When is a wetland “done?”

DSC_0278People are building wetlands. As a legal requirement for mitigation of impacts (e.g., to replace wetlands destroyed by a highway project, as in Jasper County or Louisa County), or to provide habitat for waterfowl, or to clean the water, or…for money…we are now in the business of creating (or, re-creating) wetland ecosystems. I visited the 1330-acre (540 hectare) Owego Wetland complex in Woodbury County with my Aquatic Ecology class from the Iowa Lakeside Laboratory field station. The site lies in a floodplain and was previously farmed; it also contained the now-defunct town of Owego. By virtue of size, variety of habitats contained, and position, it is an important area for birds.  All of this beauty and ecological value exists in stark contrast to the considerable alterations to the land. The wetland project began 20 years ago (1998). The project naturally involved many workers across a variety of agencies (as indicated in the sign, pictured above).

DSC_0274We had a good visit, but my students still had a lot of questions afterwards. Much of the discussion centered around the topic of wetland creation or restoration. They wanted to know how we might go about creating an ecosystem, and when it might be “done,” i.e. more-or-less appearing and functioning as a wetland ecosystem should. These are profound questions! The community of wetland scientists have been working on this for years, and I can’t answer it definitively even now. But here are a few considerations…and pretty pictures, too.

First, naturally, is hydrology. For your “wetland” to have any chance of a system worthy of the name, you must have water! Different systems (fen, marsh, slough, bottomland forest) will have different depths and timing of standing water or of soil saturation. Our visit was to a deep area near one of the northern parking lots, and it appeared to have at least knee-deep water at least most of the time. Having appropriate hydrology such as this, is necessary for anything else to happen.

Within hours of flooding, the soil begins to change. Water drives out oxygen in the soil, and chemical changes proceed (remember so-called “redox” or oxidation-reduction reactions from a chemistry class?). Eventually the soil has changed such that a reduced form of sulfur is produced; human noses are quite sensitive to the “rotten egg” odor. We smelled this at Owego as we “mucked about,” disturbing the substrate. But other characteristics may not change so quickly: my students remarked at a difference beneath our feet. As we walked around the margin of the wetland, a thin layer of squishy and slimy organic materials was noticeable as we walked; yet beneath that was a surprisingly solid, mineral soil. That terra firma might have been compacted over years of working the land for farming, or during the construction of the wetland; but in any case, students noted that it did not have the soft texture that draws us in—literally, as we sink into soft mud—like in a natural wetland. So, soil texture (and perhaps, color characteristics and certain other chemistry) may take many years to develop.

DSC_0289And what about the life in the wetland? Microorganisms (bacteria, fungi, algae) no doubt float or blow in, rapidly growing within days of flooding the site. Insects move around widely, and will lay eggs in appropriate habitats not long after; we saw many adult dragonflies and damselflies in flight that day. The water will quickly be teeming with insect larvae; a few weeks later you’ll see the emerged adults. All of this can certainly happen in the first season, and draw waterfowl thereafter. Certain ducks strain the water for small food items, and as they move between wetlands they bring much seeds, eggs, and other species attached to their bodies…or passing through their bodies…to add to the biological diversity. And plants will find their way, too, in some cases literally blowing on the wind. We saw a healthy stand of Cattail (Typha) of course, and it will colonize almost any wetland (or roadside ditch, or any possible habitat) quite rapidly. Other plants may take longer to establish, such as the Spikerush (Eleocharis) or Arrowhead (Saggitaria) we saw on the edge of the wetland. It’s possible that these were intentionally introduced when this wetland was built, but it is also likely that at least some were present in the soil “seed bank,” because a memory of a wetland can linger in a spot, despite human disturbance.

