ALBERT

Description: In natural coastal wetlands, high supplies of marine sulfate suppress methanogenesis. Coastal wetlands are, however, often subject to disturbance by dyking and drainage for agricultural use and it has been shown that they can turn to potent methane sources when rewetted for remediation, suggesting that the sulfate-related methane suppressing mechanisms were suspended by the preceding land use measures. Here, we unravel the hydrological relocation and biogeochemical S and C transformation processes that induced high methane emissions in a disturbed and rewetted peatland despite former brackish impact. The underlying processes were investigated along a transect of increasing distance to the coastline using a combination of concentration patterns, stable isotope partitioning and analysis of the microbial community structure. We found that dyking and freshwater rewetting caused a distinct freshening and an efficient depletion of the brackish sulfate reservoir by dissimilatory sulfate reduction (DSR). Despite some legacy effects of brackish impact expressed as high amounts of sedimentary S and elevated electrical conductivities, contemporary metabolic processes operated mainly under sulfate-limited conditions. This opened up favorable conditions for the establishment of a prospering methanogenic community in the top 30-40 cm of peat, the structure and physiology of which resembles those of terrestrial organic-rich environments. Locally, high amounts of sulfate persisted in deeper peat layers through the suppression of DSR, probably by competitive electron acceptors of terrestrial origin, for example Fe(III), but did not interfere with high methane emissions on ecosystem scale. Our results indicate that the climate effect of disturbed and remediated coastal wetlands cannot simply be derived by analogy with their natural counterparts. From a greenhouse gas perspective, the re-exposure of dyked wetlands to natural coastal dynamics would literally open up the floodgates for a replenishment of the marine sulfate pool and constitute an efficient measure to reduce methane emissions.

Description: During expedition EMB201 in the Baltic Sea we investigated the local producers of glycerol dialkyl glycerol tetraethers (GDGT) and their thriving depth by a combined 16S rRNA gene amplicon sequencing/ CARD-FISH and lipidomic approach. Water samples were taken in December 2018 by a pump-CTD, a giant water sampler and with Niskin bottles at the surface, suboxic and sulfidic zones of the Landsort Deep, Fårö Basin and East Gotland Basin. This data set contains the CARD-FISH and lipidomics data, while the 16S rRNA gene sequencing data is available on ENA. Cell abundance was analysed in an aliquot of 40 ml filtered (pore size 0.22 micro m) sea water fixed with particle-free formaldehyde. Archaeal cells on the filters were specifically hybridized via catalysed reporter deposition-fluorescence in situ hybridization (CARD-FISH) using the Cren537 probe. Cells on the hybridized filter were counter-stained with 40,6-diamidin-2-phenylindol (DAPI). For lipid analysis, 150–600 L sea water were filtered with a flow rate of 1.5 L min-1 on pre-ashed, 142-mm-diameter, 0.7µm pore size glass fibre GF/F filters, and frozen at –20 °C. The filters were lyophilized before different extraction methods were used to obtain intact and core GDGTs by ultra-sonification in different solvent mixtures. The combined supernatants were phase separated before analysis by high performance liquid chromatography coupled to tandem mass spectrometry (HPLC-MS2) for intact polar lipids and by high performance liquid chromatography coupled to atmospheric pressure chemical ionization mass spectrometry (HPLC APCI-MS; ThermoScientific) for core GDGTs.

Description: The dataset contains ocean bottom hydrophone (OBH) data acquired along profile P05 during RV Sonne Expedition SO267 (project ARCHIMEDES) to the Lau Basin, Southwestern Pacific in December 2018. This seismic refraction data set contains 34 OBS that all recorded the shots along the ~220 km long seismic transect successfully. Data for two different shot intervals (50m and 150m) were acquired shooting from east to west and from west to east respectively. An 84 l airgun array served as seismic source that was towed behind the vessel 8 m below sea surface. The data were processed using standard methods for relocation of the instrument at the seafloor, clock drift correction, deconvolution and filtering.

Description: During the Soviet Virgin Lands Campaign, approximately 23 million hectares (Mha) of Eurasian steppe grassland were converted into cropland in Northern Kazakhstan from 1954 to 1963. As a result Kazakhstan became an important breadbasket of the former Soviet Union. However, the collapse of the Soviet Union in 1991 triggered widespread agricultural abandonment, and much cropland reverted to grasslands. Our goal in this study was to reconstruct and analyze agricultural land-cover change since the eve of the Virgin Lands Campaign, from 1953 to 2010 in Kostanay Province, a region that is representative of Northern Kazakhstan. Further, we assessed the potential of currently idle cropland for re-cultivation. We reconstructed the cropland extent before and after the Virgin Lands Campaign using archival maps, and we mapped the agricultural land cover in the late Soviet and post-Soviet period using multi-seasonal Landsat TM/ETM+ images from circa 1990, 2000 and 2010. Cropland extent peaked at approximately 3.1 Mha in our study area in 1990, 38% of which had been converted from grasslands from 1954 to 1961. After the collapse of the Soviet Union, 45% of the Soviet cropland was abandoned and had reverted to grassland by 2000. After 2000, cropland contraction and re-cultivation were balanced. Using spatial logistic regressions we found that cropland expansion during the Virgin Lands Campaign was significantly associated with favorable agro-environmental conditions. In contrast, cropland expansion after the Campaign until 1990, as well as cropland contraction after 1990, occurred mainly in areas that were less favorable for agriculture. Cropland re-cultivation after 2000 was occurring on lands with relatively favorable agro-environmental conditions in comparison to remaining idle croplands, albeit with much lower agro-environmental endowment compared to stable croplands from 1990 to 2010. In sum, we found that cropland production potentials of the currently uncultivated areas are much lower than commonly believed, and further cropland expansion is only possible at the expense of marginal lands. Our results suggest if increasing production is a goal, improving crop yields in currently cultivated lands should be a focus, whereas extensive livestock grazing as well as the conservation of non-provisioning ecosystem services and biodiversity should be priority on more marginal lands.