About a month ago, a frack-sand mining operation near Grantsburg, WI, spilled some fine-grained sediment from a settling pond into a tributary of the St. Croix River. Local news media covered the story, and more details, for example, can be found in the Pioneer Press story by Dennis Lien.
So what’s the big deal?
Well, there are standards regarding water turbidity, which means that as a society we’ve decided that we don’t like cloudy water, at least in some settings and at some levels. For a naturally clear-water system like the St. Croix, increasing turbidity would alter the food chain at all levels. Algal primary producers rely on sunlight blocked by turbidity. Sight-based predation at the top of the food change would be altered. Benthic (bottom-dwelling) organisms that depend on coarse substrates could be smothered by siltation. Especially in the St. Croix, one of the last refugia for freshwater endangered mussel species, we must be on guard against too much fine sediment. And finally, where does the sediment end up? It’s filling up not only man-made reservoirs but also treasured natural lakes, iconically Lake St. Croix and Lake Pepin. These lakes are filling in with fine-grained sediment at about 3X and 10X their natural rates, respectively. (How do we know? See work done by the Museum’s St. Croix Watershed Research Station.)
Hey, it’s only a little bit...
Or was it? How much is a little? A little here, a little there, and a little more from over there -- it starts to add up. All water in a watershed runs downhill to the river, efficiently carrying both particles and dissolved materials. The river ultimately sees it all: all the disturbances, however seemingly minor, throughout the watershed. Rivers die a death of a thousand cuts. We have enough difficulty trying to control nonpoint sources of sediment and other pollutants. Stopping discharge of fine-grained materials from a mining operation is eminently fixable. It’s the right thing to do. Fortunately, all parties seem in agreement on this, including the mining company, which has repaired its leaky dike.