Revisiting the biogeochemistry of arsenic in the Baltic Sea: Impact of anthropogenic activity.

With the increase in anthropogenic environmental disruption, the behavior of arsenic in the Baltic Sea has received more scientific attention because of its complex forms and toxicity, and was re-visited to determine if there have been measurable changes recently. A cruise was conducted in 10-19 May 2011 to investigate the species and distribution of total dissolved inorganic arsenic (TDIAs: [TDIAs]=[As(V)]+[As(III)]) revealing links between the hydrographic dynamics and biological/chemical reactions in the Baltic Sea. In addition, long-term (2002-2010) time-series investigations of particulate arsenic in the Gotland Basin were also conducted in February every year for monitoring purposes. The behavior of TDIAs was non-conservative due to the removal and regeneration processes occurring in the Baltic Sea. Biological scavenging plays a dominant role as sink for TDIAs, with removal amount of 3.1±1.6nmol/L above the pycnocline of the Baltic Sea. Significant regeneration of TDIAs was observed below the pycnocline of the Baltic Sea, which was closely related to hypoxia. The decomposition of organic arsenic and release from the sediment by desorption of As-bearing Fe and Mn oxides were thought to be two major sources for TDIAs regeneration. The median concentration of TDIAs (8.4nmol/L) was much lower than in most marginal seas and oceans, including the near-bottom water around a chemical weapon dumpsite (13.9nmol/L). The hypoxia in the deep water contributed to the increase in As(III) concentrations based on the relationship between As(III)/TDIAs ratio and apparent oxygen utilization. If the difference of As(III) profiles (1981 and 2011) actually represents a long-term increase in As(III) concentrations and a shoaling of the As(III) chemocline, these factors could enhance the toxic effects and extend the residence time of arsenic and, hence, potentially have negative impacts on fisheries and ecosystem health in the Baltic Sea.

PUMP-CTD-System for trace metal sampling with a high vertical resolution. A test in the Gotland Basin, Baltic Sea.

It is a great challenge to sample seawater across interfaces, for example the halocline or the redoxcline, to investigate trace metal distribution. With the use of 10l sampling bottles mounted to a wire or a CTD-Rosette it is possible to obtain a maximum vertical resolution of 5m. For the detection of small vertical structures in the vertical distribution of trace metals across the redoxcline, the CTD-Bottle-Rosette is not sufficient. Therefore, a PUMP-CTD-System was developed, which enables water sampling with high resolution (1m maximum) along a vertical profile. To investigate the suitability and possible contamination sources of this device two experiments were carried out in the Gotland Basin. The first experiment consisted of two separate profiles. The first profile was obtained with the CTD-Bottle-Rosette and the second with the PUMP-CTD-System. Both were taken from the bottom to the surface water layer. The second experiment was a combined profile obtained from the surface to the bottom with the PUMP-CTD-System attached to the CTD-Bottle-Rosette. Concentrations of dissolved Pb, Cd, Cu, Zn, Fe, Mn, Co and Ni from the "Niskin Bottles" and from the PUMP were measured and compared for each investigation. We demonstrate that it is useful to perform vertical sampling from lower to higher concentrations, e.g. surface to bottom in this environment, and that a longer flushing is required for sampling seawater in the anoxic bottom water. A comparison of the two systems for oxygen and hydrogen sulphide measurements showed an improvement of the precision and the quality of the sampling when using the PUMP. Thus, metal speciation at the oxic-anoxic gradient zone and on a high vertical resolution will be accessible. As concentrations of dissolved Pb, Cd, Cu, Zn, Co, Ni, Fe and Mn in seawater sampled with both devices were in the same range, we conclude that the PUMP-CTD-System is well suited to sample seawater for trace metal analyses.

Luminescent whole-cell cyanobacterial bioreporter for measuring Fe availability in diverse marine environments.

A Synechococcus sp. strain PCC 7002 Fe bioreporter was constructed containing the isiAB promoter fused to the Vibrio harveyi luxAB genes. Bioreporter luminescence was characterized with respect to the free ferric ion concentration in trace metal-buffered synthetic medium. The applicability of the Fe bioreporter to assess Fe availability in the natural environment was tested by using samples collected from the Baltic Sea and from the high-nutrient, low-chlorophyll subarctic Pacific Ocean. Parallel assessment of dissolved Fe and bioreporter response confirmed that direct chemical measurements of dissolved Fe should not be considered alone when assessing Fe availability to phytoplankton.

Impact of different in vitro electron donor/acceptor conditions on potential chemolithoautotrophic communities from marine pelagic redoxclines.

Anaerobic or microaerophilic chemolithoautotrophic bacteria have been considered to be responsible for CO2 dark fixation in different pelagic redoxclines worldwide, but their involvement in redox processes is still not fully resolved. We investigated the impact of 17 different electron donor/acceptor combinations in water of pelagic redoxclines from the central Baltic Sea on the stimulation of bacterial CO2 dark fixation as well as on the development of chemolithoautotrophic populations. In situ, the highest CO2 dark fixation rates, ranging from 0.7 to 1.4 micromol liter(-1) day(-1), were measured directly below the redoxcline. In enrichment experiments, chemolithoautotrophic CO2 dark fixation was maximally stimulated by the addition of thiosulfate, reaching values of up to 9.7 micromol liter(-1) CO2 day(-1). Chemolithoautotrophic nitrate reduction proved to be an important process, with rates of up to 33.5 micromol liter(-1) NO3(-) day(-1). Reduction of Fe(III) or Mn(IV) was not detected; nevertheless, the presence of these potential electron acceptors influenced the development of stimulated microbial assemblages. Potential chemolithoautotrophic bacteria in the enrichment experiments were displayed on 16S ribosomal complementary DNA single-strand-conformation polymorphism fingerprints and identified by sequencing of excised bands. Sequences were closely related to chemolithoautotrophic Thiomicrospira psychrophila and Maorithyas hadalis gill symbiont (both Gammaproteobacteria) and to an uncultured nitrate-reducing Helicobacteraceae bacterium (Epsilonproteobacteria). Our data indicate that this Helicobacteraceae bacterium could be of general importance or even a key organism for autotrophic nitrate reduction in pelagic redoxclines.

Ecotoxicity assessment of natural attenuation effects at a historical dumping site in the western Baltic Sea.

During the late 1950s and early 1960s of the past century, industrial waste material highly enriched in various contaminants (heavy metals, PAHs) was dumped in the inner Mecklenburg Bay, western Baltic Sea. Large-scale shifts in the spatial distribution of heavy metals in surface sediments were mapped by geochemical monitoring in the mid-1980s and 12 years later in 1997. A further study in 2001 was designed to investigate the small-scale spatial distribution of contaminants inside, on top of, and around the historical dumping ground and to examine possible effects to benthic organisms (Arctica islandica, microbiological toxicity tests). The site is located within an area characterized by a discontinuous deposition of fine sediments, but net sedimentation rate of about 3mm/y led ultimately to a gradual coverage of the dumped material. During the first decades after the dumping, about half of the originally dumped material was already spread over the surrounding area as a result of sediment dynamics and re-suspension processes. Recent sediments of the historical dump site are still significantly enriched in heavy metals and PAHs. Microbiological toxicity test results were positive, though uptake of contaminants in mussels was found to deviate only slightly from that of a non-contaminated reference station due to a gradual dilution and decrease in bioavailability of the contaminants.