Microbial activity and biogeochemical cycling in a nutrient-rich meromictic acid pit lake     

Katrin Wendt-Potthoff  Matthias KoschorreckMarta Diez Ercilla  Javier Sánchez España 《Limnologica》2012,42(3):175-188

Microbial activity, abundance and biomass, and biogeochemical cycling of iron, sulphur and carbon were studied in the extremely acidic (pH 2.5-4.3), meromictic, nutrient-rich pit lake Cueva de la Mora in Spain. The goal was to find out (1) if the relatively high nutrient content influenced plankton abundance in the water column and alkalinity-producing microbial processes in the sediments compared to other acid pit lakes, and (2) if sediments in the shallow, mixed and the deep, stagnant parts of the lake exhibited differences in microbial activities and geochemical sediment composition related to meromixis. We hypothesised that redox cycling was more intense in the mixed part and higher amounts of reduced components would accumulate in the stagnant part. Especially phytoplankton biomass, CO₂ production, and sulphate reduction were indeed higher than reported from typical acid pit lakes and were rather within the range of neutral or weakly acidic lakes, which can be attributed to the relatively high nutrient contents of Cueva de la Mora. Even in the monimolimnion, anaerobic processes occurred mainly in the sediments. Sediments from the mixed and stagnant parts of the lake differed markedly in their biogeochemistry. Mixolimnetic sediments showed high iron and sulphate reduction rates, and they appeared to undergo substantial recycling, as supported by reactive Fe, relation between gross sulphate reduction rate and net accumulation of reduced sulphur, and viable counts of iron and sulphur bacteria. Monimolimnetic sediments exhibited lower anaerobic microbial activities, and surprisingly they accumulated more Fe(II) than mixolimnetic sediments, but less reduced sulphur and carbon. This might be explained by a strong separation of the two water bodies, resulting in comparably less input of energy (light) and allochthonous matter into the monimolimnion. Regarding the total extent of alkalinity-generating microbial processes, their net effect is not sufficient to neutralise the lake within decades.  相似文献   

Low impact surface hardness testing (Equotip) on porous surfaces – advances in methodology with implications for rock weathering and stone deterioration research          下载免费PDF全文

Katrin Wilhelm  Heather Viles  Órlaith Burke 《地球表面变化过程与地形》2016,41(8):1027-1038

The Equotip surface hardness tester is becoming a popular method for rock and stone weathering research. In order to improve the reliability of Equotip for on‐site application this study tested four porous limestones under laboratory conditions. The range of stone porosity was chosen to represent likely porosities found in weathered limestones in the field. We consider several key issues: (i) its suitability for soft and porous stones; (ii) the type of probe required for specific on‐site applications; (iii) appropriate (non‐parametrical) statistical methods for Equotip data; (iv) sufficient sampling size. This study shows that the Equotip is suitable for soft and porous rock and stone. From the two tested probes the DL probe has some advantages over the D probe as it correlates slightly better with open porosity and allows for more controlled sampling in recessed areas and rough or curved areas. We show that appropriate sampling sizes and robust non‐parametric methods for subsequent data evaluation can produce meaningful measures of rock surface hardness derived from the Equotip. The novel Hybrid dynamic hardness, a combination of two measuring procedures [single impact method (SIM) and repeated impact method (RIM)], has been adapted and is based on median values to provide a more robust data evaluation. For the tested stones in this study we propose a sample size of 45 readings (for a confidence level of 95%). This approach can certainly be transferred to stone and rock with similar porosities and hardness. Our approach also allows for consistent comparisons to be made across a wide variety of studies in the fields of rock weathering and stone deterioration research. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Loading protocols for European regions of low to moderate seismicity     

Panagiotis E. Mergos  Katrin Beyer 《Bulletin of Earthquake Engineering》2014,12(6):2507-2530

Existing loading protocols for quasi-static cyclic testing of structures are based on recordings from regions of high seismicity. For regions of low to moderate seismicity they overestimate imposed cumulative damage demands. Since structural capacities are a function of demand, existing loading protocols applied to specimens representative of structures in low to moderate seismicity regions might underestimate structural strength and deformation capacity. To overcome this problem, this paper deals with the development of cyclic loading protocols for European regions of low to moderate seismicity. Cumulative damage demands imposed by a set of 60 ground motion records are evaluated for a wide variety of SDOF systems that reflect the fundamental properties of a large portion of the existing building stock. The ground motions are representative of the seismic hazard level corresponding to a 2 % probability of exceedance in 50 years in a European moderate seismicity region. To meet the calculated cumulative damage demands, loading protocols for different structural types and vibration periods are developed. For comparison, cumulative seismic demands are also calculated for existing protocols and a set of records that was used in a previous study on loading protocols for regions of high seismicity. The median cumulative demands for regions of low to moderate seismicity are significantly less than those of existing protocols and records of high seismicity regions. For regions of low to moderate seismicity the new protocols might therefore result in larger strength and deformation capacities and hence in more cost-effective structural configurations or less expensive retrofit measures.  相似文献   

