The watersheds that drain to Narragansett Bay deliver to its waters a selection of pollutants that have significant impacts on the Bay ecosystem. Excessive levels of nutrients, particularly nitrogen, contribute to dissolved oxygen problems in the Bay. Rivers carry a large sediment load, filling in port areas in the Upper Bay and causing turbidity problems, affecting fish and wildlife. The working rivers’ legacy of toxic metals, pesticides, PCBs, petroleum products and other compounds still exists in sediments. Modern development techniques and the resulting built environment convert farms, forests and fields to lawns and impervious surfaces, channeling and accelerating the water that drains off these surfaces, scouring streambeds and concentrating pollutants.
While every estuary has its unique characteristics, the Narragansett Bay estuarine watershed shares ecological problems with estuaries throughout the United States. A report by the Association of National Estuary Programs (ANEP, 1999) identified the most common significant problems to address. These include:
- Excess Nutrients - Excessive amounts of nitrogen delivered to marine waters cause algae growth. When algae die, they decompose in a process which robs the water of oxygen making conditions difficult or impossible for fish and wildlife.
- Toxic Chemicals - Years of industrial use and current pesticide use contribute toxic metals and organic chemicals to the watershed and its waters. Other toxics such as mercury are delivered by air deposition.
- Pathogens - These are bacteria and viruses that are harmful to human health and are of concern in protecting human health.
- Habitat Loss & Degradation - As undeveloped land is cleared and developed, key habitat areas and corridors are lost and fragmented. For many years, wetlands were filled in with little thought for the ecological consequences.
- Declines/Changes in Fish & Wildlife - Scientists have documented changes in fish and wildlife populations; one example is the shift in marine fish species in Narragansett Bay. Loss of habitat is also a critical factor in this problem.
- Introduced Species - Recent surveys have discovered over 2 dozen species of organisms in the Bay that appear to be non-native. Invasive terrestrial plants such as purple loosestrife have also become a problem.
- Freshwater Flows - Water use and withdrawals can reduce the amount of water available for maintenance of sufficient stream flow to protect ecological services.