Cyanobacterial blooms of blue-green algae plague the lakes near Menomonie each summer. I was awarded the opportunity to come to Wisconsin to participate in research to combat this problem as part of the LAKES REU program.
My research project primarily looked at the impact of the Red Cedar and Hay Rivers on Tainter Lake and the development of cyanobacterial blooms. I found that as river flow increases, there is also an increase in total phosphorus to the lake as well as soluble reactive phosphorus — the type that is most readily available for cyanobacteria to use to grow. While all phosphorus causes blooms, soluble reactive phosphorus should be a target for remediation strategies.
Goes with the flow
So how does soluble reactive phosphorus increase with river flow? To understand the answer you have to look at what is going on physically within the river when a major precipitation event occurs. Most of the time, the rivers are in a low flow state, and little phosphorus enters the system.
When a storm hits hard and water begins to run off the surface of the surrounding land, the river’s volume increases greatly. Impenetrable surfaces such as tilled farm fields and paved areas are particularly susceptible to surface runoff. This is how major storms that occur throughout the summer months can cause enormous amounts of phosphorus to enter the lake.
Storms make the water travel quickly and even violently, including the water at the bottom of the river. As the river volume increases, the stream bed churns, causing phosphorus to re-suspend and dissolve into the water. This increase in soluble reactive phosphorus increases the algae “food” and prepares the next round of algae to multiply. Later in summer months this build-up of phosphorus and algae becomes too great to manage by occasional rain and the smelly, green lake is there to stay until cooler weather comes.
So how do we best approach this problem? My findings suggest that the best way to reduce soluble phosphorus in the rivers and lakes is to better manage land in the Red Cedar Watershed. Best management practices for farmlands, as well as dam and lake management, will be key areas to explore for ways to reduce phosphorus from the watershed’s system of streams, rivers and lakes.
The goal to ultimately reduce, delay, or eliminate the algal bloom is widely desired, but all people will have to work together to meet this goal. By gaining a better understanding of the problem, mitigation strategies can be tailored to best meet the needs of the Red Cedar Watershed and Tainter and Menomin Lakes.