Wetland Pollutants

Wetlands provide valuable habitat and food resources for birds and wildlife. The U.S. Environmental Protection Agency (EPA) estimates that nearly half of North American birds rely on wetland ecosystems. Wetlands also provide important flood protection by acting as natural sponges that absorb flood waters. Yet, despite their importance to wildlife and humans, over 50 percent of wetlands in the lower 48 states have been lost since the colonial period. Development, draining for farms, and pollution have reduced wetland habitat. Wetlands often contain plants sensitive to contamination by pollutants.

Fertilizers

• Fertilizers harm wetlands by disrupting the nutrient balance within wetlands. Fertilizers often contain high concentrations of phosphorus and nitrogen. Although naturally occurring in the environment, increased levels can cause algal blooms, which are explosions of rapid algae growth. As the algae dies, bacteria act on decaying plant matter. Bacteria use up the dissolved oxygen in the water, thus making the wetland inhospitable for plant life.

Pesticides

• Pesticides enter wetlands through runoff, with agricultural runoff being the primary source according to the EPA. These pollutants include non-selective pesticides, which can potentially kill any plant or organism that comes in contact with them.

Acid Water Drainage

• Abandoned mines are one source of acid water drainage. Chemicals used in mining remain trapped in soils. Surface water from precipitation washes the contaminated water into wetlands, creating acidic conditions, which wetland plants may not tolerate.

Acid Rain

• Acid rain forms when sulfur dioxide and nitrogen oxide emissions combine with moisture present in the air in a reaction fueled by the sun. Precipitation acidifies aquatic resources and soils. Acid-loving wetland plants can tolerate pH levels down to 4.5; acid rain, though, lowers pH levels even further. The result is the creation of ecological dead zones, where no wetland plants can live.

Urban Runoff

• Runoff from roads leaches salt, oil, and other road pollutants into wetlands. These chemicals can alter the soil and water chemistry as well as introduce toxins into these systems. Because wetland soils are frozen during the winter months, these pollutants can accumulate on the soil surface, increasing their negative environmental impacts.

Storm Runoff

• Urban areas are prone to flash flooding because of the high amount of impervious surfaces present. Impervious surfaces, such as roads and parking lots, replace land that can absorb flood waters. During flood events, overflow from sewers and septic tanks introduces a lethal cocktail of pollutants, bacteria, and pharmaceuticals into wetlands through surface water runoff.