Filtering pollutants and using nutrients

A wetland‘s ability to uptake, metabolize, sequester and/or remove nutrients and imported elements from the water is primarily dependent on wetland vegetative conditions. Microbial processing and bioaccumulation are associated with plant cover including floating, emergent or submergent vegetation. Vegetative density can serve as an index of primary production, which is an indicator of nutrient assimilation.

Forested wetlands retain ammonia during seasonal flooding and wetland environments are effective at denitrification.

Wetlands take up metals both by adsorption in the soils and by plant uptake via the roots. They allow metabolism of oxygen-demanding materials and can reduce fecal coliform populations. These pollutants are often buried by deposition of newer plant material, isolating them in the sediments.

Wetland vegetation needed for removing nutrients survives best in wetlands less than three feet deep.

Excessive nutrient loading to a wetland can cause nuisance algal blooms and the production of monotypic stands of invasive or weed species. Observed point source or nonpoint source of nutrients may include but is not limited to: fertilized lawns, agricultural runoff, manure storage or spreading, concentrated stormwater runoff, or pet waste inputs.

Phosphorus is removed from the water column in wetlands through plant
uptake, immobilization by microorganisms into microbial cells during decomposition
of plant material, adsorption of orthophosphate onto clay and oxyhydroxide. surfaces, and precipitation with cations such as calcium, magnesium and iron. The best long-term removal process is uptake by growing plants, and the storage of plant remains as peat or removal of plant material by harvest.

There is a limit to the amount of phosphorous that can be adsorbed because adsorption sites can become saturated with phosphorous.

Normally, most phosphorus is associated with particulate materials that are removed from the water column as sediments settle. Annual net uptake of phosphorus by growing vegetation, although significant, usually represents a small quantity relative to the soil/sediment sinks of phosphorus.

Organic matter can also have high adsorptive capacity for compounds like phosphorous and heavy metals.

A Regional Guidebook for Applying the Hydrogeomorphic Approach to Assessing Wetland Functions of Prairie Potholes (HGM), Army Corps of Engineers