Association of State Wetland Managers - Protecting the Nation's Wetlands.

Counting Cattails: Nature Vs. Man

final one againBy Melissa Mullineaux, Intern, ASWM

After writing my previous blog, Something’s Fishy, a few weeks ago about water pollution and wetlands’ ability to filter contaminants from water; I got to thinking more about the use of wetlands as a solution for filtering polluted water. So, I began to dig in and do some research to learn more about this.

As I noted in my last blog and will expand on here, natural wetlands filter runoff through a slow, natural process that allows sediment to sink down to the floor of the wetland. Excess nutrients are absorbed by the wetland’s organic matter and are then used in the regrowth of vegetation. Furthermore, the soil captures the other chemicals and heavy metals where they are either held or get broken down by microorganisms. If wetlands have the ability to do this with everyday urban runoff, would they have the ability to filter toxic contaminants from water that has been highly polluted by, say, heavy metals, acid mine drainage or other chemical leaks?

In fact, history proves that they can! Dr. André Sobolewski discusses some great examples on his website of wetlands doing just that. For example, one instance in 1898 was discovered accidentally when a farmer attempted to put sediment on his cucumber patch after a forest fire had caused destruction to the vegetation to his land. His land consisted of 2.5 acres of cupriferous bog. The sediment was applied because the vegetation was not growing back but once he did this, it formed a “black muck” that was found to be “lethal” due to high contents of copper. When revisited in 1950 it was found to contain an estimated 300 tons of copper. Sobolewski’s report states:

“Copper enters the wetland through the bottom, emerging as distinct seeps containing 0.005 to 1.0 mg/L. Its source appears to be copper mineralization associated with the Boss Point Formation (Boyle, 1977). The copper is retained in wetland sediments soon after the seepage emerges. Fraser (1961b) demonstrated that it is attenuated predominantly through association with organic matter, which in the wetland sediments reaches 10-20% (Boyle, 1977).

Fraser determined that accumulating 300 tons of copper in the wetland would require approximately 4,000 years. He notes that the wetland can’t be older than that, because sea water retreated from the area 4,000 years ago. Therefore, he concludes that this wetland has been removing copper from solution since the time it was formed.”

This is just one of many examples I found while researching this topic. Not only do wetlands retain copper contaminants but, according to Sobolewski’s report, they also trap contaminants that are released through acid mine drainage such as Uranium, Zinc, Iron, Manganese, Arsenic, Copper, Aluminum, Lead, Nickel, Cyanide, Radium, Cobalt, Thallium, and Cadmium.

132While research has shown that natural wetlands can definitely hold their own when it comes to filtering highly polluted waters, we must keep in mind that too much pollution can cause irreversible harm to a natural wetland. Excessive amounts of toxins can actually kill plants and animals that live in wetland habitats as well as important microorganisms that help with the natural filtering process. Because of this, governments and organizations have begun to create structures that mimic natural wetland systems to treat polluted water found in acid mine drainage, sewage treatment systems, urban storm runoff, and livestock wastewaters —to name a few.  These constructed systems are developed using soils, microorganisms and vegetation found in wetlands to filter water like a natural wetland.

Constructed wetlands are becoming more popular, One reason is because they take some of the burden off of natural wetlands so that they can continue to offer a dwelling for fish and wildlife, provide flood attenuation, slow shoreline erosion, and offer commercial and economic benefits. They also look better than conventional water treatment plants. Perhaps one of the most important reasons for using constructed wetlands to treat polluted water, is that constructed wetlands can be more cost-efficient for a community because they are much less costly to build than expensive water treatment infrastructure for secondary and/or tertiary treatment. Studies of natural wetlands have demonstrated how effective wetlands are. A report produced by the Environmental Protection Agency (EPA)  in a “1990 study showed that, the Congaree Bottomland Hardwood Swamp in South Carolina, removes a quantity of pollutants that would be equivalent to that removed annually by a $5 million waste water treatment plant. Another study at a 2,500 acre wetland in Georgia, indicated that it saves $1 million in water pollution abatement costs annually.”

NYC GuideAs of 2004, Europe had constructed up to 5,000 wetlands and the US had built up to 1,000 and these numbers have surely grown. Numerous handbooks have been made and are offered online, such as EPA’s “A handbook of constructed wetlands,” to guide communities in fashioning a constructed wetland. Major cities across the US, such as New York City  and San Francisco offer brochures about their constructed wetland programs and future masterplans.  It seems to me like this is a win-win water filtration strategy for everyone! And this information points to the extraordinary ability that constructed wetlands have in solving some of our most worrisome environmental issues. Stay tuned for some more blogs from Counting Cattails so that you may follow me in my journey here at ASWM.

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