What’s an environmental learning center focused on native ecology to do when faced with a nonnative, invasive plant choking one of its ponds? It’s the type of challenge that requires expert guidance, and in this case, Aquascape Environmental stepped up to provide a successful resolution. However, the road to conquering the invasive pest was not without a few twists and turns.
The Chattahoochee Nature Center is nestled northeast of Atlanta, just across the road from the Chattahoochee River in Roswell. The 127-acre property hosts camps, classes, and educational events, and features native plant gardens, wetlands, woodland trails and resident wildlife (full-time animal inhabitants are injured and non-releasable). The Chattahoochee Nature Center offers visitors of all ages unique opportunities to experience and interact with nature.
In the Spring of 2014, it became apparent that Kingfisher Pond, one of the three ponds on the property, had a significant aquatic weed problem. Chris Nelson, the Executive Director of the Chattahoochee Nature Center, called on Aquascape Environmental to tackle the issue. Aquascape Environmental identified the offending species as Eurasian Watermilfoil (Myriophyllum spicatum L.; see Figure 1), a non-indigenous aquatic species that is known for aggressively displacing native aquatic plants, decimating natural diversity and wildlife habitat in the water body. As its name suggests, the native range of Eurasian Watermilfoil is Europe, Asia, and North Africa, and it was most likely introduced to North American waterways by the aquarium trade.¹ The species is still fairly uncommon in Georgia; when it occurs locally, it has most often been introduced unintentionally by dumping of aquarium fish and/or plants into a water body.
While the ecosystem impact was the primary concern in this instance, the visual impact of Eurasian Watermilfoil clogging the pond (see Figure 2) was also a significant concern for a nature center hosting hundreds of visitors each week. The most effective and efficient removal method for Eurasian Watermilfoil is treatment with an EPA-approved aquatic herbicide. Aquascape Environmental proposed treatment options using controlled dosage of aquatic herbicides approved for management of Eurasian Watermilfoil. Chattahoochee Nature Center staff expressed reservations about introducing any herbicide into an element of their natural ecosystem. Of particular concern were the center’s resident beavers and Bald Eagles (see Figures 3 and 4), the latter of which are subject to stringent environmental protections as an endangered species.
“We took their concerns very seriously,” said Evan Carpenter, who manages lake operations at Aquascape Environmental. “Even though we knew that the treatment options we had presented would be safe, and safely applied, there were a lot of other considerations at play. So, we gave them another option.”
That other option was the stocking of triploid grass carp (Ctenopharyngodon idella). “Triploid” refers to grass carp bred with an extra set of chromosomes to ensure sterility. Triploid grass carp are used to control submersed aquatic plants; strictly herbivorous, they do not disturb the other fish or wildlife in the water body. Fertile grass carp that migrate into streams and rivers can reproduce and potentially disturb native ecosystems; thus, only sterile grass carp may be legally stocked for biological weed control in Georgia. The Chattahoochee Nature Center board agreed to the alternative plan of stocking the pond with triploid grass carp. Seventy-five 10- to 12-inch fish were introduced into the 2.55 acre pond. At approximately 25 fish per acre, this was a fairly high stocking rate, and with the largest available fish size.
“The size and number of carp stocked would be capable of consuming higher amounts of vegetation quickly, with the goal of getting the weed infestation under control as quickly as possible without the use of herbicide,” Carpenter explained.
While it was a well-reasoned approach, nature had other ideas. Shortly after the carp were stocked, river otters took up residence in Kingfisher Pond. The arrival of otters wasn’t a complete surprise, given the Chattahoochee Nature Center’s proximity to the Chattahoochee River, a natural otter habitat. The downside in this case was that the particular species of otter making a home in Kingfisher is known to prey on grass carp. Over time, the otters decimated the carp population, making the fish ineffective as a long-term method of controlling the Eurasian Watermilfoil. By summer of 2015, the invasive aquatic plant was back in a big way.
It was now clear that a herbicide treatment was going to be necessary to save the pond. The Aquascape Environmental team worked closely with experts at SePRO Aquatics, a developer and distributor of invasive aquatic plant management products, to develop an appropriate treatment plan based on the special conditions involved. The team presented three treatment options, incorporating different products, application rates, and timeframes. The team explained pros and cons of each to the Chattahoochee Nature Center staff and Board, and ultimately all parties agreed to a treatment option that provided an acceptable comfort level regarding impact to the resident wildlife as well as a high confidence level that the treatment would be effective.
In late August 2015, an Aquascape Environmental crew arrived to perform the treatment application at Kingfisher pond. At that time, another invasive aquatic species, Duckweed (Lemnoideae), was identified in the pond along with the Eurasian Watermilfoil. The product that had been selected was also labeled for control of Duckweed, so the treatment proceeded as planned.
Two months later, Mr. Nelson reported that the treatment “appeared to have had a positive impact on the invasive material,” with no known impacts to the resident wildlife.
“The team at Aquascape Environmental was wonderful to work with,” Nelson noted. “The 41-year-old mission of the Center and sensitivity to the site were always the primary concerns in any and all management proposals they recommended. It was a very positive process all the way around.”
For his part, Carpenter was pleased with the ultimate resolution to a complicated problem.
“We worked closely with both our client and SePRO to achieve an outcome that satisfied everyone,” he noted. “Education and information were key. Most importantly, now Kingfisher Pond is healthy and provides a picturesque setting so the resident wildlife and visitors to the Center can enjoy it.”
¹Pfingsten, I.A., L. Berent, C.C. Jacono, and M.M. Richerson., 2017, Myriophyllum spicatum L.: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, https://nas.er.usgs.gov/queries/FactSheet.aspx?speciesID=237. Revision Date: 3/21/2016, Access Date: 8/24/2017