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Long-Term Management Plan for Submersed Aquatic Vegetation at Chautauqua Lake

Click here  CL Management Plan to read the full plan document.

This plan was developed in response to discussions with he NYS DEC and others to clarify the goals of herbicide applications for Chautauqua Lake and to articulate a long range plan to achieve those goals.  The plan is intended to be a living document which will be amended as needed over time as the plan is implemented.  Success of this plan will transform our approach to lake management from simply targeting the worst areas from year-to-year,  to a maintenance mode where only spot treatments will be needed to keep invasive aquatic vegetation in check.

The plan was prepared by the Aquatic Plant Management Program team at North Carolina State University and funded by the Chautauqua Lake Watershed & Management Alliance.

Plan Highlights

Problem Assessment
According to recent monitoring efforts, the macrophyte community at Chautauqua Lake is largely composed of Eurasian watermilfoil in the summer and fall months, and curly-leaf pondweed in the spring. The presence of these invasive species can disrupt the overall ecosystem function and additionally impact the local fishery, water quality, and recreational opportunities at the Lake. Starry stonewort also represents an emerging threat.

Vision
The goal of this project is to achieve a balanced and sustainable aquatic ecosystem at Chautauqua Lake. Objectives include reducing the nuisance level of invasive species and maintaining or increasing the relative distribution of native species. Integrated management of invasive species is encouraged as well as monitoring of both invasive and non-native species. Implementation of this plan will be based on set priorities and will occur in defined stages to ensure that progress is completed according to a systematic design. Annual reviews should be conducted of the plan, management effectiveness, and lake surveys.

Whole-Lake Management Strategy
Chautauqua Lake is naturally divided into two sections, the North and South Basins. Studies have determined that, while connected, the physical differences between the two basins can influence dynamics of fundamental, underlying ecosystem processes (Smith et al. 2020). These physical differences likely directly influence the aquatic plant communities as well, and as such, management strategies may need to differ when comparing North and South Basin needs. However, it should also be recognized that decisions regarding lake management should be unified in a whole-lake approach to maximize effort from all entities.

The 2017 Chautauqua Lake Macrophyte Management Strategy delineates the lake into sub-sections based off of shoreline use and highlights the need to consider human interaction along with environmental sensitivities when developing management options. While this strategy is effective at assessing options for specific, small-scale situations, it shifts the strategy away from a viewpoint that should be centered on plant ecology in order to meet the primary goals of long-term macrophyte management.

Specific Goals
The goals of this long-term plan include:

  • Reduce the nuisance level of Eurasian Watermilfoil and Curly-Leaf Pondweed in the Chautauqua Lake system.
  • Identify control measures for Starry Stonewort in Chautauqua Lake.
  • Encourage native submersed aquatic vegetation species diversity throughout the system, with particular focus on South Basin assembly.
  • Limit continued spread of non-native species in the Chautauqua Lake watershed
  • Shift algal community away from cyanobacterial dominance
  • Support the local fishery, especially the established game fish population

Plan Management

Stakeholder collaboration will be an important aspect of this plan, and as such, management decisions will need to be organized through a central entity. A Lake Manager dedicated to coordinating and tracking this work could be a valuable asset for long-term success and goal achievement.

Plan Review
To address the dynamic nature of long-term aquatic plant management projects, annual reviews of the management plan shall be conducted through a collaboration between the Lake Manager and the Executive Board to evaluate yearly outcomes, navigate forthcoming needs, and continue prioritization of management goals. The annual review should take place in the winter, such that necessary modifications can be put in place prior to the onset of the subsequent growing season.

Integrated Management Plan
This plan is divided into a sequential tiered system. Each tier builds upon each other, and as such, should be completed in the defined order. The plan will define and target long-term treatment areas, short-term management goals, and habitat protection areas.

Annual Strategic Timeline
Strategic implementation of this plan not only spans work years, but also depends on the timing of critical management events in relation to the ecological factors of target and non-target species.

Curly-leaf Pondweed
Due to the unique growth pattern of curly-leaf pondweed, management efforts
specifically for this species should occur early in the growing season. It is recommended that endothall (1 – 2 ppm) should continue to be used for chemical control of curly-leaf pondweed at Chautauqua Lake. Treatment with chemical controls should begin when the plants are at the start their active growth phase (Figure 28). This timing limits treated biomass, thus reducing Curly-leaf pondweed naturally senesces in June-July, and early season management reduces overall nutrient release into the water column and decreases this nutrient source for summer algal blooms. Additionally, the timing of early season management is critical for curly-leaf pondweed to limit turion production and future growth in subsequent years. Early-season chemical control should also limit off- target impacts as fewer macrophytes will be actively growing at this time. Lastly, this timing should have reduced overlap with spawning fish activity and allow more time for native plants to reclaim curly-leaf pondweed areas before spawn (Figure 29). Studies have documented that water temperature does impact overall efficacy of selected chemical controls but biomass is still reduced, especially with a long (12 + hour) exposure period (Netherland et al. 2000). So, ideal parameters for treatment include water temperatures at 5 – 10°C in sites that do not experience high water flow.

