Isotope methods for management of shared aquifers in northern Africa     

Wallin B  Gaye C  Gourcy L  Aggarwal P 《Ground water》2005,43(5):744-749

Access to fresh water is one of the major issues of northern and sub-Saharan Africa. The majority of the fresh water used for drinking and irrigation is obtained from large ground water basins where there is minor contemporary recharge and the aquifers cross national borders. These aquifers include the Nubian Aquifer System shared by Chad, Egypt, Libya, and Sudan; the Iullemeden Aquifer System, extending over Niger, Nigeria, Mali, Benin, and Algeria; and the Northwest Sahara Aquifer System shared by Algeria, Libya, and Tunisia. These resources are subject to increased exploitation and may be severely stressed if not managed properly as witnessed already by declining water levels. In order to make appropriate decisions for the sustainable management of these shared water resources, planners and managers in different countries need an improved knowledge base of hydrological information. Three technical cooperation projects related to aquifer systems will be implemented by the International Atomic Energy Agency, in collaboration with the United Nations Educational, Scientific and Cultural Organization and United Nations Development Programme/Global Environmental Facility. These projects focus on isotope hydrology studies to better quantify ground water recharge and dynamics. The multiple isotope approach combining commonly used isotopes 18O and 2H together with more recently developed techniques (chlorofluorocarbons, 36Cl, noble gases) will be applied to improve the conceptual model to study stratification and ground water flows. Moreover, the isotopes will be an important indicator of changes in the aquifer due to water abstraction, and therefore they will assist in the effort to establish a sustainable ground water management.  相似文献   

Elemental dispersion and stable isotope fractionation during reactive fluid-flow and fluid immiscibility in the Bufa del Diente aureole,NE-Mexico: evidence from radiographies and Li,B, Sr,Nd, and Pb isotope systematics   总被引：1，自引：0，他引：1  

Rolf?L.?RomerEmail author  Wilhelm?Heinrich  Birgit?Schr?der-Smeibidl  Anette?Meixner  Carl-Otto?Fischer  Cathrin?Schulz 《Contributions to Mineralogy and Petrology》2005,149(4):400-429

The 31.6±0.3 Ma old Bufa del Diente alkali-syenite (NE Mexico) intruded a sequence of Cretaceous limestones with intercalated sub-horizontal chert layers. The cherts acted as aquifers that facilitated transport of brines and pegmatitic melts within the shallow-level (<1 kbar) contact-metamorphic aureole. Fluid-driven reactions between chert and marble wallrock, and the influx of late melts and various fluids gave rise to distinct chemical and isotopic signatures within the aquifer and across the zones of infiltration and fluid-driven reaction. Aqueous brines of magmatic origin produced thick wollastonite mantles around the chert layers. Wollastonite formation occurred at the expense of limestone and chert and generated CO₂. This CO₂-induced fluid unmixing into an aqueous brine and a low-density CO₂-rich fluid, which was lost to the overlying marble where it oxidized organic matter and caused ¹³C and ¹⁸O shifts in a zone some 5–10 cm wide. After wollastonite formation, the chert aquifers were locally intruded by pegmatite veins carrying alkali feldspar, quartz, aegirine-augite, eudialyte, zircon, and apatite. Aqueous fluids that exsolved during crystallization of the pegmatite veins escaped along late cross-fractures and migrated along the inner and outer borders of the wollastonite margins. Chemical dispersion patterns of U, Al, Na + K, P, S, Fe, and REE across the chert-to-marble boundary and its metasomatic rims are shown by autoradiography and neutron-induced radiography. Scavenging of cations at mineralogical contacts and cation transport into the marbles occurred only on the mm to cm scale. Isotopic data for Pb and Sr across a simple metachert-marble boundary and for Pb, Sr, Nd, B, and Li across a metachert-pegmatite-marble sequence demonstrate the following: (1) The Pb and Sr isotopic signature of early fluids was buffered by the carbonate wallrock. Only late fluids, shielded from wallrock interaction by a wollastonite mantle, variably preserved a memory of their initial magmatic signature. (2) Since the Nd isotope signature of marble and chert is bound to calcite and clay minerals, systematic shifts to unradiogenic Nd in marble reflect loss of carbonate-bound Nd as the wollastonite margin is approached. Nd in the wollastonite margin is dominated by Nd originally bound to clay minerals. The later emplacement of the pegmatite, which carried the Nd isotope signature of its alkali-syenite source, had little effect on the Nd isotopic composition of the wollastonite rim. (3) Although the Li and B isotopic compositions reflect the alkali-syenite source, they are also affected by isotopic fractionation and partitioning between melt, fluid, and solids.Editorial responsibility J. Hoefs  相似文献   

Climatic and limnological changes at Lake Karakul (Tajikistan) during the last ~29 cal ka     

