Sequestration of a Biologically Labile Organic Carbon in Soils by Humified Organic Matter

In a long-term (one year) experiment, a sandy Podzol and a silty-loamy Loess soil were treated with labile (polysaccharides, AG) and stable (mature compost, CMP, and two humic acids from compost, HAC, and lignite, HAL) organic matter and the organic carbon (OC) lost by mineralization was periodically evaluated. The stable materials alone induced a significant reduction of OC losses in Podzol CMP <, HAL, <, HAC, Control), whereas the same treatments, except for CMP, produced an OC loss larger than control in Loess. This was attributed to the diverse textural and physical status of the two soils. The added stable organic matter became protected in the Podzol soil within the aggregates formed by the interaction with the coarse inorganic phase, while it was more easily decomposed in the Loess soils due to the strength of the native humic-clay complexes. In both soils, when the stable organic materials were mixed with polysaccharides (AG), the OC losses from this labile fraction were significantly reduced, being CMP more OC sequestering than HAC and HAL, in the order. These results confirmed that labile organic matter in soils can be protected from biodegradation by repartition into the hydrophobic domains of the stable, humified organic matter. This study suggests that mature compost and humic acids may usefully integrate management practices aimed to sequester organic carbon in soils.     

Towards a better understanding of magnesium-isotope ratios from marine skeletal carbonates

This study presents magnesium stable-isotope compositions of various biogenic carbonates of several marine calcifying organisms and an algae species, seawater samples collected from the western Dutch Wadden Sea, and reference materials. The aim of this study is to explore the influence of mineralogy, taxonomy and environmental factors (e.g., seawater isotopic composition, temperature, salinity) on magnesium-isotopic (δ²⁶Mg) ratios of skeletal carbonates. Using high-precision multi-collector inductively coupled plasma mass spectrometry, we observed that the magnesium-isotopic composition of seawater from the semi-enclosed Dutch Wadden Sea is identical to that of open marine seawater. We further found that a considerable component of the observed variability in δ²⁶Mg values of marine skeletal carbonates can be attributed to differences in mineralogy. Furthermore, magnesium-isotope fractionation is species-dependent, with all skeletal carbonates being isotopically lighter than seawater. While δ²⁶Mg values of skeletal aragonite and high-magnesium calcite of coralline red algae indicate the absence or negligibility of metabolic influences, the δ²⁶Mg values of echinoids, brachiopods and bivalves likely result from a taxon-specific level of control on Mg-isotope incorporation during biocalcification. Moreover, no resolvable salinity and temperature effect were observed for coralline red algae and echinoids. In contrast, Mg-isotope data of bivalves yield ambiguous results, which require further validation. The data presented here, point to a limited use of Mg isotopes as temperature proxy, but highlight the method’s potential as tracer of seawater chemistry through Earth’s history.     

Entstehung und Alter der Oberharzer Gänge

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Protokoll der wissenschaftlichen Sitzung am 4. und 5. Januar 1937

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Tektonische Beziehungen zwischen Harzrand und Harzvorland

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Über Flysch und Molasse im Allgäu

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Deep Space 1 at comet 19P/Borrelly: Magnetic field and plasma observations

On September 22, 2001 the Deep Space 1 spacecraft performed a flyby at comet 19P/Borrelly at a solar distance of 1.36 AU leading the Earth by 74^° in longitude. The spacecraft-comet distance at closest approach was 2171 km. The bow shock had a magnetic compression ratio of 2.5 at a distance of 147 100 km from the nucleus. Deep Space 1 first entered the sheath region essentially from the north polar region. Fluctuations from the cometary ion pickup were present throughout the sheath region and even well upstream of the shock, as expected. The magnetic field pileup region had a peak field strength of 83 nT and was shown to be consistent with a pressure equal to the solar wind ram pressure. The peak field location was offset from the time of closest approach. It is uncertain whether this is a spatial or temporal variation. Draping of magnetic fields around the nucleus was sought, but evidence for this was not apparent in the data. A possible explanation is that the interplanetary solar wind was composed of turbulent short-scale fields, and thus the fields were not symmetric about the point of closest approach. During the flyby phase there were in general few intervals of ACE data where there were large scale Parker spiral fields. With the addition of plasma data, the shock properties are investigated. The characteristics of magnetic draping, pileup and fluctuations are explored. These comet 19P/Borrelly results are contrasted with other cometary flyby results.     

First attempts towards an integrative concept for the ecological assessment of groundwater ecosystems

Healthy aquifers deliver important ecosystem services, e.g. the purification of infiltrating water and the storage of high-quality water over decades in significant quantities. The functioning of terrestrial and surface aquatic ecosystems directly depends on groundwater and vice versa. Nowadays, legislation has started to consider groundwater not only as a resource but as a living ecosystem. The assessment of ecosystems requires consideration of ecological criteria, which, so far, are not available for groundwater systems. In the framework of a project supported by the German Federal Environment Agency (UBA), a first concept for the ecological assessment of groundwater ecosystems is developed. Steps to be taken are introduced, with a strong focus on microbes as potential bioindicators. These include (1) the typology of groundwater ecosystems, (2) the derivation of natural background values, (3) the identification of potential bioindicators, and (4) the development of an assessment model. First successes and difficulties associated with these challenges, e.g. the lack of simple correlations between abiotic and biotic variables, are discussed on the basis of a data set from a local and regional aquifer in NE Germany. The need for collaboration between ecologists, hydrogeologists and geochemists, as well as the application of modern approaches such as multivariate statistics, is emphasized.