Nutrient Contamination

A more subtle classification of contaminants are nutrients, which are the breakdown products of sewage, washing detergents or the improper use of fertilizers.  All plant and animal life needs a certain beneficial balance of nutrients for life and growth, however, excess nutrients can upset the natural balance of plant and animal life in a water body.  Chemically, nutrients are nitrates and phosphates. 

Excess nutrients in the ponds increase plant life beyond its natural balance, or equilibrium. Through the process of photosynthesis, plants produce oxygen in the water column by day and by night respire or breathe oxygen as do animals.  An over abundance of plant life can reduce the oxygen to critical levels that can be deadly to resident animal life.  The third element is the natural decomposition of dead plant and animal matter.  Depleted oxygen (to hypoxic or anoxic) levels will impede the decomposition, resulting in siltation of organic matter covering the bottom of the ponds.  This transforms a healthy well-oxygenated bottom substrate to a thick mass of soft smelly mud—known by scientists as “black mayonnaise”.  Severe hypoxia or anoxia during the hot summer months can produce fish kills, such as took place in Narragansett Bay in 2003.

Excess nutrients enter the ponds through ground water contaminated by septic systems, run-off from yards and farms, and through natural populations of wild animals. SPC research shows that nutrient levels in Charlestown waters have risen over recent years in a strikingly close ratio to the number of new houses in town.