ALBERT

Description: Oxidation of particulate organic carbon (POC) during fluvial transit releases CO2 to the atmosphere and can influence global climate. Field data show large POC oxidation fluxes in lowland rivers; however, it is unclear if POC losses occur predominantly during in-river transport, where POC is in continual motion within an aerated environment, or during transient storage in floodplains, which may be anoxic. Determination of the locus of POC oxidation in lowland rivers is needed to develop process-based models to predict POC losses, constrain carbon budgets, and unravel links between climate and erosion. However, sediment exchange between rivers and floodplains makes differentiating POC oxidation during in-river transport from oxidation during floodplain storage difficult. Here, we isolated in-river POC oxidation using flume experiments transporting petrogenic and biospheric POC without floodplain storage. Our experiments showed solid phase POC losses of 0%–10% over ∼103 km of fluvial transport, compared to ∼7% to 〉50% losses observed in rivers over similar distances. The production of dissolved organic carbon (DOC) and dissolved rhenium (a proxy for petrogenic POC oxidation) was consistent with small POC losses, and replicate experiments in static water tanks gave similar results. Our results show that fluvial sediment transport, particle abrasion, and turbulent mixing have a minimal role on POC oxidation, and they suggest that POC losses may accrue primarily in floodplain storage.

Description: A reservoir geochemical study in the Gullfaks field and its surroundings fields was performed to detect compositional differences in petroleum, from different reservoirs and sectors, which may be related to its complex filling history. The molecular composition of hetero- and polycyclic aromatic hydrocarbons, C7 hydrocarbons together with δ13C data indicate that oils from the Gullfaks South field derived mainly from more terrestrially-dominated source facies, whereas oils from the Gullfaks and Gullfaks West fields sourced mainly from marine algal material. Although, the oil sample from the Gullfaks West field has the lightest δ13C values of n-alkanes and isoprenoids, petroleum from the Brent Group and the Cook Fm. reservoirs in the Gullfaks field were not distinguished isotopically in spite of having been filled from different source basins. In contrast, hetero- and polycyclic aromatic hydrocarbons as well as light hydrocarbons allowed discriminating oil populations into the Gullfaks field, which were not differentiated using biomarkers and δ13C data. Here, the δ13C values of Pr and Ph coupled with molecular data of heterocyclic aromatic hydrocarbons and light hydrocarbons were very useful to discriminate oils from the Gullfaks area, whose compositions are more associated with source facies and depositional environment variations into Upper Jurassic source rocks.

Description: The Athabasca region of northern Alberta, Canada, is home to deposits of oil sands containing vast amounts (~ 173 billion barrels) of heavily biodegraded petroleum. Oil sands are recovered by surface mining or by in situ steam injection. The extraction of bitumen from oil sands by caustic hot water processing results in large volumes of fluid tailings, which are stored in on-site settling basins. There the tailings undergo a compaction and dewatering process, producing a slowly densifying suspension. The released water is recycled for extraction. The fine tailings will be reclaimed as either dry or wet landscapes. [1] To produce 1 barrel of crude oil, 2 tons of oil sand and 2 - 3 tons of water (including recycled water) are required. [2] Open pit mining and the extraction of the bitumen from the oil sands create large and intense disturbances of different landscapes. The area currently disturbed by mining operations covers about 530 km2 and the area of tailing ponds surpasses 130 km2. An issue of increasing importance is the land remediation and reclamation of oil sand areas in Canada and the reconstruction of these disturbed landscapes back to working ecosystems similar to those existing prior to mining operations. An important issue in this context is the identification of oil sand-derived organic compounds in the tailings, their environmental behaviour and the resulting chances and limitations with respect to land reclamation. Furthermore the biodegradation processes that occur in the tailings and that could lead to a decrease in hazardous organic compounds are important challenges, which need to be investigated. This presentation will give a detailed overview of our compositional and quantitative characterisation of the organic matter in oil sand, unprocessed and processed mature fine tailings samples as well as in tailings sands used as part of land reclamation. The analytical characterisation is based on the extraction of the soluble organic matter, its subsequent separation into asphaltenes, aliphatic hydrocarbons, aromatic hydrocarbons, neutral nitrogen, sulphur, oxygen (NSO) compounds and carboxylic acids. The asphaltene fractions are analysed using pyrolysis-GC, all other fractions are analysed by GC-MS. Additionally Fourier transform-ion cyclotron resonance-mass spectrometry (FT-ICR-MS) is used to study the chemical composition of the samples on the molecular level using different ionisation methods.

Description: Shrub encroachment has far‐reaching ecological and economic consequences in many ecosystems worldwide. Yet, compositional changes associated with shrub encroachment are often overlooked despite having important effects on ecosystem functioning. We document the compositional change and potential drivers for a northern Namibian Combretum woodland transitioning into a Terminalia shrubland. We use a multiproxy record (pollen, sedimentary ancient DNA, biomarkers, compound‐specific carbon (δ13C) and deuterium (δD) isotopes, bulk carbon isotopes (δ13Corg), grain size, geochemical properties) from Lake Otjikoto at high taxonomical and temporal resolution. We provide evidence that state changes in semiarid environments may occur on a scale of one century and that transitions between stable states can span around 80 years and are characterized by a unique vegetation composition. We demonstrate that the current grass/woody ratio is exceptional for the last 170 years, as supported by n‐alkane distributions and the δ13C and δ13Corg records. Comparing vegetation records to environmental proxy data and census data, we infer a complex network of global and local drivers of vegetation change. While our δD record suggests physiological adaptations of woody species to higher atmospheric pCO2 concentration and drought, our vegetation records reflect the impact of broad‐scale logging for the mining industry, and the macrocharcoal record suggests a decrease in fire activity associated with the intensification of farming. Impact of selective grazing is reflected by changes in abundance and taxonomical composition of grasses and by an increase of nonpalatable and trampling‐resistant taxa. In addition, grain‐size and spore records suggest changes in the erodibility of soils because of reduced grass cover. Synthesis. We conclude that transitions to an encroached savanna state are supported by gradual environmental changes induced by management strategies, which affected the resilience of savanna ecosystems. In addition, feedback mechanisms that reflect the interplay between management legacies and climate change maintain the encroached state.

Description: In eastern Hesse and western Thuringia, Germany hosts significant potassium-bearing salt deposits industrially excavated in the Werra-Fulda mining district. The salt belongs to the upper Permian (Zechstein) and was deposited around 258 to 252.5 Ma ago. In the Werra-Fulda mining district, the halite rocks (Werra-Rocksalt, z1NA) contain two minable potash seams, potash Seam Thüringen (z1KTh) and potash Seam Hessen (z1KHe), with an average thickness between 2 m and 3 m (Figure 1). To investigate the chemical and isotopic composition of the gas phase of Seam Hessen, gaseous samples were collected from five, 2-meter deep, horizontal boreholes drilled in the potash horizon which is mined at a depth of 540 m. About 4 weeks in advance of the gas sampling, the packer-closed boreholes were evacuated to about 3kPa and the pressure gradient inside the holes was continuously monitored in the boreholes D1 to D5. Selected gas samples were analyzed for their noble gas isotopic composition and the δ13C values of CO2 and CH4. The noble gas isotopic compositions were determined using a VG 5400 noble gas mass spectrometer after purification in a preparation line. The carbon isotope compositions were analysed with a GC-IRMS, comprising a GC 6890N connected to a GC-C/TC III combustion device and coupled to a MAT 253 mass spectrometer. The standard deviation of the δ13C values (in ‰ vs. VPDB) is ± 0.5 ‰.

Description: The European unconventional gas production is still a matter of political as well as public debate and concern. European countries such as Poland, Denmark and the UK ran pilot drill sites already whereas Germany plan to run pilot drill sites in black shales, from which unconventional gas recovery could be economically feasible. New laws and regulations covering unconventional gas production have not put an end to public complaints regarding quantities and quality of flowback fluid after hydraulic fracturing. Using well characterized German Posidonia shale and Danish Alum shale, we initially performed short-term and long-term experiments under elevated temperatures and ambient pressure and elevated pressures, respectively. The types of stimulation fluids used span from pure water to one that was prepared similarly to fluids used during industrial stimulation. Later on we sampled flowback taken after hydraulic stimulation of one horizontal well in the Pomerian region of Poland. All fluids were analysed for inorganic as well as organic chemical composition. Some experimental derived flowback were also subject to radioactivity measurements. In addition, geochemical simulations of fluid-rock interactions were performed. First, the data basis was adapted and amended from the literature. Second, the system was parameterized with field data provided. Third, data evaluation was performed with respect to our experimental findings. Within our presentation we will give an overview about precipitates formed during our experiments, about inorganic and organic compounds found in the experimentally as well as in the industrially derived flowback and about the results of the geochemical modelling.

Description: Petroleum hydrocarbons in reservoirs are subjected to different degrees of abiotic and biotic alteration processes, which often have strong economic consequences since they lead to a decrease in oil quality and reduce the total volume of petroleum in place. Moreover, producibility of the respective fluids strongly depends on physical properties and hence composition. To evaluate these microbial processes in more detail, different approaches can be followed. Here, the changes in stable carbon isotopic signatures of petroleum hydrocarbons are evaluated in detail as biodegradation processes are known to result in an enrichment of the heavier isotopes in the residual hydrocarbons. The change in the isotopic composition can be used to quantify biodegradation by applying the Rayleigh-equation. The Rayleigh-equation correlates the decrease in concentration and the enrichment in the isotopic composition by a fractionation factor (a). This factor depends on the degradation mechanism and the substrate molecule and can be derived from degradation experiments. Thus, the use of carbon isotope ratios has become a sensitive tool in identification and quantification of biodegradation processes in petroleum reservoirs. This quantification is demonstrated using a set of slightly to moderately biodegraded crude oils from the Gullfaks oil field which was analysed for δ13C of the light hydrocarbons.