Survey scans for elodea spread in Interior, finds naught

A variety of agencies in the state are working to eradicate the invasive aquatic plant elodea. This summer, elodea was detected and treated in Anchorage’s Lake Hood, and a survey to search for elodea along the Tanana River downstream of Fairbanks has just concluded.

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Elodea. (Photo from the U.S. Fish & Wildlife Service)
Elodea. (Photo from the U.S. Fish & Wildlife Service)

The plant has the potential to make drastic changes to aquatic ecosystems.

Elodea is a plant commonly found in aquariums that, if released in the wild, will dominate certain lake or river habitats, choking out native vegetation and altering the food web at all levels.

National Park Service Aquatic Ecologist Amy Larsen describes a few of the changes that elodea can bring about:

“It increases sedimentation rate, allowing more sediment to settle out of the water.  And it can decrease the dissolved oxygen concentration in the water because it is growing so rapidly and using up all of that oxygen.  But it also just displaces our native aquatic plants, which are good forage for a variety of waterfowl species.”

In addition, elodea can ruin the clear-water habitat needed by grayling and spawning salmon, and give an advantage to ambush predators like northern pike.

In a place like Lake Hood, elodea was perceived more as a threat to human safety than the environment, because it clogs floatplane rudders or impedes a floatplane’s ability to move along the water.

But if pieces of elodea were to hitch a ride on some of the float planes that depart from Lake Hood, it could cause trouble in other ecosystems around the state.

So a variety of agencies quickly recognized the seriousness of the situation and the state Department of Natural Resources was granted an emergency exemption to apply a series of herbicides.

Invasive Plant and Agricultural Pest Coordinator Heather Stewart with DNR explains that after an initial knockdown with the chemical diquat in July, a more lethal attack with fluridone happened in Lake Hood earlier this month.

“Diquat is a contact herbicide so it basically reduces the top biomass in aquatic systems. Whereas fluridone is a systemic herbicide, so there has to be uptake by the plant, and it prohibits the production of chlorophyll in the plant, so it has the plant starve itself in the long term.”

The last application of fluridone comes in a slow-release pellet, which continues to work throughout the winter as elodea may be trying to reestablish itself.  Stewart says that the herbicides appear to have worked, and there is no elodea visible in Lake Hood now.  The herbicides killed most of the other plant life in Lake Hood as well.

In the Interior, a multi-agency search for elodea just wrapped up, looking along the Tanana River downstream of Fairbanks and up the Tolovana River to the village of Minto.

The survey did not turn up any new pockets of elodea.

It was motivated by the discovery of the plant in Totchakat Slough near Nenana about a month ago.  That represents a big jump for elodea from its previously-known concentrations around Chena Slough and Chena Lakes.

Amy Larsen with the National Park Service says that having elodea in a major river system like the Tanana introduces many new ways for the plant to spread.

“The river itself can move that plant around, either when the Tanana floods and floods into adjacent wetlands or when streams back up and reverse flow during flooded periods.  Then fragments of elodea can move up these streams and get trapped on woody debris and then it can root.”

Elodea can also be carried downriver by ice during spring breakup.  While it is not a threat to take root in the main stem of deep, silty rivers like the Yukon, it can use these rivers to get to more conducive habitats.

It reproduces by fragmentation, when parts of the plant break off and move elsewhere.  It can also send out seed, though Heather Stewart with DNR says she has only seen a few examples of flowering elodea in the state – one of which was Chena Slough.

DNR is attempting to get the necessary permits to apply herbicides there, in addition to waterways near Cordova.  Funding is in place to eradicate elodea in Alexander Lake in the Mat-Su Borough as well, and Stewart reports elodea is nearly gone from various locations on the Kenai.

Elodea has reached a total of 22 lakes, streams and rivers in Alaska so far.