The role of iron and sulfur in the visual appearance of lake sediment varves     

Veronika Gälman  Johan Rydberg  Andrei Shchukarev  Staffan Sjöberg  Antonio Martínez-Cortizas  Richard Bindler  Ingemar Renberg 《Journal of Paleolimnology》2009,42(1):141-153

Easily discernible sediment varves (annual laminations) may be formed in temperate zone lakes, and reflect seasonal changes in the composition of the accumulating material derived from the lake and its catchment (minerogenic and organic material). The appearance of varves may also be influenced by chemical processes. We assessed the role of iron (Fe) and sulfur (S) in the appearance of varves in sediments from Lake Nylandssjön in northern Sweden. We surveyed Fe in the lake water and established whether there is internal transport of Fe within the sediment. We used a unique collection of seven stored freeze cores of varved sediment from the lake, collected from 1979 to 2004. This suite of cores made it possible to follow long-term changes in Fe and S in the sediment caused by processes that occur in the lake bottom when the sediment is ageing. We compared Fe and S concentrations using X-ray fluorescence spectroscopy (XRF) in specific years in the different cores. No diagenetic front was found in the sediment and the data do not suggest that there is substantial vertical transport of Fe and S in the sediment. We also modeled Fe and S based on thermodynamic, limnological, and sediment data from the lake. The model was limited to the five components H⁺, e^?, Fe³⁺, SO₄ ^2?, H₂CO₃ and included the formation of solid phases such as Fe(OH)₃ (amorphous), FeOOH (aged, microcrystalline), FeS and FeCO₃. Modeling showed that there are pe (redox) ranges within which either FeS or Fe(OH)₃/FeOOH is the only solid phase present and there are pe ranges within which the two solid phases co-exist, which supports the hypothesis that blackish and grey-brownish layers that occur in the varves were formed at the time of deposition. This creates new possibilities for deciphering high-temporal-resolution environmental information from varves.  相似文献   

Competition between benthic and pelagic microalgae for phosphorus and light – long-term experiments using artificial substrates     

Annika Pasternak  Helmut Hillebrand  Sabine Flöder 《Aquatic Sciences - Research Across Boundaries》2009,71(2):238-249

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First continuous temperature measurements within polar mesosphere summer echoes     

F.-J. Lübken  J. Lautenbach  J. Höffner  M. Rapp  M. Zecha 《Journal of Atmospheric and Solar》2009,71(3-4):453-463

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A note on the M w 6.3 earthquake in Iceland on 29 May 2008 at 15:45 UTC     

R. Sigbjörnsson  J. Th. Snæbjörnsson  S. M. Higgins  B. Halldórsson  S. Ólafsson 《Bulletin of Earthquake Engineering》2009,7(1):113-126

This preliminary study aims to investigate a M _w 6.3 earthquake that occurred in South Iceland on Thursday 29 May 2008 at 15:45 UTC. The epicentre was in the Olfus District between the towns of Selfoss and Hveragerdi. This study examines the data recorded and the damage observed immediately after the event. Horizontal accelerations of up to 80%g were recorded in the epicentral region and there is visual evidence that the vertical acceleration exceeded 1 g. The PGA data is compared to a ground motion estimation model developed for the South Iceland earthquakes in June 2000. In general the basic properties of this event are found to be similar to the characteristics of the South Iceland earthquakes in June 2000. The duration of strong-motion is short and the intensity attenuates rapidly with increasing distance. The earthquake action resisted by buildings in the near fault area is inspected through evaluation of elastic as well as inelastic response spectra. The vast majority of structures seemed to withstand the strong-motion fairly competently and without significant visual damage due firstly to the low-rise, predominantly reinforced concrete or timber, style of buildings. Secondly, the short duration of strong-motion contributed to the endurance of structures.  相似文献   

Functioning of intertidal flats inferred from temporal and spatial dynamics of O<Subscript>2</Subscript>, H<Subscript>2</Subscript>S and pH in their surface sediment   总被引：1，自引：1，他引：0  

Stefan Jansen  Eva Walpersdorf  Ursula Werner  Markus Billerbeck  Michael E Böttcher  Dirk de Beer 《Ocean Dynamics》2009,59(2):317-332

In this article, we describe the dynamics of pH, O₂ and H₂S in the top 5–10 cm of an intertidal flat consisting of permeable sand. These dynamics were measured at the low water line and higher up the flat and during several seasons. Together with pore water nutrient data, the dynamics confirm that two types of transport act as driving forces for the cycling of elements (Billerbeck et al. 2006b): Fast surface dynamics of pore water chemistry occur only during inundation. Thus, they must be driven by hydraulics (tidal and wave action) and are highly dependent on weather conditions. This was demonstrated clearly by quick variation in oxygen penetration depth: Seeps are active at low tide only, indicating that the pore water flow in them is driven by a pressure head developing at low tide. The seeps are fed by slow transport of pore water over long distances in the deeper sediment. In the seeps, high concentrations of degradation products such as nutrients and sulphide were found, showing them to be the outlets of deep-seated degradation processes. The degradation products appear toxic for bioturbating/bioirrigating organisms, as a consequence of which, these were absent in the wider seep areas. These two mechanisms driving advection determine oxygen dynamics in these flats, whereas bioirrigation plays a minor role. The deep circulation causes a characteristic distribution of strongly reduced pore water near the low water line and rather more oxidised sediments in the centre of the flats. The two combined transport phenomena determine the fluxes of solutes and gases from the sediment to the surface water and in this way create specific niches for various types of microorganisms.  相似文献   

