Constraining invader dominance: Effects of repeated herbicidal management and environmental factors on curlyleaf pondweed dynamics in 50 Minnesota lakes

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Abstract

Curlyleaf pondweed (Potamogeton crispus) is one of the most widespread and widely managed aquatic invasive plants in North America. Despite decades of management, the efficacy of long-term management strategies and the effects of environmental drivers on curlyleaf pondweed populations remain uncertain. To evaluate the effects of management and environmental factors on within-lake distribution and local density of curlyleaf pondweed, we collated monitoring data from point–intercept surveys collected by a variety of lake managers across Minnesota, U.S.A. Using this dataset, comprising 177 lake-years of plant data, we examined the influence of herbicide treatment, water clarity, snow depth, and ice cover duration on curlyleaf pondweed distribution and density between 2006 and 2015. We evaluated the effects of herbicides on curlyleaf pondweed at three time points relative to treatment: within year, carryover effects the following year, and cumulative effects over multiple years of treatment. All three temporal measures were associated with significant reductions of curlyleaf pondweed. Additionally, herbicidal management reduced both the density and distribution of curlyleaf pondweed. Given that herbicide management led to reductions that carried over into future years, managers may be able to design multi-year treatments to reduce total management effort over time. We also found strong effects of environmental conditions on curlyleaf pondweed. Elevated lake productivity and decreased winter snow cover were associated with increased springtime distributions of curlyleaf pondweed, whereas duration of winter ice cover had no influence. The influence of productivity suggests that reductions of this invasive species may be an ancillary benefit of water-quality improvements that lower lakes’ trophic status. Our results also show that decreased winter snow cover, as predicted under climate change, could exacerbate problematic growth of curlyleaf pondweed. Harnessing monitoring data from multiple projects, as this study does, allows for robust inference about environmental and management constraints on macrophytes. Because of environmental and management variability, we suggest that treatment regimens follow an adaptive management cycle, with outcomes of management monitored and evaluated, and strategies updated accordingly. It is also vital to continue monitoring both managed and unmanaged lakes to enable stronger inferences about treatment effectiveness.

Original languageEnglish (US)
Pages (from-to)849-862
Number of pages14
JournalFreshwater Biology
Volume65
Issue number5
DOIs
StatePublished - May 1 2020

Bibliographical note

Funding Information:
Funding for this research was provided through the Minnesota Aquatic Invasive Species Research Center from the Minnesota Environment and Natural Resources Trust Fund with additional support from the USDA National Institute of Food and Agriculture, Hatch grant MIN‐41‐081. Chip Welling (deceased) of the Minnesota Department of Natural Resources (MNDNR) suggested this project and provided significant input and assistance with obtaining data sets. Thomas Ostendorf and Adam Kautza contributed greatly to the collection and organisation of data. Data for 12 lakes were collected by graduate students James Johnson and Ajay Jones as part of a study funded by the MNDNR. Data for five lakes were collected by graduate students Josh Knopik, John JaKa, and Melaney Dunne and funded by Riley Purgatory Bluff Creek Watershed District. Additional data sets were provided by the MNDNR SLICE programme (Donna Dustin), MNDNR Invasive Species Program (Wendy Crowell, Allison Gamble, and Keegan Lund), Capitol Region Watershed District (Britta Suppes), Ramsey Washington Watershed District (Simba Blood), Three Rivers Park District (Rich Brasch), Minnehaha Creek Watershed District (Eric Fieldseth), Rice Creek Watershed District (Matt Kocian), and consulting firms Barr Engineering (Meg Rattei), Bluewater Science (Steve McComas), and Freshwater Scientific Services (James Johnson). Their cooperation was key to this project and greatly appreciated.

Keywords

  • climate change
  • herbicide
  • invasive species
  • macrophyte
  • winter severity

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