The relationship between electrical conductivity and selected macroinvertebrate communities in four river systems of south-west Victoria, Australia   总被引：2，自引：0，他引：2  

Ben J. Kefford 《International Journal of Salt Lake Research》1998,7(2):153-170

In order to relate macroinvertebrate fauna to electrical conductivity (EC), a survey of selected orders of macroinvertebrates was conducted in the Glenelg, Hopkins, Merri and Barwon River Catchments in south-west Victoria, Australia. The survey consisted of sampling 21 paired sites at confluences of streams. There was little difference between the in-stream habitat but there was a range of differences in EC between each of the paired sites. The dissimilarity of macroinvertebrate fauna between the paired sites was compared to the proportional difference in EC and other water quality variables (dissolved oxygen, water temperature, pH, NO₂−N, NO₃−N, PO₄ and turbidity). This allowed the elimination of EC being confounded with geographical scale parameters and took into account other water quality parameters that may be confounded with EC. A positive relationship was found between the dissimilarity of the fauna at each of the two paired sites and the proportional difference in EC. No such relationship was found for any other measured water quality variable. The results of this survey show that macroinvertebrate community structure is associated with EC of the river systems investigated after eliminating large scale geographical patterns, in-stream habitat and the measured water quality parameters.  相似文献   

The NdSr isotopic correlation in mantle materials and geodynamic consequences     

Claude J. Allegre  Dalila Ben Othman  Mireille Polve  Pierre Richard 《Physics of the Earth and Planetary Interiors》1979,19(4):293-306

The neodymium-strontium isotopic correlation observed in most of the Earth mantle materials is evaluated by means of direct modelling. Several geochemical models are quantitatively developed to explain the observations. The main results of this modelling are that such a correlation is not geochemically trivial and that it corresponds to specific conditions in chemical fractionation. These specific conditions seem to be satisfied by solid-liquid partitioning in magmatic conditions. The discussion of the experimental data supports a continuous convecting-magmatic fractionation model for a large proportion of the mantle.  相似文献   

Unusual Ca-rich formation-waters from Devonian-aged aquifers in western Canada: Implications for seawater chemistry     

Ben J. Rostron 《Journal of Geochemical Exploration》2009

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Angular momentum transport and disc morphology in smoothed particle hydrodynamics simulations of galaxy formation     

Tobias Kaufmann  Lucio Mayer  James Wadsley  Joachim Stadel  Ben Moore 《Monthly notices of the Royal Astronomical Society》2007,375(1):53-67

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Sea-level rise research and dialogue in North Carolina: Creating windows for policy change     

Benjamin Poulter  Rebecca L. Feldman  Mark M. Brinson  Benjamin P. Horton  Michael K. Orbach  Samuel H. Pearsall  Enrique Reyes  Stanley R. Riggs  John C. Whitehead 《Ocean & Coastal Management》2009,52(3-4):147-153

Coastal areas are among the world's most vulnerable landscapes to impacts related to climate change, including inundation from sea-level rise (SLR), increased exposure to shoreline erosion, and greater frequency and intensity of storms. The status of research on the physical, ecological, and socio-economic effects of vulnerability to SLR and progress toward planning for its consequences varies from region to region worldwide. Here, we synthesize the results of three decades of SLR research and the development of coastal management policies in North Carolina, USA. We identify the major factors responsible for opening new policy ‘windows’ that address SLR, including how stakeholders have developed an increased understanding of the risks, the extent of public dialogue about potential response strategies, and advances in political receptivity to policy change. Research and policy progress in North Carolina continue to provide a model for other regions to help guide and evaluate the development of coastal policies.  相似文献   

Temporal and spatial zonation of macroepiphytes on Posidonia oceanica (L.) Delile leaves in a meadow off Tunisia          下载免费PDF全文

Lotfi Mabrouk  Mounir Ben Brahim  Asma Hamza  Med‐Najmeddine Bradai 《Marine Ecology》2015,36(1):77-92

