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.
Highlights
Introduction published maps and institutional affilMicroplastic pollution of the environment is one of the most urgent global problems in recent years [1,2]
The results indicate that the vertical movement of MP particles is influenced by biofouling and leads to a maximum concentration at intermediate depths, where the particles oscillate vertically without reaching the bottom
A model approach was used to describe the seasonal processes of transIn this study, a model approach was used to describe the seasonal processes of transfer fer and transformation of microplastics at a qualitative level
Summary
Microplastic pollution of the environment is one of the most urgent global problems in recent years [1,2]. Microplastic (MP) refers to plastic fragments less than 5 mm in size [3]. All the natural environments from poles to the equator, including the oceans, are contaminated by MP [4]. MP can enter the ocean directly as so-called primary MP (for example, the microbeads in abrasive cleaning and self-care products, fibres of polymeric materials) or can be formed as a result of fragmentation of larger plastic objects in sea water (secondary MP). Environmental conditions, mostly mechanical abrasion, UV radiation and oxygen promote weathering of larger plastics and breakup into minute pieces (so called secondary MP). MP particles enter the aquatic coastal environment in large numbers through municipal wastewater either as treated wastewater coming from wastewater treatment iations
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