-1 yr-1. These results are consistent with other, much smaller studies, and suggest that 50 kg N ha-1 yr-1 is a reasonable threshold for the protection of eelgrass habitat.

Papers presenting the results of this study are currently under journal review. For additional information please contact Jim Latimer (

Other News in the Gulf of Maine & Bay of Fundy

Past Journals

Febuary 2015ESIP releases new smartphone app connecting people in the Gulf of Maine and watershed to the science happening all around them.

November 2015The launch of a marine debris program in the Bay of Fundy.

September 2015Climate Change Products for Atlantic Canada.

July 2015An update from the April 2015 State of the Bays Symposium in Massachusetts.

June 2015Learn about NH Department of Environmental Services' work with 65 volunteers to improve beach grass coverage at Hampton Beach State Park.

May 2015Nova Scotia recently released risk ratings for storm serge and sea level rise for all portions of the Province - this journal summarizes the findings

April 2015Learn about an exciting project between ESIP and EPA that seeks to unravel upstream pressures on downstream estuaries

February 2015Meet the new Project Leader for the Gulf of Maine Coastal Program in Falmouth, Maine - Jed Wright.

January 2015New Smart Tour of Great Marsh - largest continuous stretch of salt marsh in New England, extending from Cape Ann in Massachusetts to New Hampshire

December 2014The American Lobster Settlement Index is an important project that assesses current lobster fishery condition in both Canada and the US. The dataset is current and available through the ESIP Indicator Reporting Tool

Click here for all past ESIP journals