The aim of this survey was to study the cover and the composition of macroepiphytic species on the leaves of Posidonia oceanica in the east of Tunisia. Surveys were conducted in December 2009 (winter period), March (spring period) and August 2010 (summer period) in a fringing reef located in Chebba. At each sampling date, 15 adult leaves were randomly collected and divided into basal and apical parts. The inner face of each part was examined with ocular glasses and microscope to estimate species cover by orthogonal projection. PERMANOVA and ANOSIM were used to test for differences of cover between sampling dates and leaf parts. SIMPER, cluster analysis, and PCA were used to ordinate species assemblages. Comparison of epiphytic cover along leaf blades showed significant differences for all groups, except cyanophycea, with high cover of hydrozoans and bryozoans in the basal part and high cover of algae in the apical part. The species composition and cover also vary with sampling date; minimum values were detected in December and the epiphytic community was composed of a few pioneer species, whereas maximum epiphytic cover values were registered in August, with the epiphytic community being composed of a more mature and more diverse community, termed ‘climax’. The main regulatory factors for this distribution are discussed.  相似文献   

吉南地区万隆组燧石相微生物化石及其古环境意义     

张德军  刘鹏举  尚晓冬  杨犇 《地质学报》2023,97(12):4006-4019

拉伸纪作为承接中元古代蓝菌时代以及成冰纪生物锐减的关键地质历史时期,是探索早期生命与环境演化最重要的时期之一。吉林南部地区地处华北板块东北缘,拉伸系发育完整、出露全,在燧石条带、燧石结核和泥页岩中富含微生物化石,是开展拉伸纪古生物学、生物地层学和古环境研究的理想地区。本次工作利用岩石切片法在吉林南部二道江地区万隆组顶部燧石中发现微生物化石6属9种,其中丝状蓝菌1属4种Siphonophycus robustum,S.typicum,S.kestron,S.solidum;球状蓝菌3属3种Eoentophysalis belcherensis,Gloeodiniopsis lamellosa,Scissilisphaera bistratosa;分类位置未定2属2种Glenobotrydion majorinum,Globophycus rugosum。这些微体化石的发现为开展万隆组古环境分析及生物地层对比研究提供了新的素材。研究显示,万隆组燧石相微生物组合以发育管鞘藻席(Siphonophycus mat)为主要特征,丝状蓝菌呈横向展布,长可达400μm以上,显示原地或近原地埋藏的特点...  相似文献   

Past and future sea-level rise along the coast of North Carolina,USA   总被引：1，自引：1，他引：0  

Robert E. Kopp  Benjamin P. Horton  Andrew C. Kemp  Claudia Tebaldi 《Climatic change》2015,132(4):693-707

We evaluate relative sea level (RSL) trajectories for North Carolina, USA, in the context of tide-gauge measurements and geological sea-level reconstructions spanning the last ~11,000 years. RSL rise was fastest (~7 mm/yr) during the early Holocene and slowed over time with the end of the deglaciation. During the pre-Industrial Common Era (i.e., 0–1800 CE), RSL rise (~0.7 to 1.1 mm/yr) was driven primarily by glacio-isostatic adjustment, though dampened by tectonic uplift along the Cape Fear Arch. Ocean/atmosphere dynamics caused centennial variability of up to ~0.6 mm/yr around the long-term rate. It is extremely likely (probability P=0.95) that 20th century RSL rise at Sand Point, NC, (2.8 ± 0.5 mm/yr) was faster than during any other century in at least 2,900 years. Projections based on a fusion of process models, statistical models, expert elicitation, and expert assessment indicate that RSL at Wilmington, NC, is very likely (P=0.90) to rise by 42–132 cm between 2000 and 2100 under the high-emissions RCP 8.5 pathway. Under all emission pathways, 21st century RSL rise is very likely (P>0.90) to be faster than during the 20th century. Due to RSL rise, under RCP 8.5, the current ‘1-in-100 year’ flood is expected at Wilmington in ~30 of the 50 years between 2050-2100.  相似文献   

