We then took a snapshot water sampling approach where not only did we sample our three main stream sites but we went upstream to a number of different watersheds such as Wilson, Tiffany, South Fork of Hay River, Hay River, and Red Cedar River. Also, we sampled several different impoundments such as Lake Chetek, and Rice Lake.
As we began to do our phosphorus analysis which tested for Soluble Reactive Phosphorus (SRP) and Total Phosphorus (TP), we began to notice a specific trend on where phosphorus spikes occurred and also where more studies needed to be made. It seemed that between upstream and downstream of cattle pastures where the cattle were able to wade in the stream in order to cool off or drink water. The phosphorus concentrations would often double and even in some cases be five times higher downstream than upstream of a cattle pasture. To help explain this, simply phosphorus is a cation which in turn attaches itself to the sediment rather than being washed through as we see nitrates do (anion). So when the cattle are within the stream kicking up sediment which is then being washed downstream, it allows the phosphorus to be released and later deposited in the lakes. This is also why we see large phosphorus spikes at stormflow due to high amounts of erosion and runoff. The lake is a very large pool of stagnant warm water that allows the algae to uptake the phosphorus and grow uncontrollably. Essentially impoundments are nothing more than a large petri dish where the algae is being fed large amounts of phosphorus.
1 Pound of Phosphorus can grow up to 500 pounds of Algae
After calculating the average discharge data and calculating how much phosphorus was entering the system a day. We found that Wilson Creek input up to 2.48 lbs/day (SRP) and 5.24 lbs/day (TP) from 6/26/14 to 7/30/14. Tiffany Creek input up to 3.22 lbs/day (SRP) and 13.87lbs/day (TP) from 7/1/14 to 7/30/14. These are two very small watersheds that are inputting quite a bit of phosphorus a day. More studies need to be done for the other larger watersheds as well.
One of the most interesting graphs we found was when we were trying to plot phosphorus concentrations in correlation to the stream stage. We had one very high phosphorus spike at baseflow which did not make any sense to us at all at first. However, after looking at the data and plotting temperature instead of the stream stage. We were able to see that the spike was on one of the hottest days within our time being in Menomonie. There was also a cattle pasture a half mile upstream. What we inferred is that possibly the cattle were wading in the stream that day in order to cool off and while doing so they kicked up large amounts of sediment and phosphorus that washed downstream.
There certainly needs to be more research conducted and this is only the beginning, it's honestly only a snapshot and the preliminary data of research that could truly help with the lake. Possibly putting in larger buffers to slow down erosion, possibly having incentives for putting up fences by the stream so cattle can't wade in the stream would also have an impact on how much sediment and phosphorus is being put into the system. It's up to everyone within the community to work together and to understand that every little change could possibly make the lake a little cleaner.