Some days, I sort of can’t believe they pay me to do this job. Take for example, the day last week when my BIO 345 (Limnology) class made the forest floor down near the river all sparkly—all in the name of Science, of course!
It all starts with the flow of the river. If you’ve ever looked at an Iowa river when it is swollen, you’ve probably noticed that it is the color and clarity of chocolate pudding. That appearance is the result of the sediment load: the eroded soil washed from the land surface and into the river, then carried downstream.
If the river is high enough, it reaches flood stage, and spills over its banks, covering all those adjacent low areas. In a place like the South Skunk Area near Reasnor in Jasper County, the river flows through a broad, flat valley known as a floodplain. High-water events regularly submerge the floodplain adjacent to the river; all that muddy water spills onto those bottomlands, depositing sediments. In a previous post about Sny Magill in extreme northeast Iowa, I described how the Mississippi River there is gradually obscuring ancient burial mounds with muddy, river-deposited sediments. Would a similar process of sediment deposition occur here, too? There’s a way to measure the deposition process. It starts by establishing a plot (quadrat) of a standard size, in a known location on the floodplain. We used a Half-square-meter (roughly half-square-yard) plot.
Knowing and documenting the exact location is crucial, since that’s where sampling must occur in future years. I told the students they could expect a call from me at some point in the future, when my aged, half-senile self needs help finding the spot again. They laughed—little did they know, I wasn’t joking! Ah, but who knows what the future holds?
Actually, I’m pretty sure the future will bring more floods to the South Skunk Area floodplain. Those floodwaters will carry sediments, depositing them on the existing soil surface as the water recedes or evaporates. But in this one little rectangle, the sediments will come to rest on a layer of glitter. The students sprinkled this marker (horizon layer) of durable-yet-non-toxic glitter, to be observed within soil cores collected in future years.
What will they find? Will the rate of sedimentation slow in coming years, as farmers continue to adopt reduced or conservation tillage, keeping the soil on their fields? Will construction associated with urbanization in areas upstream, disturb soils and send them our way? Will the flow dynamics of the stream itself change, and how would that affect sediment load and deposition? I don’t really know, but I like to think our little glittery time capsule will be a tool to teach future students—mine or my successors—about floodplain wetland dynamics.
Stay sparkly, wetland friends!