Biosilicium (BSi) in Sedimenten Mecklenburger Seen (Deutschland) und das Calciumcarbonat-Biosilicium-Verhältnis als Trophie- und Wasserstandsindikator Biogenic Silica (BSi) in Sediments of the Mecklenburgian Lake District (Germany) and the Calcite-Silica-Relation as Indicator for Trophy and Water Level

The BSi content has been investigated in the surface sediments of lakes of different trophic state in the Mecklenburgian Lake District. The BSi content differs between 1 to 1000 mg BSi/g dry matter. High values were found in deep eutrophic lakes. Litoral sediments and shallow eutrophic lakes have lower contents. BSi content was found to be correlated with lake morphometry, depth, trophic level, sediment composition and especially with calcite. With the CaCO₃/BSi-value, 3 groups of lakes can be characterized:

• CaCO₃/BSi = 0 oligotrophic and dystrophic lakes
• CaCO₃/BSi ≤ 10 mesotrophic and eutrophic deep lakes
• CaCO₃/BSi ≤ 10 eutrophic shallow lakes

The results from the recent sediments have been compared with those from older sediments. Using the CaCO₃/BSi-value, climatic change, trophic state, and sea level can be detected.     

Revisiting the dissolution of biogenic Si in marine sediments: a key term in the ocean Si budget

Of the　~240*10~(12)mol year~(-1)of biogenic silica(bSi)produced by diatoms and other silicifying organisms,only roughly 3%–4%escapes dissolution to be permanently buried.At the global scale,how,where and why b Si is preserved in sediment is not well understood.To help address this,I compile 6245 porewater dissolved Si concentrations from 453 sediment cores,to derive the concentration gradient at the sediment–water interface and thus diffusive fluxes out of the sediment.These range from\0.002 to 3.4 mol m~(-2)year~(-1),and are independent of temperature,depth and latitude.When classified by sediment lithology,predominantly siliceous sediments unsurprisingly have higher mean diffusive fluxes than predominantly calcareous or clay-rich sediment.Combined with the areal extent of these lithologies,the‘best-guess’global sedimentary b Si recycling flux is69 9 10~(12)mol year~(-1).     

Equilibrium and kinetic Si isotope fractionation factors and their implications for Si isotope distributions in the Earth's surface environments

Several important equilibrium Si isotope fractionation factors among minerals,organic molecules and the H_4SiO_4 solution are complemented to facilitate the explanation of the distributions of Si isotopes in Earth's surface environments.The results reveal that,in comparison to aqueous H_4SiO_4,heavy Si isotopes will be significantly enriched in secondary silicate minerals.On the contrary,quadra-coordinated organosilicon complexes are enriched in light silicon isotope relative to the solution.The extent of ~(28)Si-enrichment in hyper-coordinated organosilicon complexes was found to be the largest.In addition,the large kinetic isotope effect associated with the polymerization of monosilicic acid and dimer was calculated,and the results support the previous statement that highly ~(28)Sienrichment in the formation of amorphous quartz precursor contributes to the discrepancy between theoretical calculations and field observations.With the equilibrium Si isotope fractionation factors provided here,Si isotope distributions in many of Earth's surface systems can be explained.For example,the change of bulk soil δ~(30)Si can be predicted as a concave pattern with respect to the weathering degree,with the minimum value where allophane completely dissolves and the total amount of sesquioxides and poorly crystalline minerals reaches their maximum.When,under equilibrium conditions,the well-crystallized clays start to precipitate from the pore solutions,the bulk soil δ~(30)Si will increase again and reach a constant value.Similarly,the precipitation of crystalline smectite and the dissolution of poorly crystalline kaolinite may explain the δ~(30)Si variations in the ground water profile.The equilibrium Si isotope fractionations among the quadracoordinated organosilicon complexes and the H_4SiO_4solution may also shed light on the Si isotope distributions in the Si-accumulating plants.     

