Poor water quality alters available habitat and can limit the success of restoration efforts. Oxygen-deprived water is considered to be the largest aquatic pollution problem in the United States and is associated with increased harmful algal blooms and large areas of “dead zones” in the Chesapeake Bay. It also causes the loss of submerged aquatic vegetation, an important habitat for a variety of species. Excess nutrients imported into the Chesapeake watershed may limit the ability to address habitat issues and are an overarching concern.
Invasive species are animals and plants not native to the watershed that spread throughout the area quickly, often overtaking native species. There are more than 200 invasive species in the watershed; some, like nutria, northern snakehead, zebra mussels, phragmites, purple loosestrife and water chestnut, cause costly ecological problems. Some invasive species can take over entire habitats while others consume the food or alter the habitat needed by our native species. For example, upland invasive plants, such as garlic mustard, tree of heaven and Japanese honeysuckle, reduce the stability of soil, which leads to increased sediment entering streams throughout the watershed.
Evidence collected in the Piedmont Province of the Potomac River suggests that the presence of endocrine-disrupting chemicals is affecting immune systems in fish and may be related to a high occurrence of intersex, or the presence of immature eggs in male fish, in smallmouth bass. Intersex is an indicator of chemical contamination. Loss of habitat can affect transport of contaminants. Human consumption advisories are in place for more than a dozen fish species in Maryland, Virginia and other states’ waters due to PCBs, mercury and pesticides in the fish.
Living resources depend on networks of healthy and connected habitats for food, water, shelter and breeding areas. Land use changes fragment or destroy these natural places and can affect others downstream, leaving fewer natural habitats available to provide plants and animals with the basics they need to live. For instance, development can create more impervious surfaces, leading to increased soil and pollutant runoff into the Chesapeake Bay.
Impacts of other stressors can result in increased disease outbreaks, high parasite loads, and decreased disease resistance. For instance, mycobacteriosis is a chronic bacterial disease currently affecting Chesapeake Bay striped bass, causing loss of fish and economic impact for recreational and commercial fisheries. Some of the mycobacteria that commonly infect fishes can also cause infections in people. Diseases have decimated native oysters and, additionally, the habitat and water quality benefits they provide. Scientists predict that disease issues will become more prominent in response to higher water temperatures caused by climate change.