Phosphorus release from resuspended sediment in the shallow and wind-exposed Lake Arresø, Denmark

Wind-induced sediment resuspension occurs frequently in the shallow and eutrophic Lake Arresø, Denmark. The impact of resuspension on internal phosphorus loading was investigated by laboratory experiments studying P-release from the undisturbed sediment surface and by experiments simulating resuspension events.Phosphorus release from undisturbed sediment sampled in May and August was 12 mg and 4 mg m^–2 d^–1, respectively. During experimental simulation of resuspension, soluble reactive phosphate (SRP) increased by 20–80 µg l^–1, which indicates that a typical resuspension event in the lake would be accompanied by the release of 150 mg SRP m^–2. The internal P loading induced by resuspension is estimated to be 60–70 mg m^–2 d^–1, or 20–30 times greater than the release from undisturbed sediment.SRP release during simulation of resuspension was mainly dependent on the equilibrium conditions in the water column and was basically independent of the increase in suspended solids and the duration of resuspension. A second simulation of resuspension conducted 26 hours later, did not result in any further release of SRP from sediment sampled in May. In contrast, there was an additional SRP release from sediment sampled in August, indicating that an exchangable P pool, capable of altering equilibrium conditions, is built up between resuspension events.It is concluded that resuspension, by increasing the P flux between sediment and water, plays a major role in the maintenance of the high nutrient level in Lake Arresø. A relatively high release rate is maintained during resuspension because of the low Fe:P ratio and the high concentration of NH₄Cl-extractable P in the sediment.     

The life cycle of Cyclops vicinus in Lake Søbygård: new aspects derived from sediment analyses

Cyclops vicinus is the only copepod species in the pelagic zone of Lake Søbygård and can be found there all year round. We studied the population dynamics of this copepod over a one-year period. In contrast to earlier studies we included the copepods in the pelagic zone as well as the copepods resting in the sediment. Cyclops vicinuswas found not only in the open water, but also in the sediment throughout the year. From the fluctuations of the abundances in both habitats we suggest that the life cycle is more complex than known so far: different diapause pattern appear within the population and the induction of diapause is different than in other populations. We assume that these features contribute to the predominance of C. vicinusin Lake Søbygård.     

Paleoenvironmental changes in northwest Mongolia during the last 27?kyr inferred from organic components in the Lake Hovsgol sediment core record

We studied organic components in the X106 sediment core (length 130.3 cm, water depth 236 m, 50°53′01″N, 100°21′22″E) from Lake Hovsgol to elucidate the biological production, source of organic components, and paleoenvironmental and paleolimnological changes during the last 27 kyr in northwest Mongolia. Total organic carbon (TOC) contents (0.20–0.70%) in the core of the last glacial period increased dramatically and attained 3.16–5.85% in the postglacial period (Holocene), together with the increase of the contribution of terrestrial organic matter. Biological production (both terrestrial and aquatic production) based on the TOC contents in the Holocene was 14 times higher than that in the last glacial period. The B?lling-Aller?d warm period and Younger Dryas cool period were both observed at depths of 55–50 cm (ca. 15–13 cal kyr BP) and 50–45 cm (ca. 13–11 cal kyr BP), respectively. We propose here a terrestrial/aquatic index (TAI) for organic matter in lake sediments. The TAI values suggest that terrestrial organic matter in the bottom of the core was less than 10%, increased to 48% in the B?lling-Aller?d warm period, decreased abruptly to 20% in the Younger Dryas cool period, and again increased to 30–40% in the Holocene. Normal-C₃₁ alkane (a biomarker of herbaceous land plants) and n-C₁₈ alkanoic acid (marker of plankton) decreased from the last glacial period to the Holocene, whereas n-C₂₃ alkane and n-C₂₂ alkanoic acid (a marker of higher vascular plants) increased from the last glacial period to the Holocene. Scarce herbaceous plant vegetation, such as Artemisia spp. of the lake basin in the last glacial period, changed into an abundance of higher woody plant vegetation (e.g., Pinus spp., Betula spp. and/or Larix spp.) in the Holocene. Stanol/sterol ratios suggest that relatively high oxygen tension of the lake bottom in ca. 27–22 cal kyr BP decreased from this age to the present, though benthic organisms are still abundant.     

