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We are overfeeding Narragansett Bay, undermining its health and making it — in some parts of the Bay at some times of the year — violently ill. This condition is caused by excess amounts of nitrogen, which kicks off a series of events that leads to eutrophication which causes algae and phytoplankton blooms, oxygen depletion and habitat loss. View diagram.

Excess nitrogen enters the Bay from a wide range of sources, but predominantly from human activities. Since European settlement, the nitrogen load to the Bay has increased approximately five-fold. Two human factors that contribute to nutrient overload are cesspools and wastewater.

The most dramatic evidence for eutrophication of the Bay occurred in the summer of 2003 with the tragic fish and shellfish kills in Greenwich Bay and the Providence River. Excess nitrogen stimulated a large phytoplankton bloom. When the bloom died off and sank to the bottom, the decomposition process used up all of the oxygen in the bottom waters. Due to the wind conditions, the oxygen-depleted water mixed with surface water, eliminating oxygen from surface to bottom. Millions of fish trapped in this area died quickly. Although special climatic conditions were necessary for such an excessive die off, the event would not have occurred if nitrogen loads to the Bay were lower. 

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Overfeeding the Bay

Eutrophication severely affects the health of the Bay ecosystem. The effects of eutrophication include:

PHYTOPLANKTON BLOOMS
Phytoplankton are like microscopic plants. When nitrogen loadings increase, phytoplankton grow and reproduce at high rates. Some of these plankton (Pfiesteria for example) can cause diseases in fish, shellfish, and humans.

NOXIOUS ALGAL BLOOMS               
Algae, also known as seaweed, also grow and reproduce more quickly with additional nitrogen. Large mats of seaweed can grow to several meters depth. When they wash up on shore, the stench of the decaying seaweed makes for unpleasant beaches, and unhealthy conditions. Bottom waters underlying thick algae mats are often very low in oxygen. Of particular concern is sea lettuce, Ulva lactuca.

HABITAT LOSS                             
The bottoms of pristine embayments are covered with eelgrass beds. These beds support a number of commercially important fin- and shellfish species. Blooms of both phytoplankton and seaweeds can decrease the amount of light that penetrates the water to the bottom. Eelgrass does not survive in the resulting low light conditions. When eelgrass beds disappear, so do species like scallops and flounder. 

HYPOXIA
Hypoxia is seen in Narragansett Bay when oxygen concentration is below 2.9 mg per liter. This is the point at which oxygen levels become harmful or fatal to organisms. Hypoxia is typically seen in the bottom water and is linked to eutrophication through the decomposition of excess algae. In this process of decomposition, oxygen is consumed in the water column.

In Narragansett Bay, hypoxia is episodic during the summer months linked to stratification in the water column (when bottom and surface waters do not mix) particularly due to large rain events and during periods of neap tides. These events can last anywhere from a few hours to a few weeks. Even short hypoxic episodes, however, can have large impacts. Compare dissolved oxyen levels in the Bay between 1999 and 2006.

Nitrogen discharge is a critical and controllable element in the mix of nutrients, sea lettuce, algae, rains, winds, heat and tides that can literally take the oxygen out of the water. This oxygen is as critical to the fish in the Bay as it is to everyone on the shore. We may not have much control over the weather elements, but we can reduce nitrogen.



News

Baykeeper John Torgan reports on the scene from Barrington's August 14, 2008 fish kill.

- Providence Journal editorial of April 14, 2006 nails nitrogen problem
- Save The Bay pushes for action on DEM nitrogen permits
- Testimony on DEM nitrogen reports, February 8, 2005
- Reducing Nitrogen: Critical for the Bay's Health
- Save The Bay comments on Draft DEM nitrogen permit modifications
- Final DEM nitrogen modifications document
- Response to DEM final nitrogen comments

- DEM Plan For Managing Nutrient Loadings to Rhode Island Waters
- 2004 General Assembly legislation requiring nutrient reduction goals
- DEM report on the August 2003 fish kill

 

 
 
 
 
 
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