Program

Previous data for the hypoxic zone pooled for 1981 have provided systematic information of arsenic in the Baltic Sea. A cruise was conducted in 10 - 19 May 2011 to investigate the species and distributions of arsenic revealed links between the dynamics and biological/chemical reactions, and hence to re-evaluate whether there was measurable effect on the behavior of the arsenic with the increase of anthropogenic activities in recent years in the Baltic Sea. High concentrations of total dissolved inorganic arsenic (TDIAs: [TDIAs] = [As (V)] + [As (III)]) in the surface waters were found near the Gotland, and decreased gradually from east to west. While the distributions of arsenite (As (III)) and As (III)/TDIAs ratio were opposite to that of TDIAs in most cases, with the maximum occurring in the western of the Arkona Basin, where relatively high concentrations of Chl-a was also observed. The vertical profiles of TDIAs, As (III) and particulate arsenic (PAs) were similar, with concentrations all increased with the water depth. The behavior of TDIAs was non-conservative due to the removal and regeneration processes occurred in the Baltic Sea. Biological scavenging and particle adsorption played very important roles for the sink of TDIAs, particularly for the latter, with more than 80% of arsenic from riverine input scavenged from the water column during the initial stage of fresh and saltier water mixing. Significant regeneration of TDIAs was observed in the deep water, with closely related to the hypoxia. The decomposition of organic arsenic and the release from sediment by desorption of Fe and Mn oxides were thought to be the two major sources of TDIAs based on the relationship between arsenic species and apparent oxygen utilization (AOU). The average concentrations of TDIAs (8.6 nmol/L) were much lower than most marginal seas and even oceans, including in the near bottom water of the chemical weapon dump, with the concentrations of 13.9 nmol/L. However, the hypoxia in the deep water was benefit for the increase in As (III)/TDIAs ratio. This process will enhance the toxic effects and extend the residence time of arsenic, and hence potentially have negative impacts on the fisheries and balance of the ecosystem in the Baltic Sea.