Liv Heinecke  Steffen Mischke  Karsten Adler  Anja Barth  Boris K. Biskaborn  Birgit Plessen  Ingmar Nitze  Gerhard Kuhn  Ilhomjon Rajabov  Ulrike Herzschuh 《Journal of Paleolimnology》2017,58(3):317-334

We present results of analyses on a sediment core from Lake Karakul, located in the eastern Pamir Mountains, Tajikistan. The core spans the last ~29 cal ka. We investigated and assessed processes internal and external to the lake to infer changes in past moisture availability. Among the variables used to infer lake-external processes, high values of grain-size end-member (EM) 3 (wide grain-size distribution that reflects fluvial input) and high Sr/Rb and Zr/Rb ratios (coinciding with coarse grain sizes), are indicative of moister conditions. High values in EM1, EM2 (peaks of small grain sizes that reflect long-distance dust transport or fine, glacially derived clastic input) and TiO₂ (terrigenous input) are thought to reflect greater influence of dry air masses, most likely of Westerly origin. High input of dust from distant sources, beginning before the Last Glacial Maximum (LGM) and continuing to the late glacial, reflects the influence of dry Westerlies, whereas peaks in fluvial input suggest increased moisture availability. The early to early-middle Holocene is characterised by coarse mean grain sizes, indicating constant, high fluvial input and moister conditions in the region. A steady increase in terrigenous dust and a decrease in fluvial input from 6.6 cal ka BP onwards points to the Westerlies as the predominant atmospheric circulation through to present, and marks a return to drier and even arid conditions in the area. Proxies for productivity (TOC, TOC/TN, TOC _Br ), redox potential (Fe/Mn) and changes in the endogenic carbonate precipitation (TIC, δ¹⁸O _Carb ) indicate changes within the lake. Low productivity characterised the lake from the late Pleistocene until 6.6 cal ka BP, and increased rapidly afterwards. Lake level remained low until the LGM, but water depth increased to a maximum during the late glacial and remained high into the early Holocene. Subsequently, the water level decreased to its present stage. Today the lake system is mainly climatically controlled, but the depositional regime is also driven by internal limnogeological processes.  相似文献   

Effects of spring warming and mixing duration on diatom deposition in deep Tiefer See,NE Germany     

Ulrike Kienel  Georgiy Kirillin  Brian Brademann  Birgit Plessen  Reinhard Lampe  Achim Brauer 《Journal of Paleolimnology》2017,57(1):37-49

Monitoring during three meteorologically different spring seasons in 2012, 2013, and 2014 revealed that temperature increase in spring, which influences spring lake mixing duration, markedly affected nutrient availability and diatom deposition in a sediment trap close to the bottom of deep Tiefer See, NE Germany. Deposition of Stephanodiscus taxa and small Cyclotella taxa was much higher after late ice out and a deep, short lake mixing period in spring 2013, compared to that after gradual warming and lengthy lake mixing periods in spring 2012 and 2014, when only brief or marginal ice cover occurred. Availability of dissolved Si and P was 33 and 20 % higher, respectively, in 2013 compared to 2014. The observed relation between high (low) diatom deposition and short (lengthy) mixing duration in spring was applied to varved sediments deposited between AD 1924 and 2008. Low detrital Si content in trapped material and a sediment core enabled use of µXRF-counts of Si as a proxy for diatom silica. The spring mixing duration for 1951–2008 was derived from FLake-model calculations. The spring warming duration related to lake mixing was approximated from air temperatures for 1924–2008 using the dates when daily mean air temperature exceeded 5 °C (start) and 10 °C (end). Diatom silica deposition showed a significant (p < 0.0001) inverse linear relationship with the modeled spring mixing duration (R² = 0.36) and the spring warming duration (R² = 0.28). In both cases, the relationship is strengthened when data from the period of low diatom production (1987–2005) is excluded (R² = 0.59 and R² = 0.35). Part of this low diatom production is related to external nutrient supply that favored growth of cyanobacteria at the expense of diatoms. This approach shows that diatom Si deposition was strongly influenced by the availability of light and nutrients, related to the duration of lake mixing and warming in spring, during most of the studied period. The remaining unexplained variability, however, indicates that additional factors influence Si deposition. Further tests in other deep, temperate lakes are necessary to verify if this relation is a common feature and consequently, if diatom Si can be used as a proxy for spring mixing duration in such lakes.  相似文献   

An Observational Case Study on the Influence of Atmospheric Boundary-Layer Dynamics on New Particle Formation     

Andreas Platis  Barbara Altstädter  Birgit Wehner  Norman Wildmann  Astrid Lampert  Markus Hermann  Wolfram Birmili  Jens Bange 《Boundary-Layer Meteorology》2016,158(1):67-92

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Fluxes of amino acids and hexosamines to the deep South China Sea   总被引：2，自引：0，他引：2  

