BC Wetlands Network March 1995
order to understand how wetlands function as "kidneys," it helps to
know a bit about how nitrogen is cycled through the ecosystem. All living things
need nitrogen. It is used to make the basic units of all life: DNA, proteins and
amino acids. However, most nitrogen exists as a gas in the atmosphere, which
very few living things can use. There are a small number of bacteria that are
able to transform nitrogen gas into ammonia, through a process called nitrogen
fixation. These bacteria use ammonia for their own growth, or they excrete it
into the surrounding soil or water, where other bacteria transform it into
nitrates. Nitrates are absorbed by plants and used for growth. Animals obtain
their nitrogen by eating plants, or other animals. Once a plant Or animal dies,
the nitrogen in its proteins is broken down to ammonia again by decomposing
bacteria, transformed into nitrate by nitrifying bacteria, and absorbed again by
other plants. In this way, nitrogen in the soil and water is recycled over and
over. At every turn of the cycle, nitrogen fixing bacteria add a little
nitrogen, and some nitrogen is released back into the atmosphere by another
group of bacteria in a process called denitrification.
These different processes occur in different places in the landscape.
Nitrogen gas is transformed into ammonia at the surface of soils and water or
just below. In the soil, ammonia and nitrates exist in an equilibrium
transformed back and forth by different groups of bacteria.
While ammonia stays with soil, nitrates are water-soluble and leach out
of the soil, flowing into groundwater and collecting in lakes and wetlands.
There, in the waterlogged soils, denitrifying bacteria transform nitrates back
into nitrogen gas and release it into the atmosphere. The nitrogen cycle of a
landscape is self-adjusting. The
activity of all of these microorganisms in the soil and water maintains
equilibrium between the amount of ammonia and the amount of nitrate in the
system, and between the amount of nitrogen fixed in upland areas, and the amount
released back into the atmosphere in wetlands. If the there is an excess of one
form of nitrogen, there are microorganisms that will quickly, transform it into
another form, thereby retaining a balance. Everything works fine, until we start
overloading the system on a continual basis.