A pilot-scale field experiment for the microbial neutralization of a holomictic acidic pit lake     

Walter Geller  Matthias Koschorreck  Katrin Wendt-Potthoff  Elke Bozau  Peter Herzsprung  Olaf Büttner  Martin Schultze 《Journal of Geochemical Exploration》2009,100(2-3):153-159

A strategy to neutralize acidic pit lakes was tested in an upscaling process using field mesocosms of 26 to ca. 4500 m³ volume in the acidic pit Mining Lake 111 in Germany. After addition of the substrates Carbokalk and straw a neutral sediment layer formed, in which microbial sulfate and iron reduction as well as sulfide precipitation occurred. The net rate of neutralization was limited by the precipitation of iron sulfides rather than by microbial reactions. Oxidation of H₂S by ferric iron in the anoxic sediment lowered the net sulfate reduction rate. Seasonal fluctuations of iron sulfides in the sediment showed that the reaction products were not necessarily stable. The long-term success of the approach depends on the net partition of the precipitated iron-(mono-/di-) sulfide that is permanently buried in the anoxic sediment. It could be shown by field experiments that the long-term success of the neutralization depends on the spatial scale and duration of the experiments. Volumes from 26 to 4500 m³, exposition times from 4 months to 5 years, and increasingly thick coverings of the sediments with straw, from zero to 40 cm, were used. Net neutralization rates decreased from 41 meq m^− 2 d^− 1 in laboratory microcosms to a mean rate of 2.3 meq m^− 2 d^− 1 in the 4500 m³ field experiment. The results show that the success of the microbial treatment of acid pit lakes lastly depends on the limnological conditions in the lake that cannot be simulated by upscaling of simple laboratory experiments.  相似文献   

Necessary restructuring or globalization failure? Shifts in regional supplier relations after the merger of the former German Hoechst and French Rhône-Poulenc groups     

Harald Bathelt  Katrin Kappes 《Geoforum》2009,40(2):158-170

A large part of the work in economic geography and other social sciences surrounding globalization processes has focused on the prospects of economic growth due to the establishment of global production chains and the rise of new clusters of industrial activity. In recent years, much less attention has been paid to former growth industries and regions that have suffered from the negative consequences of internationalization processes. This paper will explore the cases of two chemical regions, i.e. southern Hessen, Germany and Rhône-Alpes, France. Both regions were forced to undergo drastic restructuring since the mid 1990s due to the merger of the chemical groups Hoechst and Rhône-Poulenc into Aventis. The paper argues that it is beneficial to develop a relational perspective of economic action and interaction in order to better understand these regional transformations and restructuring processes and their consequences. Instead of investigating the development of activities, which became the core operations at Aventis, we will focus on other activities that were considered less important and, consequently, split off. In analyzing the logic of restructuring and the associated changes in regional supplier relations, this paper aims to contribute to a relational understanding of economic globalization and its associated threats to regional development by focusing on agents who are subject to negative restructuring consequences.  相似文献   

1D joint multi‐offset inversion of time‐domain marine controlled source electromagnetic data          下载免费PDF全文

Davood Moghadas  Martin Engels  Katrin Schwalenberg 《Geophysical Prospecting》2015,63(6):1334-1354

