Residents concerned about Ann Lake water quality are being asked to consider several options to remove excess nutrients from the water. Excess nutrients —particularly phosphorus in lakes and rivers cause algae to grow. More algae is less appealing for fishing and recreation, can cause harmful conditions for fish, wildlife and plants and can increase toxic blue-green algae blooms.
Ann Lake has been listed as impaired for nutrients since 2004. Following this impairment, the MN Pollution Control Agency followed up with a report on Ann Lake in 2013 to determine that a reduction of phosphorus (a nutrient) in the lake by 4,758 lbs. would bring the waters of Ann Lake back within the allowable state nutrient standards.
Nutrients come in many forms, from surface water runoff around the lake. Nutrient runoff can come from fertilizer applied to farm fields or lawns around the lake, from livestock manure, from inadequate septic systems or even from pet waste. It takes only one pound of phosphorus to support 500 pounds of algae. In the case of Ann Lake, nutrients area coming from the watershed that drains into the lake, but a nearly equal amount of nutrients has, over time settled into the sediment at the bottom of the lake. This is referred to as a high internal load in the lake.
A 2013 report on how to address Ann Lake’s high nutrient issues from the MN Pollution Control Agency sets an internal load reduction goal of 86% or 4,096 lbs. of phosphorus for Ann Lake.
“The internal load reduction goal for Ann Lake is significantly greater than the watershed reduction goal. It will be extremely difficult, if not impossible to restore Ann Lake to meet state water quality standards without some sort of management strategy to decrease phosphorus loading from the lake’s sediments.” (sited from the 2018 Ann Lake Internal Load Feasibility Study completed by Wenck).
This 2018 internal load study of Ann Lake completed by Wenck investigated possible treatment options to address this high internal load.
One treatment option is an aluminum sulfate (alum). Alum works by binding phosphorus to the lake bottom. Alum lake treatments have been commonly used to address high internal loading, on other lakes around the Twin Cities. It was also the least expensive, at $651,000.
In seeking out an alum treatment to address the high nutrient load at the bottom of the lake there were multiple concerns brought forward. Concerns over sulfate spikes from the treatment affecting the wild rice population would require extra environmental assessment and monitoring. Issues over the impact to the benthic invertebrates (lake bottom organisms) and the longevity of alum being on average, 23 years. For these various concerns another treatment was considered.
A second option being considered is a phoslock treatment. Phoslock is mostly clay with lanthanum, a naturally occurring soft metal. Phoslock works by binding with mobile phosphorus and creating a stable, insoluble mineral. The longevity of phoslock is encouraging with permanent bonds created. Studies of phoslock have shown no significant impact to aquatic organisms. Human health exposure to lanthanum is very low. An estimated cost of phoslock could be in the range of $1.3-1.5 million.
Funding has yet to be sought for this project. Most of these treatment options are planned out over 5-14 years. To facilitate grant funding cycles (2-3 yrs.) a treatment would potentially be split into two grant cycles. Multiple grants would be sought. However, with grant funding, local match is generally required. An anticipated local match for half of a treatment could run anywhere from $67,500-168,750 with the phoslock option.
There is a lot to consider in seeking a treatment option for Ann Lake to address the ever-present high phosphorus in the lake sediment. An important benefit to a lake treatment is improved water clarity or less algae. However, with improved water clarity will come an increase in aquatic plant growth, especially within the shallower areas of the lake.
The Kanabec County Soil and Water Conservation District will hold a public meeting from 9-11 a.m. Sept. 26, 2020 at the Ogilvie Civic Center, 102 N Hill Ave., Ogilvie, to further explain these treatment options and seek public comments.
Please RSVP as space is limited and plan to wear a mask. The meeting will also be available remotely via WebEx. Call in details will be available at www.kanabecswcd.org. To RSVP or for more information on this proposed project, contact Deanna Pomije at the Kanabec SWCD, (320) 674-1391 or Deanna@KanabecSWCD.org.