TY - JOUR A1 - Menges, Johanna A1 - Hovius, Niels A1 - Andermann, Christoff A1 - Dietze, Michael A1 - Swoboda, Charlie A1 - Cook, Kristen L. A1 - Adhikari, Basanta R. A1 - Vieth-Hillebrand, Andrea A1 - Bonnet, Stephane A1 - Reimann, Tony A1 - Koutsodendris, Andreas A1 - Sachse, Dirk T1 - Late holocene landscape collapse of a trans-himalayan dryland BT - human impact and aridification JF - Geophysical research letters N2 - Soil degradation is a severe and growing threat to ecosystem services globally. Soil loss is often nonlinear, involving a rapid deterioration from a stable eco-geomorphic state once a tipping point is reached. Soil loss thresholds have been studied at plot scale, but for landscapes, quantitative constraints on the necessary and sufficient conditions for tipping points are rare. Here, we document a landscape-wide eco-geomorphic tipping point at the edge of the Tibetan Plateau and quantify its drivers and erosional consequences. We show that in the upper Kali Gandaki valley, Nepal, soil formation prevailed under wetter conditions during much of the Holocene. Our data suggest that after a period of human pressure and declining vegetation cover, a 20% reduction of relative humidity and precipitation below 200 mm/year halted soil formation after 1.6 ka and promoted widespread gullying and rapid soil loss, with irreversible consequences for ecosystem services. KW - geomorphology KW - paleoclimate KW - human activity KW - Tibetan plateau KW - late Holocene Y1 - 2019 U6 - https://doi.org/10.1029/2019GL084192 SN - 0094-8276 SN - 1944-8007 VL - 46 IS - 23 SP - 13814 EP - 13824 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Noah, Mareike A1 - Lappe, Michael A1 - Schneider, Beate A1 - Vieth-Hillebrand, Andrea A1 - Wilkes, Heinz A1 - Kallmeyer, Jens T1 - Tracing biogeochemical and microbial variability over a complete oil sand mining and recultivation process JF - The science of the total environment : an international journal for scientific research into the environment and its relationship with man N2 - Recultivation of disturbed oil sand mining areas is an issue of increasing importance. Nevertheless only little is known about the fate of organic matter, cell abundances and microbial community structures during oil sand processing, tailings management and initial soil development on reclamation sites. Thus the focus of this work is on biogeochemical changes of mined oil sands through the entire process chain until its use as substratum for newly developing soils on reclamation sites. Therefore, oil sand, mature fine tailings (MFTs) from tailings ponds and drying cells and tailings sand covered with peat-mineral mix (PMM) as part of land reclamation were analyzed. The sample set was selected to address the question whether changes in the above-mentioned biogeochemical parameters can be related to oil sand processing or biological processes and how these changes influence microbial activities and soil development. GC-MS analyses of oil-derived biomarkers reveal that these compounds remain unaffected by oil sand processing and biological activity. In contrast, changes in polycyclic aromatic hydrocarbon (PAH) abundance and pattern can be observed along the process chain. Especially naphthalenes, phenanthrenes and chrysenes are altered or absent on reclamation sites, Furthermore, root-bearing horizons on reclamation sites exhibit cell abundances at least ten times higher (10(8) to 10(9) cells g(-1)) than in oil sand and MFF samples (10(7) cells g(-1)) and show a higher diversity in their microbial community structure. Nitrate in the pore water and roots derived from the PMM seem to be the most important stimulants for microbial growth. The combined data show that the observed compositional changes are mostly related to biological activity and the addition of exogenous organic components (PMM), whereas oil extraction, tailings dewatering and compaction do not have significant influences on the evaluated compounds. Microbial community composition remains relatively stable through the entire process chain. (C) 2014 Elsevier B.V. All rights reserved. KW - Oil sands KW - Tailings ponds KW - Reclamation KW - PAN KW - Biomarker KW - Microbial community analysis Y1 - 2014 U6 - https://doi.org/10.1016/j.scitotenv.2014.08.020 SN - 0048-9697 SN - 1879-1026 VL - 499 SP - 297 EP - 310 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Scheingross, Joel S. A1 - Hovius, Niels A1 - Dellinger, M. A1 - Hilton, R. G. A1 - Repasch, M. A1 - Sachse, Dirk A1 - Grocke, D. R. A1 - Vieth-Hillebrand, Andrea A1 - Turowski, Jens M. T1 - Preservation of organic carbon during active fluvial transport and particle abrasion JF - Geology N2 - 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 inriver POC oxidation using flume experiments transporting petrogenic and biospheric POC without floodplain storage. Our experiments showed solid phase POC losses of 0%-10% over similar to 10(3) km of fluvial transport, compared to similar 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 lasses, 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. Y1 - 2019 U6 - https://doi.org/10.1130/G46442.1 SN - 0091-7613 SN - 1943-2682 VL - 47 IS - 10 SP - 958 EP - 962 PB - American Institute of Physics CY - Boulder ER - TY - JOUR A1 - Tabares Jimenez, Ximena del Carmen A1 - Zimmermann, Heike Hildegard A1 - Dietze, Elisabeth A1 - Ratzmann, Gregor A1 - Belz, Lukas A1 - Vieth-Hillebrand, Andrea A1 - Dupont, Lydie A1 - Wilkes, Heinz A1 - Mapani, Benjamin A1 - Herzschuh, Ulrike T1 - Vegetation state changes in the course of shrub encroachment in an African savanna since about 1850 CE