Interrelations between Si and P biogeochemical cycles—a new approach to the solution of the eutrophication problem

Because the biogeochemical cycles of P and Si in temperate lakes are strongly connected by the dynamics of primary producers, it should be possible to influence the former cycle by causing changes in the latter. It is shown using the mathematical model ‘Rostherne’ that winter levels of ambient Si have a major influence both on spring levels of ambient P and on the summer cyanobacterial maxima. Additions of Si to the lakes could be used for the fine regulation of the biogeochemical balance and may prescribe a recipe for improvement of water quality, as well as a new solution to the problem of eutrophication. Copyright © 2000 John Wiley & Sons, Ltd.     

Bioavailability and Interaction of Si and P in a Coastal Saline Soil Amended with Pig Slurry

The effects of widely applied organic waste amendment on soil Si and P bioavailability and their interaction have rarely been investigated. The study examined bioavailability and interaction of Si and P in response to pig slurry (PS) amendment in a coastal saline (CS) soil. The final purposes of the study are to assess fertilizer Si and P needs and to ensure environmental quality. The results show that PS amendment can cause accumulation of bioavailable Si in surface soil (0–20 cm), and significantly improve both soil bioavailable P content and soil P lability through PS‐Si and P input, and by the input of PS‐organic matter (OM) and enhancing the complexation of OM with soil Si and P. As a result of the Si‐P competitive sorption, Si shows a more rapid increase in bioavailability than P at the preliminary stage of PS amendment. However, under the weakly alkaline conditions as a result of relatively long term PS amendment, the fixation capacity of Si by soil solid components increases causing a rapider decline of Si bioavailability than that of P.     

Geochemical and geochronological studies of the Muong Hum alkaline granitic pluton from the Phan Si Pan Zone,northwest Vietnam: Implications for petrogenesis and tectonic setting

The Phan Si Pan zone in northwest Vietnam is an important tectonic unit for understanding the geological evolution of the southeast Asian Block. Numerous late Permian A‐type granites outcrop in this zone. In this study, new geochemical and geochronological data derived from the Muong Hum alkaline granitic pluton in the Phan Si Pan zone were investigated for its petrogenesis and tectonic setting. Zircon U–Pb analyses of three samples yielded ²⁰⁶Pb/²³⁸U ages of (251.1 ±3.5) Ma, (251.2 ±3.8) Ma, and (253.9 ±1.5) Ma, respectively, coinciding with the ages of the acid member of magma from Emeishan large igneous province, southwest China. The Muong Hum granite has 10 000 × Ga/Al and A/CNK values of 4.70–4.93 and 0.87–0.90, respectively, as well as negative Eu anomalies. It shows significant depletion of Ba, Sr, Ti, and P, similar to features of A‐type granite. Zircons have positive ε_Hf(t) values (+1.9 to +8.6) and Hf model ages (T_DM1) of 595–846 Ma, originating a mantle source. Compared with the Panzhihua A‐type granite of the southwest China domain and other A‐type plutons of the Phan Si Pan zone, including Ye Yen Sun, Phu Sa Phin, Nam Xe, Tam Duong Phan Si Pan, and Taihe, the geochemical characteristics and zircon Hf isotopic compositions of the Muong Hum granite demonstrate an affinity of mantle magma. It is believed that the Phan Si Pan zone is an important part of Emeishan large igneous province. It was reworked by the Cenozoic Aillaoshan‐Red River shear fault to its present location.     

