Hot Spots of Nitrification in the Elbe Estuary and Their Impact on Nitrate Regeneration     

Tina Sanders  Andreas Schöl  Kirstin Dähnke 《Estuaries and Coasts》2018,41(1):128-138

Estuaries act as an organic matter and nutrient filter in the transition between the land, rivers and the ocean. In the past, high nutrient and organic carbon load and low oxygen concentration made the Elbe River estuary (NW Europe) a sink for dissolved inorganic nitrogen. A recent reduction in loads and subsequent recovery of the estuary changed its biogeochemical function, so that nitrate is no longer removed on its transition towards the coastal North Sea. Nowadays in the estuary, nitrification appears to be a significant nitrate source. To quantify nitrification and determine actively nitrifying regions in the estuary, we measured the concentrations of ammonium, nitrite and nitrate, the dual stable isotopes of nitrate and net nitrification rates in the estuary on five cruises from August 2012 to August 2013. The nitrate concentration increased markedly downstream of the port of Hamburg in summer and spring, accompanied by a decrease of nitrate isotope values that was clearest in summer exactly at the location where nitrate concentration started to increase. Ammonium and nitrite peaked in the Hamburg port region (up to 18 and 8 μmol L^?1, respectively), and nitrification rates in this region were up to 7 μmol L^?1 day^?1. Our data show that coupled re-mineralization and nitrification are significant internal nitrate sources that almost double the estuary’s summer nitrate concentration. Furthermore, we find that the port of Hamburg is a hot spot of nitrification, whereas the maximum turbidity zone (MTZ) only plays a subordinate role in turnover of nitrate.  相似文献   

Palynology of Triassic–Jurassic boundary sections in northern Switzerland     

Elke Schneebeli-Hermann  Nathan Looser  Peter A. Hochuli  Heinz Furrer  Achim G. Reisdorf  Andreas Wetzel  Stefano M. Bernasconi 《Swiss Journal of Geoscience》2018,111(1-2):99-115

A first palynostratigraphic scheme of Upper Triassic deposits in northern Switzerland was established based on spore-pollen associations and dinoflagellate cyst records from the upper part of the Upper Triassic Klettgau Formation and the lower part of the Lower Jurassic Staffelegg Formation. Drill cores from the Adlerberg region (Basel Tabular Jura) and from Weiach (northern part of Canton Zurich) as well as from an outcrop at the Chilchzimmersattel (Basel Folded Jura) were studied and five informal palynological associations are distinguished. These palynological associations correlate with palynological association of the Central European Epicontinental Basin and the Tethyan realm and provide a stratigraphic framework for the uppermost Triassic sediments in northern Switzerland. Throughout the uppermost Triassic to Jurassic palynological succession a remarkable prominence of Classopollis spp. is observed. Besides Classopollis spp. the three Rhaetian palynological associations A to C from the Upper Triassic Belchen Member include typical Rhaetian spore-pollen and dinoflagellate taxa (e.g., Rhaetipollis germanicus, Geopollis zwolinskae, Rhaetogonyaulax rhaetica, and Dapcodinium priscum). Association B differs from association A in a higher relative abundance of the sporomorph taxa Perinopollenites spp. and the consistent occurrence of Granuloperculatipollis rudis and Ricciisporites tuberculatus. Spore diversity is highest in the late Rhaetian palynological association C and includes Polypodiisporites polymicroforatus. A Rhaetian age for the Belchen Member is confirmed by palynological associations A–C, but there is no record of the latest Rhaetian and the earliest Jurassic. In contrast to the Rhaetian palynological associations the Early Jurassic associations W and D include Pinuspollenites spp., Trachysporites fuscus (in association W), and Ischyosporites variegatus. In the view of the end-Triassic mass extinction and contemporaneous environmental changes the described palynofloral succession represents the pre-extinction phase (associations A and B) including a distinct transgression, the extinction phase (association C) associated with a regression, and the post-extinction phase (association W).  相似文献   

The effects of visual realism,spatial abilities,and competition on performance in map-based route learning in men     

Arzu Çöltekin  Rebecca Francelet  Kai-Florian Richter  John Thoresen  Sara Irina Fabrikant 《制图学和地理信息科学》2018,45(4):339-353

