Sometimes a wetland is built by humans, and sometimes it serves several functions. Such is the case along the southern border of Jasper county, outside the city of Monroe. A wetland complex was built by the highway department to satisfy a legal requirement, and yet it is functionally a treatment wetland, removing nutrients from a small stream.
Why would a highway department be compelled to build a wetland? Because a highway project (state route 163) destroyed wetlands. The Federal law (Section 404 of the Clean Water Act) requires “mitigation” of such an impact, and that usually—like here—requires new wetlands to be built to replace those that were lost.
Your tax dollars at work: surveying, planning, moving soil, installing water control structures, planting vegetation. Wetland basins straddle the highway, each essentially a small reservoir with water depth set by a concrete structure. Water from the creek flows through the system year-round, so the water depth is constant.
“But Paul,” you say. “A creek will have lots of water at times (perhaps in spring) and little or no water at others (late summer, maybe).” That is a typical scenario, but here the flow is augmented by the effluent (outflow) of the Monroe wastewater treatment plant located just upstream…a source of constant water flow, and nutrient-rich water at that. After all, even properly-treated sewage will most certainly have a lot of nitrogen and phosphorus.
And wetlands have organisms which use nutrients to grow. At this site, my students and I have measured the impressive results: wetlands clean the water of excess nutrients. This photo shows water treated with a chemical reagent using a standardized analytical method. More color = more nutrients reacting with the chemical reagent. In the photo below, guess which water was taken from upstream of the wetlands, and which taken downstream? And these results are quite consistent. We could quantify the change, and then consider what this system does…as a mitigation for a highway project, and to fight the excess nutrient pollutants causing eutrophication. Wetlands…at your service.