Predicting summer hypoxia in the northern Gulf of Mexico: riverine N, P, and Si loading

We conducted a statistical analysis to discern the relative strengths of the loading of various forms of nitrogen, phosphorus, dissolved silicate and their molar ratios on the variance in the size of the summertime low oxygen zone found off the Mississippi River, northern Gulf of Mexico. A stable statistical model that included Year and riverine nitrate+nitrite loading for the 2 months prior to the measurement of hypoxic zone size described 82% of its variation in size from 1978 to 2004. The usefulness of the term Year is consistent with the documented increase in carbon stored in sediments after the 1970s, which is when the hypoxic zone is predicted to have become a regular feature on the shelf and to have expanded westward. The increased carbon storage is anticipated to cause a sedimentary respiratory demand influencing the size of the zone, and whose temporal influence is cumulative and transcends the annual variations in nitrogen loading. The variable Year is negatively correlated with the TN:TP ratio in a way that suggests N, not P, has become more important as a factor limiting phytoplankton growth in the last 20 years. Nitrogen, in particular nitrate+nitrite, and not phosphorus, dissolved silicate, or their molar ratios, appears to be the major driving factor influencing the size of the hypoxic zone on this shelf. This conclusion is consistent with cross-system analyses that conclude that the TN:TP ratio in the Mississippi River, currently fluctuating around 20:1, is indicative of nitrogen, not phosphorus, limitation of phytoplankton growth. Nutrient management that places stronger emphasis on reducing nitrogen loading as compared to phosphorus loading, is justified.     

Reed litter Si content affects microbial community structure and the lipid composition of an invertebrate shredder during aquatic decomposition

The decomposition of plant litter is an important mechanism in regard to energy and nutrient dynamics of ecosystems. Silicon concentration of plant tissue can affect these processes by changing litter quality, i.e. nutrient stoichiometry and cellulose and phenols content. To determine which group of microbial decomposers benefits from high Si content in plants and how this impacts on animal decomposers, a batch experiment was conducted with reed leaf litter (Phragmites australis) differing in Si content in the presence/absence of invertebrate shredders (Gammarus pulex). Lipid concentration of G. pulex, in reed litter and fine particulate matter (FPOM) were examined. High Si concentration in reed resulted in a decline of gram positive bacteria in the heterotrophic biofilm and of gram negative bacteria in FPOM. The lipid composition in the next trophic level, the decomposer G. pulex, changed too, indicating a diet shift in favor of bacteria and algae with increasing litter Si concentration. Thus, basal decomposers were affected by the Si availability in plant resources, and these effects likely persist along the food chain, as FPOM is a dominant food supply for other groups, e.g. collectors. This impact of Si content on plant substrate quality for decomposer food webs may have global relevance, due to related modifications in carbon and nutrient cycling during litter decomposition.     

An Instrument for the Determination of a Hydropneumograph in a Bubbling Spring

In order to enable greater accuracy in the determination of the mass discharge of gas and water-gas ratios (WGR) in groundwater from springs, we have developed a field-deployable instrument using commercially available components to independently measure the gas and water mass flow rates in springs with bubbling mixed-phase flow. Collecting and measuring the free gas phase will allow for further compositional analysis that may be useful in improving gas-derived parameters such as recharge temperature and age, as well as quantification of methanogenesis and flux of crustal/mantle gasses. By installing a phase separator at the spring discharge, a thermal mass flow sensor is utilized to measure the gas flow rate (ebullition + flux) generated from a spring. The water flow rate is determined by a standard weir. Field performance of the device was tested on a spring discharging from the Arbuckle-Simpson aquifer near the town of Connerville in south-central Oklahoma, USA.     

Method for the determination of the height of a solar filament

A comparison of the actual filament height above the solar photosphere with the limiting height calculated by magnetic data provides information about the filament stability margin and its readiness for eruption. A method is proposed for the determination of the height of solar filaments by a comparison of the position of the upper edge of the filament (spine) with the position of the polarity-inversion line of the potential magnetic field calculated for different heights. The line closest to the filament spine corresponds to its height. Observations of the Solar Terrestrial Relations Observatory (STEREO) spacecraft were used to verify the proposed method when they were at an angular distance of ~90° from the Earth and provided a side view of the filaments near the central meridian in observations from the Earth and near-Earth orbits. The proposed method can be useful in the estimation of the possible geoeffectiveness of filaments on the solar disk.     

