The
diversity of habitats in a watershed
or larger landscape unit is also important for other ecological functions
associated with wetlands. One such function, biogeochemical
cycling, involves the biologic, physical, and chemical transformations
of various nutrients within the biota, soils, water, and air. Wetlands are
very important in this regard, particularly relating to nitrogen, sulfur,
and phosphorous. A good example of this occurs in anaerobic (non-oxygenated)
and chemically reduced wetland soils and the muddy sediments of aquatic habitats
like estuaries, lakes, and streams, which support microbes that function in
nitrogen and sulfur cycling. Upon death and decay, the nitrogen and sulfur
in plant and animal biomass is released through mineralization. Much of this
is eventually transformed into gaseous forms and released into the atmosphere,
where it once again becomes available to certain plants and their associated
nitrogen-fixing bacteria in the soil. This is literally a major defense for
mud, since it is the anaerobic and chemically reducing conditions in the substrate,
in conjunction with various microbes, that ensure the gaseous release of the
nitrogen and sulfur. On the other hand, phosphorous does not have a gaseous
form, but vascular plants in wetlands transform inorganic forms of phosphorus
(that might otherwise be shunted into undesirable algal blooms) into organic
forms in their biomass as they grow. Thus, wetlands
provide the conditions needed for the removal of both nitrogen and phosphorus
from surface water.
Scientists
also point out that atmospheric maintenance
is an additional wetland function. Wetlands store
carbon within their live and preserved (peat) plant biomass instead of releasing
it to the atmosphere as carbon dioxide, a greenhouse gas affecting
global climates. Therefore, wetlands world-wide
help to moderate global climatic conditions. On the other hand,
filling, clearing and draining wetlands releases carbon dioxide.
Wetlands
also play an important role in the hydrologic
cycle -- a cycle we all experience quite readily, for example,
with the precipitation from a thunderstorm and the evaporation of ponded water
from a puddle or bird bath. Wetlands can receive,
store, and release water in various ways -- physically
through ground water and surface water, as well as biologically through transpiration
by vegetation -- and therefore function in this very important global cycle.
Some
specific examples of the benefits of wetlands to society are elaborated below.
In addition, since wetlands play an integral role in the ecology of watersheds,
the Watershed Academy Web module on Watershed
Ecology is very pertinent.
These additional modules will be very helpful in understanding the ecology
of watersheds and the role of wetlands in a watershed context.