A lowly earthworm can't have too much of an effect on the planet as a whole, right? Actually, it turns out that tiny earthworms really do have a global impact. According to a paper published this week in the journal Nature Climate Change, earthworms are part of the system by which many greenhouse gases enter both the soil and the atmosphere. The paper is what is known as a meta-analysis, which combines and analyzes the results of dozens of previous studies.
As the authors write, soil contributes approximately one-fifth of the carbon dioxide released into the atmosphere. Earthworms enhance this process two-fold. First, they burrow around in the soil, making it easier for CO2 to escape from the earth. Second, the earthworms eat the soil and its contents, digesting it and producing both CO2 and nitrous oxide, another potent greenhouse gas. Nitrous oxide (N2O) has 300 times the atmospheric warming effect of CO2, according to the U.S. Environmental Protection Agency.
All-told, the study found that when earthworms are present soil emits 33% more CO2 and 42% more N2O.
This isn't the only role that earthworms play in the broader cycle of greenhouse gases. They also serve to sequester carbon into the soil, but as the authors write, it is uncertain if this is enough to "sink" many greenhouses gases into the soil permanently.
If the world were a static, unchanging system, the role of earthworms in the global cycle of greenhouse gas emissions would be one of those "good to know" things. Unfortunately, that's not the case. As the researchers note in their paper, earthworm populations are growing and spreading to new areas, which means their role in the changing climate could also grow. Earthworms are actually classified as invasive species in some areas of the U.S. where they died out during the last Ice Age before being brought back to these shores by European settlers. Other native earthworm species have been expanding their range northward, reaching new areas and create ecosystem-wide changes.
A case in point is Minnesota. As the Minnesota Department of Nature Resources explains it, the state's hardwood forests "developed in the absence of earthworms. Without worms, fallen leaves decompose slowly, creating a spongy layer of organic 'duff.' This duff layer is the natural growing environment for native woodland wildflowers. It also provides habitat for ground-dwelling animals and helps prevent soil erosion." When invasive earthworms enter the region, the duff disappears, causing ferns, wildflowers and young seedlings to die off. This can ultimately cause soil to erode, forests to die off and fish habitats to become degraded, all of which could have a further role in greenhouse gas emissions.
The authors don't place any particular blame on earthworms — the creatures are "largely beneficial to soil fertility," they write. They also say that the previous studies that they studied were often limited, which means their own paper its own limitations. But all the same, this new research shows how important all of us — even lowly earthworms — are to the global system.
Also on MNN: