Sportsmen’s Club Investigates Source of Lake Vermilion Calcium

To better understand Lake Vermilion’s risk for zebra mussels, the Sportsmen’s Club of Lake Vermilion (SCLV) and its partners have begun a systematic search for the source of the moderately high calcium concentration in East Two River, one of five rivers flowing into Lake Vermilion’s east basin. Zebra mussels, a very destructive aquatic invasive species, require a moderate or high calcium level for shell growth.

“During routine water sample collection this spring, our lake association volunteers found calcium levels around 25-30 milligrams/liter in East Two River above the Tower Harbor,” said Wayne Suoja, SCLV board member and water quality leader. “Subsequent samples in the same area and further downstream confirmed those levels.”

Since no historical calcium data are available, the Sportsmen’s Club does not know whether these levels are new or long-standing.

The East Two River calcium level is worrisome, because it is well above the 15 mg/l threshold for zebra mussel larvae survival to adulthood and also above the 20-25 mg/l threshold for a reproducing adult population.

Northeastern Minnesota lakes and rivers generally have low calcium levels. Limestone from ancient sea beds, a major source of surface water calcium, was carried south during the last glacial period, leaving low-calcium bedrock at the surface.

Historically, Lake Vermilion’s highest calcium levels are about 13 mg/l in the east basin, with concentrations gradually falling off from east to west. These calcium concentrations and Vermilion’s alkalinity and pH are all below the range for a viable population of zebra mussels.

The Sportsmen’s Club is partnering with the Lake County and North St Louis County Soil and Water Conservation Districts to conduct the search. Derrick Passe, Lake County SWCD Rainy River Coordinator, is overseeing the calcium water sample collection effort. MPCA and SWCD personnel are able to collect many of the additional calcium samples while they are at traditional river and lake testing locations conducting other water chemistry monitoring.

As a precaution, the SCLV will place substrate samplers in East Two River near the marina to detect any adult zebra mussels as early as possible. The samplers are short sections of PVC pipe which provide the hard attachment surface preferred by adult zebra mussels.

The Sportsmen’s Club plans to complete the search phase of this investigation by fall. The organization is hopeful the source of the East Two River calcium can be partially or completely
removed.