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824 Ergebnisse:

Rates and geochemical processes of soil and salt crust formation in Salars of the Atacama Desert, Chile
Geoderma (2016)
Kari Finstad, Marco Pfeiffer, Gavin McNicol, Jaime Barnes, Cecilia Demergasso, Guillermo Chong, Ronald Amundson

The hyperarid Atacama Desert contains numerous local basins with surficial salt crusts, known as salars, where evaporation of shallow groundwater drives the major soil processes. We examine chemical and isotopic profiles in two soils of differing ages from the Salar Llamara to determine the geochemical processes involved in their formation. Evaporation, which provides salts to the soils through mineral precipitation, decreases with increasing salt crust thickness, and average~0.03mmm−2d−1 over geological time frames. Salt distribution varies predictably with depth and soil age, with the most soluble compounds concentrated nearest to the land surface, indicating the direction of fluid flow. δ34S values of mineral sulfate tend to decrease with decreasing soil depth, following a pattern indicative of Rayleigh-like fractionation as solute-rich waters migrate toward the land surface. δ13C and δ18O values of carbonate suggest that the uppermost halite layers, which contain very small amounts of carbonate, have a strong biological signature. In contrast, carbonate-rich layers deeper in the profiles consist of largely unmodified lacustrine carbonate that formed in highly evaporitic lake conditions. The continuous upward evaporation of water and dissolved solutes creates a rugged and physically dynamic halite crust composed of rounded salt nodules. The crust undergoes deliquescence as atmospheric relative humidity rises from marine air intrusions, and we found that the halite nodules on the surface of the Salar Llamara are nearly always at or above deliquescence relative humidity. The interiors of these nodules are therefore able to buffer the large diurnal changes in atmospheric relative humidity allowing for the survival of halophilic microbial communities in an otherwise very dry environment. Radiocarbon measurements of occluded organic C in the surface crusts indicate that C cycling occurs at differing rates depending on local micrometeorological conditions, and that a given salt crust feature may persist for thousands of years once formed.
Schlagworte: carbon , oxygen , sulfur , geol , elem , mulitcarb

Flyway population delineation in Taiga Bean Geese Anser fabalis fabalis revealed by multi-element feather stable isotope analysis
Ibis (2016)
Anthony D. Fox, Keith A. Hobson, Adriaan de Jong, Kevin J. Kardynal, Geoff Koehler, Thomas Heinicke

Fundamental to effective management of migratory waterbird populations is an understanding of their flyway delineation. Taiga Bean Geese Anser fabalis fabalis wintering in NW Denmark, Scotland and England are considered to originate from northern and central Sweden, southern and central Norway (‘Western flyway’), those wintering in southern Sweden, NE and southern Denmark are considered to originate from northern Fennoscandia and western Russia (‘Central flyway’), and those wintering in eastern Germany and Poland (which show far less favourable conservation status) are thought to come from western Siberia (‘Eastern 1 flyway’), although evidence to demonstrate this has largely been lacking. Evidence for different natal and moult origins of Taiga Bean Geese was investigated using stable isotope analyses of feathers of four elements (δ2H, δ13C, δ15N and δ34S). There were significant differences in isotopic composition of feathers from Swedish (Central) and German (Eastern 1) wintering populations and those moulting in Sweden in late summer (Western), which validated the three proposed major management flyway units above. The strong continental gradient in the stable hydrogen isotope ratios in precipitation (δ2Hp) across the region was used to assign wintering birds geospatially to natal and moulting origin, indicating separate natal and moulting areas for German (n = 37, from western Siberia) and Swedish (n = 20, Fennoscandia and more western Russia) wintering birds. These results confirm the largely discrete nature of these three flyways and contribute significantly to our ability to deliver effective targeted and appropriate research, monitoring and management actions throughout the ranges of these flyways.
Schlagworte: hydrogen , ecol , elem

Plasticity in reproduction and nutrition in wood-boring bivalves (Xylophaga atlantica) from the Mid-Atlantic Ridge
Marine Biology (2016)
Sylvie Marylène Gaudron, T. Haga, H. Wang, S. R. Laming, S. Duperron

