Rolf O. Hallberg

Biomineralization by Gallionella

A new environmental scanning electron microscopic (ESEM) technique at low vacuum (5 torr) and 99% humidity, where the sample never has been exposed to high vacuum and coating of carbon or gold, has revealed a new insight into the nature of iron mineralization that develops in association with the stalked bacteria Gallionella. The stalk fibers contain minute flaky iron precipitates. The size of the crystallites is 0.1–0.5 micron and some of them exhibit a hexagonal feature. EDAX analyses on individual crystallites give an atomic ratio between Fe and O very close to 0.67. The stoichiometric formula would thus be Fe2O3. Stoichiometry and crystallinity are in accordance with the mineral hematite. The mineralization seems to take place inside the fibers of the stalk. With time the Gallionella stalk is covered with iron oxihydroxides of different kinds that probably are controlled by inorganic processes more than by the organic chemistry of the stalk. From a thermodynamic point of view, oxygen as well as carbon dioxide are required to explain the formation of hematite inside the fibers. The precipitation takes probably place at a pH close to 5.

Sedimentary Trace Elements as Proxies to Depositional Changes Induced by a Holocene Fresh-Brackish Water Transition

A halocline developed in the GotlandDeep, Baltic Sea, at c. 8.0 14C ky BP, as theresult of a transition from fresh to brackish water.The sediment-water interface changed from oxic topredominantly anoxic, depositional conditions wereperiodically euxinic and pyrite formation wasextensive. This environmental change led topyritization of the upper part of earlier depositedsediments. This study discusses how the distributionof trace elements (As, Ba, Cd, Cu, Co, Mo, Mn, Ni, Pb,U, Zn and V) were affected by the changing redoxconditions, productivity and salinity. The reducingconditions led to pyritization of Cu, Co, Ni, Cd, Mo,Mn and As. Lead and Zn concentrations are very low inpyrite, in agreement with their coordination tosulfide being tetrahedral. Certain elements areenriched in those sediments deposited under euxinicconditions. This enrichment was caused by scavengingof elements dissolved in the water column and isrestricted to elements that have a comparably longresidence time in the Baltic Sea. Molybdenum appearsto be the most unambigious proxy for euxinicconditions, whereas enrichment of U also requiresbrackish water in the productive zone. In the brackishenvironment, enrichment of Ba and V are linked to thecycling of organic carbon. Manganese and As are theonly elements that have been significantly remobiliseddue to the downward moving pyritization front.

Effects of irradiation from uranium decay on extractable organic matter in the Alum Shales of Sweden

Abstract Extractable organic matter in the Alum Shales of Sweden is believed to have been altered by irradiation from the natural decay of uranium. The amount of extractable bitumen is inversely proportional to uranium concentration suggesting conversion of extractable bitumen by irradiation. The ratio of aromatic to saturated hy hydrocarbons increased with increasing uranium concentration, presumably because aromatic hydrocarbons are more stable in the presence of radiationthan saturated hydrocarbons. Bitumen from samples with high uranium concentrations tends to be relatively enriched in aromatic hydrocarbons and contains a larger percentage of polars, asphaltenes and resins. Acyclic isoprenoid hydrocarbons are absent in extracts and kerogen pyrolysates of samples with high uranium concentrations. They therefore appear more susceptible to irradiation induced alteration than normal alkanes, which are present in almost all extracts and kerogen pyrolysates. Parent/alkylated polyaomatic hydrocarbon (PAH) ratios are highest in shallow samples with high uranium concentrations. Extracts from samples low in uranium concentration contain C 20 , C 21 , C 26 , C 27 and C 28 triaromatic steroids, whereas extracts from samples of high uranium concentration contain only C 20 and C 21 . Alkyl side chain cleavage by irradiation is the mechanism presumed responsible. Ratios of pyrene/phenanthrene and pyrene/chrysene are highest whereas ratios of 1+9/2+3 methylphenanthrenes are lowest in shallow samples with high uranium concentrations.

Metal distribution along a profile of an inter-tidal area

Abstract The sediment from an intertidal area has been investigated with regard to the vertical and areal distribution of the following acid-soluble metals: Na, K, Mg, Ca, Fe, Co, Ni, Cu, Ag and Pb. In addition to the metals, granulometric properties, content of organic matter, carbonate concentrations and E h are measured. The metals are accumulated along the margins of the area and show a high correlation with organic matter and the finest sediment fraction. The interstitial water is diluted with infiltrated rain water. The higher level of this water, of the marsh area compared with that of the tidal flat area, gives rise to an upward percolation in the sediment of the tidal flat area. The metal interrelationships and concentrations are determined by processes in the uppermost oxidized layer and only to a minor extent by reducing processes in the lower hydrogen sulphide-rich layers.

An Empirical Model of the Fate of Organic Carbon in a Mangrove Forest Partly Affected by Anthropogenic Activity

A model of biogeochemical and hydrological processes that drive organic carbon dynamics of a mangrove ecosystem has been developed. Tidal regime parameters as well as biological factors related to macrofauna and microbiota are described within the model. The model includes three sub-models, each representing a major form of organic carbon in the mangrove ecosystem; litter organic carbon, particulate organic carbon and dissolved organic carbon (DOC). Results from the model reveal that discharge of DOC to the adjacent ocean may be one of the dominant outputs of a mangrove forest. The model confirms the observed data that DOC accounts for 80% of total organic carbon export. In order to balance the standing crop of DOC in the marine fringe zone, the model suggested that 40% is removed in this zone by microorganisms as well as resident and tidal migrant fauna.

The effects of radioactive decay of uranium on elemental and isotopic ratios of Alum shale kerogen

Abstract The organic matter in the Alum Shale of Sweden is believed to have been affected post-depositionally by irradiation from the natural decay of U. Alum Shale kerogen H/C ratios are inversely proportional to the natural log of the U concentration, presumably as a result of the liberation of H by irradiation of the organic matter. Stable isotopic ratios of13C/12C in Alum Shale kerogen are directly proportional to the natural log of the U concentration. Experimental irradiation of Green River shale generated hydrocarbon gases 18% lighter than the parent organic matter, which demonstrates the possibility that irradiation induced generation of isotopically light gases could lower13C/12C ratios in parent organic matter. Irradiation may be a factor governing the relation between13C/12C ratios in the Alum Shales. Alum Shale O/C ratios generally increase with increasing U concentration and it is suggested that irradiation of organic matter may facilitate oxidation. The “Rock-Eval” maturity parameters “P.I.” and “Tmax” decrease with increasing U concentration. “P.I.” is presumed to decrease as a result of bitumen destruction or polymerization by irradiation.

Inferences from a corrosion study of a bronze cannon, applied to high level nuclear waste disposal

Abstract A bronze cannon was used as an analogue of corrosion processes for Cu. The cannon has been embedded in clay sediments in the Baltic Sea since 1676. Corrosion products are cuprite and malachite, mainly derived from transformation of tenorite inclusions of the bronze alloy. The bronze matrix exhibits little corrosion and a conservative estimate for the maximum corrosion of Cu is

Metal chelation in sedimentary systems

Abstract An aqueous suspension of clay, dolomite, quartz, and organic matter was sedimented through a saline solution containing trace amounts of copper and zinc and accumulated on an organic‐rich layer where sulfide was being generated by sulfate‐reducing bacteria. A control system was set up in which the organic matter was omitted and the sulfide provided by diffusion of a sodium sulfide solution from beneath the sediments. In the organic system the copper and zinc were separated and fixed in different sedimentary layers, whereas in the control system they precipitated together. Metal distributions in the former system indicated that copper forms soluble metal‐organic complexes that keep the copper in solution in the presence of sulfide. Zinc also forms metal‐organic complexes, but these are apparently not resistant to sorption and precipitation processes.

Anoxic sediment reactions — A comparison between box experiments and a fjord investigation

Abstract The results of an investigation of stagnant water in a fjord basin have been compared with results obtained from the analysis of bottom water in a closed plexiglass box. It is found that the release rates (in mmol m−2 day−1) for hydrogen sulfide, hydrogen carbonate ammonium and phosphate agree remarkably well. The main reactions involved are given and the low pH in anoxic waters as well as the decrease of pH in the box experiments are explained by oxygen consumption and corresponding increase in carbon dioxide (total carbonate). The solubility products for iron(II) sulfide in both waters also agree.

Porewater mixing by microorganisms, monitored by a radiotracer method

Abstract Bioturbation is an important process for the transport and mixing of solutes and particles in sediments. Mixing of porewater caused by motile microorganisms has not previously been considered to be of significance in this context, although no conclusive evidence that it is negligible has been presented. We have developed a radiotracer method for the direct comparison of mixing of a soluble inert substance in microbially active and sterile sediments. We found clear evidence of porewater mixing caused by motile microorganisms. Estimated diffusion coefficients (expressed as “mixing”; coefficients) were found to be about 20% larger in microbially active sediments than in sterile ones.