Macrophyte trophic indicator values from a European perspective

Ecological optima and ranges of submerged macrophytes are, amongst other factors, assumed to be influenced by ecoregion and flow velocity. In order to test the influence of ecoregion within Europe, species indicator values of three European macrophyte river trophic indices were compared to each other. Species indicator values of the United Kingdom (UK), French and German bioindication methods are significantly correlated with each other. The most obvious difference between the three indicator systems is the number of included indicator taxa. Two species exhibit major differences in indicator values: Callitriche hamulata has a broader ecological amplitude in Germany and France than in the UK, where it is restricted to oligotrophic rivers, while Ranunculus fluitans has a broad ecological amplitude in the UK, whereas the species is restricted to eutrophic rivers in Germany and France.

In order to test if current velocity has an influence on macrophyte trophic indicator qualities, species indicator values of a river (Trophic Index of Macrophytes, TIM) and a lake macrophyte trophic index (Macrophyte Index, MI), both of them applicable in Bavaria, Germany, were compared to each other. Species indicator values are significantly correlated. The most important difference is that different species are included in lake and river indicator lists. Only approximately 60% of the total species are used in both TIM and MI. Three species exhibit a major difference in ecological optima between rivers and lakes: Ranunculus circinatus has a broader ecological amplitude in rivers whereas the species is restricted to eutrophic lakes, Myriophyllum spicatum and Nuphar lutea show the opposite reaction.     

Does groundwater influence the sediment fauna beneath a small, sandy stream?

Gradients in the sediment fauna comprising groundwater (GW) and hyporheic taxa were investigated in the sand/silt-bottomed Marbling Brook in Western Australia. The structure of sediment invertebrate assemblages from Marbling Brook sediments and the adjacent GW were studied at five sites over 1 year and hydrological interactions were characterized using a suite of abiotic factors. Although all five stream sites were upwelling, the sites differed in the degree of hydrological interactions between GW and surface water. Sediment fauna taxa abundances were not correlated with any of the abiotic factors investigated and did not change gradually with depth. Faunal assemblages in the stream sediments were distinct from faunal assemblages in alluvial GW. While water exchanged between alluvial GW and sediment water, as shown by abiotic factors, the distinct differences in faunal assemblages indicated an unpredicted complexity in the catchment with fundamentally different hydrogeological situations on the decimetre scale. Sampling in sandy sediments needs to take this small-scale variability into account.     

Macrophytes and phytobenthos as indicators of ecological status in German lakes — a contribution to the implementation of the water framework directive

A new assessment system for macrophytes and phytobenthos in German lakes according to the Water Framework Directive of the European Community is described. Based on biological, chemical and hydromorphological data from about 100 lake sites covering the main ecoregions, hydromorphological lake types and degradation forms, biocoenotic types could be defined. For developing a classification system the quality element macrophytes and phytobenthos was divided into two components: macrophytes and benthic diatoms. For macrophytes 4 and for benthic diatoms 4 lake types were identified. The benthic vegetation at reference conditions is described and degradation is characterised as deviation in benthic vegetation species composition and abundance from the reference biocoenosis. For classification in five ecological status classes, several metrics were developed and used in combination with existing indices. For a few of the described lake types further investigations are necessary before a classification can be developed.     

Comparison of production and degradation of organic matter at a littoral site of the prealpine Lake Constance

Biotic structures and processes of the comparatively large and deep Lake Constance are dominated by pelagic water bodies. Therefore, much more attention has thus far been paid to the carbon cycle of pelagic habitats as compared to littoral areas. Nevertheless, there is also an ongoing debate on the importance of littoral areas for the carbon cycle in this lake. Although actually existing data are certainly insufficient for a realistic carbon budget, investigations made during the past decade provide at least a rough basis for a first evaluation. Accordingly, littoral areas appear to contribute overproportionally (related to surface) both to production as well as to degradation of organic carbon in the lake. However, the relative effect seems to be more pronounced for heterotrophic activities, mostly due to intense degradation processes in littoral sediments. Related to volume, littoral water bodies exhibited similar or slightly higher microbial activities as compared to epilimnetic pelagic water bodies, while microbial abundances and activities observed for littoral sediments exceeded the corresponding overlying water layers by one to three orders of magnitude. As was confirmed by in situ measurements microbial oxygen consumption frequently exceeded photosynthetic oxygen production in the investigated littoral sites. Moreover, significant qualitative differences between water and sediment were found for the degradation potentials of xenobiotics as was exemplified for phenol and nitrilo-triacetic acid (NTA). Overall, a buffer function at the landwater interface may be ascribed to littoral areas due to which the large pelagic water bodies of the lake may become additionally protected against loads of undesired organic substances due to high littoral degradation capacities.     

