Because They Clean Our Water!
BC Wetlands Network March 1995
do we need to protect wetlands? It may seem obvious to many of us, but there are
still many people who need to be convinced, especially at the political level.
This is the first in a planned series of articles dealing with concrete
arguments for the preservation and restoration of wetlands.
play many roles in the ecology of a landscape; they provide valuable habitat for
fish and wildlife, rank among the most productive ecosystems in the world, and
serve as natural basins for water storage and flood control. The wetland’s
function, which perhaps benefits humans most directly are the role, they play in
purifying water. Wetlands, once
regarded as sources of disease, can actually clean up polluted water and help
maintain water quality. For this reason, they have been compared to the kidneys
of the body. It's a good analogy,
but what exactly does it mean? Telling a local municipal council that they
should protect local wetlands because they function as the "kidneys"
of the ecosystem is not likely to get you very much support. What it means is that wetlands have the ability to cleanse
and filter the water that flows through their layers of mucky organic sediments.
/ In particular, wetlands can remove excess nitrates from water. They do this in
two ways. One way is through
wetland plants, which absorb nitrates from the water and use them to produce all
that luxuriant growth. This in
itself is just delaying the problem; because when the plants die and decompose
the nitrates are re-released. However, nitrates are also removed from wetland
waters by a group of bacteria, called facultative anaerobes, which live in
wetland mud. Facultative anaerobes are adapted to living in places where there
is a shortage of oxygen, Such as the stagnant water and mucky sediments of
wetlands. They are extremely efficient at obtaining any oxygen available,
including the oxygen contained in nitrates. Through a process called
denitrification. They absorb nitrates from the water, and release nitrogen gas
into the atmosphere, leaving wetland water clean. It is these facultative
anaerobes that allow wetlands to perform their unique role in the ecosystem.
"The significance of this wetland function is greater now than ever
before, and still expanding, as human use of fossil fuels produces nitrates in
acid rain, and as our enthusiastic overuse of organic fertilizers in agriculture
dumps more nitrates into the earth than can reasonably be removed by soil
bacteria."* Since World War I, the amount of synthetically fixed nitrogen
used as fertilizer has increased exponentially. Virtually all fertilizers are
made from nitrates, which are water-soluble. Excess nitrates not absorbed by
plants leach into groundwater where they become a major health hazard. Nitrate
itself is not toxic, but in the gastrointestinal tract microbes transform
nitrate into nitrite, which is highly toxic, and which combines with amino
compounds to form carcinogens. Excess
nitrates also cause eutrophication. This happens when an increase in nitrates in
the water causes an increase in plant growth, particularly algae. The problem
occurs once the algae die and are decomposed by bacteria. A lot of dead plants
means a lot of decomposing bacteria, which consume a lot of oxygen. The water is
robbed of all its oxygen, and other organisms, such as fish, suffocate and die.
This is a serious problem for lakes near agricultural land that receive large
doses of nitrogen from fertilizer and animal wastes.
In wetlands, denitrification can remove anywhere from 40% to 98% of
nitrogen. Therefore, a lake with marshes around its edges has a buffer system to
guard it against excess nitrogen in runoff.
The idea of "cleaning up" a shoreline by removing marshes is
completely mistaken. Marshes are what clean the water entering a lake.
This ability of wetlands to absorb excess nitrogen has led to the
suggestion that wetlands could serve as natural waste treatment plants. However,
like all filters, wetlands have their limits.
Wetlands were not designed to handle the massive doses of nitrates now
being dumped into the ground by every agribusiness, golf course and homeowner.
The main problem is that denitrification produces more than one kind of gaseous
nitrogen. As well as harmless molecular nitrogen, denitrification also produces
nitrous oxide. When nitrous oxide rises to the stratosphere, it goes through a
series of photochemical reactions, which destroy ozone. So, excessive
denitrification, due to excess nitrates from synthetic fertilizers, leads to
depletion of the ozone layer. Wetlands
are as perfect a biological processor of excess nitrate as has ever existed and
they play a vital role in the functioning of the biosphere. However, we cannot
expect wetlands to make up for our excesses. Like any filtering system, they
have their limits. We still need to find a way to reduce the amount of nitrate
we produce. Meanwhile, we need all the wetlands we have. To remove these natural
water-filtering systems at the same time that we are increasing the amount of
nitrates that we dump into the water is shortsighted and downright suicidal.
article is based on an article by Sue Reed entitled 'Why Wetlands",
published in Landscape Architecture Review. Vol. 8 no.2, 1987. Many thanks to
Patrick Mooney of the Landscape Architecture Program at U.B.C. for passing Sue
Reed's article on to us.