Falk Pollehne

Manganese cycling in the Gotland Deep, Baltic Sea

Abstract Manganese plays an important role as both an electron donor and acceptor in redox processes of stratified marine environments. Here we present results on Mn cycling in the water column of the Gotland Deep, Baltic Sea—a basin with periodically observed anoxic conditions in bottom waters. In the period 1999–2001, the deeper part of the Gotland Basin was permanently anoxic, and no inflows of significant amounts of oxygenated North Sea water were recorded below the halocline. The upward Mn(II) flux at the chemocline varied between 28 and 77 μmol m−2 day−1 (avg. 53 μmol m−2 day−1) and it was balanced by the downward flux of oxidized Mn over the entire year. The vertical flux of Mn(II) in the water column was mostly regulated by the flux of settling Mn oxides with a minor contribution of Mn(II) diffusing from bottom sediments (7.1–8.2 μmol m−2 day−1). The potential Mn(II) oxidation contributed no more than 2% to the total transferable electron flux (potential chemosynthesis) from the anoxic into the oxic zone, whereas the flux of settling Mn oxides presumably accounted for 3–30% of sulfide oxidation. Two different morphotypes of Mn-rich particles, formed during Mn(II) oxidation in the Gotland Basin chemocline, were identified using SEM-EDX: amorphous particles (92%) and Metallogenium-like particles. About 68% of all Mn-rich particles were associated with large aggregates containing an organic matrix. Manganese represented more than 60% of the total elemental composition of the particles; calcium, iron and silica were also detected.

Nutrient budgets for European seas: A measure of the effectiveness of nutrient reduction policies

Socio-economic development in Europe has exerted increasing pressure on the marine environment. Eutrophication, caused by nutrient enrichment, is evident in regions of all European seas. Its severity varies but has, in places, adversely impacted socio-economic activities. This paper aims to evaluate the effectiveness of recently adopted policies to reduce anthropogenic nutrient inputs to European seas. Nitrogen and phosphorus budgets were constructed for three different periods (prior to severe eutrophication, during severe eutrophication and contemporary) to capture changes in the relative importance of different nutrient sources in four European seas suffering from eutrophication (Baltic Proper, coastal North Sea, Northern Adriatic and North-Western Black Sea Shelf). Policy success is evident for point sources, notably for P in the Baltic and North Seas, but reduction of diffuse sources has been more problematic.

Anaerobic sulfur oxidation in the absence of nitrate dominates microbial chemoautotrophy beneath the pelagic chemocline of the eastern Gotland Basin, Baltic Sea

Oxic-anoxic interfaces harbor significant numbers and activity of chemolithoautotrophic microorganisms, known to oxidize reduced sulfur or nitrogen species. However, measurements of in situ distribution of bulk carbon dioxide (CO(2)) assimilation rates and active autotrophic microorganisms have challenged the common concept that aerobic and denitrifying sulfur oxidizers are the predominant autotrophs in pelagic oxic-anoxic interfaces. Here, we provide a comparative investigation of nutrient, sulfur, and manganese chemistry, microbial biomass distribution, as well as CO(2) fixation at the pelagic redoxcline of the eastern Gotland Basin, Baltic Sea. Opposing gradients of oxygen, nitrate, and sulfide approached the detection limits at the chemocline at 204 m water depth. No overlap of oxygen or nitrate with sulfide was observed, whereas particulate manganese was detected down to 220 m. More than 70% of the bulk dark CO(2) assimilation, totaling 9.3 mmol C m(-2) day(-1), was found in the absence of oxygen, nitrite, and nitrate and could not be stimulated by their addition. Maximum fixation rates of up to 1.1 mumol C L(-1) day(-1) were surprisingly susceptible to altered redox potential or sulfide concentration. These results suggest that novel redox-sensitive pathways of microbial sulfide oxidation could account for a significant fraction of chemolithoautotrophic growth beneath pelagic chemoclines. A mechanism of coupled activity of sulfur-oxidizing and sulfur-reducing microorganisms is proposed.

Uncoupling of bacterial and terrigenous dissolved organic matter dynamics in decomposition experiments.

