Pre-post treatment comparisons, curly-leaf pondweed management

APM pre-post comparison for curly-leaf pondweed control

Aquatic plant point-intercept survey workbook - June 14, 2021

Aquatic plant point-intercept survey workbook, May 5, 2021

Curly leaf pondweed pre-post treatment analysis writeup

CLP rake fullness rating trends over time

Long Lake and the Long Lake Protection and Rehabilitation District (LLPRD) have an extended history of battling Curly-leaf pondweed (Potamogeton crispus) (CLP) - an exotic invasive plant species that thrives in the nutrient-rich sediments found in many parts of the lake. In the past, CLP often grew so densely in the spring and early summer that it made lake access and boating difficult for residents. CLP’s late-June to early-July senescence was also cited in past studies by Barr Engineering and the Polk County Land and Water Conservation Department (PCLWCD) as a significant contributor to the lake’s overall phosphorus load, and it was at least partially responsible for the lake’s frequent late-summer toxic blue-green algae blooms.

Long Lake (WBIC 2478200) is a 272 acre seepage lake in central Polk County, Wisconsin in the Town of Balsam Lake (T34N R17W S07 NE NE). It reaches a maximum depth of just over 17ft in the central basin and has an average depth of approximately 11ft (Busch et al. 1969) (Figure 1). The lake is eutrophic trending toward hypereutrophic, and visibility is generally poor with summer Secchi readings averaging 4.9ft since 1992; however, the 2020 mean reading of 9.0ft was the highest since 1995 (WDNR 2020). The bottom substrate in the lake’s bays and central basin is predominately thick organic muck, while exposed points and most north/south shorelines are dominated by gravel and sand.

Zip folder of pre and post treatment surveys and comparison survey files. 20 files. 2010-2020

Long Lake and the Long Lake Protection and Rehabilitation District (LLPRD) have an extended history of battling Curly-leaf pondweed (Potamogeton crispus) (CLP) - an exotic invasive plant species that thrives in the nutrient-rich sediments found in many parts of the lake. In the past, CLP often grew so densely in the spring and early summer that it made lake access and boating difficult for residents. CLP’s late-June to early-July senescence was also cited in past studies by Barr Engineering and the Polk County Land and Water Conservation Department (PCLWCD) as a significant contributor to the lake’s overall phosphorus load, and it was at least partially responsible for the lake’s frequent late-summer toxic blue-green algae blooms.

Long Lake (WBIC 2478200) is a 272 acre seepage lake in central Polk County, Wisconsin. In 2010, the Long Lake Protection and Rehabilitation District, under the direction of Harmony Environmental, developed an Aquatic Plant Management Plan that authorized chemical treatment of the lake’s Curly-leaf pondweed (Potamogeton crispus) infestation. Following an alum treatment in 2018, the LLPRD and the Wisconsin Department of Natural Resources authorized three lakewide surveys 2019 to compare how the lake’s vegetation had changed since the last point-intercept surveys in 2016. We completed a CLP density survey on May 31st, a CLP bed mapping survey on June 12th, and a full point-intercept survey for all aquatic macrophytes on July 26, 2019.

The fall 2017 turion survey predicted there would be little CLP outside the northwest bay; and, following a long winter with nearly record late ice-out, the May 12, 2018 pretreatment survey found so little CLP that it was decided to cancel the 2018 treatment (Figure 3). Hoping CLP’s recovery without treatment would be minimal, the LLPRD, requested a late fall survey to determine the level of any latent CLP turions in the lake’s substrate.

Graphs and data as part of the Curly-leaf pondweed (Potamogeton crispus) Pretreatment and Follow-up Surveys - Long Lake, Polk County, Wisconsin document.

Prior to the planned 2018 herbicide application, we conducted a pretreatment survey of the lake on May 12th to determine initial CLP levels and finalize treatment areas. Because this survey found little CLP, it was decided to cancel the 2018 treatment. However, in order to see how CLP and native plant populations responded to skipping treatment, it was requested that we do a follow-up survey on June 11th. This report is the summary analysis of these two surveys.