DSC_0294Back on campus, we analyzed samples of soil and water, and thought about what they tell us. This was a good complement to a reading we discussed, examining wetland “success” and time to establishment in human-made wetlands in Illinois. It seems obvious to me that such systematic monitoring and analyses of built wetlands is the only way to know the state of the art, and “lessons learned” from our work. And yet, despite decades of such activity (including wetlands built as a legal requirement in the mitigation process), we don’t have the knowledge base we need, in my opinion. Surely we need to ask if a particular built wetland has water, plants (but not weeds), and is sufficiently large. Surprisingly, we can’t even assure those basic requirements in mitigation monitoring, because it just isn’t required in many cases. And beyond the basics, as a question of science and engineering, we need (but lack) an organized system to assess the development of wetlands and make corrections as needed to individual systems. And we need a way to consistently and routinely report back the lessons learned from the individual sites, to improve our technique.

During our discussion, students asked questions about “wetland health,” using an analogy to the human body. I challenged them to expand that thought. So a child of various ages is supposed to have certain anatomy, physiology, and behavior to be considered “healthy” (within certain percentage ranges, such as height or weight on a growth chart). The physician may make a diagnosis or suggest a change in the child’s routine if the various parameters are inappropriate. Now, what would the “growth chart” or “well-baby checkup” checklist for a wetland include? What diagnostic techniques would we use to check against the list? Who will be the “wetland healthcare professional” and when will they perform the “examination?” Answering such questions is important, and we do have some techniques being developed to do this work. I hope we can continue that work, and make sure our wetlands are “done,” ecologically. Perhaps some of my students will see this through…

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Author: Paul Weihe

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

2 thoughts on “When is a wetland “done?””

  1. If “done” means the recreated wetland is similar in composition and function to the natural one “that should have been there”, then they are probably never done. There are papers reporting on studies that compare restored wetlands to natural ones. I did such a study about 10 years ago. The take home was, with regard to plants, the restored ones were not very similar (missing many species, and therefore some function) to the native wetlands. We had a range of restored sites between 1 and 10 years old, and the data showed that they did not improve or become more like natural wetlands over that 10 year time span. Certainly the restored wetlands provided for some of the function of natural ones, in particular as bird and herp habitat. But with respect to plants, we cannot create a wetland that fully replaces native ones. Same goes for prairie. Most important lesson — all remnants need to be protected and saved.

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  2. Tom Rosburg said it very well. I’ll add that at an Illinois wetland-mitigation conference I attended years ago, the speakers pointed out that the most problematic wetlands, meaning “we already know we can’t possibly mitigate the loss of these,” were the shallow “special hydrology” groundwater-driven wetlands like sedge meadows and fens. Anyone who has seen a stretch of blooming Grass of Parnassus flowers can understand that.

    At that time, and probably still, the way those special wetlands were being “mitigated” was by trading quality for quantity. In other words, if a good three-acre sedge meadow was being destroyed, the mitigation agency would require a much bigger mitigation wetland, maybe eight acres. But as the speakers also pointed out, the new mitigation wetland usually ended up being, at that time, a cattail-dominated open-water wetland, even if the mitigation project builders attempted some kind of sedge meadow or fen (and in many cases, no such effort was made). I’m guessing that in spite of subsequent improvements in wetland restoration methodology, that is still fundamentally true.

    There has been more of a shift toward mitigation banking since that conference, because it was becoming increasingly clear back then that most small isolated urban/suburban wetland-mitigation wetlands were not working well. (We conference attendees saw a slide show of bad mitigation “wetlands” in the Chicago metro area, and it was both hilarious and infuriating. Some of them were steep, deep, and bone-dry.

    But there was, and probably still is, discussion of a fundamental dilemma. If the best sites for functional mitigation banks are some distance from the site of the wetland destruction, usually meaning that the bank sites are rural and the destruction sites are on the developing edges of towns and cities, is it okay to allow mitigation many miles outside the destruction-area zone? Or do we need to try to replace destroyed wetlands with new wetlands in the same area, even if we already know that the new wetlands will not be very good wetlands?

    Aldo Leopold was eloquent as usual. “When the logic of history hungers for bread and we hand out a stone, we are at pains to explain how much the stone resembles bread.” Thank you, Paul and Tom, for educating students who will always know the difference between stone and bread.

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