The Earthworm Effect: Unraveling Soil Weathering Dynamics
Pittsburgh, Pa., USA: Earthworms, the hardworking invertebrates that grace
the upper layers of soil, have long been considered helpful in our home
gardens. Earthworms are prolific munchers, grinding up organic material and
sediment grains that make up soils. Although they are very different
animals, worms, like many poultry, have gizzards. “Worms will ingest some
larger soil grains, and then they use the strongest and largest of those
grains, retaining them in their gizzard,” explains Adrian Wackett, a soil
science doctoral student at Stanford University. These gizzards are great
for breaking down soil to release nutrients.
While earthworms may benefit your garden or compost pile, they can be
invasive and potentially cause damage to natural ecosystems. Physical
weathering (or breaking down rocks or sediment into smaller pieces of the
same material) of soils by worms has implications for soil processes,
including how much organic matter and nutrients a soil can hold. By
breaking down sediment, worms also create new soil textures which can
impact how water soaks into soil and affect chemical processes.
Weathering is also a big factor in carbon dioxide cycling. “Geologists
often think about weathering rates being one of the major factors that
controls Earth’s ‘thermostat,’” says Wackett. Chemical activities,
including the sequestration of carbon into new minerals, are aided by the
worms grinding up minerals. But earthworms also break down organic
material, releasing carbon dioxide into the atmosphere.
Wackett wondered how much mineral weathering earthworms could produce. In
new research presented Wednesday at the Geological Society of America’s GSA Connects
2023 meeting, Wackett and his colleagues will demonstrate the invasive
expansion of earthworms—or “global w’o’rming”—triggers a significant amount
of silicate breakdown.
To better understand how worms break down sediment, the team examined soils
in the El Yunque National Forest in Puerto Rico. They found significant
changes in sediment sizes within the soil column, with smaller median
particle sizes in areas where earthworm burrowing occurred. In fact, quartz
grains in the worm-bioturbation zone were nearly 50% smaller than those
grains without worm activity.
While other shorter-term laboratory experiments have been done on worm
weathering, this is the first study on worm-induced silica breakdown of
in situ soils. The team found that worms cause roughly 2% of the
total weathering in El Yunque soils. Wackett adds that this is a
conservative estimate for worm-weathering and points out that worms could
be an even more forceful weathering mechanism than these initial estimates
Weathering rates could proliferate by the spread of earthworms into new
territories. Wackett notes that earthworms are making their way into
northern latitude forests that didn’t have worms in the past.
The team assessed grain size changes across a series of soil profiles
spanning earthworm invasion gradients in Alaska, Minnesota, Finland, and
Sweden where the timing of earthworm arrival––and hence worm weathering––is
more tightly constrained. They noted appreciable shifts in median particle
size in these historically worm-free sites.
Wackett concludes although each worm produces “small changes, once you
scale up, you actually come up with pretty sizable [weathering
Exploring whether worms weather silicates in soils
Contact: Adrian Wackett, Stanford University, firstname.lastname@example.org
207: D1. Advances in Geomorphology and Quaternary Geology
Wednesday, 18 Oct. 2023, 11:40 a.m. EDT
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