Recent stratigraphy and accumulation of sediment in the deep,oligotrophic Lake Pääjärvi in South Finland

Laminated sediment is deposited in the deep areas (> 30 m) of Lake Pääjärvi. In the diatom microstratigraphy a regular alteration of planktonic and littoral floras, which goes in pace with the visual structure, reflects the yearly cycle of sedimentation. Considerable variation in sedimentation was found to have occurred during the past two decades. A sequence, dated to the early 1960's, in which the organic content was exceptionally high, could be identified in the sediment at 6–14 cm depth even in shallower areas where laminations are not formed. This level was used as a marker horizon when determining the recent distribution of sediment by means of 19 cores taken from different parts of the lake. The average annual sediment accumulation in the profundal zone of the lake is 340 g m^?2a^?1 dry weight, of which 25 g m^?2 a^?1 (1100 kJ m^?2 a^?1) is organic carbon.     

Deposition and soil leaching in stands of Norway spruce and European Beech: Results from the Höglwald research in comparison with other European case studies

Stands of Norway spruce (Picea abies K.) and European beech (Fagus sylvatica L.) were investigated at the Höglwald research area, Southern Germany from 1985–1988 and from 1994–1997 in order to determine the effects of tree species on deposition and soil solution fluxes. The results were compared to 15 European case studies representing different deposition levels and site conditions. At the Höglwald site, which is characterised by a high nitrogen and a moderate sulphur load, throughfall deposition of nitrogen and sulphur compounds was about two-fold higher in spruce stands compared to beech stands. The differences in elemental input were clearly reflected in soil solution chemistry with a higher leaching of nitrate and sulphate in the spruce stands. The turnover of sulphur and nitrogen compounds induced a strong soil internal production of protons especially in the spruce stands. These results are in accordance with the other European case studies. Throughfall deposition and soil leaching of nitrogen and sulphur compounds was generally higher for spruce stands compared to beech stands. The species-related differences were mainly caused by dry deposition and were relatively small in remote areas. The consequences for the forest ecosystem itself and for the hydrosphere are discussed.     

The Göttingen minipig for assessment of retinoid efficacy in the skin: comparison of results from topically treated animals with results from organ-cultured skin

Göttingen minipigs were treated topically for 6 d with a novel retinoid (MDI 301) at concentrations ranging from 0.3% to 30% in cream vehicle. Treatment of the minipigs did not adversely affect their health (hematological and necropsy parameters) or produce changes in the skin suggestive of retinoid-induced skin irritation. After killing the animals, skin samples from each treatment site were excised and maintained in organ culture for 6 d. In addition, untreated skin was also maintained in organ culture and treated with MDI 301 (0.1–5 μg/ml). After 3 d, the culture supernatants were collected and analyzed for levels of collagen type I and for matrix metalloproteinases (MMPs). Both skin samples treated in vivo and skin samples exposed to MDI 301 in culture demonstrated increased collagen production. Only slight changes in levels of MMP-2 (gelatinase A) or MMP-9 (gelatinase B) were seen. After 6 d, the organ-cultured skin was fixed in formalin and prepared for histology. The organ-cultured skin was compared to skin that was fixed at killing after in vivo treatment. Epidermal hyperplasia was quantified at various MDI 301 concentrations. In vivo and in vitro treatments showed similar results—although the thickness was not substantially changed on average, there were focal areas of hyperplasia at higher retinoid concentrations. Taken together, these data suggest that MDI 301 enhances collagen production in minipig skin, without irritation. Furthermore, these studies suggest that minipig skin exposed to the retinoid in organ culture is equally predictive as topically treated skin. The in vitro organ culture approach may provide a cost-effective alternative model to that of the intact animal for skin retinoid testing.     

Changes in water quality in Lake Päijänne following decrease of effluent load from the pulp and paper industry in 1969–1989

Lake Päijänne, the second largest lake in Finland, has been seriously polluted since the 1960s due to the effluents from pulp and paper mills, notably the Äänekoski sulphate and sulphite pulp mills situated about 50 km north of the lake, and the sulphite pulp mill and paper mills of Jämsänkoski and Kaipola on Central Lake Päijänne.A sulphite lye evaporation and combustion plant installed at the Jämsänkoski sulphite pulp mill in 1969 reduced the organic pollution of Central Päijänne. Lignin concentration decreased and the oxygen balance improved. The sulphite pulp mill was closed in 1981 and replaced by a thermo-mechanical pulp mill. Eutrophication is the main threat to water quality in Central Lake Päijänne at present.A significant improvement in the water quality, especially in oxygen balance, was achieved in the watercourse of Äänekoski and in Northern Päijänne after replacement of the old sulphite and sulphate pulp mills at Äänekoski by a large sulphate pulp mill with a biological purification plant employing the activated sludge method. The BOD₇-loading dropped from 46 to 3–4 t d^–1, but the nutrient loading has not decreased sufficiently, and the Äänekoski watercourse and Northern Päijänne are still eutrophic.     

