The quality of our surface waters is a key component in maintaining a high quality habitat for aquatic organisms and the wildlife that depend on them. The States, by mandate of the federal Clean Water Act, must develop standards for various pollutants that can degrade stream, lake, estuary or ocean habitats. Standards include numerical or narrative criteria for water temperature, dissolved oxygen, pH, pathogens, solids, color/turbidity, toxics, toxicity, oil/grease and taste/odor. All surface waters are required to meet these standards to protect the uses by man or wildlife that are associated with the water body.

Sources of Pollution:
Pollution can be categorized into point source and non-point sources based on their origin. Point sources are discharged from sewage treatment plants, industries, combined sewer overflows, spills and dredged material disposal. Although the heated effluent of power plant cooling water is not a pollutant, per se, it can increase temperature of the receiving water and substantially degrade its water quality. Non-point source pollution occurs when rainfall, snowmelt, or irrigation runs over land or through the ground, picks up pollutants, and deposits them into rivers, lakes, and coastal waters or introduces them into ground water. Sources include atmospheric deposition through the settling of particulates (from incineration or power plants) or precipitation; runoff from urban, agricultural or residential areas; and leachate from landfills or contaminated groundwater. Sulfur dioxide and nitrogen oxide emissions from power plants also create acid precipitation which can eliminate fish in isolated lakes, but acid impacts on lakes are concentrated in northeastern lakes and mining States and are not widespread across the country as a whole.

The United States has made tremendous advances in the past 25 years to clean up the aquatic environment by controlling pollution from point sources such as industries and sewage treatment plants. However, non-point sources remains the Nation's largest source of water quality problems. It's the main reason that approximately 40 percent of our surveyed rivers, lakes, and estuaries are not clean enough to meet basic uses such as fishing or swimming. The state and federal pollution control agencies are working together to control these sources with permit limits on point sources and best management practices for non-point sources.

Types of Pollutants:

Types of pollutants include:

• sediments (eroded from land runoff) or solids (from point sources); removal of shoreline vegetation may accelerate erosion of sediment and nutrients into a stream or lake;
• biological or chemical oxygen demanding substances (BOD/COD = organic and inorganic substances that can reduce dissolved oxygen in the water and sediments);
• nutrients such as phosphorous, nitrogen and silica that can enhance algae and phytoplankton growth;
• pathogens such as bacteria, viruses or protozoans which can cause closure or restrictions on swimming and shellfish harvesting;
• toxics, particularly, heavy metals, pesticides, PCBs, PAHs (polycyclic aromatic hydrocarbons) and dioxins, which can be accumulated and concentrated in the food web; Toxicity is expressed as adverse acute or chronic effects of sensitive aquatic organisms in response to the exposure to the mix of toxics in a point source discharge (whole effluent) or in sediments (whole sediment) in the receiving water of a discharge.

Potential Effects of Pollutants on Habitat Quality:

Sediments/Solids:

• Siltation alters aquatic habitat and suffocates fish eggs and bottom-dwelling organisms. Aquatic insects live in the spaces between cobbles, but their habitat is destroyed when silt fills in these spaces. The loss of aquatic insects adversely impacts fish and other wildlife that eat these insects. Siltation of special habitats, such as trout or salmon
  spawning beds, may will prelude use of such areas which require a clean sand or gravel substrate for successful spawning;
• Settlement of solids may degrade bottom communities due to the enhanced load of organic matter;
• Reduction in water clarity which can reduce depth of light penetration needed for photosynthesis (primary production), oxygen production and impact visual behavior of aquatic animals;
• Excessive sediments and solids in the water can clog or irritate the gills and filter-feeding organs of sensitive invertebrates or fish reducing respiration and feeding activities.

BOD/COD:

• Increased discharge of these pollutants can reduce to deplete dissolved oxygen levels in the water or sediments hence limiting uses by organisms that require high DO, such as trout or salmon.
• Fish kills and foul odors may result if dissolved oxygen is depleted.

