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Kenai Peninsula racing to eradicate elodea

Posted: August 1, 2013 - 5:26pm  |  Updated: August 2, 2013 - 10:53am

We had a scare the other day. Staff at the Kenai Municipal Airport suspected elodea, a nasty invasive freshwater plant, was in their floatplane basin, so we scrambled to see what was there. Elodea can be spread by floatplanes, boat props, and even fishing equipment.

The good news is that they just had a bountiful growth of native aquatic plants including a couple kinds of pondweed, mare’s tail, northern bur-reed, Siberian watermilfoil, water-starwort and muskgrass. On the downside, their call and our response reflects the uncertainty of our knowledge of the status of elodea on the Kenai Peninsula. It means that while we have some management options for elodea, the appropriate path isn’t quite yet crystal clear.

Without question, we’d like to eradicate elodea from the Kenai Peninsula. It poses an enormous ecological and economic threat to our fisheries and aquatic resources. It has grown so thick elsewhere in North America that boat traffic is hindered and dissolved oxygen is reduced to the point that fisheries populations are impaired. Elodea is also insidious, in that only a plant fragment is needed to infest a waterbody because it reproduces vegetatively.

The weapon of choice for eradicating elodea is fluridone. Fluridone is a selective systemic aquatic herbicide which inhibits the formation of carotene, a plant pigment, causing rapid degradation of chlorophyll by sunlight, which then prevents the formation of life-sustaining carbohydrates. Fluridone may be applied to an entire water body (whole-lake) or on smaller but discrete infestations within a water body (partial-lake). In the former, fluridone is generally applied as a liquid via surface or underwater drip equipment. In the latter, fluridone is often applied as time-release pellets.

Fluridone has amazingly few non-target impacts. Applied at approved concentrations (below 150 ppb), fluridone has limited toxicity to waterfowl and wildlife, is not a carcinogen or mutagen, nor is it associated with reproductive or developmental effects in animals. There are no restrictions on swimming or eating fish from treated waterbodies.

The problem is that although fluridone works, it is expensive to completely eradicate elodea from a waterbody. Until very recently, we thought that elodea distribution on the Peninsula was restricted to the 400-acre Stormy Lake and about 50 acres of the 620-acre Daniels Lake. Based on those acreages, bathymetry, and elodea survey data, we’ve estimated it would cost $130,000 for a partial-lake treatment of Daniels Lake and $260,000 for a whole-lake treatment of Stormy Lake over three years. That’s not chump change.

And now elodea has been recently confirmed in the 200-acre Beck Lake, part of the same Bishop Creek watershed that includes Daniels Lake. The total estimated bill for eradicating elodea from these three lakes is now over half a million dollars!

To get a better handle on whether elodea eradication is do-able, we are continuing to survey lakes all over the peninsula. Between the Kenai Fisheries Office and the Kenai National Wildlife Refuge, we have already sampled over 40 lakes-at-risk both on and off the refuge.

I suspect we’ll find that elodea is more widely distributed in the Nikiski area but does not occur elsewhere on the Peninsula. If that’s the case, then we’ll likely argue that it is technically feasible to eradicate elodea from the peninsula but we’ll need a lot more money. At the end of the day, however, eradication is cheaper than fixing the damage that elodea will have on our future fisheries habitat. Pay the piper now or really pay for it later.

Our collective decision to try to eradicate elodea from the Peninsula is postponed until early fall when we’ll have a more complete understanding of its current distribution. In the meantime, Alaska State Parks has taken the high road and pre-emptively closed Stormy Lake to public access in order to prevent the spread of elodea to other waterbodies.

The interagency advisory group that is trying to strategically respond to elodea on the Peninsula has decided to pursue treating Daniels Lake with diquat dibromide this summer. Unlike fluridone, which is a systemic herbicide that kills the entire plant over an extended period of uptake, diquat is a cheaper nonselective aquatic herbicide that kills exposed vegetation (but not the roots) on contact. The short-term goal is to suppress elodea growth in Daniels Lake so that fluridone treatments don’t go from partial- to whole-lake — a very expensive outcome that would result in more herbicide being used.

This has been a tough nut to crack. Elodea is the first exotic freshwater plant to get established in Alaska. Those of us that are “-ologists” have had to wrap our heads around the biology of this organism and learn about its management in a very short time frame, even as both state and federal regulatory agencies have grappled with new permitting requirements. It’s been a learning process, but unfortunately one in which time really counts.

We likely have only a very small window of opportunity to rid the Kenai Peninsula of elodea (if it’s not already too late) before it gets so established that eradication isn’t viable. Needless to say, if elodea was at the floatplane basin in Kenai, we really would have had to scramble. But the clock is ticking. ...

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