Submersed aquatic plants play an important role in freshwater systems, affecting
nutrient dynamics, trophic interactions, biological assemblages, and fish productivity.
However, waters infested with non-native invasive aquatic plants often experience severe
impairment of ecological and recreational quality due to excessive plant growth.
Curlyleaf pondweed (Potamogeton crispus L.), one such exotic submersed aquatic plant,
has become a widespread nuisance in temperate regions of North America. Curlyleaf’s
early-season growth, propensity to form dense surface mats, and ability to out-compete
native aquatic plants allow it to degrade the ecological and recreational quality of lakes.
Consequently, there has been a great deal of interest in adopting lake-wide management
strategies that can reduce the negative impacts of curlyleaf and provide some degree of
We collaborated with the Minnesota Department of Natural Resources in 2006,
2007, and 2008 to evaluate lake-wide, early-season herbicide treatments for curlyleaf
management. Six curlyleaf-infested lakes were treated with herbicide (endothall or
fluridone) for at least three consecutive years. Three additional lakes with established
curlyleaf infestations were selected to serve as untreated reference lakes during the same
period. For all study lakes, we annually assessed the frequency and biomass of curlyleaf in May and June, documented the production of new curlyleaf turions (reproductive
buds) on standing plants, and tracked changes in the abundance and viability of turions in
Previous studies have shown that biomass is a key metric for evaluating aquatic
plant management projects. We used a boat-based rake method for collecting biomass samples rather than the standard diver (SCUBA) quadrat method because it allowed us to
collect a greater number of samples in each lake and provided a higher degree of safety
than the diver quadrat method. However, this boat-based rake method had not been
thoroughly evaluated to determine whether it produced biomass estimates that were
comparable to the diver quadrat method. Consequently, we conducted a separate study to
compare the vertical rake sampling method to the diver quadrat method. Results of this
study showed that biomass estimates from rake samples were comparable to diver
quadrat samples for most individual plant taxa. However, the rake method produced
substantially higher estimates than the quadrat method when sampling in dense stands of
aquatic plants, particularly in areas dominated by coontail (Ceratophyllum demersum L.).
Although rake estimates of plant biomass were significantly less precise than quadrat
estimates, we determined that the rake method allowed us to collect a sufficiently greater
number of samples to offset the method’s lower precision. Consequently, we concluded
that the biomass data we collected were precise enough to make meaningful relative comparisons in our study lakes. After three to four consecutive years of herbicide treatment, curlyleaf frequency,
biomass, turion production, and sediment turion abundance were all reduced and were all
significantly lower in treated lakes than in untreated reference lakes. However, viable
turions remained in lake sediments after three consecutive years of treatment. These
results suggest that serial lake-wide, early-season herbicide treatments can effectively
decrease the negative impacts of curlyleaf infestation and reduce the abundance of
curlyleaf turions in lake sediments, but ongoing management will likely be required to
maintain long-term control of curlyleaf in infested lakes.
University of Minnesota M.S. thesis. May 2010. Major: Water Resources Science. Advisor: Dr. Raymond M. Newman. 1 computer file (PDF); viii, 88 pages.
Johnson, James Aaron.
Evaluation of lake-wide, early-season herbicide treatments for controlling invasive curlyleaf pondweed (Potamogeton crispus) in Minnesota Lakes..
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