Prepared by: EOR & Blue Water Science For the Lake Minnetonka Conservation District DRAFT Lake Minnetonka Vegetation & AIS Master Plan: Aquatic Vegetation Harvesting Program Evaluation DRAFT - 10.09.2019 TABLE OF CONTENTS 1. INTRODUCTION ............................................................................................................................................. 3 2. PURPOSE ....................................................................................................................................................... 3 3. EXISTING PROGRAM OVERVIEW ................................................................................................................... 4 3.1. LMCD Harvesting Program Goals ............................................................................................................... 4 3.2. Harvesting Priorities ................................................................................................................................. 4 3.3. Staffing ..................................................................................................................................................... 5 3.3.1. Staff Roles and Responsibilities ................................................................................................................. 6 Site Supervisor .......................................................................................................................................... 6 Harvesters, High Speed Transporters, Shoreline Conveyors ....................................................................... 7 3.3.2. Staff Training, Protocol, and Program Review ............................................................................................ 9 3.3.3. Safety Program Review ........................................................................................................................... 11 3.4. Equipment .............................................................................................................................................. 12 3.5. Cost of Existing Mechanical Harvesting Program ..................................................................................... 13 3.5.1. Financial summary .................................................................................................................................. 13 3.5.2. Cost Comparison..................................................................................................................................... 13 4. EXISTING PROGRAM EVALUATION .............................................................................................................. 16 5. FUNDAMENTALS OF MECHANICAL HARVESTING ......................................................................................... 18 5.1. Aspects of a Successful Mechanical Harvesting Program ......................................................................... 18 5.2. Positive and Negative Aspects of Mechanical Harvesting ......................................................................... 18 Mechanical Harvesting Advantages and Disadvantages ........................................................................... 18 Mechanical Harvesting Comparison with Herbicides ............................................................................... 20 Mechanical Harvesting Case Studies ....................................................................................................... 21 5.3. Implications for Lake Minnetonka ........................................................................................................... 22 6. LMCD MECHANICAL HARVESTING PROGRAM RECOMMENDATIONS........................................................... 23 6.1. Short Term Goals .................................................................................................................................... 23 6.1.1. Goal 1: Increase Program Transparency through Social Media ................................................................. 23 6.1.2. Goal 2: Cleary Define, Prioritize and Map Harvesting Priorities. ............................................................... 23 Recommended Steps for Achieving Goal #2 ............................................................................................ 23 6.2. Long Term Goals ..................................................................................................................................... 26 6.2.1. Native Aquatic Plant Community Restoration .......................................................................................... 26 EOR: water | ecology | community Page | i Case Studies ........................................................................................................................................... 27 7. REFERENCES ................................................................................................................................................ 28 LIST OF FIGURES Figure 1. LMCD Public Harvesting Illustration. .......................................................................................... 4 Figure 2. Examples of Lake Minnetonka Harvest Maps, 2010 to 2015. ................................................... 17 Figure 3. Lake Monona (Madison, Wisconsin) harvesting priorities for aquatic plants. ........................... 22 Figure 4. Lake Mendota (Dane County) Harvesting Priorities for Aquatic Plants (source: Dane County Aquatic Plant Management Harvesting Program). .................................................................. 24 Figure 5. 2018 LMCD Harvesting Locations. ........................................................................................... 25 LIST OF TABLES Table 1. LMCD Harvesting Staff Qualifications.......................................................................................... 5 Table 2. Site Supervisor Routines and Responsibilities: Source: LMCD...................................................... 6 Table 3. Harvester and High Speed Transporter Routines and Responsibilities. ........................................ 7 Table 4. Shore Conveyor Routines and Responsibilities. ........................................................................... 8 Table 5. General Training Protocol. Source – LMCD. .............................................................................. 10 Table 6. Summary of existing lake harvesting equipment owned by the LMCD. ..................................... 12 Table 7. Financial summary of LMCD Harvesting Program 2008-2018. ................................................... 14 Table 8. Financial summary of LMCD Harvesting Program, 2020 to 2040 cost projections.. .................... 15 Table 9. Advantages and disadvantages of mechanical harvesting (McComas 2011). ............................. 18 Table 10. Comparison of mechanical harvesting vs. herbicides (prepared by DNR)…. ............................. 20 Table 11. Positive and negative impacts of mechanical harvesting and associated case studies. ............ 21 EOR: water | ecology | community Page | ii 1. INTRODUCTION In the Upper Midwest, mechanical harvesting is primarily used to manage Eurasian watermilfoil (EWM) and to a lesser extent, to control dense stands of native vegetation. Most often, mechanical harvesting is used to enhance or provide recreational access to and from publicly used spaces such as docks, swimming piers, or public boat landings. Literature suggests that harvesting provides temporary, short-term reductions in aquatic plant biomass. Mechanical harvesting is often viewed as a maintenance technique rather than a long-term management strategy. In Lake Minnetonka, Crowell et al. (1994) observed that a mid-growing season harvest reduced average EWM biomass in plots for 6 weeks after the initial harvest, when compared to reference areas. Other studies have shown that the effects of mechanical harvesting may last as little as 3-4 weeks (Rawls, 1975, Cooke et., al, 1989). Still, other studies show that despite the potential for rapid regrowth of biomass, there may be beneficial long-term effects (maintenance of navigable channels) especially when harvesting is conducted later in the growing season and cuts are made closer to the sediment surface (Unmuth et., al, 1998). For example, in Lake Wingra (Madison, WI), EWM averaged only 4% of its original length in harvested, shallower water sites (less than 3 meters deep), three years after a one-time harvesting effort (Unmuth et., al, 1998). While all aquatic plant management techniques have strengths and weaknesses, mechanical harvesting can be a component of an integrated aquatic plant management approach. 2. PURPOSE The purpose of this evaluation is to: 1) Define the aspects of a successful mechanical harvesting program for the Lake Minnetonka Conservation District (LMCD), 2) Identify the strengths and weaknesses of the existing harvesting program, and 3) Develop a recommendation for aspects of the program that should be sustained, and highlight areas of the harvesting program that are in need of improvement. This report will also outline short-term and long-term quantifiable goals for the mechanical harvesting program. These goals will specify when and under what conditions mechanical harvesting is most likely to produce optimum results in Lake Minnetonka. EOR: water | ecology | community Page | 3 3. EXISTING PROGRAM OVERVIEW 3.1. LMCD Harvesting Program Goals The LMCD Harvesting Program has been in operation since 1989. The goal of the LMCD Harvesting Program is to ensure