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Freshwater Management Series No. 7


A Technical Approach in Environmental Management

III. Examples of Environmental Applications of Phytotechnology >

B. Natural Wetlands

Natural wetlands are important for maintaining aquatic ecosystem biodiversity and should be considered as part of an effective ecosystem management strategy. There are four major groups of natural wetlands:

Fringe wetlands, which include salt marshes and lakeside marshes in which water typically flows in two opposite directions, influenced by lunar and/or storm tides,
Riverine wetlands, which occupy floodplains, are usually characterised by water flowing in one direction,
Depressional wetlands, such as prairie potholes, which usually receive much of their water from runoff and/or groundwater seepage rather than from surface water bodies, so that water residence times are longer,
Peatlands also have long water residence times, but the accumulated peat creates a unique hydrologic regime that differs from the previous three types of wetlands.

Large marshy area

Geomorphic setting, water source, and hydr odynamics generate considerable variation within each of these different categories of wetlands.

Water quality improvement is a positive service attributed to wetlands that absorb and recycle nutrients from human settlements. The denitrification potential of wetlands is often surprisingly high. As much as 2,000 to 3,000 kg of nitrate-nitrogen can be denitrified per hectare of wetlands per year, depending on the hydraulic conditions. This is important for the protection of surface waters because a significant amount of nitrate is released by agricultural activities. As much as 100 kg nitrate-nitrogen per hectare may be found in the drainage water from intensive agriculture. Since the denitrification is accompanied by the oxidation of organic matter, this process also removes a significant amount of organic matter.

Table 6 provides an overview of the different types and characteristics of wetlands are found adjacent to surface water bodies (i.e., wet meadows, freshwater marshes, forested wetlands, saltwater marshes, bogs, and shoreline wetlands). Their different abilities to cope with various non-point pollution problems are also summarized.

Table 6: Characteristics of Wetlands Adjacent to Lakes and Their Ability to Retain Non-Point Source Pollutants (UNEP/IETC, 1999)

Type of Wetland Characteristics Ability to Retain Non-Point SourcePollutants
Wet meadows Grassland with waterlogged soil; standing water for part of the year Denitrification only in standing water; removal of nitrogen and phosphorus by harvest.
Fresh water marshes Reed-grass dominated, often with peat accumulation High potential for denitrification, which is limited by the hydraulic conductivity
Forested wetlands Dominated by trees, shrubs; standing water, but not always for the entire year High potential for denitrification and accumulation of pollutants, provided that standing water is present
Salt water marshes Herbaceous vegetation, usually with mineral soil Medium potential for denitrification; harvest possible
Bogs A peat-accumulating wetland with minor flows High potential for denitrification but limited by small hydraulic conductivity
Shoreline wetlands Littoral vegetation of significant importance for lakes and reservoirs High potential for denitrification and accumulation of pollutants, but limited coverage
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