High densities of the wood-boring bivalve Xylophaga atlantica colonized pine wood cubes in colonization devices deployed at 2279 m depth for 414 days (14 July 2007–31 August 2008) near hydrothermal vents at the Rainbow site on the Mid-Atlantic Ridge (36°13.7454′N/33°54.0513′W). Histological and biometric observations on specimens with shell lengths (SLs) of 0.5–4.2 mm revealed three cohorts in this dioecious population. The first cohort was dominated by mature females, each with an estimated fecundity of ~450 oocytes with a mean diameter of 28.0 ± 3.9 µm (maximum diameter 40.0 µm); an intermediate cohort was a mix of males and females with SL at first maturity of ≤1.7 mm; the third cohort was exclusively morphologically distinct, mature, dwarf males, SL ~500 µm. These dwarf males were attached to the dorsal shell surfaces of females in the first cohort. The difference in the SL of Prodissoconch I (~60 µm) and Prodissoconch II (500–530 µm) confirmed planktotrophy. Based on their carbon and nitrogen stable isotope ratios, and a paedomorphic morphology suggesting they are ill-equipped to bore wood, it seems likely that the dwarf males are heterotrophic filter-feeders. Fluorescence in situ hybridization showed, however, that dwarf males hosted a few Gammaproteobacteria in their gills. The absence of a bacterial signal in the germ cells and developing oocytes of females implies that direct trans-ovarial inheritance of symbiotic bacteria does not occur in X. atlantica.
Schlagworte: carbon , nitrogen , ecol , elem

Elucidating the relationship between the later Cambrian end-Marjuman extinctions and SPICE Event
Palaeogeography, Palaeoclimatology, Palaeoecology (2016)
Angela Gerhardt, Benjamin Gill

The late Cambrian-early Ordovician transition contains several discrete marine extinction events. The first of these extinctions, the end-Marjuman, occurs in two phases and is thought to coincide with the beginning of the Steptoean Positive Carbon Isotope Excursion, or SPICE, a large excursion in the marine carbon isotope record that represents a large perturbation to the carbon cycle during this time. Additionally, the carbon isotope record from the Deadwood Formation in the Black Hills of South Dakota, USA, displays a small negative δ13C excursion near the end-Marjuman extinctions. Here we examine the carbon isotope stratigraphy of the Upper Cambrian portion of the Conasauga Group of the Southern Appalachians, USA, to determine the relative timing between the extinction events and changes in the carbon cycle represented by excursions within the carbon isotope record. Previous high-resolution biostratigraphic studies have identified a thick stratigraphic record of end-Marjuman extinctions within the Conasauga Group, making it an excellent target for a high-resolution chemostratigraphic study. In the Conasauga Group, there is no change in carbon isotope stratigraphy across the first phase of the end-Marjuman extinctions, suggesting no major change occurred in the carbon cycle during this time. Further, a negative δ13C excursion is absent in the Conasauga Group across the interval that contains the end-Marjuman extinctions. This suggests that the excursion in the Deadwood Formation is either a local oceanographic signal or a diagenetic feature. Finally, the onset of the SPICE occurs at the same stratigraphic point as the second phase of the end-Marjuman extinctions and at the appearance of a low diversity, potentially low oxygen tolerant, trilobite fauna. The stratigraphic positions of these biological and geochemical events suggest a role for marine anoxia in the second phase of the end-Marjuman extinctions.

Temperature sensitivity of soil organic carbon decomposition as affected by long-term fertilization under a soybean based cropping system in a sub-tropical Alfisol
Agriculture, Ecosystems & Environment (2016)
Avijit Ghosh, Ranjan Bhattacharyya, B.S. Dwivedi, M.C. Meena, B.K. Agarwal, P. Mahapatra, D.K. Shahi, R. Salwani, R. Agnihorti

Understanding temperature sensitivity of soil organic carbon (SOC) decomposition from bulk soils and aggregates of long-term fertilized plots is imperative to forecast soil C dynamics. We evaluated the impacts of 43 years of fertilization under a soybean (Glycine max) based cropping system on temperature sensitivity of SOC decomposition (Q10) in an Alfisol. Treatments were: no mineral fertilizer or manure (control), 100% recommended dose of nitrogen (N), N and phosphorus (NP), N, P and potassium (NPK), NPK+lime at 0.4Mgha−1 (NPK+L), 150% recommended NPK (150% NPK), and NPK+farmyard manure (FYM) at 10Mgha−1 (NPK+FYM). Bulk soils as well as macro- and micro-aggregates were incubated for 24days at 25°C and 35°C. Cumulative SOC mineralization (Ct) in the 0–15cm soil layer of bulk soils with NPK+FYM and NPK treated plots were similar but significantly higher than unfertilized control plots. However, both Ct and Q10 values in the NPK+FYM plots were higher than NPK in the 15–30cm soil layer. In the 0–15cm soil layer, NPK+FYM plots had ∼10 and 26% greater Q10 values of macro- and microaggregates than NPK. Activation energies required for bulk soils C mineralization was ∼2 and 3 times higher in NPK+FYM and NPK+L plots, respectively, compared with unfertilized control plots in that layer. Lime along with NPK application increased the activation energy of SOC decomposition. Thus, long-term NPK+FYM and NPK+L applications have great potential for less proportional SOC decomposition than NPK or unfertilized control plots under a temperature rise in these acid soils. However, NPK+FYM management practice is recommended as it has highest SOC accumulation and can have less SOC losses under a temperature rise.