Mixing,hypersalinity and gradients in Hervey Bay,Australia     

Ulf Gräwe  Jörg-Olaf Wolff  Joachim Ribbe 《Ocean Dynamics》2009,59(5):643-658

Hervey Bay, a large coastal embayment situated off the central eastern coast of Australia, is a shallow tidal area (average depth = 15 m), close to the continental shelf. It shows features of an inverse estuary, due to the high evaporation rate (approx. 2 m/year), low precipitation (less than 1 m/year) and on average almost no freshwater input from rivers that drain into the bay. The hydro- and thermodynamical structures of Hervey Bay and their variability are presented here for the first time, using a combination of four-dimensional modelling and observations from field studies. The numerical studies are performed with the Coupled Hydrodynamical Ecological Model for Regional Shelf Seas (COHERENS). Due to the high tidal range (>3.5 m), the bay is considered as a vertically well-mixed system, and therefore, only horizontal fronts are likely. Recent field measurements, but also the numerical simulations, indicate characteristic features of an inverse/hypersaline estuary with low salinity (35.5 psu) in the open ocean and peak values (>39.0 psu) in the head water of the bay. The model further predicts a nearly persistent mean salinity gradient of 0.5 psu across the bay (with higher salinities close to the shore). The investigation further shows that air temperature, wind direction and tidal regime are mainly responsible for the stability of the inverse circulation and the strength of the salinity gradient across the bay. Due to an ongoing drying trend, the occurrence of severe droughts at the central east coast of Australia and, therefore, a reduction in freshwater supply, the salinity flux out of the bay has increased, and the inverse circulation has also strengthened.  相似文献   

Elimination of Carbamazepine,Diclofenac and Naproxen from Treated Wastewater by Nanofiltration     

Markus Röhricht  Jürgen Krisam  Ulrich Weise  Uta R. Kraus  Rolf‐A. Düring 《洁净——土壤、空气、水》2009,37(8):638-641

Most conventional wastewater treatment plants remove very small amounts of micropollutants, such as pharmaceuticals. Here, the ability of two different types of submerged nanofiltration flat sheet modules to remove pharmaceuticals from wastewater is analyzed. The two nanofiltration membranes were used at relatively low pressures of only 0.3 and 0.7 bar. At such low pressures, the membranes did not retain salts to a great extent. This is advantageous in wastewater treatment because no salt concentrate is produced. Carbamazepine was retained only slightly by the nanofiltration membranes, whereas approximately 60% of diclofenac and naproxen were retained by both membranes. This level of effectiveness might not be enough to justify the use of such a system as an additional treatment step in wastewater treatment plants.  相似文献   

Book Reviews: Pharmaceuticals in the Environment: Sources,Fate, Effects and Risks. Edited by Klaus Kümmerer     

Moritz Schübler 《洁净——土壤、空气、水》2009,37(7):514-514

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Biorefining of Green Biomass – Technical and Energetic Considerations     

Birgit Kamm  Petra Schönicke  Michael Kamm 《洁净——土壤、空气、水》2009,37(1):27-30

The development of biorefineries is the key for access to an integrated production of food, feed, chemicals, materials, goods, fuels and energy of the future. This communication considers an integrated green biorefinery combined with today's production of feed in the green agriculture. Special attention is given to the combination of physical and biotechnological processes for the production of proteins as well as platform chemicals such as lactic acid and lysine. Mass and energy flows (steam and electricity) are given for the biorefining of green biomass to produce platform chemicals, proteins, feed and biogas from residues.  相似文献   

Chronology building using objective identification of annual signals in trace element profiles of stalagmites     

Claire L. Smith  Ian J. Fairchild  Christoph Spötl  Silvia Frisia  Andrea Borsato  Steven G. Moreton  Peter M. Wynn 《Quaternary Geochronology》2009,4(1):11-21

Determination of annual lamination provides important additional constraints to radiometric dates on speleothems, both for dating the duration of specific growth intervals and optimizing growth models. In the absence of visible laminae, however, speleothem age models are reliant upon curve fitting through discretely dated points and are therefore inherently more uncertain than annual chronologies from laminae. Given that the impact of seasonality on speleothems is expected to be strong enough to generate an annual pulse in trace element chemistry regardless of whether or not visible or fluorescent growth laminae are visible, we demonstrate the potential for deriving high-resolution stalagmite chronologies from non-laminated samples using annual chemical variations in stalagmites from two Alpine caves (Obir, Austria and Ernesto, NE Italy). Trace element data were obtained by ion microprobe analyses for H, P, Mg, Na, Sr and Ba and the annual signal was sought using spectral and wavelet analysis. An automated chemical peak-counting software tool was developed in MATLAB^©. It counts significant annual peaks using criteria of minimum amplitude in relation to the local standard deviation of signal variation and minimum separation between peaks determined by the thickness of the preceding layers. Verification of the tool using visibly laminated samples suggests the software is a reliable and accurate method of chronology building, with hit ratios greater than 0.93 and less than 0.75% false alarm occurrences. Used in conjunction with other dating methods such as radiocarbon, U–Th and sulphur peak dating, the automated chemical laminae chronology-building approach provides a more meaningful alternative to simple age-depth curve fitting for non-laminated samples.  相似文献