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In the early 1980's scientific studies conducted in the Chesapeake Bay watershed concluded that deteriorating conditions resulted from three major problems, excess nutrients, sediment runoff, and toxic chemicals. Excess nutrient loading was identified as the largest issue of immediate concern. If nutrients help plants grow, how can nutrients be blamed for the decline in water quality? High levels of nutrients cause excess algae to grow. As the algae die, settle to the bottom and decompose, they use up the dissolved oxygen in the water. This lack of dissolved oxygen adversely affects all animals living in the water. Bay grasses, or submerged aquatic vegetation (SAV), is also affected by excess algae and nutrients. SAV provides food and shelter for fishes, food for waterfowl and habitat for shellfish. It also positively affects nutrient cycling, water turbidity, and the stability of shorelines and sediments. These plants need sunlight to survive, and are sensitive to high levels of nutrients. They are severely weakened or killed by shading caused by excess algae in the water.
The Patuxent River is a western shore tributary which drains 932 square miles. Forests and wetlands comprise approximately one half of the land area in the watershed. Nearly one third of the land is agricultural, and the remaining 20 percent is developed. Much of the development is concentrated in the corridor between Baltimore and Washington. This area has experienced a large population increase over the past several decades. In the early 1980's the State and local governments agreed to reduce point source or "end of pipe" and nonpoint source or diffuse nutrient loads to a degree similar to the 40% nutrient reduction later adopted Bay-wide. Because the upper watershed has become so highly populated, point source loads from municipal waste water treatment plants (WWTP) are a significant nutrient source to the river. Point source loads are monitored at wastewater treatment plants and industries throughout the watershed. Stringent phosphorus and nitrogen controls have been implemented at WWTP's resulting in major declines despite increasing flows. The dramatic decline in point source phosphorus loads which occurred in the mid 1980's resulted from implementation of the phosphate detergent ban and numerous WWTP upgrades. The equally dramatic summer declines in point source total nitrogen after 1991 are the result of the implementation of biological nutrient removal at the eight major WWTP's in the watershed beginning in 1991.
Declines in nutrient loads to the Patuxent River are resulting in a significant improvement in water quality. Improvements in water quality resulting from improved wastewater treatment would be expected to be seen first in the fresh water areas which receive much of the municipal discharge from the rapidly growing Baltimore-Washington corridor. Indeed, substantial declines (>40% improvement) are already being seen in the nutrient concentrations measured at water quality monitoring stations in the tidal fresh water and even farther downstream in the transition salinity zone (30% improvement). Improvements in the water quality conditions in the tidal fresh Patuxent are paralleled by improvements in the living resources in these areas. Submerged aquatic vegetation (SAV) was abundant in the Patuxent River prior to the 1960's when deteriorating water quality conditions resulted in its virtual disappearance. SAV reappeared in the tidal, freshwater Patuxent River mainstem in 1993 in levels detectable by aerial photography. Coverage increased from 10 hectares in 1993 to 75 hectares in 1994. This is still far below healthy levels, but it represents a very encouraging trend. In the upper reaches of the tidal fresh, oxygen levels have increased, leading to improvements in the health of bottom-dwelling organisms.
Much progress has been made in controlling point source nutrient loads to the Patuxent River. Efforts to maintain adequate wastewater treatment facilities to accommodate the continuously increasing population in the watershed must continue. Additional effort is required to implement nonpoint source controls. Management strategies include such things as stormwater management, erosion and sediment control, agricultural best management practices, and planting forest buffers. There are many ways that local residents can contribute to pollution control efforts. Limit your use of lawn fertilizers. Have your septic tank pumped every three years. If you are a boater, use marine pumpouts to empty holding tanks. |
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Updated on November 5, 1996
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