Ultra-calcic Magmas Generated from Ca-depleted Mantle: an Experimental Study on the Origin of Ankaramites

Ultra-calcic ankaramitic magmas or melt inclusions are ubiquitousin arc, ocean-island and mid-ocean ridge settings. They areprimitive in character (X_Mg > 0·65) and have highCaO contents (>14 wt %) and CaO/Al₂O₃ (>1·1). Experimentson an ankaramite from Epi, Vanuatu arc, demonstrate that itsliquidus surface has only clinopyroxene at pressures of 15 and20 kbar, with X_CO2 in the volatile component from 0 to 0·86.The parental Epi ankaramite is thus not an unfractionated magma.However, forcing the ankaramite experimentally into saturationwith olivine, orthopyroxene and spinel results in more magnesian,ultra-calcic melts with CaO/Al₂O₃ of 1·21–1·58.The experimental melts are not extremely Ca-rich but high inCaO/Al₂O₃ and in MgO (up to 18.5 wt %), and would evolve tohigh-CaO melts through olivine fractionation. Fractionationmodels show that the Epi parent magma can be derived from suchultra-calcic experimental melts through mainly olivine fractionation.We show that the experimental ultra-calcic melts could formthrough low-degree melting of somewhat refractory mantle. Thelatter would have been depleted by previous melt extraction,which increases the CaO/Al₂O₃ in the residue as long as someclinopyroxene remains residual. This finding corrects the commonassumption that ultra-calcic magmas must come from a Ca-richpyroxenite-type source. The temperatures necessary for the generationof ultra-calcic magmas are     

Ein Latit-Tuffit in der Laaer Serie („Helvet”) des Wiener Beckens

Zusammenfassung Durch die Tiefbohrung Orth 1 der ÖMV-AG wurde in den Laaer Schichten (Helvet) des Wiener Beckens eine Latit-Tuffitlage durchfahren. Nach der Untersuchung ist das Gestein dem leicht kalibetonten, miozänen Vulkanismus des Alpenostrandes (Oststeiermark) zuordenbar. Eine chemische Analyse bestätigt dieses Ergebnis.

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A latite-tuffite layer in the Laa beds (Helvetian) of the Vienna Basin

Summary In the Laa beds (Helvetian) of the Vienna Basin a latite-tuffite-layer was penetrated by a drill hole of the ÖMV-AG (Österreichische Mineralölverwaltung-AG). According to this investigation the rock is closely related to the Miocene volcanism of the Eastern End of the Alps (Eastern Styria). A chemical analyse confirms this.

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Mit 6 Abbildungen     

Regional and local patterns of low-grade metamorphism in the North Shore Volcanic Group, Minnesota, USA

Abstract The North Shore Volcanic Group in northern Minnesota is part of the Middle Proterozoic Keweenawan sequence, one of the largest plateau lava provinces in the world. The primary geochemistry of the basalts suggests that volcanism occurred in an intracontinental rift environment. The subaerial lava flows, mainly amygdaloidal olivine tholeiites and tholeiites, have undergone low-grade metamorphism from zeolite to lower greenschist facies. On the basis of alteration phases replacing the primary magmatic minerals, infilling amygdales and veins, and replacing secondary minerals, the following zones have been distinguished: (1) thomsonite-scolecite-smectite, (2) heulandite-stilbite-smectite, (3) laumontitechlorite-albite, (4) laumontite-chlorite-albite ± prehnite ± pumpellyite and (5) epidote-chlorite-albite ± actinolite zone. In addition to the overall zonation based on mineral parageneses, zonations in the composition of the Ab content of the newly formed albite replacing primary Ca-rich plagioclase and of the newly formed mafic phyllosilicates are observed within the sequence and within single flows. Mafic phyllosilicates in the upper part of the sequence (mainly smectites and mixed-layer smectite/chlorites) display high Si and Ca + Na + K contents, whereas in the lower part of the sequence the amounts of Si and Ca + Na + K are markedly lower (mainly chlorites and mixed-layer chlorite/smectites). Similar zonations are observed within the individual flows. The albite content of the newly formed plagioclase is highest, and the Si and Ca + Na + K content of the phyllosilicates lowest in the amygdaloidal flow top while the opposite is true for the massive flow interior. The above features suggest that the overall pattern is one of burial-type metamorphism associated with extension in the rift setting. In detail, the mineral assemblages are controlled not only by the stratigraphic position but also by the flow morphology controlling permeability whose effect on the assemblages is most pronounced in the stratigraphically upper parts. This suggests that at the first stages of alteration (lowest grade) the patterns of fluid flow were important effects in controlling the assemblages. At greater burial depth, assemblages are more homogeneous, perhaps representative of a more even and pervasive flow pattern. Using the observed assemblages at face value to define grade and/or facies, different conditions would be assigned within the different morphological flow portions. Thus at low-grade metamorphic conditions it is essential to integrate assemblages from different morphological flow portions in order to define satisfactorily the overall metamorphic conditions.     

