Large Milfoil Infested Pond RestoredAquatic Weed and Algae Control Case Study
Location and Acreage:Goshen, CT | 42-Acres
Project Timeframe: April – September 2018
Project Manager:Joshua Perry, Environmental Scientist
Site Description:This pond is a 42-acre naturally-formed waterbody. The pond consists of a single basin with a limited littoral zone. The maximum recorded depth in the pond is 32 ft and the average depth is approximately 15 ft. The primary inflow enters the pond via West Side Pond Brook, to the north, and outflows at the southern end, eventually flowing into Tyler Lake. A public boat ramp capable of accommodating trailered boats is located along the western shoreline. The pond exhibits an extensive and unique vegetation assemblage which includes both invasive, native, and rare species. The invasive vegetation includes Eurasian watermilfoil (Myriophyllum spicatum) and variable milfoil (Myriophyllum heterophyllum). The dominant native vegetation in the pond includes but is not limited to coontail (C. demersum), bladderwort (Utricularia spp.), tapegrass (Valisneria americana), and pondweed species (Potamogeton spp.). The rare species, alternate-flowered watermilfoil (Myriophyllum alterniflorum), was limited to one isolated area. There is also a healthy buffer of emergent vegetation along the shoreline.
Scope of Work:SOLitude worked with the pond’s association to develop an effective management program for the long-term control of invasive submersed aquatic vegetation, specifically Eurasian watermilfoil (Myriophyllum spicatum) and variable milfoil (Myriophyllum heterophyllum). This project provided some difficult challenges, as there was presence of alternate-flowered watermilfoil, a state-listed endangered species that could be impacted by the proposed management of the invasive milfoil species. The program that was developed included, pre- and post-treatment vegetation surveys, multiple herbicide Sonar (fluridone) herbicide applications to maintain low target concentration lake-wide, and herbicide residue monitoring necessary for the timing and dosing of subsequent booster herbicide applications.In addition to the treatment program, SOLitude prepared, filed, and complied with the Incidental Take Request (ITR), as required by the Connecticut Department of Energy and Environmental Protection (CT DEEP) Wildlife Division to protect the endangered alternate-flowered watermilfoil. Per requirements of the ITR, SOLitude provided and installed limno-curtain barriers around identified areas of alternate-flowered watermilfoil. The barrier is installed to reduce water exchange and help keep fluridone out of the beds of the rare milfoil species. Charcoal filtration socks were also installed within the barrier, to absorb any fluridone that may have inadvertently entered.
Project Description:The management program began early in the growing season, with the first application, taking place on May 22nd. Low dose application programs yield highest efficacy when started early in the season, when plant biomass is low. Multiple interim inspections were conducted throughout the course of the 2018 season, to observe plant response to the herbicide, as well as perform residual sampling to help guide subsequent “booster” treatments. The product is a slow acting herbicide, effective concentrations must be maintained within the water column for upwards of 60 days for full systemic control. Following the initial application, pond water samples were collected at three locations for herbicide residue on June 14th and August 10th. Two booster applications, guided by sampling results, were performed on July 2nd and September 11th to maintain desired concentrations of herbicide. During the interim inspections, plant response was also documented. Approximately 4 weeks following the initial application, it was evident that chlorosis had started on the target plants, as they were significantly discolored. An additional inspection following the 2nd herbicide application indicated an extensive reduction in density and distribution of the target species. The final inspection performed in mid-October revealed a complete reduction in the target species Eurasian watermilfoil, as well as a significant reduction in variable milfoil. Reduction of the target species, paired with a “thinning” of native vegetation helped to provide a snapshot of the conditions that can be anticipated through the 2019 season. The rare and endangered species within the pond will continue to be monitored in subsequent seasons.