The Effects of Soil Calcium on Invasive Earthworms in the Adirondacks, NY
Final Report to Edna Bailey Sussman Foundation
Caity Homan, SUNY-ESF
December 5, 2014
Background
The negative ecological effects of invasive earthworms span from alterations in soil
physical and chemical properties, to shifts in plant, fungi and arthropod diversity and community
composition. These effects are particularly pronounced in previously glaciated areas of North
America, which developed in the absence of earthworms for thousands of years. Soil acidity and
soil calcium availability are important factors influencing whether or not earthworms can invade
and successfully become established at given site. The majority of invasive earthworm species in
North America are generally found in low densities, or not at all, in base poor soils with a pH
below 4.5.
Few studies examining invasive earthworm populations in the Adirondacks NY have
been conducted. The Adirondack region of New York is underlain primarily by base-poor
bedrock, which has made this area particularly sensitive to the negative effects of acidic
deposition from fossil fuel combustion. In forested systems in the Adirondacks acidic deposition
has resulted in the leaching of base cations, subsequently increasing soil acidity. With
amendments to the Clean Air Act of 1990 acidic deposition has decreased, however recovery of
forest soils will be slow. Of particular interest is the Honnedaga Lake watershed in the
southwestern Adirondacks which contain the most acidic soils in the region. In an effort to
accelerate recovery the Honnedaga Lake watershed has undergone whole-ecosystem restoration
through liming. While the watershed is being monitored to examine the response of the system to
liming earthworms are not currently being studied despite their potential negative impacts.
The goals of the internship were to examine the effects of soil calcium on the invasibility
of earthworms in the Adirondacks. Specifically with the internship I aimed to 1) examine the
distributions of invasive earthworms across a soil calcium gradient in the Adirondacks and 2)
determine how soil liming in the Honnedaga Lake watershed would affect the biomass and
mortality of the invasive earthworm Lumbricus terrestris, the Canadian nightcrawler.
Methods
Field Study
I surveyed 15 sites along a soil Ca gradient in the Adirondacks for earthworms in June
and October of 2014. At each site earthworms were sampled using timed search and mustard
extraction methods. Earthworms were preserved and later identified to species. Prior soil and
vegetation data were collected at each site. Thirteen of the fifteen sites were located in the central
Adirondacks and two were located at the Honnedaga Lake Watershed in the southwestern
Adirondacks.
Experimental Study
A 3x3 factorial experiment was conducted with 3 time treatments, 2, 4 and 6 weeks, and
3 soil treatments, no lime, 4.85g lime (equivalent to the liming rate of the experimental
Honnedaga Lake Watershed) and 9.7g (twice the liming rate of the experimental Honnedaga
Lake Watershed). There were a total of 9 treatments with 6 replications for a total of 54
experimental units.
In August 2014 soil was collected from the un-limed reference watershed at Honnedaga
Lake. Soil was dried, mixed, sieved placed into containers. Lime treatments were dissolved in
water and applied as a slurry to the surface of the mircrocosm. Leaf litter from the reference
watershed was collected in August 2014 and ten grams were added to each microcosm. Two
individuals of Lumbricus terrestris, purchased from Carolina Biological Supply, were weighed
and added to each container. All microcosms were placed in a growth chamber. Microcosms
were destructively sampled after 2, 4 or 6 weeks. At each sampling period earthworm survival
and biomass were measured. The experiment began at the end of September and ran until the
beginning of November.
Preliminary Results
Field Study
Of the 15 sites sampled 6 sites had earthworms present in June and 4 sites had
earthworms present in October. Sites where earthworms were present are locations with the
largest amounts of soil Ca in relation to the gradient. No earthworms were present at locations
with an Oa horizon calcium content below 18 cmol/kg. Earthworm identifications are currently
being verified but thus far a total of 10 species were sampled in June and 7 were sampled in
October. One native species was sampled at the site with the largest amount of available soil
calcium in June.
Experimental Study
Earthworm mortality increased over time, and was greatest in the un-limed soil treatment.
More earthworms survived in the 9.7g lime treatment as compared to the 4.85g lime treatment.
Earthworm biomass loss was also greatest in the un-limed soil treatment, while biomass gains
were greatest in the 9.7g lime treatment.
Ongoing Work
Earthworms will continue to be identified, to species when possible. All unknown
specimens will be sent to an earthworm taxonomist for analysis. Soil from the earthworm liming
experiment will be sent to USGS collaborators for chemistry analyses, including percent organic
matter, base cation availability and pH. Statistical analyses will be conducted in order 1)create a
model that best explains factors influencing earthworm distributions across the calcium gradient
and 2) compare mean biomass and mortality across the earthworm experimental treatments.
Acknowledgements
I would like to thank the following people and organizations for providing essential
support for my project: the Edna Bailey Sussman Foundation, my major professor Colin Beier,
my committee members Pete Ducey and Tim McCay, my internship advisor Greg Lawrence of
the USGS, Dan Josephson, the Moser family, and Patricia Dombrowski, Annie Homan, Sam
Quinn, Angela Vitale and John Wiley for field work assistance.
Sampling for earthworms using liquid mustard extraction at Honnedaga Lake.
Soil from the reference watershed at Honnedaga Lake that was used in the earthworm
experiment.
Microcosm container used in the earthworm experiment.
Surface of a limed microcosm after 2 weeks. Leaf litter has been consumed by earthworms,
and castings (byproduct of earthworms consuming organic material) are present.
Surface of an unlimed microcosm after 2 weeks, with no evidence of earthworm activity.