NUTRIENTS - Marine Pollution: What Everyone Needs to Know - page 19

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NUTRIENTS
Why are nutrients considered pollutants, since they are
required for life?
Input of excess nutrients such as nitrogen (N) and phosphorus
(P) causes major problems in the aquatic environment. While
phosphorus tends to be the main cause in freshwater, nitrogen
is the major source of problems in the marine environment.
Where do the nutrients come from?
Sources of nutrients include sewage and food wastes plus ani-
mal wastes and fertilizers that are discharged or run off from
agricultural areas. From land, excess N flows from agricultural
fields, suburban lawns, and stockyards, entering freshwater
and going down to estuaries via streams and rivers, altering
water chemistry and ecology. As stormwater runoff flows over
the land or impervious surfaces such as paved streets, park-
ing lots, and building rooftops, it accumulates debris, chemi-
cals, sediment, and other pollutants that can impair water
quality. Urban areas contribute food wastes, human sewage,
animal wastes, and lawn fertilizers. Even after treatment, sew-
age contains high levels of nutrients. Waste from septic tanks
enters estuaries through seepage into groundwater. Wherever
there is more residential development and more septic tanks
in the neighborhood, more nitrogen seeps into nearby bod-
ies of water, marshes, and estuaries. Nutrient enrichment due
to excessive amounts of N is the primary cause of impaired