Nutrients:

Extra inputs of nutrients can destabilize lake and estuarine ecosystems. When temperature and light conditions are favorable, excessive nutrients stimulate population explosions of undesirable algae, phytoplankton and aquatic weeds. The algae sink to the lake bottom after they die, where bacteria consume the available dissolved oxygen as the bacteria decompose the algae and may trigger fish kills and foul odors. In addition, explosive growth of algal populations can reduce light penetration and inhibit growth of beneficial aquatic plants such as submerged aquatic plants which provide critical habitat for numerous fish and invertebrates including shellfish, such as scallops. Increased nutrients also can cause shifts in types of algae or phytoplankton (which can change an aquatic ecosystem or encourage nuisance or toxic phytoplankton blooms) and promote general eutrophication of an aquatic ecosystem.

Pathogens:

Pathogens, such as bacteria and viruses, are associated with failing sewage treatment plants, combined sewer overflows, failing septic systems and runoff (particularly, agricultural or urban). They have been responsible for:

• closure or restrictions of swimming areas
• closure or restrictions of shellfish areas.
• adverse effects on the health of certain aquatic organisms.

Toxics:

The adverse effects of toxic substances, particularly persistent bioaccumulative chemicals, effects have documented in the scientific literature for many years. Although most of these chemicals have been banned for 2-3 decades, many are still in the environment because of their persistence. Many contaminants discharged in water or accumulated from non-point sources are very mobile in aquatic systems. Most of these contaminants are accumulated at the lower trophic levels (primary producers or primary consumers) and are passed up the aquatic food web through fish and invertebrates which are staple foods of numerous wildlife species. Because some of these contaminants are biomagnified in the food web (e.g., PCBs, DDT, methyl mercury), they can have far and wide reaching effects to aquatic organisms and the wildlife species that depend on them. Toxics that are biomagnified means that the concentration of the toxicant in the tissue of animals increases as it goes up the food web. Thus, top level consumers, such as salmon, tuna, sharks, and fish-eating birds and mammals are at the greatest risk accumulating contaminants at toxic levels. In the case of edible species such as salmon or tuna, these effects can effect humans such as methyl mercury poisoning of the Japanese people of Minimata Bay in the 50's and 60's. Many of these compounds, such as pesticides and PCBs, are carcinogenic. More recently, there is strong circumstantial evidence that many of these and other compounds mimic estrogenic compounds which may be responsible for a variety of adverse reproductive effects in most if not all vertebrate taxa, including man.

Role of Wetlands in Preserving Water Quality:

Loss of wetlands can lead to increased flooding; species decline, deformity, or extinction and declines in water quality. Forty-five percent of the threatened and endangered species listed by the Fish and Wildlife Service rely directly or indirectly on wetlands for their survival. The Nature Conservancy estimates that two-thirds of freshwater mussels and crayfishes are rare or imperiled and more than one-third of freshwater fishes and amphibians dependent on aquatic and wetlands habitats are at risk. Relative to water quality, wetlands loss and degradation can reduce water quality purification functions performed by wetlands. The Congaree Bottomland Hardwood Swamp in South Carolina provides valuable water quality services, such as removing and stabilizing sediment, nutrients, and toxic contaminants. The total cost of constructing, operating, and maintaining a tertiary treatment plant to perform the same functions would be $5 million.

Forested riparian wetlands play an important role in reducing nutrient loads entering the Chesapeake Bay. In one study, a riparian forest in a predominantly agricultural watershed removed about 80% of the phosphorus and 89% of the nitrogen from the runoff water before it entered a tributary to the Bay. Destruction of such areas adversely affects the water quality of the Bay by increasing undesirable weed growth and algae blooms. A study of two similar sites on the Hackensack River in New Jersey demonstrated the increase in erosion that results from the destruction of marshlands. In the study, marsh vegetation was cut at one site and left undisturbed at the other site. The bank at the cut site eroded nearly 2 meters (more than 6 feet) in 1 year while the uncut site exhibited negligible bank erosion.

Note: This write-up is based in part on The 1996 annual EPA National Water Quality Report to Congress