The Bog That Wasn’t

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A Depression-era shelter, built by the Civilian Conservation Corps, overlooks Dead Man’s Lake. The Corps also built an observation tower nearby.

I was pretty excited to hear about Iowa’s only bog, noted as an important feature at Dead Man’s Lake at Pilot Knob State Park in Hancock County. Bogs are an amazing type of wetland, with interesting biota and water chemistry. The cool climate in northern Iowa, the lake formed by a glacier and situated in a sort of bowl raised above the surrounding land, and reports of a floating peat mat on the lake were all intriguing. But the big draw was an iconic bog species, the carnivorous plant Round-leaved Sundew (Drosera rotundifolia). This is the only spot in Iowa to find this “animal-eating plant,” and I wanted to see it!

So, several years ago, I took my Aquatic Ecology students from Iowa Lakeside Laboratory to the site. We braved the difficult crossing of the lake margin to get onto the floating (quaking!!) peat mat, and after a short search found the plant. I went back the following year with that class, and again we found Sundew. Then last year (2017) we saw no sign of the plant. And…what about this year??

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We roamed about freely on the peat mat, searching for the elusive Sundew…

We spent considerable time searching, but without success. The students and I had a great conversation about why we didn’t find the plant, with one possibility being that the plant was not yet out and about for the year (winter had hung on late in northern Iowa this year). We speculated about whether we would find the plant if we visited later, or whether the plant was now simply missing from the site (a disappointing development if true!).

What we did find was the bog-like peat, a buildup of dead, undecomposed plants such as Sphagnum moss accumulated over many years. (Earlier measurement of a mat 3-meters thick would take about 2,000 years to accumulate at typical rates). On the mat we found, growing out of the moss, a dense collection of sedges, cattails, ferns, and wildflowers. Scattered, stunted small trees gamely tried to grow on the unstable substrate. That peat mat not only offers no soil, and bounces like a waterbed, it is saturated with water of unusual properties.

 

 

Let’s start with the color…rather like iced tea, a cloudy brown. This is typical of water in a bog, darkened by tannins leached from the peat. And despite a sunny, uncomfortably hot day, the water was also iced-tea cold: a mere 1 meter (3.3 feet) down, the water was a chilly 10 degrees Celsius (50 F). Also, as might be expected in a bog, the water was acidic: pH values ranged among the different samples but averaged 5.426. Specific conductivity (ability to conduct electricity) was 76 micro Siemens, much less than at many fens I’ve encountered.

“But Paul,” you say. “Are all these observations consistent with a fen, or a bog? How are they distinguished, anyway?” Those are more complicated questions than might be supposed at first! But really, is it any surprise that categorizing various types of wetland ecosystems might be challenging? Deciding what set of attributes define a particular biological species makes taxonomists engage in fisticuffs. Drawing a line around a wetland ecosystem is a complex process, requiring a lengthy manual and specialized training. Just the catalog of different wetland ecosystems, the widely regarded Cowardin et al (1979) publication “Classification of Wetlands and Deepwater Habitats of the United States,” is 142 pages long (!). So, yes, this is a complicated question.

Given the caveat that reasonable scientists could see things differently, I’ll say that by most definitions, this site would be called a fen, not a bog.  Both types of wetland build up peat. Both are perennially wet. Chemistry can vary over quite a range in each system, but we are more comfortably within the range of fen than bog. Surely, bogs are acidic (low pH), but fens can be acidic too. I suspect low nitrogen concentration in the water—hence the need for a plant to “eat” animals as a source of nitrogen—but this can be true in a “poor fen.”

Further study of the hydrology, in particular a water budget to estimate how much water comes from the sky as opposed to groundwater, would be helpful. I’d like more tests on the water chemistry as well. I hinted to my students that this work would make a EXCELLENT Master’s Thesis (not sure any of them will rush to do the work, but a guy can hope!). Bog or fen, this is a curious and fascinating wetland, and beautiful too. Don’t get bogged down in the details of ecosystem classification, or offended by what I choose to call it. Just call it one of our 99 wonderful Iowa wetlands, and thanks for visiting with me.

*EDIT: the “Blue Flag Iris” in the photo below is identified as Iris versicolor. That common name is also used for a related species, I. virginica. A sharp-eyed reader pointed out the similarity, and provided a link to a web page describing the two species…might have a look!

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Blue Flag Iris (Iris versicolor*), a most photogenic plant

Author: Paul Weihe

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

9 thoughts on “The Bog That Wasn’t”

  1. Thank you for explaining why the bog-or-fen question is not simple. I feel better now:-). And measuring water chemistry in the field sounds like a lot more fun than what some of us were required to do in the chem lab long ago. I have the impression that college field ecology classes have been getting better and better.

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    1. My pleasure Cindy! It’s funny how it can be difficult to get specific criteria…and of course, no one make force one to accept another’s pronouncement! And no doubt, the chemistry is just a lot easier with advances in instrumentation.

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  2. The bog vs fen debate is difficult. There is also another wetland type – the wet seep — that adds to the confusion. There seems to be a certain amount of history that gets wrapped up in the distinction as well as European tradition. Years ago I did a research project on Iowa fens, and visited many fens across northern Iowa. I have also visited my bogs in the north country, as well as what I think are bogs in Iowa. (Deadman’s Lake is not the only bog in Iowa).

    My view is that hydrology should be the only criteria used to make the distinction. The pH and plants provide additional insight, but in the end it is the hydrology that is important. Like all wetlands (and other water features) both have a connection to the water table. The difference in my mind is that fens obtain all their wetness from an aquifer that produces positive hydrostatic pressure. Ground water from an aquifer exits at the surface of a slope (usually), and builds up peat over time. The hydrostatic pressure forces water up through the peat which adds depth to the peat and creates a “mound”. Some fens have over 10 feet of mounded peat.

    Bogs form in basins mainly from precipitation and surface runoff that collects in the basin. There is no positive hydrostatic groundwater. Bogs form in associations with lakes, often along their margins or in bays that are more shallow. Wetland plant growth slowly fills in the shallow water with peat. Bogs can be dangerous where the bog and lake merge. The peat layer thins and it is possible to “fall” through the peat. That happened to me and a student at Deadman’s Lake when we hiked near the eastern edge of the bog where it grades into the lake/marsh at the far east end of the basin.

    To me, the basin and hydrology at Deadman’s Lake, as well as the sphagnum, the sundew, and the plant community in general say that it is a bog, and not a poor fen.

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    1. Thanks Tom for this additional information. My PhD advisor’s adage is that “the three most important determinants of wetland function are hydrology, hydrology, and hydrology.” The placement in that bowl-like basin certainly makes me wonder about it, as you suggest…

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  3. Hoping to explore this summer for the sundew. Reading an 1955 article where the author called it a bog. Neither here or there for me. Just hope to find the plant! Would love to hear more from you if you go back. Katie Byerly, Mason City

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    1. Hi Katie! Thanks for sharing that. I will teach at Lakeside Lab again this year, and plan to visit the site again. Too amazing a place to pass up…and maybe just maybe will see the plant…

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