The Wetland as Traffic Cop

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entrance near the south end of the marsh, along Hwy 110. Note the wood duck housing complex.

Last week, we visited the Twin Lakes in Calhoun County. We saw how a wetland adjacent to South Twin Lake sits at the base of a slope, catching silt, sediments, nutrients, and other substances in runoff. Wetlands naturally “clean the water,” as we have discussed many times. This week, let’s expand that idea a bit.

Little Storm Lake in Buena Vista county is not really a lake at all: it is a wetland adjacent to the northwest edge of Storm Lake, an actual (shallow glacial) lake. It’s a great place to think about a wetland “cleaning the water.”

In my Limnology class, I sometimes ask students to think of a lake as a giant container of water in which chemical reactions happen. Much like the glassware holding aqueous (watery) solutions in their chemistry classes, a lake will be affected by light and heat energy, circulation (that is, mixing), atmospheric pressure, and other inputs to the system from outside. Reactions in the water will depend on pH, dissolved gasses, and the activity of organisms. Particular chemical reactions all occur (or not) in that context. This “lake as a big glass beaker” mental image is then kept in mind as we discuss specific chemical parameters and reactions.

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access road leads in to water control structures, and forms a berm or dike

Then again, a wetland (like Little Storm Lake) is perhaps like a chemist, adjusting the characteristics of water entering the lake. It’s often said that a wetland “cleans the water,” but truly a wetland transforms chemicals in the water in ways we categorize as “cleansing.” For example, silts and sediments settle out of the muddy water, depositing (and slowly filling) the wetland; the water leaves the wetland “cleaner.” Phosphorus sorbs (adheres to) the silts and sediments, and so are removed from the water as well. Nitrogen is transferred from water to air, by an entirely different process—denitrification—and we’ll consider that next week. These are all examples of the “wetland as chemist.”

Little Storm Lake is a natural marsh, but it was recently extensively modified to move beyond that role as “chemist,” into a role as “Traffic Cop.” Much like a public safety officer directing vehicles safely and efficiently on roadways, this wetland is now equipped to direct the flow of water safely and efficiently. Let’s have a look!

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dueling water control gates

About eight years ago, the DNR partnered with the local lake association, non-profit groups, university staff and others to undertake a large wetland restoration (more correctly, engineering enhancement) and lake protection project. This Storm Lake page describes the project, and a DNR lake restoration white paper has more details (starting on page 17). The basic idea is this: construct walls (dikes), and channels or culverts (plumbing) store and move water as desired; they prohibit fish movement (ideally, keeping nuisance species like carp under control); and workers periodically dredge out the accumulating silts and sediments.

If a wetland like Little Storm Lake exemplifies the slogan “Better Living Through Chemistry” by the transformations cleaning the water, then this project now adds “Better Living Through Plumbing.” Water in this wetland can be adjusted to appropriately process high flows, normal flows, or even to drain the system of water. Drying out a wetland seems counterproductive, but an occasional decrease in water depth and even emptying (“drawdown”) encourages seed germination, facilitates maintenance, and kills off undesirable aquatic species. If the wetland (and adjacent lake) function is determined mainly through water dynamics, then this project provides a powerful tool.

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Probably a pumping station, although it also reminds me of a nuclear reactor. Cordoned off, so I couldn’t examine it well enough to know which.

Furthermore…let’s be honest: Iowa’s streams and rivers, such as the one flowing into this wetland (Powell Creek), carry a heavy load of runoff…and everything runoff brings. Wetlands are helpful—perhaps critical—in protecting our water quality. It’s a theme we’re considering in these weeks, with wetlands from three counties and an upcoming essay considering the challenge we face regarding Nitrogen in particular. I wish to address the news reports and controversy, and ask if wetlands might just help us solve the problem. Please come back in the coming weeks for that discussion.

In the meantime, if you’re near Storm Lake, check out the marsh. On the north side, near the intersection of state highways 7 and 110, you’ll find the Little Lake Discovery Boardwalk. Informational signs adorn a floating walkway among the cattail, and a tall tower provides a stunning view (complete with free telescope!). Admire the flora and fauna and another hard-working wetland…”at your service.”

 

 

Author: Paul Weihe

Associate Professor of Biology at Central College, traditional author (Textbook of Limnology, Cole & Weihe, 5th ed.; Waveland Press), and now...blogger!

3 thoughts on “The Wetland as Traffic Cop”

  1. My spouse and I are the fortunate owners of a small “traffic-cop” prairie/wetland complex designed by the NRCS. That complex hosts a wonderful diversity of wildlife (yay sandhill cranes!) The wetlands also work to reduce the nutrient pollution flowing into the nearby officially-impaired South Skunk River, which needs all the help it can get.

    To continue the very interesting good metaphor above, however, traffic cops cannot fairly be expected to solve traffic anarchy. In a situation where traffic laws are non-existent or mostly ignored, the cops can end up so stressed that they suffer significantly themselves.

    Many if not most rural Iowa traffic-cop wetlands, including ours, are dealing with large amounts of nutrient pollution from surrounding rowcropped land that could be greatly reduced if that land had cover crops and adequate grassed waterways, or at the very least, no-till. Those conservation methods would also improve soil health, and Iowa’s degraded rowcropped soils also need all the help they can get.

    Two of my downstream neighbors, both natural-area professionals, tell me that the creek that runs from our land through their land has been much clearer and healthier since our land was converted to prairie and wetlands. It would be nice if our wetlands could also enjoy the benefits of better upstream conservation. With cover crops and better grassed waterways upstream, our biggest wetland would not be so overloaded with algae in the summer. And it could do a more effective job of helping the Skunk.

    We do need many more traffic-cop wetlands in Iowa. But we also need either good traffic laws or a vast majority of drivers who drive as if good traffic laws exist.

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    1. Thanks for another thoughtful post. I especially appreciate hearing about your own experiences! Iowa is fortunate to have good stewards like you…and we could use a few more…

      Like

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