Elaboration of a Regional Concept for Developing a Water Disposal System for the Central Ecological Zone of the Baikal Natural Territory

Water Resources - A unified concept of the elaboration of a water disposal system has been developed stage-by-stage for a large area in the central ecological zone of Baikal region with the use of...     

Solution of the inner stokes problem for a sphere

Summary In the present paper the inner Stokes problem is solved.     

Variability of the dissolved nutrient (N,P, Si) concentrations in the Bay of Annaba in relation to the inputs of the Seybouse and Mafragh estuaries

Dissolved inorganic nitrogen (DIN), phosphate (PO₄) and silicic acid (Si(OH)₄) loads from the Seybouse and the Mafragh estuaries into the Bay of Annaba, Algeria, were assessed at three stations of the Bay over three years. The Seybouse inputs had high levels of DIN and PO₄, in contrast to the Mafragh estuary’s near-pristine inputs; Si(OH)₄ levels were low in both estuaries. The DIN:PO₄ molar ratios were over 30 in most samples and the Si(OH)₄:DIN ratio was less than 0.5 in the Seybouse waters, but nearly balanced in the Mafragh. The specific fluxes of Si–Si(OH)₄ (400–540 kg Si km⁻² yr⁻¹) were comparable in the two catchments, but those of DIN were several-fold higher in the Seybouse (373 kg N km⁻² yr⁻¹). The inner Bay affected by the Seybouse inputs had high levels of all nutrients, while the Mafragh plume and the outer marine station were less enriched.     

Conditions for the arrest of a vertical propagating dyke

Magma ascent towards the Earth’s surface occurs through dyke propagation in the vast majority of cases. We investigate two purely mechanical effects unrelated to cooling or solidification that lead to the arrest of propagation, so that no eruption occurs. The first is that the input of magma from the source is not maintained continuously, such that a fixed volume of magma is released. Laboratory experiments show that, in this case, the dyke stops at a finite distance from the source. This behaviour is specific to the fracturing process in 3-D. We derive a relationship for the minimum magma volume required for an eruption as a function of magma buoyancy and source depth. When large magma volumes are available, eruption may also be prevented by a thick low density layer in the upper crust. Numerical studies of dyke propagation show that the dyke continues to rise even though it is negatively buoyant. Magma accumulates in a swollen nose region at the interface between the low density layer and the dense basement. Magma overpressure is largest at this interface and increases with increasing penetration into the upper layer. It may become large enough to induce horizontal fractures in the dyke walls and lateral intrusion of a sill, which prevents eruption. This requires that the thickness of the low density layer exceeds a threshold value that depends on the density contrast between magma and host rock. If the magma volume is smaller than a threshold value, neither sill intrusion nor eruption are possible and magma gets stored in a horizontal blade-shaped dyke straddling the interface. Scaling laws for variations of ascent rate and for the minimum magma volume allow diagnosis of a failed eruption.     

New methods for measuring the permeability of rock samples for a single-phase fluid

A complex of methodology, instrumentation, and software tools is worked out, which makes it possible to accomplish high-precision measurements of permeability for a single-phase fluid and its anisotropy within a wide range of values both under the normal conditions and high temperature and pressure.The transient method, modified with allowance for the dependence of the properties of a percolating gas on the parameters of its state, enables one to simultaneously determine, from the data of a single experiment, the permeability values for a sample of condensed fluid and the Klinkenberg constant, which characterizes the pore space of rock. This approach made it possible to substantially increase the accuracy of measurements, reducing their labor-intensiveness.The method of varying the flow shape makes it possible to simultaneously determine, in the course of a single experiment, the axial and radial components of the permeability tensor of anisotropic rocks with layered structure. The instrumentation and software implementing these new methodologies are developed and thoroughly tested.     

On the validity of a model for the reversals of the Earth's magnetic field

Abstract

We have used techniques of nonlinear dynamics to compare a special model for the reversals of the Earth's magnetic field with the observational data. Although this model is rather simple, there is no essential difference to the data by means of well-known characteristics, such as correlation function and probability distribution. Applying methods of symbolic dynamics we have found that the considered model is not able to describe the dynamical properties of the observed process. These significant differences are expressed by algorithmic complexity and Renyi information.     

