Effects of microplastics and earthworm burrows on soil macropore water flow within a laboratory soil column setup

Abstract

Several earlier studies reported that microplastics (MP) accumulated on soil surfaces could be transported into the subsoil and ingested by soil biota, such as earthworms. The present study explores how networks of earthworm burrows and MP (low-density polyethylene, LDPE) in subsoil affect the soil hydraulic properties and saturated water flow. A repacked and saturated sandy soil column experiment was conducted in an environment-controlled laboratory with earthworms (anecic, Lumbricus terrestris) inoculated into the soil columns to form networks of macropore. The macropore network parameters (i.e., number, length, volume, diameter, soil saturated conductivity, and tracer breakthrough curves of soil columns) have been determined. The relative arrival times of the tracer mass (i.e. T5%, T25%, and T50%) were determined in order to describe the shapes of the breakthrough curves. The results show that in some breakthrough curves for the treatments with earthworms, there are two peaks. This is an indication that water was flowing faster in the macropores than in the soil matrix. There is a significant correlation between 5% arrival time and the median burrow volume, and the correlation coefficient was .571 (at the level of p < .05). The formation of macropores due to the burrowing activities of earthworms is considered the main cause of nonequilibrium water flow in the present study. The MP did not show any significant effect on the saturated water flow. This may be attribute to the low concentrations of MP used in the present study.

Current understanding of subsurface transport of micro‐ and nanoplastics in soil

“…Instead of artificially incorporating microplastics into soil, Yu, van der Ploeg, Ma, Ritsema, and Geissen (2020) placed polyethylene pieces (∼4 g) on the surface of a sandy soil (7 kg air-dried soil in a 11.6-cm × 50-cm column) in the absence and presence of earthworms, and they found that although polyethylene pieces were transported by earthworms into soil, polyethylene did not affect the saturated hydraulic conductivity of the soil. These results indicate that the effect of microand nanoplastics on soil hydraulic properties depends on plastic characteristics as well as soil texture.…”

The concept, approach, and future research of hydrological connectivity and its assessment at multiscales

“…8 ). Water flows through soil macropores; in fact, we regard the phenomena as soil macropore flow (Yu et al 2020 ). In general, soil macropore flow is mainly influenced by the size and number of soil macropores, the hydrophobic organic coatings of soil macropores boundaries, the amount of surface water supply, and the temperature of infiltrating water (Watanabe and Kugisaki 2017 ; Beven 2018 ).…”

Interactions between water flow and microplastics in silt loam and loamy sand

“…Agricultural soil is a research focus, where the technology of polyethylene film-mulching is used extensively to alter crop microclimates and reduce water evaporation (Liu et al, 2019;Wang et al, 2020), causing mass production of MP in agricultural farmland (Wanner, 2021). Plastics are fragmented into MPs during the tillage, and some remain on the surface of the soil while others are buried under the soil (Ding et al, 2019); the MPs further travel and redistribute in soils with water flow (Song et al, 2017;Yu et al, 2020). Therefore, the impact of MP accumulation in various soil mediums should be assessed.…”

“…Therefore, the impact of MP accumulation in various soil mediums should be assessed. Recently, MP production and migratory and accumulative behaviors have attracted significant interest (Cesa et al, 2017;Hurley & Nizzetto, 2018;Maaß et al, 2017;Yu et al, 2020). Microplastic pollution in agricultural soils has also been of increasing concern.…”

“…Microplastic pollution in agricultural soils has also been of increasing concern. Microplastics affect soil physicochemical and hydrological properties and further alter water flow features (de Souza Machado, Lau, et al, 2018;Qi et al, 2020;Yu et al, 2020). So far, there are no potential key findings on how MP accumulation affects water movement in various soil mediums.…”