Lost Lake in Vilas County has had a curly leaf pondweed (CLP) problem for several years. Last April members of the Long Lake Protection and Rehabilitation District (LLPRD) met with members of the DNR and environmental consultants, Onterra, to create a plan to deal with the CLP problem on the lake. While Eurasian watermilfoil (EWM) chemical treatments are well documented and research has been done regarding collateral damage to other species of aquatic plants, less was known about the effects of chemically treating CLP. Onterra was hired to put together a summary report, and then proposed a CLP treatment on the lake. Much like EWM, CLP does not always create the worst case scenario in a lake. Indeed, in some lakes it has died off on its own. On other lakes, it continues to grow and expand. CLP had been mapped since it was found in 2014, and it became obvious it was not going to wane in this case, but continue to grow and take over. In the end, it was decided CLP would continue to be a problem in Lost Lake, and it was already impeding recreation and pushing out native species of plants.
The summary report went through some changes as a result of that meeting in April, and tentative plans to chemically treat the CLP, based on that report, were put into place.There was some concern about collateral damage and how the rest of the plant community may respond.
"If we kick people out of the apartments, other people can move in," said Tim Hoyman from Onterra in that meeting as an analogy to help others understand how the plant community might respond to CLP being knocked down in the bay where it has taken hold.
"We might just have to accept some collateral damage," Marv Anderson of LLPRD had countered. "We have to take that because, 30 acres, you can't go through it with a kayak. I go back and say, OK, the collateral damage is going to happen. How much does that play into the decision to treat the curly leaf pondweed and maybe we just have to take our lumps?" Together, the LLPRD, the DNR and Onterra ultimately decided it was time to chemically treat the CLP with endothall, which is commonly used to fight the invasive.
Point intercept surveys have been done on Lost Lake in 2007, 2010, and 2017. Both invasive and native plants were taken into consideration. It was found, in the western bay, where the CLP had taken hold, there were five native species present: flat-stemmed pondweed, coontail, common waterweed, northern watermilfoil and fern-leaf pondweed. In Onterra's experience they knew flat-stemmed pondweed, northern watermilfoil and fern-lead pondweed are particularly susceptible to early season endothall treatments. Coontail, they said, is somewhat more resilient. It was expected common waterweed would be unimpacted. In some cases, common waterweed populations had even increased with early-season endothall treatments.
In the pre-treatment survey in May of last year, Onterra found CLP in 84 percent sample locations in the treatment area. The plan was to manipulate the dam in such a way to keep the herbicide treatment from being flushed downstream before it could have its full affect on the CLP and also to minimize impacts downstream. However, heavy amounts of rain shortly after treatment made for less than optimal conditions in that respect.
After treatment, endothall concentrations in the treatment area were lower than target, but were sustained for at least 72 hours, according to a recent report prepared by Onterra entitled the 2017 AIS Monitoring and Control Strategy Assessment Report for the Lost Lake Protection and Rehabilitation District. It was thought the extended duration of exposure would offset the lower than optimal concentrations and still be effective in controlling the CLP.
Three days after treatment, the center of the lake was tested for endothall concentrations. They were at 0.009 ppm, almost immeasurable. Onterra, from their experience, said three days after treatment, the lake likely had an equilibrium concentration throughout the lake. Due to the low concentration levels, it was deduced the spot treatment was likely confined to the treatment area and would not have lake-wide impacts.
In late June, another survey of the treatment area took place. No CLP was found in the western bay of Lost Lake, pointing to a highly effective treatment. The CLP, which was noted at 84 percent of points in the previous survey, was not found at any of the 101 sample points during the late June survey. In the August survey, however, nine sampling locations contained CLP, with the majority of those locations being in the western bay, the area of treatment. CLP regrows from turions that fall off the mature plants and can stay dormant in the substrate for years. Seed banks can build up in the soil and grow in subsequent years after treatment. For that reason, multiple-year treatments are usually necessary to push back the CLP and keep it from regrowing. The CLP found in August, this suggests, sprouted from turions after the last survey in late June.
The study also looked at the impact on native plant populations. Point-intercept data was collected and complied and validated anecdotal reports stating the submergent aquatic plant population of Lost Lake was much lower than previous years. Different plants reacted differently during the time of treatment. A lake-wide decline in white-stem pondweed and fern-leaf pondweed as seen from 2014 to 2017, but the decline was higher in the treatment area. Lake-wide, coontail, which is not normally affected by early-season endothall treatments, experienced a decline from 38.7 percent in 2014 to 13.2 percent in 2017, and the decrease in the treatment area was greater than that lake-wide. Lake-wide common waterweed was basically unchanged from 2014 to 2017, but had experienced a sharp decline in 2014 from 2010 surveys.
Slender naiad, which Onterra said is very susceptible to large-scale 2,4-D treatments, saw an uptick after the endothall treatment. Wild celery increased lake-wide, but at a smaller rate in the treatment area. Clasping-leaf pondweed indicated a decline within the treatment area.
Water quality was also included in the recent report, but early season rains washing nutrients and organic acids into the lake greatly impacted water clarity in 2017. Further examination of the water quality parameters will be included in future lake management project planning, according to the report.
The main conclusions were summarized at the end of the report. It stated for plant species in decline, the decline was consistent over time and were present not only after treatment or only within the treatment area. Also, with the heavy rains, the dam was open at its highest level for 10 consecutive days in an attempt to control water levels within Lost Lake.
It is thought more herbicide dissipated out of the lake in that direction rather than to the east into the main body of the lake. Herbicide concentrations in Lost Creek, the report said, were similar to those in the treatment area when tested. It was also said if the herbicide applied to the treatment area were to be spread out across the entire lake, concentrations would be far too low to have an impact on the plant community.
Lastly, three days after treatment, herbicide concentration monitoring showed an almost undetectable amount of the chemical endothall in the center of the lake. The endothall treatment was considered a success in the western bay of Lost Lake. However, with turions likely still in the soil from previous years, CLP will again grow in 2018, as was evidenced by the mid-August survey.
In January of this year, the LLPRD directors voted unanimously to conduct another endothall spot treatment in the same treatment area this year. This treatment, which is done before plants shed their turions for the season, will likely need to take place for at least two more years to ensure any turions left in the soil are gone.
Aquatic plant monitoring is also planned for 2018 and the LLPRD will be looking to the DNR for funding assistance. Water sampling for herbicide concentrations will also continue this year, to be done by volunteers on the lake. At some point in March or April, the Lost Lake Planning Committee and Onterra will meet again to discuss project results thus far and to further review and refine management goals for both Eurasian watermilfoil and CLP.
Beckie Gaskill may be reached via email at firstname.lastname@example.org.