Inferring the timing of long-distance dispersal between rail metapopulations using genetic and isotopic assignments
Ecological Applications (2016)
Laurie A. Hall, Steven R. Beissinger

The stochastic and infrequent nature of long-distance dispersal often makes it difficult to detect. We quantified the frequency, distance, and timing of long-distance dispersal in a non-migratory, secretive wetland bird, the California black rail (Laterallus jamaicensis coturniculus), between an inland and a coastal metapopulation separated by greater than 100 km. Using 15 microsatellites in conjunction with stable carbon, nitrogen, and sulfur isotopes, we classified rails as: residents of their capture population, recent migrants that dispersed to their capture population less than one year before capture, established migrants that dispersed to their capture population more than one year before capture, and seasonal migrants that dispersed away from their capture population to forage, but returned the next season. Most rails (195 of 204 or 95.6%) were classified as residents, but we detected two established migrants that had moved >100 km more than a year before capture. Seven rails appeared to be seasonal migrants, but comparisons of feather isotope values with isotope values from wetland soils indicated that the isotope values in the feathers of these rails likely resulted from natural environmental variation (e.g., source element effects) rather than long-distance dispersal of individuals. Thus, these seven rails were most likely misassigned by isotopic population assignments due to small-scale variation in the isoscape. Using genetic data in conjunction with isotopic data allowed us to not only infer the timing of long-distance dispersal events, but to successfully track long-distance movements of non-migratory rails between metapopulations even when environmental variation of isotopes occurred across small spatial scales.
Schlagworte: carbon , nitrogen , sulfur , ecol , elem

Geochemistry of Campanian–Maastrichtian brachiopods from the Rørdal-1 core (Denmark): Differential responses to environmental change and diagenesis
Chemical Geology (2016)
R. Harlou, C.V. Ullmann, C. Korte, B.W. Lauridsen, N.H. Schovsbo, F. Surlyk, N. Thibault, L. Stemmerik

Past marine environmental conditions can be reconstructed from geochemical signatures of both benthic and planktic organisms and particularly brachiopods have been extensively used for this purpose. However, it is seldom possible to investigate the links between environmental conditions and shell geochemistry in monospecific records over extended periods of time. Here, we present geochemical data from the ~100m thick, brachiopod-rich upper Campanian – upper Maastrichtian chalk (~73.8–68.6Ma) with of the Rørdal-1 drill core (northern Denmark). Two species that lived attached to small substrate (Argyrotheca bronnii Roemer and Gisilina jasmundi Steinich) and one secondarily free-living species (Magas chitoniformis Schlotheim) have been studied for element concentrations as well as C and O isotope signatures. Each species has a unique chemical signature, with M. chitoniformis showing lowest Mg and Mn concentrations, A. bronnii the highest Mn concentrations and G. jasmundi the highest Sr concentrations. All three species display decreasing Mg/Ca ratios throughout the studied interval and distinct Mn enrichments in the Campanian–Maastrichtian boundary (CMB) interval. In the Campanian part of the succession, the three species are slightly enriched in 13C (median Δ13C values of +0.0 to +0.5‰) and 18O (median Δ18O values of +0.3 to +0.6‰) with respect to coeval chalk. In the course of the Maastrichtian, the two attached species acquire progressively lighter isotopic compositions with A. bronnii reaching δ13C and δ18O values >1.0‰ lower than coeval chalk. The secondarily free-living species M. chitoniformis, on the other hand, becomes isotopically heavier and reaches δ13C and δ18O enrichments of ~1.0‰ at the top of the core. The observed differences between the species illustrate species-specific signatures of biomineralisation, diagenesis and response to environmental change. This geochemical complexity illustrates that a comprehensive geochemistry-based picture of the Late Cretaceous Chalk Sea can only be painted using detailed multi-species and multi-proxy datasets.
Schlagworte: carbon , oxygen , geol , gashead

Isoscapes resolve species-specific spatial patterns in plant-plant interactions in an invaded Mediterranean dune ecosystem.
Tree physiology (2016)
Christine Hellmann, Katherine G Rascher, Jens Oldeland, Christiane Werner