We report on how visual realism might influence map-based route learning performance in a controlled laboratory experiment with 104 male participants in a competitive context. Using animations of a dot moving through routes of interest, we find that participants recall the routes more accurately with abstract road maps than with more realistic satellite maps. We also find that, irrespective of visual realism, participants with higher spatial abilities (high-spatial participants) are more accurate in memorizing map-based routes than participants with lower spatial abilities (low-spatial participants). On the other hand, added visual realism limits high-spatial participants in their route recall speed, while it seems not to influence the recall speed of low-spatial participants. Competition affects participants’ overall confidence positively, but does not affect their route recall performance neither in terms of accuracy nor speed. With this study, we provide further empirical evidence demonstrating that it is important to choose the appropriate map type considering task characteristics and spatial abilities. While satellite maps might be perceived as more fun to use, or visually more attractive than road maps, they also require more cognitive resources for many map-based tasks, which is true even for high-spatial users.  相似文献   

Correction to: Leveraging HPC accelerator architectures with modern techniques — hydrologic modeling on GPUs with ParFlow     

Hokkanen  Jaro  Kollet  Stefan  Kraus  Jiri  Herten  Andreas  Hrywniak  Markus  Pleiter  Dirk 《Computational Geosciences》2021,25(5):1591-1591

Computational Geosciences - A Correction to this paper has been published: https://doi.org/10.1007/s10596-021-10065-y  相似文献   

Complex fault structure interactions of crustal shear zones revealed by seismic anisotropy: an example in the eastern betic cordillera (Spain)     

Luisa Buontempo  Andreas Wuestefeld 《地学学报》2013,25(1):57-64

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Trends,drivers and impacts of changes in swidden cultivation in tropical forest-agriculture frontiers: A global assessment     

Nathalie van Vliet  Ole Mertz  Andreas Heinimann  Tobias Langanke  Unai Pascual  Birgit Schmook  Cristina Adams  Dietrich Schmidt-Vogt  Peter Messerli  Stephen Leisz  Jean-Christophe Castella  Lars Jørgensen  Torben Birch-Thomsen  Cornelia Hett  Thilde Bech-Bruun  Amy Ickowitz  Kim Chi Vu  Kono Yasuyuki  Jefferson Fox  Christine Padoch  Alan D. Ziegler 《Global Environmental Change》2012,22(2):418-429

This meta-analysis of land-cover transformations of the past 10–15 years in tropical forest-agriculture frontiers world-wide shows that swidden agriculture decreases in landscapes with access to local, national and international markets that encourage cattle production and cash cropping, including biofuels. Conservation policies and practices also accelerate changes in swidden by restricting forest clearing and encouraging commercial agriculture. However, swidden remains important in many frontier areas where farmers have unequal or insecure access to investment and market opportunities, or where multi-functionality of land uses has been preserved as a strategy to adapt to current ecological, economic and political circumstances. In some areas swidden remains important simply because intensification is not a viable choice, for example when population densities and/or food market demands are low. The transformation of swidden landscapes into more intensive land uses has generally increased household incomes, but has also led to negative effects on the social and human capital of local communities to varying degrees. From an environmental perspective, the transition from swidden to other land uses often contributes to permanent deforestation, loss of biodiversity, increased weed pressure, declines in soil fertility, and accelerated soil erosion. Our prognosis is that, despite the global trend towards land use intensification, in many areas swidden will remain part of rural landscapes as the safety component of diversified systems, particularly in response to risks and uncertainties associated with more intensive land use systems.  相似文献   

Epikarst hydrology and implications for stalagmite capture of climate changes at Grotta di Ernesto (NE Italy): results from long‐term monitoring     

Renza Miorandi  Andrea Borsato  Silvia Frisia  Ian J. Fairchild  Detlev K. Richter 《水文研究》2010,24(21):3101-3114

