The Higgins Lake Foundation is funding an independent study of shoreline nutrient loading which is being conducted by Michigan State University. One of the goals of the study is to see if there is a link between subsurface nutrient delivery and snail populations, an important part of the swimmer’s itch life cycle.
The water quality of Higgins Lake is routinely measured by volunteers as part of the Cooperative Lakes Monitoring Program. However, these measurements are taken in the deepest sections of the lake and do not accurately represent the shallow shelf area. Measurements from the North Basin usually display relatively low nutrient levels (about 10ug/L Total Phosphorus). However, nutrient levels in the near-shore area of the lake are significantly higher.
The Michigan State University Hydrogeology lab is currently performing a study on the shelf region of Higgins Lake to look at the high levels of nutrients that have recently been found. The researchers are looking to see if high numbers of septic tanks influence water quality near shore, and as a result, increase the levels of Swimmer’s Itch incidence in Higgins Lake.
Preliminary water samples were collected in the summer of 2012. Throughout the summer of 2014, the MSU team will be taking measurements of snail populations, groundwater and surface water quality.
Swimmer’s Itch is caused by an allergic reaction to a parasitic infection. The lifecycle of this parasite involves both a snail host and an avian host (in particular the Common Merganser). Between these two hosts, the parasite floats in the water where it burrows into exposed human skin.
The snail host feeds on lake-bottom algae, which grows with high levels of nutrients and sunlight. The study being done by MSU is researching the abundance of snails to see if they are linked to high nutrient levels in near-shore water. The following background information is from the MSU Hydrogeology Lab:
Higgins Lake is Michigan’s 10th largest inland lake, and one of its deepest. Despite its long history of clean water, Higgins Lake is experiencing ecological changes in water quality, underwater vegetation, invasive species, and Swimmer’s Itch. Many of these changes impact the shallow region near shore, in the area called the shelf.
The area surrounding Higgins Lake includes two state parks, more than 1300 riparian landowners and thousands of residents and visitors. In 1996, a USGS study of Higgins Lake reported a link between residential density and lower water quality due to nutrient contamination. The majority of the shoreline of Higgins Lake is populated by septic-served homes. These septic systems may act as a major source of near-shore nutrient contamination, especially during high occupancy times, such as summer.
To determine if there is a relationship between Swimmer’s Itch and septic tanks, multiple water samples are needed. Samples will be collected during large storm events, after significant changes in residential population (related to holidays and seasonal occupancy), and other ecologically important events (ex. lake turnover).
At each site, snails will be collected to determine population densities relative to the shoreline features and water chemistry. This data will help us understand if snail populations respond to increased nutrients delivered through the groundwater, creating potential hotspots for snail populations, and therefore hotspots for snail parasites.