一次北京大暴雨过程低空东南风气流形成机制的数值研究

2002年6月24~25日,北京门头沟附近发生了一次大暴雨过程.观测资料和数值模拟均发现,在暴雨发生前和发生过程中,北京地区边界层内出现了一支强盛的东南风气流.东南风气流沿太行山东坡爬升,触发了对流.为探讨这支低空东南风气流的形成原因,本文通过数值模拟和敏感性试验,对这支东南风气流的形成机制进行了研究.结果表明,这支低层东南风气流是一支冷湿的、伴有较强风速辐合的气流,主要是在天气尺度系统作用下生成的.东南风气流形成过程中,地表感热加热作用对其强度有加强作用.大暴雨开始后的潜热加热作用对这支东南风气流有正反馈作用,使气流的强度大大增强,因此,在降水开始后气流强度也增强,降水最强时低空急流的强度达最强.暴雨开始后,由于夜间地表降温造成山风效应,导致在北京西部山脚下出现偏北风.     

On a method for estimating the shape of a gravitationally and magnetically disturbing body

Summary The demagnetisation depends on the shape of the magnetised body. Here we investigate the possibility of calculating the shape of the magnetised body by means of the demagnetisation. It can be done if the gravity field and the induced magnetic field of a body with constant susceptibility and density are known. As the method is approximative it is not restricted just to bodies with a 2nd degree surface, but can be applied to all bodies, for which the demagnetisation can be regarded as constantly dependent on the direction. This means, with certain approximation, all bodies that are homogeneously magnetised, but not in the direction of the magnetising field due to demagnetisation.

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Zusammenfassung Die Demagnetisierung hängt von der Gestalt des magnetisierten Körpers ab. Hier soll untersucht werden, inwieweit es möglich ist, aus der Demagnetisierung Rückschlüsse über die Gestalt des magnetisierten Körpers zu ziehen. Dazu besteht die Möglichkeit, wenn das Gravitationsfeld und das induzierte Magnetfeld eines Körpers mit konstanter Dichte und Suszeptibilität gegeben sind. Da die Methode approximativ ist, ist sie nicht auf Körper mit Oberfläche 2ten Grades beschränkt, sondern sie kann in allen Fällen angewandt werden, in denen die Demagnetisierung als konstant richtungsabhängig angesehen werden kann. Dies bedeutet mit einer gewissen Approximation alle Körper, die homogen magnetisiert sind, aber infolge der Entmagnetiseerung nicht in der Richtung des magnetisierenden Feldes.

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A Tool for Forecasting the Arrival Time of a Tracer or a Pollutant at a Karst Spring

Karst aquifers are a groundwater resource of global importance. Protection and contamination of karst water resources are often tackled by means of land-use planning and monitoring of physico-chemical and microbial water properties coupled to early-warning systems. However, these solutions of management do not integrate observational data on karst hydrodynamic, for example, tracer tests. Thus, this technical note aims at introducing a straightforward method for forecasting the arrival time of a tracer or a pollutant at a karst spring. Deliverables from the proposed method can assist professionals in the case of a pollution involving a swallow hole of the karst network. The approach is based on repeated tracer testing, gauging of spring flow rate and mathematical curve fitting. Tracer tests and gauging of spring flow rates are repeated under low, middle, and high flow periods. Arrival times of tracer from a given swallow hole of the network are plotted as a function of measured flow rates at the karst spring. The observational data are finally fitted by a mathematical function. Flow rate monitoring at high-temporal resolution at the karst spring and the mathematical functions allow forecasting the arrival of a tracer or a pollutant at the spring in the case of an accident involving a swallow hole of the network or estimating the duration of a pollution if hydrodynamic conditions do not change abruptly. The applicability of the method is documented by three study sites in Switzerland.