Nitrogen and Phosphorous
As forests surrounding the Chesapeake Bay were gradually replaced by farms, cities, and suburbs, the amount of nutrients entering the Bay increased tremendously. While small amounts of nutrients are vital to all life, excessive amounts can be damaging. Nutrients are found nearly everywhere --- in the atmosphere, the water, the soil, and in plants. Forests contribute lower amounts of nitrogen and phosphorous to waterways than do other land uses.
The primary nutrients polluting the Chesapeake Bay are nitrogen and phosphorous. High amounts of these nutrients increase the growth of algae. Algae becomes so abundant that the color of the water turns brownish or greenish. Sunlight is blocked from reaching other plants. When the algae die and decompose, oxygen dissolved in the water is used. Often, so much oxygen is used by decomposing algae that fish and other animals must move to areas with more oxygen. Plants and animals that cannot move may die.
In 1987, the Chesapeake Bay Agreement was amended to include the specific goal of reducing the amount of nutrients entering the Bay by 40% of the 1985 levels by the year 2000. This reduction would significantly increase the amount of dissolved oxygen in the Bay improving conditions for plants and animals. In the late 1980's, progress was made by controlling the amount of phosphorous, especially from wastewater treatment plants. More recently, controls of nitrogen and nonpoint sources of pollution are beginning to improve nutrient levels. The water quality in the Bay has improved with these decreases in nutrients.