A comparison of the sexual systems in the trees from the Australian tropics with other tropical biomes--more monoecy but why?

Rainforests in tropical Australia occupy a very small, discontinuous area (<1% of the continent), yet they are floristically diverse (c. 2800 vascular species) with high endemicity. There is a distinctive Gondwanan and autochthonous element, and some of the world's ancestral links to the basal angiosperms are uniquely found here. The rainforests can be evergreen or deciduous, but there is a distinct dry season with intermittent drought years. With these characters, the evolutionary pressures on species may be very different to that experienced elsewhere. Sexual systems of 1113 tree species (83 families) from northern Australia were compared with published accounts from the paleo- and neotropics. Hermaphroditic systems dominated all tree floras, and within all floras but Australia dioecy was the most common unisexual system. In tropical Australia, however, significantly more monoecy than dioecy occurred at landscape and community levels. Incorporating phylogeny revealed that sex and fruit types are significantly clustered. The Euphorbiaceae and Sapindaceae contributed c. 50% of the monoecious taxa. Inefficient pollinators (e.g., beetles) may have favored the maintenance of monoecy at the expense of dioecy in the Australian tropics although <1% of the flora has been studied for pollinators and none of the monoecious tree species.     

Ferredoxin from Halobacterium of the Dead Sea — Mössbauer and EPR spectra and comparison with mössbauer spectrum of whole cells

Recoil-free measurements were carried out on a 2 Fe-ferredoxin, which was isolated and purified from an extreme halophile, Halobacterium of the Dead Sea. The spectrum of this ferredoxin in the oxidized state at 82 K is a superposition of two quadrupole doublets, representing two non-equivalent Fe³⁺ sites of equal intensity. The spectrum of the reduced ferredoxin is consistent with the presence of two pure classes of iron atoms, ferric (lower isomer shift) and ferrous (higher isomer shift). Interpretations of the recoil-free spectra are discussed. Mössbauer measurements were also carried out on frozen whole bacterial cells and the resulting spectrum was found to be quite different from that observed in the isolated ferredoxin. Tentative conclusions are reached concerning the localization of this ferredoxin in the cytosol of the Halobacteria.The EPR spectrum of the reduced ferredoxin obtained at 24 K exhibits rhombic symmetry with the following g values: 1.894, 1.984 and 2.07. These values are similar to those obtained with 2 Fe-ferredoxins of the plant type, except that the g _y and g _z values are somewhat higher. Both from the EPR and Mössbauer data, it is deduced that the spin relaxation times in reduced halophilic ferredoxins are faster than in the reduced plant ferredoxins.     

Reproducing Authigenic Carbonate Precipitation in the Hypersaline Lake Acıgöl (Turkey) with Microbial Cultures

In the present study, laboratory precipitation experiments using similar water chemistry and two different bacterial cultures from Lake Ac?göl sediments, a hypersaline lake in Turkey, were performed to reproduce mineral assemblages similar to those found in the lake. Two different bacterial cultures induce various calcium/magnesium carbonates precipitation under all the experimental conditions (solid vs. liquid): Hydromagnesite, dypingite, huntite, monohydrocalcite, and aragonite. The geochemical program PHREEQC was used to calculate the mineral saturation indexes in the cultures and in lake water. Carbonate mineral assemblages identified in the experiments seem to be independent of the type of microorganisms but rather controlled by the chemical composition and physical conditions of the media. The relative amounts of monohydrocalcite, hydromagnesite, and dypingite are controlled by varying sulfate concentration from 0 to 56 mM. This demonstrates a kinetic effect that could similarly affect the mineral assemblage in the lake. Also the spherical morphology of hydromagnesite points to growth of these minerals under partial inhibition in the brine under high concentrations of ions and organic polymers produced by the microbial communities. As reproduced by the culture experiments, the authigenic carbonate mineral assemblage of Lake Ac?göl most likely results from interplay of ionic composition of the brine and microbial effects.     

