Summary:
Ocean uptake of anthropogenic CO2 alters ocean chemistry and when combined with
hypoxic phenomena affects carbon and nutrient biogeochemistry, and dissolved
trace metal species and complexes’ stability causing changes in benthic fluxes
in the sediment-water interface. Therefore, experiments combining acidification
and low oxygen conditions are essential to fully understand and correlate the
various observations in coastal environments. The mobility of arsenic is
controlled largely by pH and redox changes and can be present at high
concentrations in both natural and contaminated environments. Release of
arsenic from sediments into porewaters has been attributed to reductive
dissolution of iron oxyhydroxides to which arsenic has been absorbed.
The goal of this project was to study the ocean acidification impacts on a
coastal industrialized system (Elefsis Bay) affected by intermittent anoxic
conditions during summer using laboratory experiment microcosms, containing
water and sediment from the greater depth (33 m) of the Gulf (at a proportion
80% to 20% respectively). Water samples were collected daily during the four
week period of the experiment, sediment samples were collected twice for trace
metals determinations with ICP-MS and also for the colorimetric determination
of Fe species; supplementary analyses included organic and inorganic carbon
determinations (TOC and CaCO3), mineral composition with XRF,XRD analyses,
nutrients’ determinations (TP, TN). The results of this study revealed that
under OA conditions, metals such as Al, Ni, Cd, Fe, Mn and As seem to follow a
source type mechanism from sediment towards the water column. In contrast, OA
along with anoxia conditions, a diverse sink type mechanism was observed for
these metals. Cr, Zn and Pb, followed a sink-type mechanism under enhanced CO2,
while in OA along with anoxic conditions, a source type mechanism from the
sediment towards the water column was found. Hg seemed to act as a source type
mechanism under acidification, regardless of the oxygen conditions but it
remains unknown whether it is maintained in the dissolved form or it is
released in the atmosphere. Regarding the Fe ratio, it became evident that in
both experiments Fe(II) was the dominant Fe species, even without anoxic
conditions prevailing, indicating the increased stability of Fe (II) as a
result of increased CO2.
Keywords:
Ocean Acidification, Gulf of Elefsis, Sediments, Metal, Anoxia
