Composition and origin of organic matter in surface sediments of Lake Sarbsko: A highly eutrophic and shallow coastal lake (northern Poland)

We present an organic geochemical study of surface sediments of Lake Sarbsko, a shallow coastal lake on the middle Polish Baltic coast. The aim was to provide evidence concerning the origin of the organic matter (OM) and its compositional diversity in surface deposits of this very productive, highly dynamic water body. The content and composition of the OM in the bottom sediments were investigated at 11 sampling stations throughout the lake basin. OM sources were assigned on the basis of bulk indicators [total organic carbon (TOC), total nitrogen (TN), δ¹³C_TOC and δ¹⁵N and extractable OM yield], biomarker composition of extractable OM and compound-specific C isotope signatures. The source characterization of autochthonous compounds was verified via phytoplankton analysis. The distribution of gaseous hydrocarbons in the sediments, as well as temporal changes in lake water pH, the concentration of DIC (dissolved inorganic carbon) and δ¹³C_DIC were used to trace OM decomposition.The sedimentary OM is composed mainly of well preserved phytoplankton compounds and shows minor spatial variability in composition. However, the presence of CH₄ and CO₂ in the bottom deposits provides evidence for microbial degradation of sedimentary OM. The transformation of organic compounds in surface, bottom and pore waters via oxidative processes influences carbonate equilibrium in the lake and seasonally favours precipitation or dissolution of CaCO₃.The data enhance our understanding of the relationships between the composition of sedimentary OM and environmental conditions within coastal ecosystems and shed light on the reliability of OM proxies for environmental reconstruction of coastal lakes.     

Temperature changes on the Tibetan Plateau during the past 600 years inferred from ice cores and tree rings

The climatological signal of δ¹⁸O variations preserved in ice cores recovered from Puruogangri ice field in the central Tibetan Plateau (TP) was calibrated with regional meteorological data for the past 50 years. For the period AD 1860–2000, 5-yearly averaged ice core δ¹⁸O and a summer temperature reconstruction derived from pollen data from the same ice core were compared. The statistical results provide compelling evidence that Puruogangri ice core δ¹⁸O variations represent summer temperature changes for the central TP, and hence regional temperature history during the past 600 years was revealed. A comparison of Puruogangri ice core δ¹⁸О with several other temperature reconstructions shows that broad-scale climate anomalies since the Little Ice Age occurred synchronously across the eastern and southern TP, and the Himalayas. Common cold periods were identified in the 15th century, 1625–1645 AD, 1660–1700 AD, 1725–1775 AD, 1795–1830 AD, 1850–1870 AD, 1890–1920 AD, 1940–1950 AD, and 1975–1985 AD. The period 1725–1775 AD was one of the most prolonged cool periods during the past 400 years and corresponded to maximum Little Ice Age glacier advance of monsoonal temperate glaciers of the TP.     

Differences between Mean Sea Levels for the Pacific,Atlantic and Indian Oceans From Topex/Poseidon Altimetry

Geopotential values W of the mean equipotential surfaces representing the mean ocean topography were computed on the basis of four years (1993 - 1996) TOPEX/POSEIDON altimeter data: W = 62 636 854.10m ² s ^–2 for the Pacific (P), W = 62 636 858.20m ² s ^–2 for the Atlantic (A), W = 62 636 856.28m ²s^–2 for the Indian (I) Oceans. The corresponding mean separations between the ocean levels were obtained as follows: A – P = – 42 cm, I– P = – 22 cm, I – A = 20 cm, the rms errors came out at about 0.3 cm. No sea surface topography model was used in the solution.     

The time dependent magnetization of fine-grained iron in lunar breccias

Lunar breccias of low metamorphic grade offer a unique opportunity to investigate the magnetic properties of dispersed fine grained iron. These rocks exhibit a pronounced time dependent magnetization whose acquisition and decay are well explained by Ne´el's single domain theory. The effect is due to iron grains in the range of 120A?to 150A?in diameter which covers the transition from superparamagnetic to stable single domain behavior.     

Stabilitätsbeziehungen zwischen Chlorit,Cordierit und Almandin bei der Metamorphose

The stability relations between cordierite and almandite in rocks, having a composition of CaO poor argillaceous rocks, were experimentally investigated. The starting material consisted of a mixture of chlorite, muscovite, and quartz. Systems with widely varying Fe²⁺/Fe²⁺+Mg ratios were investigated by using two different chlorites, thuringite or ripidolite, in the starting mixture. Cordierite is formed according to the following reaction: $${\text{Chlorite + muscovite + quartz}} \rightleftharpoons {\text{cordierite + biotite + Al}}_{\text{2}} {\text{SiO}}_{\text{5}} + {\text{H}}_{\text{2}} {\text{O}}$$ . At low pressures this reaction characterizes the facies boundary between the albite-epidotehornfels facies and the hornblende-hornfels facies, at medium pressures the beginning of the cordierite-amphibolite facies. Experiments were carried out reversibly and gave the following equilibrium data: 505±10°C at 500 bars H₂O pressure, 513±10°C at 1000 bars H₂O pressure, 527±10°C at 2000 bars H₂O pressure, and 557±10°C at 4000 bars H₂O pressure. These equilibrium data are valid for the Fe-rich starting material, using thuringite as the chlorite, as well as for the Mg-rich starting mixture with ripidolite. At 6000 bars the equilibrium temperature for the Mg-rich mixture is 587±10°C. In the Fe-rich mixture almandite was formed instead of cordierite at 6000 bars. The following reaction was observed: $${\text{Thuringite + muscovite + quartz}} \rightleftharpoons {\text{almandite + biotite + Al}}_{\text{2}} {\text{SiO}}_{\text{5}} {\text{ + H}}_{\text{2}} {\text{O}}$$ . Experiments with the Fe-rich mixture, containing Fe²⁺/Fe²⁺+Mg in the ratio 8∶10, yielded three stability fields in a P,T-diagram (Fig.1):

1. Above 600°C/5.25 kb and 700°C/6.5 kb almandite+biotite+Al₂SiO₅ coexist stably, cordierite being unstable.
2. The field, in which almandite, biotite and Al₂SiO₅ are stable together with cordierite, is restricted by two curves, passing through the following points:
   1. 625°C/5.5 kb and 700°C/6.5 kb,
   2. 625°C/5.5 kb and 700°C/4.0 kb.
3. At conditions below curves 1 and 2b, cordierite, biotite, and Al₂SiO₅ are formed, but no garnet.

