Effects of seawater scrubbing on a microplanktonic community during a summer-bloom in the Baltic Sea

Erik Ytreberg,Maria Karlberg,Ida-Maja Hassellöv,Mikael Hedblom,Amanda T Nylund,Kent Salo,Henrik Imberg,David Turner,Lucy Tripp,Joanne Yong,Angela Wulff

doi:10.1016/j.envpol.2021.118251

Abstract

The International Maritime Organization (IMO) has gradually applied stricter regulations on the maximum sulphur content permitted in marine fuels and from January 1, 2020, the global fuel sulphur limit was reduced from 3.5% to 0.5%. An attractive option for shipowners is to install exhaust gas cleaning systems, also known as scrubbers, and continue to use high sulphur fuel oil. In the scrubber, the exhausts are led through a fine spray of water, in which sulphur oxides are easily dissolved. The process results in large volumes of acidic discharge water, but while regulations are focused on sulphur oxides removal and acidification, other pollutants e.g. polycyclic aromatic hydrocarbons, metals and nitrogen oxides can be transferred from the exhausts to the washwater and discharged to the marine environment. The aim of the current study was to investigate how different treatments of scrubber discharge water (1, 3 and 10%) affect a natural Baltic Sea summer microplanktonic community. To resolve potential contribution of acidification from the total effect of the scrubber discharge water, “pH controls” were included where the pH of natural sea water was reduced to match the scrubber treatments. Biological effects (e.g. microplankton species composition, biovolume and primary productivity) and chemical parameters (e.g. pH and alkalinity) were monitored and analysed during 14 days of exposure. Significant effects were observed in the 3% scrubber treatment, with more than 20% increase in total biovolume of microplankton compared to the control group, and an even greater effect in the 10% scrubber treatment. Group-specific impacts were recorded where diatoms, flagellates incertae sedis, chlorophytes and ciliates increased in biovolume with increasing concentrations of scrubber water while no effect was recorded for cyanobacteria. In contrast, these effects was not observed in the “pH controls”, a suggestion that other parameters/stressors in the scrubber water were responsible for the observed effects.

Highlights

Shipping is emitting a vast number of harmful substances; primarily sulphur oxides (SOX) and nitrogen oxides (NOX) (Karl et al, 2019; Raudsepp et al, 2019) and fine particulate matter (PM2.5) (Jalkanen et al, 2014), polycyclic aromatic hydrocarbons (PAHs) (Teuchies et al, 2020) and metals (Turner et al, 2017)
The results showed a significant increase in chlorophyll a, POP, Particulate organic carbon (POC) and Particulate organic nitrogen (PON) when the microplanktonic community was exposed to 10% scrubber discharge water
To what extent a specific scrubber discharge water will impact the marine environment will be dependent on the concentrations and distribution of these stressors

Summary

Introduction

Shipping is emitting a vast number of harmful substances; primarily sulphur oxides (SOX) and nitrogen oxides (NOX) (Karl et al, 2019; Raudsepp et al, 2019) and fine particulate matter (PM2.5) (Jalkanen et al, 2014), polycyclic aromatic hydrocarbons (PAHs) (Teuchies et al, 2020) and metals (Turner et al, 2017) These emissions can result in severe health effects (SOX, NOX and PM2.5) (Corbett et al, 2007; Sofiev et al, 2018), acidification (SOX and NOX) (Hassellov et al, 2013), eutrophication (NOX) (Raudsepp et al, 2019; Zhang et al, 2021), and ecotoxicological responses in marine organisms (PAHs and metals) (Koski et al, 2017; Teuchies et al, 2020). The market is dominated by open loop installations (81% of market share), followed by hybrid systems (17%) and a small share of closed loop systems (1.5%) (DNV GL, 2020)

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