144-1 QGG 2025 Marie Morisawa Award: Subsurface Dynamics of Microplastics in the Land of Headwaters

Session: Microplastics in the Environment (Posters)

Presenting Author:

Authors:

Abstract:

Despite growing scientific attention, most microplastic research focuses on sources and accumulation in major sinks, leaving the dynamics of land-based subsurface systems understudied. While studies have examined MPs in soil and sediment, the samples were collected at the surface. Very few studies have investigated subsurface MP distribution using soil cores, yet this is critical for understanding MP fate and transport. Here we attempt to bridge the gap by using soil coring, finer sample increments, and radioactive dating to align MP characteristics with deposition and accumulation rates.

Our first field site is located near the headwaters of the Cache La Poudre River in northern Colorado, USA. We established a transect extending from a dual-use road and trail (a direct input point source) downslope to the riverbank. Along the transect, we marked five sampling sites and extracted five soil cores from each site, giving us 25 total soil cores. Additionally, we dug three 30 x 30 cm soil pits and deployed one passive atmospheric dust collector in the study area.  To date, we have isolated MPs via density separation, characterized grains using a Dynamic Image Particle Analyzer, and quantified soil factors such as moisture, organic matter, and texture to contextualize our findings.

We hypothesized MPs would move more easily through coarse, angular, well-draining soil, while a fine-grained, organic-rich, wetter soil will retain more MPs. Preliminary findings based on visual microscope inspection suggest that a higher volume of certain types of MPs are present downslope in finer grained, wetter, more organic-rich soils. This could indicate that some types of MP are more likely to mobilize in surface runoff, while others are more likely to penetrate deeply into the soil.

Next, we will use the soil cores and samples from the soil pits to more quantitatively classify the MPs via microscopic FTIR, as well as date the soil using ²¹⁰Pb and ⁷Be. Multi-variate regression will be used to evaluate predictors of MP distribution, and spatial statistical analysis will be performed to characterize spatial continuity in the distribution of MPs. Radiometric dating will be used to construct a model for MP accumulation over time.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-5276

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