Source: Laboratories of Margaret Workman and Kimberly Frye - Depaul University

Using mustard, Lumbricus terrestris earthworm populations can be sampled directly from soil depths without landscape disturbance or toxicity. Earthworms can then be counted for data and statistical analysis using a bar graph and student’s t-test.

Monitoring earthworm populations is a vital technique for environmental scientists, as multiple species of earthworms (most notably those from the suborder Lumbricina) have been invasively spreading throughout North America and South America. Exotic earthworms can be found on nearly every land mass and in nearly every ecosystem on the planet, and where and when these species become invasive has been a focus of international environmental research.¹

Ecological invasion typically lowers biodiversity of an ecosystem by directly outcompeting, endangering, or otherwise contributing to the extirpation of native species. As ecosystem engineers, invasive earthworm species alter the cycling of nutrients through decomposition rates of organic matter on the upper horizons of soil, where plant roots mine for nutrients. Invasive Lumbricus species have both extirpated native earthworm species and have been shown to increase the available nitrogen concentration and rates of nitrogen in invaded soils.² In a positive feedback loop, accelerated levels of nitrogen in turn make the system more hospitable to invasive plant species that are adapted to high levels of nitrogen compared to native plant species, and will outcompete natives in a phenomenon known as “invasion meltdown.” An invasion meltdown relationship has been proposed for invasive earthworm species Lumbricus terrestris (European earthworm) and an invasive plant species Rhamnus cathartica (European Buckthorn).³

1. Preparation of Mustard Concentrate Solution

1. Turn on balance, place a weigh boat on top, and zero the balance.
2. Weigh out 38.1 g of ground oriental mustard into weigh boat and transfer to a plastic container with cap.
3. Measure 100 mL of tap water in a graduated cylinder and add to the plastic container with mustard.
4. Secure cap on container and shake vigorously until all mustard is mixed off the bottom of the plastic container and dissolved into the tap water.
5. Let soluti

Sampling site 1 was a managed park, which sees significant disturbances such as aeration and fertilizers.  Sampling site 2 was an unmanaged area, which sees no human interferences.  As shown in Figure 1, site 1 has a higher density of earthworm populations, likely due to the increased hospitability due to human disturbances.  However, site 1 also has higher variability of sampling, indicating the earthworm population may not be as consistently dense as the average suggests.

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Invasive species are a major threat to biodiversity. Exotic earthworms (eg: Lumbricus terrestris) and European buckthorn (Rhamnus cathartica) have been implicated as part of an “invasional meltdown” occurring in mid-western United States wooded communities. An invasional meltdown is the process where one invasion of a species facilitates the invasion of others. Thus, the rate of loss of ecological health can greatly accelerate as one invasive species makes way for additional ones. As undesir

1. Belote, R.T., Jones, R.H.  Tree leaf litter composition and nonnative earthworms influence plant invasion in experimental forest floor mesocosms. Biological Invasions. 11, 1045-1052 (2009).
2. Costello, D.M., Lamberti, G.A.  Non-native earthworms in riparian soils increase nitrogen flux into adjacent aquatic ecosystems. Oecologia. 158, 499-510 (2008).
3. Nuzzo, V.A., Maerz, J.C., Blossey, B. Earthworm invasion as the driving force behind plant invasion and community change in northeastern north American forests. Conserve Biol.23, 4. 966-974 (2009).