EUREC<Superscript>4</Superscript>A: A Field Campaign to Elucidate the Couplings Between Clouds,Convection and Circulation

Trade-wind cumuli constitute the cloud type with the highest frequency of occurrence on Earth, and it has been shown that their sensitivity to changing environmental conditions will critically influence the magnitude and pace of future global warming. Research over the last decade has pointed out the importance of the interplay between clouds, convection and circulation in controling this sensitivity. Numerical models represent this interplay in diverse ways, which translates into different responses of trade-cumuli to climate perturbations. Climate models predict that the area covered by shallow cumuli at cloud base is very sensitive to changes in environmental conditions, while process models suggest the opposite. To understand and resolve this contradiction, we propose to organize a field campaign aimed at quantifying the physical properties of trade-cumuli (e.g., cloud fraction and water content) as a function of the large-scale environment. Beyond a better understanding of clouds-circulation coupling processes, the campaign will provide a reference data set that may be used as a benchmark for advancing the modelling and the satellite remote sensing of clouds and circulation. It will also be an opportunity for complementary investigations such as evaluating model convective parameterizations or studying the role of ocean mesoscale eddies in air–sea interactions and convective organization.     

Basalt–trachybasalt samples in Gale Crater,Mars

The ChemCam instrument on the Mars Science Laboratory (MSL) rover, Curiosity, observed numerous igneous float rocks and conglomerate clasts, reported previously. A new statistical analysis of single‐laser‐shot spectra of igneous targets observed by ChemCam shows a strong peak at ~55 wt% SiO₂ and 6 wt% total alkalis, with a minor secondary maximum at 47–51 wt% SiO₂ and lower alkali content. The centers of these distributions, together with the rock textures, indicate that many of the ChemCam igneous targets are trachybasalts, Mg# = 27 but with a secondary concentration of basaltic material, with a focus of compositions around Mg# = 54. We suggest that all of these igneous rocks resulted from low‐pressure, olivine‐dominated fractionation of Adirondack (MER) class‐type basalt compositions. This magmatism has subalkaline, tholeiitic affinities. The similarity of the basalt endmember to much of the Gale sediment compositions in the first 1000 sols of the MSL mission suggests that this type of Fe‐rich, relatively low‐Mg#, olivine tholeiite is the dominant constituent of the Gale catchment that is the source material for the fine‐grained sediments in Gale. The similarity to many Gusev igneous compositions suggests that it is a major constituent of ancient Martian magmas, and distinct from the shergottite parental melts thought to be associated with Tharsis and the Northern Lowlands. The Gale Crater catchment sampled a mixture of this tholeiitic basalt along with alkaline igneous material, together giving some analogies to terrestrial intraplate magmatic provinces.     

FREQUENCY AND MAGNITUDE OF BEDLOAD TRANSPORT IN A MOUNTAIN RIVER

Magnitude and frequency of bedload transport was examined in the Lainbach River, Bavaria, using magnetically tagged particles. During the study, 18 small to moderate events and one major event occurred. About 1 per cent of the flow period exceeded the entrainment threshold and at least once every year about 50 per cent of the tagged particles were mobile. Themajor event which occurred during the study period resulted in the deposition of a thick layer of sediment in parts of the channel and passive burial of most of the recovered particles. The step–pool pattern, which characterized the study site prior to the large event, was obliterated. However, the channel recovered quickly and has returned to a new step–pool pattern. The event changed the boundary conditions by increasing the availability of loose sediment and creating higher river-bed slopes in reaches between breached check dams. As a result, movement of individual particles measured for events of both the same magnitude and duration, occurring before and after the large event, yielded different values. For events which occurred after the large event, the range and the mean distance of movement were about ten times higher.