Experts believe a 40 percent reduction will greatly improve oxygen levels in bay waters. This would improve the habitat and health of the bay's living resources. Oysters, fish, crabs, waterfowl and many kinds of underwater plants need sufficient dissolved oxygen in the water to survive. Excess nutrients, mainly nitrogen and phosphorus, overfertilize bay waters causing an abundance of algae that prevents sunlight from reaching underwater plants. When the algae die, the process of their decay robs the water of oxygen.
Some nutrients are natural and some are caused by human activity.
The trib strategies address only those nutrients from controllable sources such as sewage treatment plants. In Virginia, the 40 percent reduction in nutrient levels will be achieved through non-point source programs, some of which DCR has managed for more than 10 years, through new point source technology and through consensus building at the local level among diverse interests. Virginia's approach depends on building partnerships with communities and the private sector so that citizens can contribute to restoring water quality in the bay and its rivers. A mathematical computer model has shown that nutrients from the Potomac and more northern rivers have a much greater impact on the bay's health than do those of the more southern tributaries that together contribute less than one percent of the dissolved oxygen problem in the main stem of the bay. As a result, the Potomac strategies are being designed to meet the 40 percent goal while goals for the lower tributaries are still being developed.