The Chena Slough of today looks nothing like it did 50 years ago, it runs slow and clear, filled with aquatic vegetation that would not have survived in a fast-flowing, glacier-fed slough. The slough has been filling itself in, as all sloughs cut off from their headwaters will. The slower water is much more inviting to plant growth. A recent addition, "Elodea," has been cause for concern since its discovery in the Chena Slough system in 2010. In Part 2, we will take a look at Elodea and the other plants growing in the Chena Slough.
Part 2 - The Weeds
The Chena Slough is home to an array of plant life. Along its banks grow willows, alder, poplar, fireweed, raspberries, lilies, lingonberries, cattails, native grasses, and sedges mainly. Dozens of species of wildflowers, fungi, and other plants as well. Living an aquatic life in the waters of the slough, we find pondlily, marestail, buttercup, burreed, water milfoil, pondweed, and numerous undescribed cryptogram-types (Dyrness et al., 1992).
In 2009 or 2010, "Elodea" was noted to be growing in the Chena Slough (FSWCD, 2011). It was believed to get its start after someone dumped an aquarium containing the plant into the slough near Repp Rd (see figure 1).
|Elodea Origination in Chena Slough (Photo from UAF.EDU)|
Elodea is a member of the Hydrocharitaceae ("waterleaf") family. There are five recognized species:
- Elodea bifoliata (occurs primarily in temperate western North America)
- E. potamogeton (native to South America)
- E. callitrichoides (native to South America)
- E. canadensis (native to North America)
- E. nuttallii (native to North America)
The Elodea found in the Chena Slough was first described as the species Elodea canadensis, but later determined to be Elodea nuttallii (Etcheverry, 2012). Here is a recent picture of the Elodea present in the Chena slough, compared with nuttallii and canadensis.
|Elodea Collected 6/23/15 (by author)|
|Elodea Nuttallii ("ElodeaNuttallii2" by Christian Fischer. Licensed under CC BY-SA 3.0 via Wikimedia Commons - https://commons.wikimedia.org/wiki/File:ElodeaNuttallii2.jpg#/media/File:ElodeaNuttallii2.jpg)|
|Elodea canadensis ("ElodeaCanadensis" by Christian Fischer. Licensed under CC BY-SA 3.0 via Wikimedia Commons - https://commons.wikimedia.org/wiki/File:ElodeaCanadensis.jpg#/media/File:ElodeaCanadensis.jpg)|
Judging from appearance, the Elodea found in Chena Slough is neither nuttallii or canadensis. Its growth habits and appearance more favor a species of Hydrilla, yet it has leaves in whorls of three, an attribute of Elodea. A paper from the Fish and Wildlife Service describes Alaska's Elodea found in several lakes as (Cite):
Genetic analysis of specimens from these three lakes indicates that it is a hybrid, Elodea canadensis X nuttalli.
Assuming the genetic evaluation is correct, it would behoove the groups managing the eradication efforts to standardize the term. Elodea alaskana, perhaps?
Elodea was first reported in Alaska in 1982 when it was found in Eyak Lake near Cordova. The next sighting was in the Chena Slough in 2009. Then several lakes on the Kenai Peninsula and in the city of Anchorage in 2012 and 2013. Genetic reports confirmed that Elodea from three lakes (Stormy, Beck, and Daniels Lakes) were the hybrid described above. The three areas where Elodea alaskana have been found are hundreds of miles apart and not connect by water in any way. Pictures of Elodea from all sites in Alaska look identical. If the Elodea found in Chena Slough originated from an aquarium clean-out, how did the aquarium owner acquire Elodea alaskana? And how did it hybridize so fast? Possibly a better explanation is that the Elodea alaskana was brought to the Chena Slough by migrating birds from Eyak Lake or elsewhere. It's unlikely that the introduction was by floatplane or boat as the section of Chena it was found in is inaccessible by both. A true mystery! Is it possible that Elodea alaskana is a native species?