Environmental heterogeneity and plant-plant interactions are key factors shaping plant communities. However, the spatial dimension of plant-plant interactions has seldom been addressed in field studies. This is at least partially rooted in a lack of methods that can accurately resolve functional processes in a spatially explicit manner. Isoscapes, that is, spatially explicit representations of stable isotope data, provide a versatile means to trace functional changes on spatial scales, for example, related to N-cycling (foliar δ(15)N) and water use efficiency (WUEi, foliar δ(13)C). In a case study in a nutrient-depleted Mediterranean dune ecosystem, we analysed the spatial impact of the invasive N2-fixing Acacia longifolia on three native species of different functional types using δ(15)N and δ(13)C isoscapes and spatial autocorrelation analyses. Isoscapes revealed strong spatial patterns in δ(15)N and δ(13)C with pronounced species-specific differences, demonstrating distinct spatial ranges of plant-plant interactions. A coniferous tree and an ericaceous dwarf shrub showed significant enrichment in δ(15)N within a range of 5-8 m surrounding the canopy of A. longifolia, indicating input of N originating from symbiotic N2-fixation by the invader. In the dwarf shrub, which was most responsive to invader influence, enrichment in δ(13)C additionally demonstrated spatially explicit changes to WUEi, while a native N2-fixer was unresponsive to the presence of the invader. Furthermore, δ(15)N and δ(13)C isoscapes yielded different patterns, indicating that plant-plant interactions can have distinct spatial distributions and ranges based on the process measured. Additionally, the magnitude of the effect differed between field situations with high and low invasion pressure. This study highlights that the spatial scale must be accounted for when assessing the effects and outcome of species interactions. Functional tracers such as stable isotopes enable us to quantify spatial ranges of plant-plant interactions, providing empirical data that can help to better understand and predict complex species interactions in multifaceted natural environments.
Schlagworte: carbon , nitrogen , soil , elem

Palaeoecological evidence for sustained change in a shallow Murray River (Australia) floodplain lake: regime shift or press response?
Hydrobiologia (2016)
Giri Kattel, Peter Gell, Atun Zawadzki, Linda Barry

Paleolimnological techniques can reveal long-term perturbations and associated stable state transitions of lake ecosystems. However, such transitions are difficult to predict since changes to lake ecosystems can be abrupt or gradual. This study examined whether there were past transitions in the ecological regime of Kings Billabong, a shallow River Murray wetland in southeast Australia. A 94-cm-long core, covering c. 90 years of age, was analysed at 1 cm resolution for subfossil cladocerans, diatoms and other proxies. Prior to river regulation (c. 1930), the littoral to planktonic ratios of cladocerans and diatoms, and bulk sediment δ13C values were high, while the period from c. 1930 to c. 1970 experienced considerable changes to the wetland ecosystem. The abrupt nature of changes of planktonic cladocerans and diatoms, particularly after the onset of river regulation (1930s), was triggered by inundation, high rates of sedimentation and shifts in bulk sediment δ15N values. However, the transition of a once littoral-dominated community, to one favouring an increasingly turbid, plankton-dominated trophic condition following river regulation was relatively slow and lasted for decades. The progression to a new regime was likely delayed by the partial recovery of submerged plant communities and related internal dynamics.
Schlagworte: carbon , nitrogen , geol , ecol , elem

Impact of river regulation and hydropeaking on the growth, condition and field metabolism of Brook Trout ( Salvelinus fontinalis )
Ecology of Freshwater Fish (2016)
Brianne Kelly, Karen E. Smokorowski, Michael Power

Brook Trout (Salvelinus fontinalis) is an important fish species in Ontario, Canada, supporting recreational fisheries that contribute significantly to local economies. Hydroelectric dams disrupt the river continuum, altering downstream conditions and impacting riverine fish populations. Specifically, Brook Trout activity has been found to increase during hydropeaking periods, when dam operators rapidly increase river discharge to meet electricity demands. Higher energetic outputs driven by hydropeaking may decrease the energy available to allocate towards fish growth and condition, negatively impacting Brook Trout. We investigated the impact of two different hydropeaking regimes on resident Brook Trout populations downstream from a 15-MW dam used for hydropeaking, compared to a population in a nearby naturally flowing river. Length-at-age as determined by otolith back-calculations was higher in the regulated river relative to the naturally flowing river. Muscle tissue caloric content and weight–length relationships did not differ between rivers. Field metabolism, as inferred from fish otolith δ13C values, was higher in the regulated river relative to the naturally flowing river and was significantly positively related to time spent hydropeaking. Higher metabolic outputs in the regulated river were likely offset by an increased food supply, allowing for higher Brook Trout length-at-age. The opposing and complicated impacts of river regulation on Brook Trout highlight the need for studies to consider multiple indicators of fish health when characterising the response of fish populations to river regulation.
Schlagworte: carbon , nitrogen , ecol , elem