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21.
Caroline Marie Clémence Tramier Pierre Genthon Quentin Réginald Camille Paul Delvienne Nicolas Luc Sauvan Jean-Jérôme Olivier Cassan Etienne Ebrard Pascal Sébastien Dumas Yann Queffélean 《水文研究》2021,35(3):e14071
In New Caledonia wildfires and invasive mammals (deer and wild pigs) constitute the major agents of land surface degradation. Our study reveals the linkage between land cover and water balance on the northeast coast of New Caledonia (2400 mm annual rainfall) located on a micaschist basement. The hydrological regime of characteristic and representative land surfaces is assessed using a 1-year record from three 100 m2 plots each, located in a forest area degraded by an invasive fauna, in a woody savannah which is regularly burned, and in a healthy forest area. The three plots present highly contrasting hydrological regimes, with annual and maximum runoff/rain ratios during a rain event of, respectively, 0.82, 0.16, 0.03, and 2.7, 0.7, 0.2, for the degraded forest, the savannah and the healthy forest. Such results suggest that subsurface flow originating from the contributing area above the degraded forest plot should exfiltrate inside the plot. A conceptual model for the degraded forest plot shows that water exfiltrating inside the plot represents 61% of the observed runoff. In savannahs, water should mainly be transferred downstream by subsurface flow within a thick organic soil layer limited by an impervious clay layer at a 20–30 cm depth. Savannahs are generally located above forests and generate the transfer of rainwater to downslope forests. Exfiltration into the forests can be the result of this transfer and depends on the thickness and permeability of the forest topsoils and on topographic gradients. Water exfiltration in forest areas highly degraded by pigs and deer enhances erosion and increases further degradation. It probably also limits percolation in the areas located downstream by increasing the amount of superficial runoff concentrated in gullies. 相似文献
22.
Lahaye V Bustamante P Dabin W Van Canneyt O Dhermain F Cesarini C Pierce GJ Caurant F 《Marine pollution bulletin》2006,52(10):1219-1230
This study aimed at comparing toxic element (Hg, Cd) bioaccumulation in relation to age for bottlenose (Tursiops truncatus) and striped dolphins (Stenella coeruleoalba) from Mediterranean and Atlantic waters. Metal concentrations were also measured in selected prey to infer metal exposure through the diet. As expected, Mediterranean prey exhibited the highest Hg levels, probably as a consequence of the Hg enrichment of the Mediterranean Sea. Comparing the predators from each area and taking age into account, Mediterranean bottlenose dolphins displayed higher Hg levels than Atlantic dolphins (p = 0.032), whereas Mediterranean striped dolphins did not (p = 0.691). The consumption of Myctophid fish, which showed the highest Hg levels (105+/-80 ngg(-1) w.wt.) among Atlantic prey, may explain the high Hg levels in the liver of the Atlantic striped dolphins and suggested a preferential offshore feeding behaviour in this area. Concerning Cd, no clear differences were found between geographical areas. 相似文献
23.
The partitioning of a number of trace elements (Ba, Nb, Zr, Y, REE, etc.) between orthopyroxene, garnet, and carbonate-silicate melt was experimentally studied using a belt apparatus at pressures of 3.5–4.2 GPa and temperatures of 1300–1500°C. The experimental products were investigated by electron microprobe analysis and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The experimental melts varied from carbonatitic (~5 wt % SiO2) at low temperatures (1300–1350°C) to kimberlitic compositions (30 wt % SiO2) at high temperatures (1500°C). The partition coefficients of most elements between orthopyroxene and melt (D i Opx/L ) and garnet and melt (D i Grt/L ) were almost independent of melt composition (temperature). The D i Opx/L values ranged from <0.01 for the most incompatible Ba and light REE to 0.02–0.08 for moderately incompatible Zr, Y, and heavy REE. The D i Grt/L values were approximately an order of magnitude higher, ~0.07 for light REE, 0.7 for Y, and 1.5 for Yb. The character of D i Grt/L variations in the systems studied is in general similar to that established for silicate melts without volatile components. However, the differences in the behavior of moderately incompatible and compatible elements (e.g., light and heavy REE) in the experimental systems are less pronounced compared with CO2-free systems. Considering carbonate-silicate and silicate melts as possible agents of mantle metasomatism, it can be concluded that the former can efficiently transport heavy REE, and the latter have a greater affinity for Nb, Ba, and light REE. A characteristic feature of mantle rocks enriched by carbonate-silicate melts is high Ba/La ratio coupled with relatively weakly fractionated REE distribution patterns. It was shown that the high degrees of enrichment observed in natural kimberlites can be explained by a two-stage scenario, including a preliminary invasion of carbonate-silicate melt into depleted harzburgites in the lower parts of the lithosphere and subsequent very low degree melting. 相似文献
24.