Grotta di Ernesto is a cave site well suited for palaeoclimate studies because it contains annually laminated stalagmites and was monitored from 1995 to the end of 2008 for microclimate, hydrology and hydrochemistry. Long‐term monitoring highlighted that cave drips show three different hydrological responses to rainfall and infiltration: (1) fast seasonal drips in the upper part of the cave, which are mostly fed by fractures, (2) slow seasonal drips, located at mid‐depth in the cave characterized by mixed feeding and (3) slow drips, mostly located in the deeper gallery, which are fed by seepage flow from bulk porosity with a minor fracture‐fed component. The slow drips display daily cycles during spring thaw. Monitoring also indicated that drip waters are only slightly modified by degassing within the soil zone and aquifer and by prior calcite precipitation. Hydrochemical studies show a clear seasonality in calcite saturation index, which results in most cave calcite precipitation occurring during late autumn and winter with similar amounts of precipitated calcite on most stalagmites, regardless of drip rate (discharge) differences. Drip rate, and drip rate variability, therefore, has a minor role in modulating the amount of annual calcite formation. In contrast, drip rate, when associated with moderate reduction in calcite saturation index, clearly influences stalagmite morphology. Increasing drip rate yields a passage from candle‐, to cone‐ to dome‐shaped stalagmites. Very high drip rates feed speleothems with flowstone morphology. In summary, monitoring provides information about the karst aquifer and how hydrology influences those physical and chemical characteristics of speleothems which are commonly used as climate proxies. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Compactional behavior of fine-grained sediments — examples from Deep Sea Drilling Project cores     

Ulf Bayer  Andreas Wetzel 《International Journal of Earth Sciences》1989,78(3):807-819

Laboratory experiments, statistical analysis of field data and theoretical models are combined in the attempt to derive standard compaction curves for various deep-sea sediments which are in compaction equilibrium with the overburden. A revised and generalized version of Athy's law together with laboratory experiments allows the classification of sediments in terms of the amount of porewater structurally bound to the particles' surfaces. Especially suction pressure experiments are useful in quantifying the forces that bind water on the particle surfaces. The sediments analyzed almost range from systems of »suspended grains« to nearly perfect »colloidal systems«. The methods and equations required to derive the relevant parameters are given for both, downhole porosity/density measurements and laboratory experiments.

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Zusammenfassung Die Synthese experimenteller Labordaten, statistischer Analysen von Messungen an Kernen und theoretischer Modellierung der Kompaktion im Gleichgewicht mit der Auflast ermöglicht die Definition von Typ-Kurven für das Kompaktionsverhalten von verschiedenen Tiefsee-Sedimenten. Eine erweiterte und verbesserte Form der Athy'schen Gleichung erlaubt zusammen mit Laborexperimenten, Sedimente entsprechend des Anteils an strukturell gebundenem Porenwasser zu klassifizieren. Anhand von Saugspannungsexperimenten können die Bindungskräfte zwischen Wasser und Partikeloberflächen abgeschätzt werden. Die untersuchten Sedimente reichen von »suspendierten Körnern« bis zu einem »kolloidalen System«. Die notwendigen Methoden und Gleichungen zur Bestimmung der relevanten Parameter aus Bohrlochdaten und Laborexperimenten werden diskutiert.

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Résumé A partir d'une synthèse de résultats d'expériences de laboratoires, d'analyses statistiques de données de terrain et d'une modélisation théorique, il est possible d'établir des courbes standard du processus de compaction pour divers types de sédiments de mer profonde, pour lesquels la compaction est en équilibre avec la charge. Une version revue et généralisée de la loi d'Athy permet, en accord avec les résultats expérimentaux, de classer les sédiments selon la quantité d'eau intersticielle liée structuralement à la surface des particules. Les sédiments analysés correspondent à des systèmes qui vont du type à «grains suspendus» à des colloïdes presque parfaits. Les auteurs présentent une discussion détaillée des méthodes et des équations néssaires à l'obtention des paramètres significatifs tant à partir des expériences de laboratoire qu'à partir des mesures de porosité/densité effectuées dans les forages.

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Brine Discharge and Salinization, Concho River Watershed, West Texas     

Alan R. Dutton  Bernd C. Richter  Charles W. Kreitler 《Ground water》1989,27(3):375-383

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Book reviews     

Krings  Th.  Bora  Lakshmi N.  West  Robert C.  Rugg  Dean S.  Tietze  Wolf  Grotewold  Andreas  Hellen  J. A. 《GeoJournal》1990,22(3):381-384

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