and their potential drivers JF - Ecology and evolution N2 - 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 (delta C-13) and deuterium (delta D) isotopes, bulk carbon isotopes (delta(13)Corg), 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 delta C-13 and delta(13)Corg 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 delta D record suggests physiological adaptations of woody species to higher atmospheric pCO(2) 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. KW - climate change KW - fossil pollen KW - land-use change KW - savanna ecology KW - sedimentary ancient DNA KW - state and transition KW - tree-grass interactions Y1 - 2019 U6 - https://doi.org/10.1002/ece3.5955 SN - 2045-7758 VL - 10 IS - 2 SP - 962 EP - 979 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Wilke, Franziska Daniela Helena A1 - Schettler, Georg A1 - Vieth-Hillebrand, Andrea A1 - Kühn, Michael A1 - Rothe, Heike T1 - Activity concentrations of U-238 and Ra-226 in two European black shales and their experimentally-derived leachates JF - Journal of Environmental Radioactivity N2 - We performed leaching tests at elevated temperatures and pressures with an Alum black shale from Bomholm, Denmark and a Posidonia black shale from Lower Saxony, Germany. The Alum shale is a carbonate free black shale with pyrite and barite, containing 74.4 mu g/g U. The Posidonia shales is a calcareous shale with pyrite but without detectable amounts of barite containing 3.6 mu g/g U. Pyrite oxidized during the tests forming sulfuric acid which lowered the pH on values between 2 and 3 of the extraction fluid from the Alum shale favoring a release of U from the Alum shale to the fluid during the short-term and in the beginning of the long-term experiments. The activity concentration of U-238 is as high as 23.9 mBq/ml in the fluid for those experiments. The release of U and Th into the fluid is almost independent of pressure. The amount of uranium in the European shales is similar to that of the Marcellus Shale in the United States but the daughter product of U-238, the Ra-226 activity concentrations in the experimentally derived leachates from the European shales are quite low in comparison to that found in industrially derived flowback fluids from the Marcellus shale. This difference could mainly be due to missing Cl in the reaction fluid used in our experiments and a lower fluid to solid ratio in the industrial plays than in the experiments due to subsequent fracking and minute cracks from which Ra can easily be released. KW - Unconventional gas production KW - Black shales KW - Flowback KW - Radioactivity KW - NOR KW - Batch experiments Y1 - 2018 U6 - https://doi.org/10.1016/j.jenvrad.2018.05.005 SN - 0265-931X SN - 1879-1700 VL - 190 SP - 122 EP - 129 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Wilke, Franziska Daniela Helena A1 - Vieth-Hillebrand, Andrea A1 - Naumann, Rudolf A1 - Erzinger, Jörg A1 - Horsfield, Brian T1 - Induced mobility of inorganic and organic solutes from black shales using water extraction: Implications for shale gas exploitation JF - Applied geochemistry : journal of the International Association of Geochemistry and Cosmochemistry N2 - The study reported here evaluates the degree to which metals, salt anions and organic compounds are released from shales by exposure to water, either in its pure form or mixed with additives commonly employed during shale gas exploitation. The experimental conditions used here were not intended to simulate the exploitation process itself, but nevertheless provided important insights into the effects additives have on solute partition behaviour under oxic to sub-oxic redox conditions. In order to investigate the mobility of major (e.g. Ca, Fe) and trace (e.g. As, Cd, Co, Mo, Pb, U) elements and selected organic compounds, we performed leaching tests with black shale samples from Bornholm, Denmark and Lower Saxony, Germany. Short-term experiments (24 h) were carried out at ambient pressure and temperatures of 100 degrees C using five different lab-made stimulation fluids. Two long-term experiments under elevated pressure and temperature conditions at 100 degrees C/100 bar were performed lasting 6 and 2 months, respectively, using a stimulation fluid containing commercially-available biocide, surfactant, friction reducer and clay stabilizer. Our results show that the amount of dissolved constituents at the end of the experiment is independent of the pH of the stimulation fluid but highly dependent on the composition of the black shale and the buffering capacity of specific components, namely pyrite and carbonates. Shales containing carbonates buffer the solution at pH 7-8. Sulphide minerals (e.g. pyrite) become oxidized and generate sulphuric acid leading to a pH of 2-3. This low pH is responsible for the overall much larger amount of cations dissolved from shales containing pyrite but little to no carbonate. The amount of elements released into the fluid is also dependent on the residence time, since as much as half of the measured 23 elements show highest concentrations within four days. Afterwards, the concentration of most of the elemental species decreased pointing to secondary precipitations. Generally, in our experiments less than 15% of each analysed element contained in the black shale was mobilised into the fluid. (C) 2015 Elsevier Ltd. All rights reserved. KW - Unconventional gas KW - Black shales KW - Stimulation fluids KW - Element mobility KW - Batch experiments Y1 - 2015 U6 - https://doi.org/10.1016/j.apgeochem.2015.07.008 SN - 0883-2927 VL - 63 SP - 158 EP - 168 PB - Elsevier CY - Oxford ER -