Monitoring degradation in arid and semi-arid forests and woodlands: The case of the argan woodlands (Morocco) 总被引:1,自引:0,他引:1
Yann le Polain de Waroux 《Applied geography (Sevenoaks, England)》2012,32(2):777-786
Arid and semi-arid forests and woodlands (hereafter called «dryland forests»), in spite of their ecological and social importance, have received little attention in land change studies. Growing evidence shows that these forests have been receding at very high rates in many places, suggesting a need for a better understanding of the processes and causes of dryland forest degradation. Changes in the extent of dryland forests are debated in part because estimates of forest and woodland areas in drylands are uncertain. Causal explanations of the degradation tend to draw on the literature on desertification and tropical deforestation, and to emphasize either local or remote, and either social or biophysical drivers. This study contributes to a better understanding of dryland forest degradation as a basis for conservation policies. Firstly, we argue that monitoring arid and semi-arid forests and woodlands using area estimates may lead to an underestimation of the severity of change because tree density change often exceeds area change. Secondly, we argue that the analysis of degradation processes in these multifunctional landscapes should integrate both local and remote, and both social and biophysical factors. We use a case study of degradation in the argania woodlands in semi-arid to arid Southwest Morocco to test these two claims. We used gridded tree counts on aerial photographs and satellite images to estimate forest change between 1970 and 2007, and we tested several possible causes of change on the basis of original socio-economic field surveys and climatic and topographic data. We found that forest density declined by 44.5% during this period, a figure that is significantly underestimated if forest area change is used as a measure of degradation. Increasing aridity and, to a lesser extent, fuelwood extraction were related to forest decline. No effect of grazing by local livestock was found. 相似文献
25.
The two world’s largest complexes of highly alkaline nepheline syenites and related rare metal loparite and eudialyte deposits, the Khibina and Lovozero massifs, occur in the central part of the Kola Peninsula. We measured for the first time in situ the trace element concentrations and the Sr, Nd and Hf isotope ratios by LA-ICP-MS (laser ablation inductively coupled plasma mass spectrometer) in loparite, eudialyte an in some other pegmatitic minerals. The results are in aggreement with the whole rock Sr and Nd isotope which suggests the formation of these superlarge rare metal deposits in a magmatic closed system. The initial Hf, Sr, Nd isotope ratios are similar to the isotopic signatures of OIB indicating depleted mantle as a source. This leads to the suggestion that the origin of these gigantic alkaline intrusions is connected to a deep seated mantle source—possibly to a lower mantle plume. The required combination of a depleted mantle and high rare metal enrichment in the source can be explained by the input of incompatible elements by metasomatising melts/fluids into the zones of alkaline magma generation shortly before the partial melting event (to avoid ingrowth of radiogenic isotopes). The minerals belovite and pyrochlore from the pegmatites are abnormally high in 87Sr /86Sr ratios. This may be explained by closed system isotope evolution as a result of a significant increase in Rb/Sr during the evolution of the peralkaline magma. 相似文献
26.
