Understanding the Role of Organic Matter Cycling for the Spatio-Temporal Structure of PCBs in the North Sea

Ute Daewel,Elena Mikheeva,Evgeniy V Yakushev,Luca Nizzetto,Corinna Schrum

doi:10.3390/w12030817

Abstract

Using the North Sea as a case scenario, a combined three-dimensional hydrodynamic-biogeochemical-pollutant model was applied for simulating the seasonal variability of the distribution of hydrophobic chemical pollutants in a marine water body. The model was designed in a nested framework including a hydrodynamic block (Hamburg Shelf Ocean Model (HAMSOM)), a biogeochemical block (Oxygen Depletion Model (OxyDep)), and a pollutant-partitioning block (PolPar). Pollutants can be (1) transported via advection and turbulent diffusion, (2) get absorbed and released by a dynamic pool of particulate and dissolved organic matter, and (3) get degraded. Our model results indicate that the seasonality of biogeochemical processes, including production, sinking, and decay, favors the development of hot spots with particular high pollutant concentrations in intermediate waters of biologically highly active regions and seasons, and it potentially increases the exposure of feeding fish to these pollutants. In winter, however, thermal convection homogenizes the water column and destroys the vertical stratification of the pollutant. A significant fraction of the previously exported pollutants is then returned to the water surface and becomes available for exchange with the atmosphere, potentially turning the ocean into a secondary source for pollutants. Moreover, we could show that desorption from aging organic material in the upper aphotic zone is expected to retard pollutants transfer and burial into sediments; thus, it is considerably limiting the effectiveness of the biological pump for pollutant exports.

Highlights

The ocean plays a vital role in controlling the environmental transport and overall fate of many chemical pollutants that are relevant to the global environment and human population
It was assumed that the chemical pollutant was partitioned between the free fraction (CFREE ) and fractions that are associated with BIO (CBIO ), particulate organic material (POM) (CPOM ) and dissolved organic matter (DOM) (CDOM )
When compared to the observed magnitude and spatial distribution of nitrogen in the North Sea, we found that the simulated concentrations of nitrogen that were associated with BIO, POM, DOM and NUT (Figure 3) sufficiently represented the observed pattern of phytoplankton, particulate organic nitrogen, dissolved organic nitrogen, and nitrate, respectively, in the North Sea

Summary

Introduction

The ocean plays a vital role in controlling the environmental transport and overall fate of many chemical pollutants that are relevant to the global environment and human population. Water 2020, 12, 817 causing reproductive and development problems as well as harming the immune system following chronic exposure [1,2] These contaminants have long half-lives and can be especially detrimental in pristine areas due to long-range transport in the atmosphere and ocean [3]. Despite the relatively low concentrations that have been measured in marine waters, the presence of PCBs in marine systems is of concern They can, biomagnify, increasing concentration by several orders of magnitude in the tissues of marine organisms at the higher trophic levels, including populations of fish and other marine resources that are relevant for fisheries and human consumption. The impacts of PCBs on the exploitability and safety of these marine resources has been debated in several previous assessments and policy documents, e.g., [6,7,8,9]

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