There is a place just outside of Colfax, WI, off of highway 40, where a person can put on some waders, step into a stream, and imagine that they are a pioneer exploring their way through new territory. I have been to this place where the silt grabbed at my feet and the water flirted dangerously close to the tops of my waders. Eighteen Mile Creek is beautiful. It looks pristine as it rustles softly over the rocks at its bottom, but this creek has a secret that it shares with many other streams and rivers in the Red Cedar Watershed. It is absolutely full of P.
P is the symbol for the element phosphorus which is a widely used additive to agricultural fields because it is an essential nutrient for plant growth. It is only present in the earth as nonrenewable mineral deposits which must be mined and manufactured into fertilizers. Once P is applied to the field approximately 80 to 85% of it is immobilized by a reaction with Ca, Fe, or Al ions present in the soil making that P unavailable to plants.
After application P can be mobilized through surface flow, which is one of the main ways P moves from agricultural systems to surface water. A major source of surface flow is row crops due to the large amount of bare soil that is exposed for a majority of the year. Insoluble P is bound to eroded soil particles. When rain falls on bare soil it detaches soil particles and causes additional erosion via runoff. Both runoff water and soil are unavailable to plants. While not readily available to most organisms, insoluble P can become a long-term source of soluble P once it has entered aquatic systems.
Unlike many other nutrients essential to plant life that have an atmospheric pathway as part of their biogeochemical cycle, the phosphorus cycle is strictly geologic in nature. Once P has found its way into a system it is very hard for the system to balance it out. In aquatic environments the element phosphorus is often a limiting factor to plant growth. However, in the Red Cedar Watershed P has become abundant. This has led to ongoing water quality issues like algal and cyanobacterial blooms that pose hazards to both human health and ecosystem integrity.
The LAKES REU biology team analyzed stream sediment from Wilson and Eighteen Mile Creeks to determine its composition and viability for different reclamation measures focusing on phosphorus as well as potassium, soluble salts, and regulated heavy metal content. We found that the levels of heavy metals were well below the ceiling limits set by the EPA. This indicates that sediment collected from the Red Cedar Watershed could be safely applied to land as a soil additive. Monitoring of all the heavy metals found within the sediment would have to be done each time it is pulled from the stream for the purpose of a nutrient additive, including mercury which was not done in our study. The sediment in both streams was found to have sufficient amounts of soluble P for corn growth. This indicates that the stream sediments could be used as a fertilizer and replace traditional sources of P.
Halfway down the stream I wanted to stop wading. It was too deep. The mud was too sticky. The bottom of the stream was so stirred up I did not know where I was putting my feet. My next step could lead to slipping, sticking, or topping my waders. I watched my teammates forging ahead, one fearless and the other one slow and deliberate. Did they make mistakes? Yes. A number of times I watched them slip, backtrack, get stuck in the mud, and even top their waders. They kept going and so did I. In the end we got all of our samples. Taking sediment from the streams is a mitigation strategy. It would allow us to stop inputting new phosphorus into our waterways. It would help prevent the problem from getting worse. It has been done in other watersheds just like fish exclusions, common carp fishing, constructed wetlands, floating islands, sediment traps, and dredging. What other watersheds have done are paths we could follow.
We have a choice. We can either stand uncertain and stuck in the mud or we can begin wading forward. We know what waits for us if we stand still. The deceptively clear water of our streams turns green and smelly when it flows into our lakes every summer. If we begin wading forward, trying out different mitigation strategies, we might get wet or even stuck in the mud but at the end of our stream we might find a clear lake, shimmering in the sun. Wouldn’t that be worth a muddy, water logged pair of waders?