Microbially influenced formation of Mg‐calcite and Ca‐dolomite in the presence of exopolymeric substances produced by sulphate‐reducing bacteria     

Tomaso R. R. Bontognali  Judith A. McKenzie  Rolf J. Warthmann  Crisogono Vasconcelos 《地学学报》2014,26(1):72-77

Some species of sulphate‐reducing bacteria (SRB) are known to mediate the formation of dolomite and Mg‐calcite. However, their exact role in the mineralization process remains elusive. Here, we present the result of a laboratory experiment that was designed to test whether formation of carbonate minerals by SRB can occur in the absence of living cells, through passive mineralization of their exopolymeric substances (EPS). SRB capable of mediating dolomite were cultivated in the laboratory, allowing them to secrete EPS. Microbial activity within the cultures was subsequently inhibited with antibiotics. Only after this step, Ca²⁺ and Mg²⁺ were added to the solution and carbonate minerals could form. Mg‐calcite and disordered Ca‐dolomite precipitated in association with EPS. The mol.% of Mg²⁺ in the crystals increased with longer incubation times. This result demonstrates that organic compounds produced by SRB can mediate the formation of Ca‐Mg carbonates in the absence of an active metabolism.  相似文献   

Catchments of German surface water bodies     

Andreas Gericke  Judith Mahnkopf  Markus Venohr 《水文研究》2021,35(7):e14272

The European Water Framework Directive demands to assess and report the chemical and ecological status of water bodies (WB). Linking their status to drivers and pressures and deriving suitable mitigation measures require knowledge of the shape and area of WB catchments. We derived a network of 26 570 WB catchments in Germany using the hydrologically-defined drainage basins of the German federal states. We established a network of 338 149 drainage basins. This network underwent plausibility checks and a validation with the catchment areas of 348 monitoring stations across Germany. To this network, we assigned the longest intersecting or the next downstream WB code. To account for geometric inaccuracies we revised spurious intersections resulting in splittings and cycles in the WB network. As WB may be ecologically but not hydrologically well defined, we split them at confluences and intersections. The network of drainage basins matched the monitoring stations with a Nash-Sutcliffe efficiency of 1.00. The final WB network contained 11 005 out of the 11 586 original WBs longer than 1 m. The corresponding local catchment areas range from <<0.0001 to 446 km², with a median of 10 km². The dataset combines the requirements of hydrological and ecological modelling applications at basin or national scales with the needs of the EU reporting which can foster their acceptance by state authorities and river-basin management.  相似文献   

Floods and livelihoods: The impact of changing water resources on wetland agro-ecological production systems in the Tana River Delta,Kenya     

Crystele Leauthaud  Stéphanie Duvail  Olivier Hamerlynck  Jean-Luc Paul  Hubert Cochet  Judith Nyunja  Jean Albergel  Olivier Grünberger 《Global Environmental Change》2013,23(1):252-263

Wetlands are highly dynamic and productive systems that have been under increased pressure from changes in land use and water management strategies. In Eastern Africa, wetlands provide resources at multiple spatial and temporal levels through farming, fishing, livestock ownership and a host of other ecosystem services that sustain the local economy and individual livelihoods. As part of a broader effort to describe future development scenarios for East African coastal wetlands, this qualitative study focuses on understanding the processes by which river water depletion has affected local food production systems in Kenya's Tana River Delta over the past 50 years, and how this situation has impacted residents’ livelihoods and well-being. Interviews performed in six villages among various ethnic groups, geographical locations and resource profiles indicated that the agro-ecological production systems formerly in place were adapted to the river's dynamic flooding patterns. As these flooding patterns changed, the local population diversified and abandoned or adopted various farming, fishing and livestock-rearing techniques. Despite these efforts, the decrease in water availability affected each subcomponent of the production systems under study, which led to their collapse in the 1990s. Water depletion negatively impacted local human well-being through the loss of food security. The current study provides a detailed account of the dynamics of agro-ecological production systems facing the effects of river water depletion in a wetland-associated environment in Sub-Saharan Africa.  相似文献   

A New Generation Earth Mantle Model from Global Adjoint Tomography     

Youyi Ruan  Wenjie Lei  Matthieu Lefebvre  Ryan Modrak  James Smith  Ridvan Orsvuran  Ebru Bozdag  Judith Hill  Norbert Podhorszki  Dave Pugmire  Jeroen Tromp 《《地质学报》英文版》2018,92(Z1):140-140

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What does the occurrence of Sporormiella (Preussia) spores mean in Australian fossil sequences?          下载免费PDF全文

