Potamogeton crispus Interrelationships with Ecosystem Metabolism: An Aquatic Plant Survey of Lake Menomin

Abstract

Preserving the quality of Lake Menomin is a shared concern that unites every resident.

When we think about the causes of the blue-green water Lake Menomin is known for, the first that come to mind are farm runoff, septic tanks, or lawn fertilizers. But what if there was a contributing factor already present in the lake? Potamogeton crispus, an invasive species known as curly leaf pondweed, has been a restricted species in Wisconsin since 2009 due to its ability to survive and thrive in a variety of conditions. This invader can outcompete native species and form dense mats that eventually store and then deposit phosphorus as they deteriorate with age. This leads to excessive nutrient loads in a body of water which can, in turn, create dead zones or harmful algal blooms. Is it possible that the invader P. crispus has an additional effect on the already EPA-designated impaired Lake Menonomin?

A Survey of Lake Menomin

We conducted a plant and water survey to estimate the amount and number of different species throughout Lake Menomin. From the plant samples we collected, we were able to identify ecosystem composition and how prevalent P. crispus was. Ultimately, P. crispus made up only 15% of the plants collected from sample sites, with sites having an unexpected diversity of native plants. In short, while P. crispus may be an effective invader across Wisconsin, native plants are still be able to compete at a small scale within Lake Menomin.

We also measured disolved oxygen, temperature, and light levels at multiple locations. This data allows us to assess the amount of photosynthesis and respiration happening at each site, which is referred to as “gross primary productivity” or GPP. While we did find a moderate correlation between GPP and total biomass, we did not find a relationship between the presence of P. crispus and GPP. This indicates that while P. crispus is present in Lake Menomin, it was not seen to be an aggressive invader at the recorded sites. This data further supports the idea that native species are likely able to compete with this invader, even in nutrient rich environments. However, because we were only able to sample a limited number of sites, it is possible that P. crispus is dominant in other locations. Thus a large-scale plant survey for the lake is still needed as this is vital to understaning how the lake has responded to increasingly nutrient-rich conditions and how it will evolve over time.

While confronting the challenges of eutrophication and invasive species, our newfound knowledge of native biodiversity equips us with hope to move forward. Through continued research, our shared concern for Lake Menomin empowers us to understand the developing intricacies of the disturbed ecosystem. With each summer research cohort, we gain new perspectives on preserving the health and vibrancy of this water body.