The biodegradability of terrigenous dissolved organic matter (tDOM) exported to the sea has a major impact on the global carbon cycle, but our understanding of tDOM bioavailability is fragmentary. In this study, the effects of preparative tDOM isolation on microbial decomposition were investigated in incubation experiments consisting of mesocosms containing mesohaline water from the Baltic Sea. Dissolved organic carbon (DOC) consumption, molecular DOM composition, bacterial activities, and shifts in bacterial community structure were compared between mesocosms supplemented with riverine tDOM, either as filtered, particle-free river water or as a concentrate obtained by lyophilization/tangential ultrafiltration, and those containing only Baltic Sea water or river water. As shown using ultra-high-resolution mass spectrometry (15 Tesla Fourier-transform ion cyclotron resonance mass spectrometry, FT-ICR-MS) covering approximately 4600 different DOM compounds, the three DOM preparation protocols resulted in distinct patterns of molecular DOM composition. However, despite DOC losses of 4–16% and considerable bacterial production, there was no significant change in DOM composition during the 28-day experiment. Moreover, tDOM addition affected neither DOC degradation nor bacterial dynamics significantly, regardless of the tDOM preparation. This result suggested that the introduced tDOM was largely not bioavailable, at least on the temporal scale of our experiment, and that the observed bacterial activity and DOC decomposition mainly reflected the degradation of unknown, labile, colloidal and low-molecular weight DOM, both of which escape the analytical window of FT-ICR-MS. In contrast to the different tDOM preparations, the initial bacterial inoculum and batch culture conditions determined bacterial community succession and superseded the effects of tDOM addition. The uncoupling of tDOM and bacterial dynamics suggests that mesohaline bacterial communities cannot efficiently utilize tDOM and that in subarctic estuaries other factors are responsible for the removal of imported tDOM.

The Plankton Tower. IV. Interactions Between Water Column and Sediment in Enclosure Experiments in Kiel Bight

Neritic ecosystems in the boreal zone generally maintain more plankton biomass over a longer period of the year than off-shore systems in the same latitude. Productivity is higher particularly during the summer stratification, between the spring and autumn phytoplankton blooms brought about by nutrients from sources other than pelagic remineralization. Plankton biomass levels maintained by recycling within a pelagic system tend to decrease with time if limiting nutrients bound in sedimenting particles are not replenished. In neritic environments, surface waters can receive nutrients from the land, but depending on water depth and local weather and geomorphology, replenishment can also come from nutrient-rich subthermocline water and sediments. In deeper bodies of water with a steep coastline, such as fjords, the sediment contribution will be less important (Takahashi et al. 1977) than in shallow water systems with more of their sediment surface within the euphotic zone (von Bodungen et al. 1975, Rowe et al. 1975).

The exceptional Oder Flood in summer 1997 — the fate of nutrients and particulate organic matter in the Baltic Sea

The distribution of dissolved inorganic nutrients, particulate organic matter and phytoplankton pigments in the Oder plume was investigated at peak discharge of the Oder River during the exceptional flood event in summer 1997. Mixing diagrams of dissolved inorganic nutrients (NO3-, PO43-, SiO44-) reveal a nearly complete removal of nitrate during the first steps of estuarine mixing, whereas phosphate and silicate were still available over the entire salinity range. In contrast to silicate and phosphate, the nitrate riverine end-member concentration was about 3–4 times lower than during peak discharge in spring. It appears that during the summer flooding event inorganic nitrogen was not as available as in spring due to a stronger dilution effect and the advanced retention of nitrogen by land vegetation within the drainage area in summer. Therefore, algal biomass production in the Pomeranian Bight was most certainly nitrogen limited and significant removal of other dissolved inorganic nutrients by phytoplankton blooming did not occur.

Macrozoobenthic biodiversity patterns in the northern province of the Benguela upwelling system

This paper describes macrozoobenthos diversity in the vicinity of the Angola–Benguela Frontal Zone between 15° and 23° S in offshore waters of the Namib biogeographic province in a comprehensive zoogeographical context. At 38 selected stations, about 500 different macrozoobenthic taxa could be identified, including 209 bivalve, gastropod and peracarid species. These 209 taxa were reduced to 85 species by statistical procedures, to ensure the database was reliable in terms of statistics and taxonomy for community analysis. The evaluation of macrobenthic distribution patterns revealed three distinct biodiversity clusters, which are probably the result of different adaptation strategies to the diverse environmental conditions within the Benguela upwelling ecosystem. The dominating driver for benthic diversity is the extent of the oxygen minimum zone (OMZ). Temporal and spatial stability of the OMZ is, however, not fixed. Therefore, only the particular spatial pattern in total community structure during the cruises can be described in this study. Perennial temporal variability in the extent of OMZs can, however, be assessed by the distribution of longer-living molluscs’ shells. The assignment of macrofauna communities to recent patterns of frontal systems, upwelling cores and oxygen supply makes the hard-shell fraction of the communities a potential indicator of historic changes in these external conditions.