John Dodson  Judith H. Field 《第四纪科学杂志》2018,33(4):380-392

Understanding the loss of the final few species of Australian megafauna is beset by a paucity of data on human arrival, well‐provenanced megafauna, human/megafauna population range and distribution (coexistence and interaction), and the range, scale and impact of environmental changes spanning the human–megafauna period. To overcome these shortcomings, the occurrence and decline of coprophilous fungal spores of Sporormiella in sediments have been used as a proxy for extinct megaherbivores. The Sporormiella evidence is presented as the key indicator of extinction timing and these reports are often from locations where there is no known archaeological record or megafauna remains. However, interpreting fungal spore occurrence is not straightforward, as demonstrated by studies investigating taphonomy, taxonomy and the types of animal dung where Sporormiella occurs. No detailed studies on these problems exist for Australia and no evidence supporting the use of Sporormiella as a valid proxy has been reported. Here we examine the occurrence of Sporormiella spores from Cuddie Springs in south‐eastern Australia. Despite a well‐preserved suite of megafauna fossils, Sporormiella occurrence is sporadic and frequencies are low. We conclude that using Sporormiella alone as an indicator for the presence of megafauna is premature for the Australian context.  相似文献   

Characterization of fluid inclusions from mineralized pegmatites of the Damara Belt,Namibia: insight into late-stage fluid evolution and implications for mineralization     

Ashworth  Luisa  Kinnaird  Judith Ann  Nex  Paul Andrew Martin  Erasmus  Rudolph Marthinus  Przybyłowicz  Wojciech Józef 《Mineralogy and Petrology》2018,112(6):753-765

Mineralogy and Petrology - Mineralized NYF and LCT pegmatites occur throughout the northeast-trending Neoproterozoic Damara Belt, Namibia. Mineralization in the pegmatites varies geographically,...  相似文献   

Fabric evolution and crack propagation in salt during consolidation and cyclic compression tests     

Shen  Xianda  Ding  Jihui  Lordkipanidze  Ilia  Arson  Chloé  Chester  Judith S.  Chester  Frederick M. 《Acta Geotechnica》2021,16(6):1679-1697

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Use of GIS in Optimizing Timber Thinning Strategies in the Eastern Sierra Nevada*     

Paul A. Knapp  Judith M. Lancaster  Kathleen A. Bishop  Richard L. Taylor 《The Professional geographer》1993,45(3):323-331

This paper demonstrates the use of a Geographic Information System (GIS) to develop timber thinning strategies on the Kyburz Planning Area of the Tahoe National Forest in northeastern California. The primary criteria used in an assessment of selective thinning potential were forest health and fire hazard ratings. By eliminating environmentally sensitive, economically unfeasible, or low fire hazard areas from consideration, the use of GIS reduced the area that was considered appropriate for thinning by approximately 58%. GIS offers considerable potential for improving resource management strategies.  相似文献   

Magnetic Surveying for Buried Metallic Objects     

Larry Barrows  Judith E. Rocchio 《Ground Water Monitoring & Remediation》1990,10(3):204-211

Field tests were conducted to determine representative total-intensity magnetic anomalies due to the presence of underground storage tanks and 55-gallon steel drums. Three different drums were suspended from a non-magnetic tripod and the underlying field surveyed with each drum in an upright and a flipped plus rotated orientation. At drum-to-sensor separations of 11 feet, the anomalies had peak values of around 50 gammas and half-widths about equal to the drum-to-sensor separation. Remanent and induced magnetizations were comparable; crushing one of the drums significantly reduced both. A profile over a single underground storage tank had a 1000-gamma anomaly, which was similar to the modeled anomaly due to an infinitely long cylinder horizontally magnetized perpendicular to its axis. A profile over two adjacent tanks had a smooth 350-gamma single-peak anomaly even though models of two tanks produced dual-peaked anomalies. Demagnetization could explain why crushing a drum reduced its induced magnetization and why two adjacent tanks produced a single-peak anomaly.
A 40-acre abandoned landfill was surveyed on a 50- by 100-foot rectangular grid and along several detailed profiles. The observed field had broad positive and negative anomalies that were similar to modeled anomalies due to thickness variations in a layer of uniformly magnetized material. It was not comparable to the anomalies due to induced magnetization in multiple, randomly located, randomly sized, independent spheres, suggesting that demagnetization may have limited the effective susceptibility of the landfill material. A different 6-acre site survey conducted on a 10- by 10-foot grid was analyzed to determine the maximum station spacing and line separation that could have been used. Essentially, all of the anomalies at this site would have been resolved by a survey conducted on a 20- by 20-foot grid and the larger anomalies would have been detected by a 50- by 50-foot grid.  相似文献   

The privatisation of secondary schooling and the desegregation of central Johannesburg     

Susan Parnell  Heather Webber 《GeoJournal》1990,22(3):267-273

African education controlled by the state's Department of Education and Training has collapsed. Insufficient spending, low standards and persistent student boycotts have made township schools undesirable places of learning. African students with any financial means now seek secondary education at multi-racial private schools in affluent white suburbs or at street-academies in the centre of Johannesburg. The establishment of schooling services for African pupils in the traditionally white central business district contributes to the wider process of desegregation of South Africa's major urban area, Johannesburg.  相似文献