The accurate estimation of sub‐seafloor resistivity features from marine controlled source electromagnetic data using inverse modelling is hindered due to the limitations of the inversion routines. The most commonly used one‐dimensional inversion techniques for resolving subsurface resistivity structures are gradient‐based methods, namely Occam and Marquardt. The first approach relies on the smoothness of the model and is recommended when there are no sharp resistivity boundaries. The Marquardt routine is relevant for many electromagnetic applications with sharp resistivity contrasts but subject to the appropriate choice of a starting model. In this paper, we explore the ability of different 1D inversion schemes to derive sub‐seafloor resistivity structures from time domain marine controlled source electromagnetic data measured along an 8‐km‐long profile in the German North Sea. Seismic reflection data reveal a dipping shallow amplitude anomaly that was the target of the controleld source electromagnetic survey. We tested four inversion schemes to find suitable starting models for the final Marquardt inversion. In this respect, as a first scenario, Occam inversion results are considered a starting model for the subsequent Marquardt inversion (Occam–Marquardt). As a second scenario, we employ a global method called Differential Evolution Adaptive Metropolis and sequentially incorporate it with Marquardt inversion. The third approach corresponds to Marquardt inversion introducing lateral constraints. Finally, we include the lateral constraints in Differential Evolution Adaptive Metropolis optimization, and the results are sequentially utilized by Marquardt inversion. Occam–Marquardt may provide accurate estimation of the subsurface features, but it is dependent on the appropriate conversion of different multi‐layered Occam model to an acceptable starting model for Marquardt inversion, which is not straightforward. Employing parameter spaces, the Differential Evolution Adaptive Metropolis approach can be pertinent to determine Marquardt a priori information; nevertheless, the uncertainties in Differential Evolution Adaptive Metropolis optimization will introduce some inaccuracies in Marquardt inversion results. Laterally constrained Marquardt may be promising to resolve sub‐seafloor features, but it is not stable if there are significant lateral changes of the sub‐seafloor structure due to the dependence of the method to the starting model. Including the lateral constraints in Differential Evolution Adaptive Metropolis approach allows for faster convergence of the routine with consistent results, furnishing more accurate estimation of a priori models for the subsequent Marquardt inversion.  相似文献   

A Multi-Step Assessment Scheme for Seismic Network Site Selection in Densely Populated Areas     

Katrin Plenkers  Stephan Husen  Toni Kraft 《Journal of Seismology》2015,19(4):861-879

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True polar wander in mantle convection models with multiple, mobile continents     

Benjamin R. Phillips  Hans-Peter Bunge  Katrin Schaber 《Gondwana Research》2009,15(3-4):288-296

The geologic record supports numerous instances during which continents apparently moved at speeds significantly faster than any of today's tectonic plates. While the time dependence of convective driving forces likely explains some such observations, rapid motions of large continents in particular are often attributed to true polar wander (TPW). In order to gauge the potential for connections between continents, mantle temperature anomalies, and polar motion, we present the first calculations of TPW derived from models that couple mantle convection with multiple, mobile continents. We find that the aggregation and dispersal of supercontinents can lead to two types of TPW, driven either by a well developed hot upwelling axis that creates a stable maximum moment of inertia, or by the homogenization of mantle thermal structure following continent dispersal that leads to destabilization of the principal axis and possible large magnitude polar wander. These supercontinent-modulated thermal heterogeneities drive model TPW events as large as 90° at rates of up to 2.5° Ma^− 1. Such magnitudes and speeds are greater than those attained in similar models lacking continents, but comparable to those for episodes inferred from paleomagnetic data for some large continents in the past.  相似文献   

Histological Identification of Macroalgae from Stomach Contents of the Antarctic Fish Notothenia coriiceps Using Semi-thin Sections     

Katrin Iken  Maria-Liliana Quartino  &Christian Wiencke 《Marine Ecology》1999,20(1):11-17

A histological method is described allowing the identification of macro-algal fragments from stomach contents of fish. The rhodophytes Porphyra endiviifolium and Neuroglossum ligulatum were determined from the stomach contents of the Antarctic fish Notothenia coriiceps . The results show P. endiviifolium to be a more important part in the diet of this fish than previously expected. On the basis of the depth distribution of the identified algae it is suggested that N. coriiceps can migrate to very shallow waters for feeding.  相似文献   

富营养湖泊中的微囊藻优势：原因—后果—对策     

Martin T. Dokulil  Katrin Teubner 《湖泊科学》1998,10(S1):357-370

Cyanobacterial dominance in lakes has received much attention in the past because of the great success and frequent bloom formation in lakes of higher trophic levels. In this paper underlying mechanism of cyanobacterial dominance are analyzed and discussed using both original and literature data from various shallow mixed and deep stratifying lakes from temperate and (subtropical regions. Examples include all four ecotypes of cyanobacteria sensu MUR et al. (1993), because their behavior in the water column is entirely different.Colony forming species (Microcystis) are exemplified from the large shallow Lake Taihu, China. Data from a shallow urban lake, Alte Donau in Austria are used to characterize well mixed species (Cylindrospermopsis) while stratifying species (Planktothrix) are analyzed from the deep alpine lake Mondsee. Nitrogen fixing species (Aphanizomenon) are typified from a shallow river-run lake in Germany.Factors causing the dominance of one or the other group are discussed as well as consequences for restoration measures. Existing knowledge on cyanobacterial dominance is summarized.  相似文献