An appreciable MnO-content in the system lowers the pressures needed for the formation of almandite garnet, but the quantitative influence of the spessartite-component on the formation of almandite could not yet be determined. the Mg-rich system with Fe²⁺/Fe²⁺+Mg=0.4 garnet did not form at pressures up to 7 kb in the temperature range investigated. Experiments at unspecified higher pressures (in a simple squeezer-type apparatus) yielded the reaction: $${\text{Ripidolite + muscovite + quartz}} \rightleftharpoons {\text{almandite + biotite + Al}}_{\text{2}} {\text{SiO}}_{\text{5}} {\text{ + H}}_{\text{2}} {\text{O}}$$ . Further experiments are needed to determine the equilibrium data. The occurence of garnet in metamorphic rocks is discussed in the light of the experimental results.     

Long-Term Stability Of Geoidal Geopotential FromTopex/Poseidon Satellite Altimetry 1993–1999

The TOPEX/POSEIDON (T/P) satellite altimeter data from January 1, 1993to October 24, 1999 (cycles 11–261) was used for investigating thelong-term variations in the geoidal geopotential W₀ and/orin the geopotential scale factor R₀ = GM/W₀ (GM is theadopted geocentric gravitational constant). The mean valuesdetermined for the whole period covered are: W₀ =(62 636 856.161 ± 0.002) m² s^-2, R₀ =(6 363 672.5448 ± 0.0002) m. The actual accuracy is limited bythe altimeter calibration error (2–3 cm) and it isestimated to be about ± 0.5 m² s^-2 (± 5 cm).The yearly variations of the above mean values are at the formalerror level. No long-term trend in W₀, representing the oceanvolume change, was found for the seven years period 1993–9 on thebasis of T/P altimeter (AVISO) data. No sea surface topography modelwas used in the solution. This revised version was published online in July 2006 with corrections to the Cover Date.     

Preliminary reconstruction of sediment-source linkages for the past 6000 yr at the Petit Lac d'Annecy, France, based on mineral magnetic data

An 8 m core from the central plain of the Petit Lac d'Annecy, France, two floodplain cores, river bedload sediments and several hundred soil samples from the catchment have been studied using magnetic techniques. The soils, mainly developed on limestones and local glacial tills, show widespread magnetic enhancement with higher ferrimagnetic concentrations and contents of SP grains than found in the lake sediments. Some soils show significant concentrations of canted antiferromagnetic minerals (mainly haematite). Using magnetic quotient parameters the surface soils are classified into four mineralogical types. The lake and floodplain sediment properties over the past 6000 yrs can largely be explained by the erosion and deposition of these sources, with a smaller superimposed biogenic (magnetosomes) signal. Derived sediment-source linkages allow the construction of several hypotheses about geomorphological changes in the catchment system: (i) the long-term erosion of high altitude unweathered substrates has gradually increased towards the present day; (ii) the erosion of high altitude soils has increased within the last 1000 yrs, possibly during the period of the 'Little Ice Age'; (iii) shifts towards an increased erosion of surface lowland soil occurred ~2000 and 1000 yrs ago and may be linked to an accelerated accretion of floodplain overbank deposits; (iv) there has been a significant storage of surface soil within floodplains, which leads to an underestimation of the importance of soil erosion in the lake sediment records; (v) the sediment transported by high magnitude, low frequency flood events has shifted in source from high altitude soils before ~1000 cal. yr BP to lowland and mid-altitude free draining soils after ~1000 cal. yr BP.     

Improvement and comparison of the rainfall–runoff methods in SWAT at the monsoonal watershed of Baocun,Eastern China

ABSTRACT

A new physics-based rainfall–runoff method of the Soil and Water Assessment Tool (SWAT) was developed, which integrates a water balance (WB) approach with the variable source area (WB-VSA). This approach was further compared with four methods—soil-water-dependent curve number (CN-Soil), evaporation-dependent curve number (CN-ET), Green and Ampt equation (G&A) and WB—in a monsoonal watershed, Eastern China. The regional sensitivity analysis shows that volumetric efficiency coefficient (VE) with river discharges is sensitive to the most parameters of all approaches. The results of model calibration against VE demonstrate that WB-VSA is the most accurate owing to its reflection of the spatial variation of runoff generation as affected by topography and soil properties. Other methods can also mimic baseflow well, but the G&A and CN-ET simulate floods much worse than the saturation excess runoff approaches (WB-VSA, WB and CN-Soil). Meanwhile, CN-Soil as an empirical method fails to simulate groundwater levels. By contrast, WB-VSA captures them best.

Editor M.C. Acreman; Associate editor S. Kanae     

Application of micro-computed X-ray tomography for improving the hole erosion test analysis on high plastic clay

Acta Geotechnica - The hole erosion test (HET) was developed to simulate piping erosion and to study the erosion parameters of cohesive soils. The erosion rate in the HET is evaluated by the...