Modelling the Influence from Biota and Organic Matter on the Transport Dynamics of Microplastics in the Water Column and Bottom Sediments in the Oslo Fjord

Abstract

The fate of microplastics (MP) in seawater is heavily influenced by the biota: the density of MP particles can be changed due to biofouling, which affects sinking, or MP can be digested by zooplankton and transferred into fecal pellets with increased sinking rate. We hypothesize that seasonal production and degradation of organic matter, and corresponding changes in the plankton ecosystem affect the MP capacity for transportation and burying in sediments in different seasons. This is simulated with a coupled hydrodynamical-biogeochemical model that provides a baseline scenario of the seasonal changes in the planktonic ecosystem and changes in the availability of particulate and dissolved organic matter. In this work, we use a biogeochemical model OxyDep that simulates seasonal changes of phytoplankton (PHY), zooplankton (HET), dissolved organic matter (DOM) and detritus (POM). A specifically designed MP module considers MP particles as free particles (MPfree), particles with biofouling (MPbiof), particles consumed by zooplankton (MPhet) and particles in detritus, including fecal pellets (MPdet). A 2D coupled benthic-pelagic vertical transport model 2DBP was applied to study the effect of seasonality on lateral transport of MP and its burying in the sediments. OxyDep and MP modules were coupled with 2DBP using Framework for Aquatic Biogeochemical Modelling (FABM). A depletion of MP from the surface water and acceleration of MP burying in summer period compared to the winter was simulated numerically. The calculations confirm the observations that the “biological pump” can be one of the important drivers controlling the quantity and the distribution of MP in the water column.

Microplastic-specific biofilm growth determines the vertical transport of plastics in freshwater

“…A maximum possible thickness of 500 µm was reported for a biofilm in seawater (Van Melkebeke et al, 2020). Furthermore, various defouling processes are expected to happen in the environment including grazing, algae mortality due to loss of photosynthetic potential (darker environment), inter-or intra species competition or erase-and-restart scenarios (Berezina et al, 2021;De Tender et al, 2017;Fazey & Ryan, 2016;Kooi et al, 2017), which could cause resurfacing of submerged particles (Ye & Andrady, 1991). Future research should therefore focus to gather knowledge on the complexity of the biofilm process by e.g.…”

Applications of mathematical modelling for assessing microplastic transport and fate in water environments: a comparative review

“…However, biological inclusion might be one of the main variables that influence the amount and distribution of microplastics in the water column. The work by Berezina et al ( 2021 ) and Besseling et al ( 2017 ) addressed the influence of biogeochemical processes on microplastic transport by integrating biochemical and biogeochemical models. Their findings highlight the role of biota and organic matter in transporting light-density floating microplastics into deep layers and sediments.…”

Understanding microplastic pollution in the Nordic marine environment – knowledge gaps and suggested approaches

“…Lusher et al [127] reported up to a tenfold difference in MP concentrations between water masses originating from the Atlantic and Polar seas, respectively. The concentrations and composition of MPs (sizes, morphological features, polymers) in different environmental matrices depend on intrinsic factors of the MPs as well as on external abiotic (e.g., hydrodynamics, temperature, salinity, concentration of other particles) and biotic (e.g., biofouling, species composition, season) factors [195,77,13]. The "fate pathway" of MPs is key to linking MP composition of a matrix to its source.…”