A tiny blurb from a Fish and Wildlife document may shed some light on the initial appearance of Elodea alaskana:
Elodea is insidious, in that only a plant fragment is needed to infest a water body because it reproduces vegetatively. Likely initial vectors on the Kenai Peninsula are dumped aquaria and discarded commercial lab kits. However, as these early populations of elodea become better established, motor boats, anchors, fishing gear, float planes and even waterfowl will become the greater risk. [Emphasis added]
According to a document written by the Anchorage Soil and Water Conservation District in 2014, the Elodea found in the Chena Lakes and Chena Slough are somewhat unexplainable. A lab examined samples from the Chena district, and found that it displayed the hallmarks of a canadensis/nuttellii hybrid. This, they said, seems most unlikely (ASWCD, 2014).
It also appears that the Chena Lake infestation is comprised of both male and female plants. Dr. Les is also questioning the native/invasive status because of the presence of both male and female plants in Chena Lake, which is uncommon in plant introduction scenarios. Cecil pointed out that the pattern of discovery (urban areas and high plant density) and lack of identification in past Alaska vegetation surveys is good evidence toward its invasive status, but thinks we should leave definitions ambiguous until we have a more definitive answer. Dr. Les has requested more Alaska Elodea samples this summer to sort out the morphological vs. genetic identification confusion, especially with flowers for identification purposes.
It would seem plausible that Elodea alaskana is not an invasive species at all. If it were invasive, where are the parent species? Why have canadensis and nuttellii not invaded local waterways as they have in Europe and Asia? Further discussion in the ASWCD document makes it seem likely that Elodea alaskana has been present in Alaska since the Ice Age.
Part of this discussion is somewhat intuitive in the thought that if two varieties have hybridized often enough that we are seeing the 'Alaskanized' Elodea that has adapted to its environment and evolved, the two varieties have likely been in close proximity for some amount of time, with the presence of both female and male plants.
Only one problem...canadensis and nuttelli have not been found in Alaska, only a hybrid! A likely scenario is that at one time both of these species were found in Alaska, possibly in isolated lakes, they hybridized there and are now being carried around the state by waterfowl and people.
Another option is that researchers experimented with hybridizing Elodia and inadvertently released it to the environment. The assessment of "discarded commercial lab kits" may be a valid hypothesis. Did someone try breeding an Elodea hybrid here? Would there be a precedent?
Another invasive species, Vicia cracca, commonly called "Bird Vetch" was brought to Alaska in the 1970s as a forage crop by University of Alaska researchers (UAF, 2012). Bird Vetch now lines nearly every street within 20 miles of the university despite decades of eradication attempts.
At any rate, Elodea, like bird vetch, is here. Is it here to stay or can it be eradicated? Does it need to be eradicated? Does anyone care what it really is and where it came from? For some reason, state officials want it gone and have begun using herbicides to do so.
An aquatic herbicide, Fluridone, has been applied to three remote lakes in the south-central part of Alaska. Now more government agencies are looking at applying Fluridone in the city of Anchorage and the town of North Pole, including Chena Slough. In Part 3, we'll look at the War on Elodea, in Alaska and elsewhere.
ASWCD (2014). Sand Lake Vegetation Management Study (Draft). Retrieved from http://www.aswcd.org/SL%20Report/Sand_Lake_Elodea_Study_v35_published_optimized_Part4.pdf
Dyrness, C. T., Batten, A. R., & Wenzlick, K. J. (1992). The Alaska vegetation classification.
Etcheverry, D. (2012). Elodea management in Fairbanks. Retrieved from http://www.uaf.edu/files/ces/cnipm/otherresources/12th-annual/Elodea_Management_in_Fairbanks_A_Review_of_2011_Findings.pdf
Fairbanks Soil and Water Conservation District. (2011). Elodea canadensis infestation in Chena Slough. Retrieved from http://www.fairbankssoilwater.org/resources_Chena_Slough_Invasive.html