Yahara River and Lake Monona Subwatershed

 Currently, I live on State Street in downtown Madison, Wisconsin. My residence resides in the Yahara River Watershed, but more specifically, it is within the bounds of the Yahara River and Lake Monona Subwatershed. A variety of issues have arisen in this watershed, including ecological problems with surface water and groundwater. 

Highlighted in Yellow is the Yahara River and Lake Monona Subwatershed

(Source = Google Maps)

One issue in my current subwatershed is the contamination of groundwater. Polyfluoroalkyl substances (PFAS) have been found in the groundwater wells surrounding Lake Monona. PFAS are found in various manufactured items, such as fire-extinguishing foam and chrome plating. PFAS are not naturally occurring compounds, in fact, they are only in existence due to human synthesis. PFAS are extremely toxic to humans and wildlife in low concentrations. In humans specifically, excessive PFAS exposure may lead to developmental defects in children, complications with pregnancy in females, and kidney cancers (1). Personally, I would like to have children when I am older and knowing that there are chemicals in my watershed currently, that may pose health risks to children makes me consider moving somewhere else when I decide to have a child.

The picture above is the chemical structure of a PFA. These chemicals are not biodegradable.

(Source = Wikipedia)

In terms of surface water issues in the Yahara and Lake Monona Subwatershed, cultural eutrophication is a significant issue for Lake Monona in particular. According to the Wisconsin DNR, Lake Monona has both phosphorus and nitrogen concentrations well above the threshold for a eutrophic lake (2). I have been to Lake Monona many times in the past few years and I have seen blue-green algae blooms occasionally in the summer months. Lake Monona has closed at increasing rates due to blue-green algae (cyanobacteria) blooms, which pose a threat to human health. 

Beach Closures Due to Cyanobacteria and E. coli

(Source = cleanlakesalliance.org)

Reasons for this cultural eutrophication vary. Some of the excess phosphorus and nitrates entering Lake Monona are due to urban runoff and point source manufacturing pollution. Madison is an urban city, so some pollution from the city is expected, especially considering Lake Monona is bordering the downtown area. Another, likely more major, the reason for nutrient runoff entering Lake Monona is agriculture. Currently, many farmers use solubilized phosphorus fertilizers in areas surrounding Madison. These chemicals runoff into the Yahara River, which feeds Lake Monona. Solubilized phosphorus is readily taken up by algae, like blue-green algae (2).  Nutrient runoff is currently being managed by clearing leaves within the city before they reach the lake and a coalition of farmers, called the Yahara Pride Farmers, have pledged to reduce their phosphorus use in their fields (3).

The introduction of the invasive spiny water flea may also be a reason why blue-green algae blooms have gotten more frequent in the summers on Lake Monona. The spiny water flea was first discovered in 2009 in Lake Monona's waters (4). This invasive species eats the native species of zooplankton that feed on algae in the lake. With diminishing numbers of zooplankton unable to feed on algae, algal numbers will increase annually, in theory. Currently, there are no known control methods to stop or mitigate the effects of the spiny water flea once it is introduced into an ecosystem. Chemical controls to kill spiny water fleas can not distinguish the invaders from natives, so they are ineffective (5). No fish in Lake Monona are able to eat this invasive due to its long, spiny tail. 

The notorious invader, the spiny water flea. Note its extremely small size and long, spiny tail.

(Source = Outdoor Life)

Sources:

1. https://www.epa.gov/pfas/our-current-understanding-human-health-and-environmental-risks-pfas

2. https://dnr.wi.gov/lakes/grants/largereports/mononabaygrant.pdf

3. https://blog.limnology.wisc.edu/2020/04/29/learn-your-lakes-spring-runoff-and-nutrient-loading/

4. https://dnr.wi.gov/lakes/invasives/AISDetail.aspx?roiseq=33549285

5. https://www.michigan.gov/-/media/Project/Websites/invasives/Documents/Response/Status/egle-ais-bythotrephes-longimanus.pdf?rev=0ddc4f4752374ac6bc06f78ec5362ba3