Hydrodynamic in vitro comparison of a new artificial heart valve with the Bj?rk-Shiley valve (standard)

Measurements performed to compare a newly developed tilting disc valve with the Bj?rk-Shiley valve included velocity profiles downstream of the heart valves, valve-induced flow turbulence and pressure drop across the opened valves. The velocity profiles measured with pulsed Doppler ultrasound are similar, although they do not permit a quantitative comparison of the valves. The interpretation of the 90 degrees-component of Doppler signals as a measure of the turbulence permits a quantitative comparison without the need for extensive measurements. However, only large vortices are recorded, so that our turbulent shear stresses are lower than these reported in the literature. The pressure drop across the opened valve is a measure of the energy loss, and important parameters for the valve can be derived from it. The pressure drop is dependent on the test conditions, and is therefore not a characteristic constant of the valve. The transformation of the power law Q = C delta P beta into a relation between Re- and Eu-number gives a nondimensional similarity number that is characteristic for tilting disc valves. Its verification requires more investigations, involving variation of valve size and the viscosity of the test fluid.     

Neolithic land use in the northern Boreal zone: high-resolution multiproxy analyses from Lake Huhdasjärvi,south-eastern Finland

Two high-resolution pollen and charcoal analyses were constructed from sediments obtained from a small bay in eastern Finland in order to gain information on human activity during the Neolithic Stone Age, 5200–1800 bc. We used measurements of loss on ignition (LOI), magnetic susceptibility and geochemical analyses to describe the sedimentological characteristics. Palaeomagnetic dating and measurements of ¹³⁷Cs-activity were supported by ¹⁴C-datings. The analyses revealed human activity between 4400 and 3200 bc, which is synchronous with archaeological cultures defined through different stages of Comb Ware pottery types and Middle Neolithic pottery types with asbestos as a primary temper. Direct evidence of Hordeum cultivation was dated to 4040–3930 cal bc. According to the pollen data, more significant effort was put into the production of fibres from hemp and lime than the actual cultivation of food.     

Do moss samples,pollen traps and modern lake sediments all collect pollen in the same way? A comparison from the forest limit area of northernmost Europe

Moss polsters, pollen traps and lake surface sediment samples are commonly used as climate calibration data or as modern analogues for reconstructing vegetation from fossil profiles, but the differences in pollen content between these media have received little attention. This study aims to analyse how the three media differ in reflecting individual vegetation types and spatial differences in vegetation. 119 modern samples (64 moss polsters, 37 lake surface sediment samples and 18 pollen traps from which a collection was made annually) were taken from northern Fennoscandia and the Kola Peninsula as a broad transect crossing the northernmost forest limits of Betula pubescens ssp. czerepanovii (mountain birch), Pinus sylvestris (Scots pine) and Picea abies (Norway spruce). The pollen assemblages from these samples were compared with the surrounding vegetation visually and via PCA (principle components analysis) and cluster analysis. Both comparisons allow a correct distinction between pollen assemblages of arctic/alpine heath, mountain birch dominated areas, and boreal coniferous forests. The differences between the vegetation zones are stronger than the differences between the sampling media. Nevertheless, lake sediment samples from the mountain birch woodland zone tend to overestimate pine and underestimate birch. Pollen traps are biased towards lower tree pollen percentages and higher values of shrubs, herbs and Cyperaceae. This bias is especially strong in traps that have missing years in the data. Irrespective of the vegetation zone, pollen traps tend to have lower Pinus pollen percentages than in the adjacent moss polsters.     

Simulation,quantification and comparison of in-channel and floodplain sediment processes in a lowland area – A case study of the Upper Stör catchment in northern Germany

Erosion and sedimentation processes within the channel and on the floodplain are indicative of catchment hydrodynamic procedures, as well as the associated nutrient and contaminant transportation. In this paper, we linked the SWAT model with the hydraulic HEC-RAS model to set up a sediment model for 10 river sections in the Upper Stör catchment and simulated the sediment processes from 2001 to 2010. Based on the HEC-RAS output, quantification and comparison of channelized and floodplain sediment processes were conducted. The results indicate that (1) with an average sedimentation depth of 2.85 cm, the deposition process dominated the Upper Stör catchment at the decadal time scale, and the land use/cover condition resulted in differences in sedimentation amounts between different sub-catchments, and (2) the mean deposition rates were 1.75 g/m²/d in the channel and 1.69 g/m²/d on the floodplain, and the floodplain deposition accounted for only 1% of the total sedimentation amount. This observation was mainly caused by the stream power distribution in the channel and on the floodplain. (3) The granularity of the channelized sedimentation was determined by the altitude of the river section, while the granularity of the floodplain sedimentation was positively correlated with the stream power of the flood. The D50s of the channelized and floodplain sediments were 0.92 mm and 0.16 mm, respectively, while the D90 of the sediment was 4.2 mm in the channel and 0.32 mm on the floodplain. Despite the higher uncertainty of the sediment simulation, the results yielded by the combination of the HEC-RAS and SWAT models are comparable to the traditional radioactive dating, sediment trapping or combined model methods used in similar and nearby catchments.     

