b'How Does Discharge from a Watershed Aff ectthe Ecosystems of our Waters?Chatham relies on clean, productive and aesthetically pleasing waterways for tourism, recreational swimming, boating and commercial fi nfi shing and shellfi shing.There are two main types of pollution that are of concern for Chathams waterways: nutrients and bacteria.Nutrients enable plant life to growNitrogen Aff ects our Saltwater Embayments Drawing by Kassie FossIn a saltwater pond or estuary, the marine plants at the base of the food chain require nutrients in order to grow and repro-duce.The excessive supply of nutrients to an ecosystem is called eutrophication. In general, algal growth in salt water is stimulated by nitrogen.When a watershed supplies too much of the nutrient nitrogen:l Microscopic phytoplankton (microalgae) increase dramatically, causing the water to become cloudy and, in extreme cases, green or brown.l Slime algae increase on the surfaces of pilings, rocks, and eelgrass blades.l Drift algae (macroalgae) grow to excess, break loose, and pile up onto the shore or eelgrass beds. Eelgrass is a vital component of shallow estuaries. It is a rooted marine plant that provides habitat for bay scallops, blue crabs, tautog, winter fl ounder, and tomcod, among others. Because eelgrass is very sensitive to poor water quality and algal growth on its leaves, its decline is a warning bell that must be heeded.Shellfi sh help to improve water quality as they feed by fi ltering microscopic particles from the water. One study has calculated that 100,000 rapidly growing oysters can cancel the nitrogen pollution from 27 people living in the watershed. Fertilize Your Estuaries and Salt Ponds with Nitrogen Only if You Like Them Green!The rampant growth of microscopic algae causes the green, murky look that makes salt ponds and sea water uninviting and ecologically unhealthy.This excess plant material, when it decomposes, takes oxygen out of the water, suff ocating marine life.Algae blooms also reduce the amount of sunlight that can penetrate the water.Valuable marine plants like eelgrass cannot photosynthesize in cloudy water and soon die off .In the last decade, eelgrass meadows have disappeared from nearly all of Chathams waters.Chatham is blessed with many square miles of salt and brackish coastal ponds, marshes, bays, and harbors that are at risk from nutrient overloading. The water quality in every coastal waterway is aff ected by the addition of nitrogen from its watersheds.Where Does Nitrogen Come From?Us!The most signifi cant source of nitrogen that we can control is human wastewater. Although your septic system removes about a quarter of the nitrogen present in urine, the wastewater that leaves your leaching fi eld is still highly concentrated with nutrients100 times more concentrated than the desired levels of nitrogen in coastal waterways. For most of the estu-aries, wastewater is the source of more than half the annual nitrogen input.Page 15bluepages.indd 15 8/26/2009 1:49:40 PM'