ELODEA CANADENSIS

Recording the impact of an invasive species

Story by Patty Karafotias & Michael Hampton

Photos by Patty Karafotias

Submerged under fresh water lies a dense aquatic herb invasive to Cordova, Alaska. Elodea canadensis - or as field workers call it, ELCA7 - has sprouted many concerns for Alaskans as they note the impact this species has on their environment.

 An invasive species like Elodea is a non-native plant producing offspring in large quantities and in cases like this, well-establishes itself in freshwater systems. Such bodies of water house potential for the species to spread and replace native vegetation. In addition, the opaque underwater bed of Elodea deters aquatic life; excessive growth of the plant may reduce levels of dissolved oxygen. Similar to the air humans breathe, “the survival of aquatic life depends on a sufficient level of oxygen dissolved in water” (Elodea 1). Moreover, “reduced levels of dissolved oxygen can impact growth and development of different life stages of salmon, including eggs, alevins, and fry, as well as the swimming, feeding and reproductive ability of juveniles and adults” (Carter 1).

Levels of dissolved oxygen in water is a good environmental indicator; this is especially true in Cordova as “salmon are a keystone species in the Copper River Delta ecosystem” which contribute to the region’s other aquatic and terrestrial organisms (Lang 2).

Since Elodea’s first reported sighting in Eyak Lake in 1982, the U.S Forestry Service began surveying several locations throughout Eyak River and the surrounding Cannery Ponds. Questions still remain about the plant’s initial introduction to Alaska but scientists hypothesize that a fish tank was dumped into Eyak Lake and through Elodea’s ability to spread through stem and leaf fragments, the plant easily found its way to Eyak River, Alaganik Slough, Mckinley Lake, and Martin Lakes in Cordova alone. There have also been sightings in Anchorage and Fairbanks.

 Herbicides are currently the only known treatment for Elodea canadensis and with such treatment comes field work to ensure its effectiveness on invasive species and lack thereof on native plants. Herbicidal concentrations of diquat and fluoridone are precisely calculated by chemists for specific bodies of water to prevent harm to native fish. Through the U.S. Forestry Service, Emily Love Platt and her crew of field scientists - James Ianni and Dan Schmalzer - are continuing a five-year study monitoring aquatic plant populations and implemented water treatments.

Drifting past children as they ride the waves of the jet boat in Eyak River, Schmalzer parallels a set of small wooden stairs leading to the first testing location: West Cannery West Reference A, the name scientists have given to one of the many ponds around Eyak River. Here is where the field work truly begins.

Each generated testing point in the ponds are indicated by green dots on a map which are to be repeated during each trial. The vegetation assessment also involves randomly generated locations which are tested using the same method. Rather than treading through these ponds by foot, small rafts and kayaks are used.

“We use the boats mainly because this is really super silty and all the aquatic vegetation is really easy to stir up, so the idea of the boat is to not disturb the vegetation,” said Love Platt.

Plastic transects made from PVC piping represent a designated surface area to be tested beneath the pond’s murky water. Points have been marked with another piece of piping visible above water. “You see a little post and we go and use those as the corner and use the PVC water frame on the substrate and we estimate the percent cover from above and call it out to a person to record some data,” Love Platt explained.

After placing the transects at the base of the pond, the fun begins. For one to identify species below water, it may be necessary to go down under. It is through identification of these plants that one can calculate the density of each species. The more dense, the greater threat to other populations.

 It becomes important to know both the density of Elodea canadensis and the success of native species; they are loosely dependent. An increased population of Elodea may contribute to a lesser presence of another aquatic plant. The two variations of ponds - treated and control - may show differing amounts of Elodea when the herbicide is either present or absent. Transects that show a high density of Elodea are a realistic view of its threat to Alaska’s biodiversity as the plant continues to spread. Elodea reproduces through stem fragments, meaning that only a snip of the plant is needed to invade a body of water. It is easily transferred from location to location whether on the bottom of Xtratuf boots or on the floats of float planes.

“In Alaska a lot of people get on a float plane and they are really concerned about that because those float planes can just move things into these far remote reaches that you don’t know. They might not have detected that they are getting weeds out there so that is a big worry, and the places where Elodea is growing comes from these kind of places,”  said Love Platt, who has been venturing to these ponds for the last four months as part of her post-undergraduate job with the U.S. Forestry Service in Cordova. “That is a bummer because those planes from there go literally all over the state. It's kind of a nightmare as far as that's concerned.”

Carter, Katherine. The Effects of Dissolved Oxygen on Steelhead Trout, Coho Salmon, and Chinook Salmon Biology and Function by Life Stage. California Regional Water Quality Control Board North Coast Region, Aug. 2005.

Earl, Elizabeth. “Invasive Elodea Leads to Alexander Lake Shutdown.” Alaska Journal of Commerce, 20 June 2019.

Lang, Dirk W. “A Survey of Sport Fish Use on the Copper River Delta, Alaska.” United States Department of Agriculture, July 2010.

Risberg, Jeff. “Low Dissolved Oxygen in Water.” Minnesota Pollution Control Agency, Feb. 2009.

“Elodea.” Copper River Watershed Project, 19 May 2016.