The Impact of Wind Engine Constructions on Benthic Growth Patterns in the Western Baltic

Global-scale environmental degradation and its association with nonrenewable fossil fuels have led to an increasing interest in generation of electricity by renewable energy resources (Gill 2005). Since the planning of large offshore wind energy facilities in the German Bight and the Baltic Sea was initiated, concerns about the ecological compatibility of these structures have been expressed. Apart from direct impacts of disturbance during construction, operational sounds and rotating parts, which might primarily affect birds, bats, marine mammals and fish, the potential long term effects on the benthic environment have been discussed. These concerns are mainly focused on the questions, whether and how the natural benthic habitat in the vicinity of the constructions is modified by changes in bottom currents and turbulence, and whether the effects of the installations as artificial settling substrates are properly assessed. The ecologically relevant effects of offshore wind parks include e.g., increased habitat heterogeneity, and changes in hydrodynamic conditions and in sediment transport patterns. The potential ecological response of the macrozoobenthos could involve long-term changes in diversity, abundance, biomass, community structure and such functional properties as nutrient regeneration or bio-turbation. These problems have been in the focus of a project in the western Baltic which that was part of a national combination of projects called BeoFINO.1 This effort has addressed the overall ecological risks of offshore wind-power facilities in the North and Baltic Seas. Such questions are most often viewed in the primary context of the effects on the biodiversity of the benthic community. In the Baltic Sea however, the specific hydrographical conditions emphasizes a problem which also involves the absolute biomass accumulation rates of epifauna

DISTRIBUTION OF PROKARYOTIC ORGANISMS IN A TROPICAL ESTUARY INFLUENCED BY SUGAR CANE AGRICULTURE IN NORTHEAST BRAZIL

In a joint Brazilian-German case study, distribution patterns of microorganisms were compared with environmental variables in the tropical coastal Manguaba lagoon in northeast Brazil, which is situated downstream of several sugar cane processing plants . 16S rDNA and 16S rRNA single strand conformation polymorphism (SSCP) gene fingerprinting were used to follow the composition and distribution of microorganisms throughout the salinity gradient of the lagoon. Potentially abundant microorganisms were identified by sequencing representative SSCP bands. It could be demonstrated that the distribution of microbes was in close relation to the physico-chemical environmental settings and followed a common scheme. In the in- and outlet areas of the lagoon rather transient microbial communities were found, whereas in the central part a stable, diverse community was encountered, that due to the long residence time of the water, had ample time for development and adaptation.

Dynamics of halocarbons in coastal surface waters during short term mesocosm experiments

Environmental context Halocarbons are trace gases important in atmospheric ozone chemistry whose biogenic production – among other factors – depends on light-induced stress of marine algae. Several studies have confirmed this effect in laboratory experiments but knowledge in natural systems remains sparse. In mesocosm experiments, which are a link between field and laboratory studies, we observed that the influence of natural levels of ultraviolet radiation on halocarbon dynamics in the marine surface waters was either insignificant or concealed by the complex interactions in the natural systems. Abstract The aim of the present study was to evaluate the influence of different light quality, especially ultraviolet radiation (UVR), on the dynamics of volatile halogenated organic compounds (VHOCs) at the sea surface. Short term experiments were conducted with floating gas-tight mesocosms of different optical qualities. Six halocarbons (CH3I, CHCl3, CH2Br2, CH2ClI, CHBr3 and CH2I2), known to be produced by phytoplankton, together with a variety of biological and environmental variables were measured in the coastal southern Baltic Sea and in the Raunefjord (North Sea). These experiments showed that ambient levels of UVR have no significant influence on VHOC dynamics in the natural systems. We attribute it to the low radiation doses that phytoplankton cells receive in a normal turbulent surface mixed layer. The VHOC concentrations were influenced by their production and removal processes, but they were not correlated with biological or environmental parameters investigated. Diatoms were most likely the dominant biogenic source of VHOCs in the Baltic Sea experiment, whereas in the Raunefjord experiment macroalgae probably contributed strongly to the production of VHOCs. The variable stable carbon isotope signatures (δ13C values) of bromoform (CHBr3) also indicate that different autotrophic organisms were responsible for CHBr3 production in the two coastal environments. In the Raunefjord, despite strong daily variations in CHBr3 concentration, the carbon isotopic ratio was fairly stable with a mean value of –26‰. During the declining spring phytoplankton bloom in the Baltic Sea, the δ13C values of CHBr3 were enriched in 13C and showed noticeable diurnal changes (–12‰ ±4). These results show that isotope signature analysis is a useful tool to study both the origin and dynamics of VHOCs in natural systems.