Summary of Management Events (specific timing to be based on water temperature):

  •  March-April – Management Zone Confirmation
  • April-May – Application of Chemical Control and/or Mechanical Harvesting
  • May-June – Post-treatment Assessment and survey for population extent delineation.
  • No mechanical harvesting during flowering and turion formation.
  • September – Turion Bank Sampling

Eurasian Watermilfoil
Florpyrauxifen-benzyl (3 – 6 ppb) is highly effective for Eurasian watermilfoil control. This herbicide is selective for milfoil species, even at low (0.5 hour) exposure times, and should limit off-target impact to the diverse native plant community (Mudge et al. 2021). Ideal application timing is during the active growth phase but before peak biomass. Early treatment will limit the release of excess nutrients into the water column by reducing the amount of biomass that will be left to break down in the system.

Summary of Management Events:

  • June – Management Zone Confirmation
  • July – Application of Chemical Control followed by Mechanical Harvesting
  • August – Post-treatment Assessment & Survey for remaining population extent delineation

Algae Management
Although algae and aquatic plants share similar roles in the environment, and are closely connected in aquatic ecosystems, algal and aquatic plant management tactics are quite different. The Harmful Algal Bloom Action Plan for Chautauqua Lake (NYSDEC 2018) outlines critical steps for reducing the presence and continual recurrence of algal blooms in the Chautauqua Lake system. Algal bloom dynamics are closely related to large-scale environmental conditions, such as nutrient loading, temperature, seasonality, water movement, and weather events. With this, algal management efforts should focus on watershed-level or lake-wide initiatives that aim to disrupt driving factors of the process of algal bloom formation when possible – in a proactive approach rather than a reactive approach.

Introductions of non-native macroalgae, such as starry stonewort, require a shift in this standard algal management strategy. The ecological characteristics and life history traits of starry stonewort closely mimic those of a weedy, troublesome aquatic plant species by way of the overwhelming production of bulbils, or reproductive propagules, and fast vegetative growth rates (Larkin et al. 2018). With these features, starry stonewort has been able to outcompete some of the most problematic aquatic plant species, including Eurasian watermilfoil, in shallow, inland waterbodies (Ginn et al. 2021). Because starry stonewort growth and distribution does not fit into the classic definition of a harmful algal bloom, alternate management options for this species should be considered. If left alone, starry stonewort has the ability to disrupt the interconnected functions of Chautauqua Lake’s ecosystem – thereby influencing the composition and diversity of the submersed aquatic plant and fishery communities and having a larger impact than the management practices themselves.

Eradication of starry stonewort has proven to be very difficult in systems where it is currently invading. Factors that have influenced the success of management efforts include early detection, aligning timing with phenological growth patterns, and integrated approaches that combine the utility of multiple strategies including  chemical and mechanical control options (Glisson et al. 2018).

General Guidelines

Mechanical Harvesting
Mechanical harvesting efforts at Chautauqua Lake may provide immediate relief to invasive and nuisance plant growth and can be a valuable tool for maintaining open surface water. A standardized approach to mechanical harvesting efforts should be
followed:

  • Continue small-scale or manual harvesting invasive or nuisance species in near-shore (< 3’) management areas
  • Ensure that at least 2 feet of SAV biomass remains in main lake (> 3’) harvested areas (or 1 foot in High Use Areas)
    • Presence of aquatic plants is beneficial for nutrient uptake, sediment stabilization, habitat for small fish and macroinvertebrates. Due to this, mechanically harvesting plants below a 2 foot threshold could compromise the integrity of the beneficial native submersed plant population at Chautauqua Lake and influence the balance of higher trophic levels
  • Examine harvested material in real time
    • Collect floating debris
    • Return harvested fish or other bycatch back to the lake when possible
  • Harvest Area Priorities
    • Regions of the lake where mechanical harvesting occurs should be strategically organized. Priority level descriptions are provided in Table 6.

Chemical Controls
The use of chemical methods may provide long-term control of target non-native
species at selected management sites when implemented appropriately. A standardized approach to chemical management should be followed:

  • Treatment timing should be based on target life cycle. Target species as early in their life cycle as possible to inhibit reproduction and nutrient release.
  • Streamline permitting process with municipalities to accomplish early treatment
  • Refine treatment design and application based on available data

Biological Controls
It is recommended that monitoring of milfoil weevil populations and impacts to Eurasian watermilfoil be monitored periodically. This is especially important in Habitat Protection Zones where low-impact management is mandated. If weevil densities are low in these areas, additional stockings of 3,000 weevils per acre should be considered (Madsen et al. 2000). Note that reduction of overall Eurasian watermilfoil in the lake may impact biocontrol efficacy over time.

Management Monitoring
Monitoring sites at pre- and post-management time points should continue and data used to inform management decisions on an annual basis. For example, if results demonstrate that a treatment was ineffective at controlling curly-leaf pondweed in Year 1, then management operations the following year should be altered to obtain better control. Collected data should include:

  • Aquatic Plant Community Ratings
    • Standardized Rake Tosses
    • Biovolume/Sonar Data
    • Total Abundance Estimation
    • Species Abundance Estimation
    • Overall Plant Health
  • Water Quality
    • Nutrient sampling (Phosphorus, Nitrogen)
    • Physical profiles (Dissolved Oxygen, Temperature, pH, Chlorophyll-a)
  • Algal Community
    • Species Composition
    • Species Abundance
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