At the Floyd River Wildlife Complex A in Sioux County, at the junction of highway and river, I found signs of Ecological (Trophic) Production. I’ll use this wetland to encourage professional networking; we’ll ponder this solar-powered planet of ours; and I’ll talk about highway projects. And away we go!
I heard about this wetland from my friend and colleague Todd who lives not far from the site. Also, I know a bit about projects such as this from other colleagues, including several who studied a bunch of them (more on that later). As I have suggested in other posts about my journey around Iowa, personal recommendations—and hearing the stories behind the wetlands—is really helpful. Please join the conversation!
This wetland is located along the Floyd River, but is also adjacent to State Route 60. In fact, the wetland was built by the state highway department as mitigation for impacts to existing wetlands during highway construction projects. As I described in posts about Brush Creek and Indian Slough, the Federal law protecting wetlands (Section 404 of the Clean Water Act) allows for permission to “mitigate” impacts through a legal contract. In this case, the state highway department was required by law to build this wetland. Would you like to build a wetland, too? Here’s a piece of advice: make sure to provide water. One possible source of water is an adjacent river, if available. A notch in the riverbank provides a hydrologic connection to the Floyd River.
In Iowa, your river water will almost certainly contain nutrients like nitrates, and they will act as a fertilizer for the plants and algae in your wetland. (They will also contribute to microbial processes like denitrification, but that’s another story). Generally, plant growth is slow and steady, imperceptible and relentless. We might find it difficult to visualize the photosynthesis and resulting production of plant biomass; we might even forget about this most basic energy conversion process. That’s unfortunate, because essentially all life on Earth is powered by the Sun, as plants and algae convert radiant energy (light) to biological energy (food) by photosynthesis.
One way to estimate this energy conversion of photosynthesis is to cut down plants, burn them, and measure the heat energy given off during combustion. It is however an indirect measure, since you can’t harvest and measure lost energy, such as is used in the plant’s own metabolism. Think of overall photosynthesis as Gross pay in a worker’s earnings, compared to the Net (“take-home”) pay of standing crop (biomass harvested). Ecologists estimate gross primary production (GPP) and net primary production (NPP) in ecosystem studies such as “trophic-dynamics.” Wouldn’t it be nice to directly observe the photosynthesis itself?
Actually, you may have observed, and even quantified, photosynthesis yourself…as a child in school. A common (and fun) way to study photosynthesis is using an aquatic plant like Waterweed (Elodea) in a tank or test tube, watching bubbles formed by the plant as it photosynthesizes; those bubbles are oxygen, a byproduct of photosynthesis. Want to know the effects of fertilizer, temperature, light color or intensity, or some other variable on photosynthesis? Count bubbles!
At Floyd River, I observed floating filamentous algae with trapped bubbles forming in the bright sun. Photosynthesis! Primary Production! A wetland with a green, active solar-energy-conversion system! Actually, certain wetlands are among the world’s most productive ecosystems. Plenty of water, nutrients, and off we go. And that serves as the base of a food chain, with plant-eating grazers, herbivore-eating carnivores, and sometimes additional levels beyond. I observed snails, backswimmers, tadpoles, small fish, and waterfowl. The wetland teemed with life, and the water spread around a bend along the river. A productive wetland.
The time frame required for wetland development, the criteria we should use to measure mitigation success, and who will be keeping score of those parameters are important considerations. A decade ago, a team of Iowa scientists compared highway mitigation wetlands with natural reference wetlands, and found similar ecological performance in both types of wetlands. I suggest caution in generalizing beyond that one study. In particular, I worry that wetlands built by others, for other purposes, may not have as high quality of design nor construction, as those built by the Highway Department. I strongly suspect that the highway wetlands had at least some monitoring and active management, while I worry that many mitigation wetlands are built and abandoned to their own devices..which seldom ends well.
Floyd River appears productive and functional. Can all of our wetland projects achieve this status? Perhaps we can, and should, inspect our constructed wetlands, and expect them to perform to “engineering standards.” What would you like in a constructed or restored wetland? Consider leaving a comment. Thanks for reading…