Historical water level change of Lake Weishan in East China from 1758–1902 AD: relationship with the flooding of the Yellow River

In order to understand high-resolution environmental changes, historical water level changes on decadal and centennial scales have been conventionally analyzed employing documentary records and lake sediments. However, annual records are still limited. Here we report the discovery of water level observations (up to monthly) in the historical literature of the Qing Dynasty (1644–1912 AD). We reconstruct the chronologies of annual mean, maximum and minimum water level changes of Lake Weishan from 1758–1902 AD. The chronologies are compared with the precipitation data (dryness/wetness index data) of four stations in the vicinity of Lake Weishan (i.e., Heze, Jinan, Linyi and Xuzhou). We suggest that the annual water level changes are related to the amount of precipitation at the four stations. In addition, the flooding of the Yellow River significantly affects Lake Weishan, always resulting in extremely high annual mean, maximum and minimum water levels in the lake. The flooding in 1871 and 1873 AD even destroyed the banks between Lake Weishan-Zhaoyang-Nanyang and Lake Dushan, thus forming a united lake. In particular, we identify a high water level interval from 1851–1855 AD, just prior to the Yellow River channel change event in 1855 AD.     

Description of the oöcysts of three new species of coccidia (Apicomplexa: Eimeriidae) from lizards in Namibia

Three new species of coccidian were recovered from the intestinal contents and faeces of lizards in Namibia, southwest Africa. Oöcysts of Eimeria barnardi n. sp. are described from Rhoptropus barnardi (Gekkonidae) and are ellipsoidal, 24.3 × 19.9 (21–26.5 × 16–22) m; shape index (length/width) 1.22 (1.12–1.30). A micropyle and oöcyst residuum are absent but a fragmented polar granule is present. Sporocysts are subspherical, 9.2 × 8.3 (8–11 × 7.5–9) m; shape index 1.11 (1.02–1.27). Oöcysts of Eimeria pachybibroni n. sp. were found in Pachydactylus bibroni (Gekkonidae) and are ellipsoidal, 26.2 × 18.2 (21.5–28 × 16–19) m; shape index 1.44 (1.30–1.52). A micropyle and oöcyst residuum are absent but a polar granule is present. Sporocysts are subspherical, 8.9 × 8.0 (8–9.5 × 7–8.5) m; shape index 1.12 (1.03–1.20). Oöcysts of Isospora spilogaster n. sp. are reported from Mabuya spilogaster (Scincidae) and are subspherical, 27.4 × 26.0 (21.5–35 × 21–35) m; shape index 1.05 (1.00–1.13). Micropyle, oöcyst residuum and polar granules are absent. Sporocysts are ellipsoidal, 13.2 × 9.7 (10.5–15 × 9–11) m; shape index 1.36 (1.08–1.50).     

A new probable stem lineage crustacean with three-dimensionally preserved soft parts from the Herefordshire (Silurian) Lagerstätte, UK

A new arthropod with three-dimensionally preserved soft parts, Tanazios dokeron, is described from the Wenlock Series (Silurian) of Herefordshire, England, UK. Serial grinding, digital photographic and computer rendering techniques yielded 'virtual fossils' in the round for study. The body tagmata of T. dokeron comprise a head shield and a long trunk. The head shield bears six pairs of horn-like spines and the head bears five pairs of appendages. The antennule, antenna and mandible are all uniramous, and the mandible includes a gnathobasic coxa. Appendages four and five are biramous and similar to those of the trunk: each comprises a limb base with an endite, an enditic membrane, and two epipodites, plus an endopod and exopod. The hypostome bears a large cone-like projection centrally, and there may be a short labrum. The trunk has some 64 segments and at least 60 appendage pairs. A very small telson has the anus sited ventrally in its posterior part and also bears a caudal furca. Comparative morphological and cladistic analyses of T. dokeron indicate a crustacean affinity, with a probable position in the eucrustacean stem group. As such the epipodites in T. dokeron are the first recorded in a eucrustacean stem taxon. The new species is interpreted as a benthic or nektobenthic scavenger.