Why Wetlands?  Because They Clean Our Water!

By Laura Jamieson

From BC Wetlands Network March 1995


Why 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. 


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.



This 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.