Abstract
Microplastic (MP) contamination of freshwaters and soils has become one
of the major challenges within the Anthropocene. MP is transported in
large quantities through river systems from land to sea. However, the
question is whether there is transport only or also deposition within
the system? Floodplains and their soils as part of the river system are
known for their sink function for sediments, nutrients, and pollutants.
The present case study analyzes the spatial distribution of large (L-MP,
2,000–1,000 μm) and medium (M-MP, 1,000–500 μm) MP particles in
floodplain soils of the Lahn River (Germany). Based on a geospatial
sampling concept, the MP contents in floodplain soils are investigated
down to a depth of 2 meters through a holistic method approach. The
analysis of the plastic particles is carried out by density separation,
visual fluorescence identification, and additional ATR-FTIR analysis. In
addition, grain size analyses and 210Pb/137Cs dating was performed to
reconstruct the MP deposition conditions in floodplains. The results
prove a spatial frequent accumulation of MP in upper floodplain soils
(0–50 cm) deposited by flood dynamics since the 1960s. MP detection
over the entire soil column to a depth of 2 meters and below recent
(>1960) sediment accumulation indicates MP relocation and
in-situ vertical transfer of mobile MP particles through natural
processes (e.g., preferential flow, bioturbation). Furthermore, the role
of MP as a potential marker of the Anthropocene is assessed based on the
findings. This study advances our understanding of the deposition and
relocation of MP at the aquatic-terrestrial interface.