Niko Lahajnar  Martin G. Wiesner  Birgit Gaye 《Deep Sea Research Part I: Oceanographic Research Papers》2007,54(12):2120-2144

Settling particles collected by sediment traps deployed between 1987 and 1999 in the northern, central and southwestern South China Sea (SCS) were analysed to study seasonal, interannual and spatial variations in the composition and flux of labile particulate matter. Results were combined with remote-sensing and surface-sediment data in order to describe the factors controlling the preservation of organic matter en route from the upper ocean to the seafloor. Organic carbon, amino acid and hexosamine fluxes generally follow the fluxes of total particulate matter, with maxima during the SW and NE monsoon periods. During non-El Niño conditions spectral amino acid distributions show that degradation of organic matter in the water column decreases as the flux rates increase. This is suggested to be the combined result of enhanced primary productivity, greater input of lithogenics serving as ballast to increase settling rates, and sorption of labile components to clay minerals. During El Niño conditions, in contrast, the degree of organic matter degradation is at very high and comparable levels at all trap sites. Flux component seasonality is strongly reduced except for the coastal upwelling areas, particularly off central Vietnam, which show significantly higher fluxes of organic carbon and lithogenic matter as compared to the open SCS. This suggests that the fluxes are affected by lateral advection of reworked organic matter from riverine sources or resuspended sediments from the nearby shelf/slope. Comparison of the measured organic carbon fluxes in 1200 m depth with those accumulating in surface sediments results in a more than 80% loss of organic matter before final burial in the sediments. The degree of organic matter preservation in the surface sediments of the deep SCS is distinctly lower than in other monsoonal oceans. This may be due to varying lithogenic input and almost complete dissolution of protective biogenic mineral matrices at greater water depth.  相似文献   

Utilization of discards and offal from commercial fisheries by seabirds in the Baltic Sea   总被引：1，自引：0，他引：1  

Garthe  Stefan; Scherp  Birgit 《ICES Journal of Marine Science》2003,60(5):980-989

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Depletion-induced seismicity in NW-Germany: lessons from comprehensive investigations     

Gudehus  Gerd  Lempp  Christof  Scheffzük  Christian  Műller  Birgit I.  Schilling  Frank R. 《Acta Geotechnica》2023,18(2):951-969

Acta Geotechnica - Evaluating various investigations for north-German gas fields, we discuss past and actual evolutions of the rock fabric in the light of dilatant driven and spontaneous...  相似文献   

Landslide cost modeling for transportation infrastructures: a methodological approach     

Martin Klose  Bodo Damm  Birgit Terhorst 《Landslides》2015,12(2):321-334

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Advances in understanding calcite varve formation: new insights from a dual lake monitoring approach in the southern Baltic lowlands     

Patricia Roeser  Nadine Dräger  Dariusz Brykała  Florian Ott  Sylvia Pinkerneil  Piotr Gierszewski  Christin Lindemann  Birgit Plessen  Brian Brademann  Michał Kaszubski  Michał Fojutowski  Markus J. Schwab  Michał Słowiński  Mirosław Błaszkiewicz  Achim Brauer 《Boreas: An International Journal of Quaternary Research》2021,50(2):419-440

We revise the conceptual model of calcite varves and present, for the first time, a dual lake monitoring study in two alkaline lakes providing new insights into the seasonal sedimentation processes forming these varves. The study lakes, Tiefer See in NE Germany and Czechowskie in N Poland, have distinct morphology and bathymetry, and therefore, they are ideal to decipher local effects on seasonal deposition. The monitoring setup in both lakes is largely identical and includes instrumental observation of (i) meteorological parameters, (ii) chemical profiling of the lake water column including water sampling, and (iii) sediment trapping at both bi-weekly and monthly intervals. We then compare our monitoring data with varve micro-facies in the sediment record. One main finding is that calcite varves form complex laminae triplets rather than simple couplets as commonly thought. Sedimentation of varve sub-layers in both lakes is largely dependent on the lake mixing dynamics and results from the same seasonality, commencing with diatom blooms in spring turning into a pulse of calcite precipitation in summer and terminating with a re-suspension layer in autumn and winter, composed of calcite patches, plant fragments and benthic diatoms. Despite the common seasonal cycle, the share of each of these depositional phases in the total annual sediment yield is different between the lakes. In Lake Tiefer See calcite sedimentation has the highest yields, whereas in Lake Czechowskie, the so far underestimated re-suspension sub-layer dominates the sediment accumulation. Even in undisturbed varved sediments, re-suspended material becomes integrated in the sediment fabric and makes up an important share of calcite varves. Thus, while the biogeochemical lake cycle defines the varves’ autochthonous components and micro-facies, the physical setting plays an important role in determining the varve sub-layers’ proportion.  相似文献