Growth of bultfonteinite and hydrogarnet in metasomatized basalt xenoliths in the B/K9 kimberlite, Damtshaa, Botswana: insights into hydrothermal metamorphism in kimberlite pipes   总被引：1，自引：0，他引：1  

Ben Buse  John C. Schumacher  R. Stephen J. Sparks  Matthew Field 《Contributions to Mineralogy and Petrology》2010,160(4):533-550

Metamorphic assemblages within Karoo basalt xenoliths, found within volcaniclastic kimberlite of the B/K9 pipe, Damtshaa, Botswana, constrain conditions of kimberlite alteration. Bultfonteinite and chlorite partially replace the original augite-plagioclase assemblage, driven by the serpentinisation of the kimberlite creating strong chemical potential gradients for Si and Mg. Hydrogarnet and serpentine replace these earlier metamorphic assemblages as the deposits cool. The bultfonteinite (ideally Ca₂SiO₂[OH,F]₄) and hydrogarnet assemblages require a water-rich fluid containing F⁻, and imply hydrothermal alteration dominated by external fluids rather than autometamorphism from deuteric fluids. Bultfonteinite and hydrogarnet are estimated to form at temperatures of ca. 350–250°C, which are similar to those for serpentinisation. Alteration within the B/K9 kimberlite predominantly occurs between 250 and 400°C. We attribute these conditions to increased efficiency of mass transfer and chemical reactions below the critical point of water and a consequence of volume-increasing serpentinisation and metasomatic reactions that take place over this temperature range. A comparison of the B/K9 kimberlite with kimberlites from Venetia, South Africa suggests that the composition and mineralogy of included xenoliths affects the alteration assemblages within kimberlite deposits.  相似文献   

Evidence for mass-dependent isotopic fractionation of strontium in a glaciated granitic watershed     

Gregory F. de Souza  Ben C. Reynolds  Bernard Bourdon 《Geochimica et cosmochimica acta》2010,74(9):2596-5573

The stable isotope composition of strontium (expressed as δ^88/86Sr) may provide important constraints on the global exogenic strontium cycle. Here, we present δ^88/86Sr values and ⁸⁷Sr/⁸⁶Sr ratios for granitoid rocks, a 150 yr soil chronosequence formed from these rocks, surface waters and plants in a small glaciated watershed in the central Swiss Alps. Incipient chemical weathering in this young system, whether of inorganic or biological origin, has no resolvable effect on the ⁸⁷Sr/⁸⁶Sr ratios and δ^88/86Sr values of bulk soils, which remain indistinguishable from bedrock in terms of Sr isotopic composition. Although due in part to the chemical heterogeneity of the forefield, the lack of a resolvable difference between soil and bedrock isotopic composition indicates that these soils have thus far witnessed minimal net loss of Sr; a low degree of chemical weathering is also implied by bulk soil chemistry. The isotopic composition of Sr in streamwater is more radiogenic than median soil, reflecting the preferential weathering of biotite in the catchment; streamwater δ^88/86Sr values, however, are indistinguishable from bulk soil δ^88/86Sr values, implying that no resolvable fractionation of Sr isotopes takes place during release to the weathering flux in the Damma forefield. Analyses of plant tissue reveal that plants (Rhododendron and Vaccinium) preferentially assimilate the lighter isotopes of Sr such that their δ^88/86Sr values are significantly lower than those of the soils in which they grow. Additionally, δ^88/86Sr values of foliar and floral tissues are lower than those of roots, contrary to observations for Ca, for which Sr is often used as an analogue in weathering studies. We suggest that processes that discriminate against Sr in favour of Ca, due to the different nutritional requirement of plants for these two elements, are responsible for the observed contrast.  相似文献