Many wetlands exist because of very specific hydrological, biological,
geological, chemical, and climatic conditions.
As these conditions change, so do the wetlands.
Some wetlands, such as oxbow lakes and beaver ponds, gradually fill in
and are covered by non-wetland plant life.
Other wetland types, such as large bogs and prairie potholes, may exist
in a similar state for thousands of years.
Humans have had a dramatic effect on wetlands by altering one or more of
the conditions supporting the wetlands, hence many wetlands on the landscape are
in some state of ecological distress. Most
often humans have altered the vegetation through grazing or clearing, or altered
the hydrology by draining or filling the wetland.
Wetland health or condition can be determined by observing the
wetland’s structure (its parts) and function (what it’s doing).
Examples of wetland structure include: water quality, soil condition,
geology, hydrology, topography, morphology, carrying capacity, species
composition, food web support, and nutrient content.
Examples of wetland function include: surface and ground water storage,
recharge, and supply, floodwater and sediment retention, nutrient cycling,
biomass production, reduction of erosion, and purification of water.
There is no one definition that describes a healthy wetland because of
the huge diversity of wetland types. The
most reasonable way of describing wetland health is to compare the wetland of
interest with other less altered similar sites. This helps answer the question, “what is the potential of
this site?” Another method of discovering and describing degradation is to
measure attributes over time. This
kind of data collection could range from comparing historic aerial photographs
to more recent ones, to measuring hydrological changes over several years.
If the wetland’s structure and function no longer measure up to its
potential, it is said to be unhealthy.