Wetlands and Chemistry

What are wetlands?

Wetlands are described by their name. They are parts of land that are water saturated on a regular basis. This includes swamps and swampy areas of prairies and forests, marshes, bogs, estuaries, and shallow ponds. It does not include lakes because these are more or less permanent bodies of water and are dominated by aquatic life and the associated chemistry.

The wetlands are below the water table and the ground is saturated with water. The wetlands act as filters to remove sediment and many contaminents. Water is slowly released from the wetlands to permanent bodies of water: rivers, lakes, ocean.

Intact forests typically become swampy when there is heavy rain. The ground, with organic matter and vegetation absorbs water and slows the rate of runoff. This reduces erosion.

Chemistry of Wetlands

Wetlands contain lots of organic matter, peat moss for example. Microorganisms are typically limited by nitrogen in these environments. When effluent from agricultural land goes through a marsh or wetland, the local microorganisms use the nitrate nutrients to oxidize some of the carbon. The water going into the ocean or lake does not have the excess nitrate concentration that it would otherwise have. The microorganisms also break down or sequester many other organic and inorganic pollutants in the water.

Iron sulfides are typically insoluble and become sequestered in wetlands. They don't react with oxygen in this environment. This prevents the acidification that would result from the reaction of iron sulfides with O2.

Chemistry of Estuarine and Marine Wetlands

Estuarine shrub wetlands make up 13 percent of the total US wetlands area and nonvegetated saltwater wetlands are 14 percent.

From a chemical standpoint, salt concentrations are most important for estuary and marine wetlands. Concentrations of NaCl and other salts can be higher or lower than seawater. The water is frequently diluted by freahwater but at times, through evaporation, the salt concentration can actually be very high.

Chemistry of Freshwater Wetlands

In the freshwater system, forested wetlands made up 51 percent of the total area and are the single largest freshwater category. Freshwater emergents (areas that are swampy only part of the year) made up an estimated 25.5 percent of the total area, shrub wetlands 17 percent, and freshwater ponds 6.5 percent.

Inland water is dominated by four major cations, calcium (Ca+2), magnesium (Mg+2), sodium (Na+), and potassium (K+); and three major anions, carbonate (C032-), sulfate (SO42-), and chloride (Cl-)


Professor Patricia Shapley, University of Illinois, 2009