Spatiotemporal reconstructions of black carbon, organic matter and heavy metals in coastal records of south-west Sweden

Abstract

This study presents reconstructions of black carbon (BC), including spheroidal and amorphous carbonaceous particles (SCP and ACP), organic matter (OM; total organic carbon, TOC; total nitrogen, TN; total sulfur, TS), and heavy metals (Fe, Zn, Pb, Cu, As and Hg) in coastal sediments off the south-west coast of Sweden. Sediment records from eight stations along a north-south transect off the south-west of Sweden were retrieved. Samples of 0-1 cm depth from each station representing recent depositions and a sediment core from the Öresund extending back to approximately AD 1912 were analyzed.

For investigations of BC, the samples were pre-treated using the chemothermal oxidation (CTO) method. For the particle counting of SCP and ACP, the samples were pre-treated chemically before they were analyzed under a microscope. The burial fluxes of BC, SCP and ACP showed an increasing trend since the start of the record in 1912 with a slight decrease of the trend between 1965 and 1986. This decrease seemed to be the result of some legislative actions to improve the air quality since the beginning of the 1960s. The BC burial flux was already high from the early 1990s with the highest peak about 636 µg/cm2 /yr in year 2008. Looking at the trend from 1912 to 2011 the trend of BC and SCP and ACP burial fluxes are positive with a slight decrease from the 1960s until late 1980s.

OM and calcium carbonate (CaCO3) were studied as biogeochemical markers for oxygen bottom water conditions and biological activity, respectively. OM dropped in the 1960s until 1986 and CaCO3 started to increase from 1965 until the top of the record. CaCO3 and OM could be evidence of BC oxidation in the Öresund record and might have caused underestimation of the BC burial flux between the 1960s and 1990s because of more oxic bottom water conditions. Samples analyzed for heavy metal concentrations were ground in a mortar and analyzed with an XRF scanner. All trends of heavy metals except Fe showed strong increase from 1960 and lasted partly until the early 1990s. Fe displayed a very similar pattern as TS. There were no or low correlations between any burial flux of BC, SCP and ACP and any heavy metal pointing out that heavy metals were mainly produced and emitted from a different source or process than combustion.

Popular Abstract

Black carbon (BC) is an aerosol and by-product of combustion, which is introduced into the environment in greater amounts with the beginning of the industrial revolution and intensifying combustion of fossil fuels. BC is differentiated in fractions (i.e. charcoal, spheroidal carbonaceous particles (SCP), and soot), which are produced at different temperatures and from different kinds of fuel. These fractions are differently recalcitrant against degradation (charcoal less recalcitrant than SCP and soot). It affects the Earth's energy balance since it warms up the atmosphere and lowers the albedo on Earth's surfaces due to its black character. Furthermore, it can be carcinogen and harmful for organisms. BC deposits in soils and sediments as soon as is washed out from the atmosphere. These depositions can be investigated using chemical and thermal pre-treatments, elemental analyzing and light microscopy. In addition several heavy metals (Fe, Zn, Pb, Cu, As and Hg) were measured using an XRF scanner which are also partly introduced by fossil fuel combustion.

This thesis presents reconstructions of BC, including its minor fractions of charcoal and spheroidal carbonaceous particles (SCP), and their correlations to organic matter (OM; total organic matter, TOC; total nitrogen, TN; total sulfur, TS), and several heavy metals in coastal sediments off the south-west coast of Sweden. Sediment records from eight stations along a north-south transect off the south-west of Sweden were retrieved. Samples of 0-1 cm depth from each station representing recent depositions and a sediment core from the Öresund extending back to approximately AD 1912 were analyzed. The burial fluxes of BC, SCP and charcoal showed an increasing trend since the start of the record in 1912 with a slight decrease of the trend between 1965 and 1986. This decrease seemed to be the result of some legislative actions to improve the air quality since the beginning of the 1960s. The BC burial flux was already high from the early 1990s with the highest peak about 636 µg/cm2/yr in year 2008. Looking at the trend from 1912 to 2011 the trend of BC, SCP and charcoal burial fluxes are positive with a slight decrease from the 1960s until late 1980s.

OM and calcium carbonate (CaCO3) were studied as biogeochemical markers for oxygen bottom water conditions and biological activity, respectively. OM dropped in the 1960s until 1986 and CaCO3 started to increase from 1965 until the top of the record. CaCO3 and OM could be evidence of BC oxidation in the Öresund record and might have caused underestimation of the BC burial flux between the 1960s and 1990s because of possibly more oxic bottom water conditions. Samples analyzed for heavy metal concentrations were ground in a mortar and analyzed with an XRF scanner. All trends of heavy metals except Fe showed strong increase from 1960 and lasted partly until the early 1990s. Fe displayed a very similar pattern as TS. There were no or low correlations between any burial flux of BC, SCP and charcoal and any heavy metal pointing out that heavy metals were mainly produced and emitted from a different source or process than combustion.

• author: Rudolf, Marcus
• supervisor: Karl Ljung
• organization: Dept of Physical Geography and Ecosystem Science
• alternative title: Pollutants in coastal sediments off south-west Sweden - spatial and temporal perspectives
• course: NGEM01 20161
• year: 2016
• type: H2 - Master's Degree (Two Years)
• subject: Earth and Environmental Sciences
• keywords: organic matter, spheroidal carbonaceous particles, black carbon, geology, physical geography, Ecosystem analysis, heavy metals, coastal sediments, Sweden
• publication/series: Student thesis series INES
• report number: 406
• language: English
• id: 8896900
• date added to LUP: 2017-01-03 13:36:24
• date last changed: 2018-01-02 04:10:24