In a public presentation on Thursday, Kenai Wildlife Refuge Supervising Biologist John Morton said that herbicide treatments have eliminated elodea from two of the three known elodea-infested lakes on the Kenai Peninsula.
Elodea, an aquatic plant with long, floating stalks of dense leaves, is native to parts of the Lower 48 and South America. Before the Alaska Department of Natural Resources quarantined elodea in March 2014, it was a popular aquarium decoration. Escaping into the Alaskan wild, the pretty plant with a pretty name become the state’s first invasive freshwater weed.
Elodea reproduces by fragmentation — a small piece can quickly grow into a cluster of stalks up to eight feet tall, Morton said.
“It has the potential to degrade any sort of habitat for fish, basically by filling the water column with biomass,” said Heather Stewart, an invasive plant and agricultural pest coordinator at the Alaska Department of Natural Resources’ Plant Materials Center. “When it fills the water column with biomass it slows water velocity, increasing sedimentation. You’re changing the hydrology completely.”
“It get so thick it affects boat traffic,” Morton said. “Ultimately, it can knock your dissolved oxygen content almost to zero in some instances.”
Stewart said she is coordinating the efforts of “at least a dozen” groups, including state and federal agencies and conservation non-profits, to wipe out the Alaskan elodea population. On the Kenai Peninsula, that effort is being led by biologists such as Morton.
In 2012, the first elodea infestation on the Kenai Peninsula was discovered in the 400 acre Stormy Lake, near Nikiski. Five smaller areas of infestation were found in Daniels Lake. A 2013 survey of 64 Kenai Peninsula lakes by the Kenai Wildlife Refuge found a third infestation in Beck Lake, which had the largest elodea population and was especially troubling to elodea managers because it has an outlet into the Peninsula’s larger water system through Bishop Creek.
“We think that Beck Lake is ground zero for Elodea in the Nikiski area,” Morton said. “It’s got the most elodea, and it makes sense with what we know about a guy who owned a tropical fish shop — he might have dumped in Beck Lake when he closed it out in the 90s. We think Daniels is the last to get hit.”
Because elodea can travel from lake to lake through plant fragments caught in boat propellers, the Stormy Lake boat launch was closed in 2013. The closure may have halted elodea, but the reduction of the Peninsula’s existing population was accomplished with a herbicide called fluridone, which kills by inhibiting photosynthesis. Fluridone was chosen for its selective effect on elodea.
“Elodea just happens to be highly sensitive (to fluridone),” Morton said. “It’s lethal to elodea at very low concentrations.” Because of elodea’s sensitivity, fluridone could be deployed at a concentration too low to cause major damage to other plants. Nonetheless, other aquatic plants in the fluridone-treated lakes may not have escaped totally without damage. A native water-weed called myriophyllum was also thought to be vulnerable to the levels of Fluridone necessary to kill elodea. Morton didn’t expect the myriophyllum populations in the treated lakes to be wiped out, but said that if they were, the plant would be relatively easy to re-introduce.
In the five partially-infested areas of Daniels Lake, a second herbicide, diquat, was applied in June. Morton said diquat was “a contact killer” of aquatic plants.
“It kills anything it comes in contact with that’s green,” Morton said. “Fluridone literally takes weeks to have an impact. Diquat, it takes 72 hours.”
However, parts of a plant untouched by diquat, such the roots, remain alive. Morton said that the more rapid but less thorough Diquat was used to quickly stop the five elodea masses in Daniels Lake from spreading while the Fluridone worked to eradicate it completely.
“We killed everything on the surface (using Diquat),” Morton said. “That means that everything that’s regrowing, from the roots up, is growing up into a fluridone-laced water system.”
The herbicide treatments began in June 2014.
Before application at Beck Lake, the Cook Inlet Aquiculture Association used floating nets to block the outlet into Bishop Creek to prevent elodea fragments stirred up by the boat propeller from escaping and spreading. Outlets at Daniels Lake were similarly blockaded.
Fluridone was applied to the three lakes in the form of slow-release clay pellets, which were scattered into the lake using a blowing machine. To achieve a more rapid effect, the diquat was released in the five target areas of Daniels Lake in liquid form.
Following the treatments, elodea was monitored at 50 sample points at each of the three lakes.
Morton said that when elodea begins to die, the tips of its stalks turn a pale, sickly pink. At a later stage, the plant becomes brittle. Successive elodea samples gathered from the lakes two weeks and eight weeks after herbicide application showed these stages of decline.
“At 14 weeks, we were getting real honest-to-god death,” Morton said.
In May 2015, the samplers found that Beck and Daniels Lake were elodea-free.
“After we sampled our fifty points we went around looking for it, and we couldn’t even find anything that looked like elodea dead,” Morton said of Beck Lake.
Stormy Lake has a shrunken, but still extant, elodea population.
“It’s still there, but it’s not right in your face,” Morton said. “You have to go look for it.”
As for the herbicides, they will be monitored at 6 sample sites in Beck and Stormy Lakes, and 19 in Daniels Lake. The first sample was made June 15, and future samples will be made in July, August, and October. Morton said fluridone is gradually broken down by exposure to ultraviolet light, while diquat leaves the ecosystem by being bound to sediment particles. However, Morton said the herbicide surveys have found that “the fluridone is staying in the lakes better than we thought it would.”
Because fluridone is continuing its effect longer than expected, fluridone treatments in Beck Lake in August and Stormy Lakes in September will use half the amount deployed in the June 2014 treatments. The partially-treated Daniels Lake will receive the same amount in its treatment in July. There are no current plans to use Diquat again. Sediment samples from the lakes will also be tested for herbicide residue this summer and the next. As the herbicide treatments continue, field supervisor Jeff Anderson of the Fish and Wildlife Service Soldotna Office said his team is monitoring other measures of water quality and comparing them to control lakes.
“This year and last year, we didn’t really see any differences among the parameters within the lakes and between the lakes,” Anderson said.
A more thorough survey of all vegetation in the three lakes will be conducted this summer to determine conclusively whether elodea is gone, and what side-effects there might have been on native plants. Morton said he will also survey other Nikiski-area lakes for elodea.
The Stormy Lake boat launch will stay closed this summer, but Morton said that “if things go the way I think they’re going to, I think we can probably open it in the fall. I think by then, the last of the elodea will be gone for all practical purposes.”
However, Morton said he remains concerned because elodea could easily return to Kenai Peninsula lakes.
“As long it isn’t totally dried out, (elodea) can be carried,” Morton said. “And it only needs a fragment.”
Stewart said that there are 19 known elodea-infested lakes in Alaska. Most are in Cordova, with three in Anchorage, one in the Mat-Su Valley, and three in Fairbanks.
Morton said that Alaska presents special problems for aquatic invasive control: it has thousands of remote lakes inaccessible by road, where elodea infestations are much harder to detect and treat. Once infected, these lakes can become hidden elodea reservoirs. Morton said that the spread of elodea by floatplanes, which can access these remote lakes, is a special danger.
Morton said that Anchorage is planning to begin a similar fluridone application program.
“I’m excited about that, because I think that’s the buffer we need,” Morton said. “Assuming we’re successful (with elodea eradication) here, that may be the buffer we need to keep Kenai safe for a little bit longer.”