Lake Management and The Lake District

 

PRELIMINARY SURVEY REPORT – 2010 EWM TREATMENT

Greetings,

Field crews from Onterra visited North and South Twin Lakes during the last week of August to conduct various surveys aimed at understanding the Eurasian water milfoil (EWM) population in the lake. A whole-lake point intercept survey was completed on South Twin Lake (621 total points, approximately 300 points within the range of plant growth) and 41 point-intercept sub-sample locations were visited on North Twin. These locations were visited to aid in the monitoring of the 2010 treatments. These same locations were sampled before the respective treatments took place and comparing the datasets will allow an understanding of treatment efficacy (is there less EWM) and collateral damage (were valuable native plants impacted). While the data has not been worked up yet, it will be included within the treatment report that will be provided later this winter. Herbicide use carries with it an inherent risk, especially to the native plant population of our lakes. Our data will be able to understand how the native plants reacted to these treatments and this data will also be provided within the upcoming treatment report.

The US Army Corps of Engineers and WDNR enlisted North and South Twin Lakes into a joint research project aimed at understanding the residual concentrations of the herbicide in the lakes at various times after the treatment. Once this data becomes available, it will be integrated into the treatment report provided to the association roughly in December/January.

South Twin Lake
In 2010, liquid 2,4-D (Weedar 64) was applied by Bonestroo at 2.5 mg/L over the treatment areas to achieve a calculated lake-wide concentration of 0.239 mg/L. This low-dose herbicide treatment was applied at a slightly higher concentration than was used in 2009. The preliminary results of the point-intercept survey indicate that EWM frequency of occurrence of the entire lake was reduced from 10% in 2009 to 0% in 2010. Also during August 2010, the entire lake was visually scoured by Onterra ecologists and no EWM was located during this survey either. We did locate a number of floating EWM fragments possibly originating from: 1) EWM that went undetected during our surveys, 2) EWM that had died and floated to the surface, and/or 3) EWM originating from North Twin Lake.

While this is great news for South Twin Lake, by no means do we want to indicate that EWM is gone from the lake. It simply means that EWM populations were reduced to a level where remaining occurrences were not detected during the August 2010 surveys. However it is safe to assume that no large colonies of EWM exist on the lake, the conditions that greatly threaten the ecological integrity of the system. Careful monitoring in 2011 will prove increasingly important in understanding the EWM population on South Twin Lake. At this point, it appears that an herbicide treatment will not occur on South Twin Lake in 2011.

North Twin Lake
Since past treatments on North Twin Lake have not been particularly effective, the association’s herbicide applicator suggested the use of Renovate MaxG (combination granular 2,4-D and triclopyr). This combination granular 2,4-D and triclopyr product is theorized to have synergistic affects compared with the respective herbicide components. The sub-sample point-intercept locations were placed over targeted EWM colonies, therefore all locations were within areas treated in 2010. This is not the case when looking at the whole-lake point-intercept survey results of South Twin Lake which were spread evenly over the lake. EWM frequency of occurrence was approximately 36% within the treatment areas on North Twin Lake before the treatment and was reduced to approximately 15% after the treatment.

During our visual mapping surveys, EWM was not visible from the surface in many of the areas but random rake tows did pick up some small EWM sprigs. It is perceived that good control was observed within these areas. The site closest to South Twin Lake (E-10) was not as successfully controlled. While the mapping data has not been worked up yet, field notes from this site indicate that much EWM continues to exist within this site similar to last year, possibly even at a slightly higher density.

With the help of a volunteer on the lakes (Ryan Goetz), a few additional EWM colonies were located on North Twin Lake. A treatment strategy will be developed for North Twin Lake that will include targeting these new occurrences.

Thanks, eddie

Eddie J. Heath Aquatic Ecologist Onterra, LLC
Voice: 920.338.8860
Fax: 920.338.8865
Email: eheath@onterra-eco.com
Web: www.onterra-eco.com

 

Lake District

Objectives of the North South Twin Lakes District Lake Management Plan

Download the Lake Association FACT SHEET here
Download the Lake District FACT sheet here

 

 

Fact Sheets

Download the Lake Association FACT SHEET here

Download the Lake District FACT sheet here