Thomas Wagner Martin Okrusch Stefan Weyer Joachim Lorenz Yann Lahaye Heiner Taubald Ralf T. Schmitt 《Mineralium Deposita》2010,45(3):217-239
The Spessart district (SW Germany), located at the southwestern margin of the Permian Kupferschiefer basin in Central Europe,
hosts abundant stratabound and structurally controlled base metal mineralization. The mineralization styles identified are
(1) stratabound Cu-Pb-Zn-(Ag) ores in Zechstein sedimentary rocks, (2) structurally controlled Cu-As-(Ag) ores in Zechstein
sedimentary rocks, (3) crosscutting Co-Ni-(Bi)-As and Cu-Fe-As veins, (4) stratabound metasomatic Fe-Mn carbonate ores in
Zechstein dolomite, (5) barren barite veins, and (6) Fe-Mn-As veins in Permian rhyolites. Building on previous work that involved
mineralogical, textural, and chemical characterization of the major mineralization types, we have performed a comprehensive
sulfur isotope study that applied both conventional and novel laser-ablation multi-collector inductively coupled plasma mass
spectrometry techniques. The δ34S values of sulfide minerals from the different ore types are consistently negative and highly variable, in the range between
−44.5‰ and −3.9‰, whereas the δ34S values of barite are all positive in the range between 4.7‰ and 18.9‰. Remarkably, stratabound and structurally controlled
mineralization in Zechstein sedimentary rocks has the least negative δ34S values, whereas vein-type deposits have consistently more negative δ34S values. The observed pattern of sulfide δ34S values can be best interpreted in terms of fluid mixing at the basement-cover interface. Hydrothermal fluids originating
from the crystalline basement migrated upward along subvertical fault zones and were periodically injected into groundwaters
that were flowing in the post-Variscan sedimentary cover. These groundwaters had interacted with the Zechstein sedimentary
rocks, resulting in fluids characterized by elevated concentrations of reduced sulfur (with negative δ34S values) and alkaline pH. Repeated mixing between both chemically contrasting fluids caused rapid and efficient precipitation
of sulfide ore minerals in hydrothermal veins with highly variable but distinctly negative δ34S values. 相似文献
27.
2008年5月12日,汶川Mw7.9级地震在青藏高原东缘沿龙门山逆冲断裂带中段形成了两条NE向和一条NW向逆冲走滑型地表破裂。依据同震地表陡坎形态特征,将其分为8种类型:逆断层陡坎、上盘垮塌陡坎、挤压推覆陡坎、右旋挤压推覆陡坎、断层相关褶皱陡坎、后冲挤压陡坎、上冲叠覆陡坎和局部正断层陡坎。汶川地震所形成的同震地表破裂主要由以逆冲为主的映秀破裂段和兼具逆冲、右旋走滑的北川破裂段两部分组成,这两个破裂段分别对应于Mw7.8与Mw7.6级地震事件;它们还可进一步细分为分别对应于Mw7.5、Mw7.7、Mw7.0和Mw7.5等4个次级事件的4个次级破裂段。这些次级破裂段的级联破裂可以用来解释为什么汶川地震的持续时间长达110 s。余震震源机制分析结果表明,发震断层的倾角随深度的增加而变缓,且从西南向北东逐渐变陡可以用来解释走滑分量增加的成因。此次大地震还表明,沿青藏高原东缘地形抬高的主要驱动力可能是地壳挤压缩短,而不一定是下地壳物质流动和膨胀引起上地壳的隆升。 相似文献
28.
Yann Le Drézen Laurent Lespez Michel Rasse Aline Garnier Sylvie Coutard Eric Huysecom Aziz Ballouche 《Comptes Rendus Geoscience》2010,342(3):244-252
Research conducted in the Yamé Valley (Dogon Country, Mali) provides valuable information about the river systems and their Holocene evolution in Sudano-Sahelian West Africa. Past research in the region has relied primarily on marine and lacustrine records. The new results confirm correlation between palaeoclimatic fluctuations recorded in both the river system and in tropical African lakes. They offer a new continental milestone for understanding of the environmental repercussions of Holocene monsoon oscillations. These studies demonstrate the value of river systems as a palaeoenvironmental record and the role of palaeoclimatic and anthropogenic factors in the Holocene dynamics of Sudano-Sahelian hydrosystems. 相似文献
29.
David Besson Olivier Parize Jean-Loup Rubino Jean-Pierre Aguilar Marie-Pierre Aubry Bernard Beaudoin William A. Berggren Georges Clauzon Philippe Crumeyrolle Yann Dexcoté Nicolas Fiet Silvia Iaccarino Gonzalo Jiménez-Moreno Cécile Laporte-Galaa Jacques Michaux Katharina von Salis Jean-Pierre Suc Jean-Yves Reynaud Roland Wernli 《Comptes Rendus Geoscience》2005,337(12):1045-1054
An integrated study combining facies analysis, multiple group biostratigraphy, identification of depositional sequences and mapping has been conducted on the Miocene Molasse Basin of the external Alps (southeastern France). The filling of the basin is described as resulting from a succession of fluvial incisions subsequently filled during marine transgressions. The major incision is dated as Latest Burdigalian and the major transgression as Langhian. This revised interpretation of the Miocene physiographic evolution of the Molasse Basin implies a re-examination of previous stratigraphic correlations within the basin. To cite this article: D. Besson et al., C. R. Geoscience 337 (2005). 相似文献
30.