Watershed structural influences on the distributions of stream network water and solute travel times under baseflow conditions          下载免费PDF全文

Anna Bergstrom  Brian McGlynn  John Mallard  Tim Covino 《水文研究》2016,30(15):2671-2685

Watershed structure influences the timing, magnitude, and spatial location of water and solute entry to stream networks. In turn, stream reach transport velocities and stream network geometry (travel distances) further influence the timing of export from watersheds. Here, we examine how watershed and stream network organization can affect travel times of water from delivery to the stream network to arrival at the watershed outlet. We analysed watershed structure and network geometry and quantified the relationship between stream discharge and solute velocity across six study watersheds (11.4 to 62.8 km²) located in the Sawtooth Mountains of central Idaho, USA. Based on these analyses, we developed stream network travel time functions for each watershed. We found that watershed structure, stream network geometry, and the variable magnitude of inputs across the network can have a pronounced affect on water travel distances and velocities within a stream network. Accordingly, a sample taken at the watershed outlet is composed of water and solutes sourced from across the watershed that experienced a range of travel times in the stream network. We suggest that understanding and quantifying stream network travel time distributions are valuable for deconvolving signals observed at watershed outlets into their spatial and temporal sources, and separating terrestrial and in‐channel hydrological, biogeochemical, and ecological influences on in‐stream observations. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Modelling atmospheric and hydrologic processes for assessment of meadow restoration impact on flow and sediment in a sparsely gauged California watershed          下载免费PDF全文

N. Ohara  M. L. Kavvas  Z. Q. Chen  L. Liang  M. Anderson  J. Wilcox  L. Mink 《水文研究》2014,28(7):3053-3066

The restoration of meadowland using the pond and plug technique of gully elimination was performed in a 9‐mile segment along Last Chance Creek, Feather River Basin, California, in order to rehabilitate floodplain functions such as mitigating floods, retaining groundwater, and reducing sediment yield associated with bank erosion and to significantly alter the hydrologic regime. However, because the atmospheric and hydrological conditions have evolved over the restoration period, it was difficult to obtain a comprehensible evaluation of the impact of restoration activities by means of field measurements. In this paper, a new use of physically based models for environmental assessment is described. The atmospheric conditions over the sparsely gauged Last Chance Creek watershed (which does not have any precipitation or weather stations) during the combined historical critical dry and wet period (1982–1993) were reconstructed over the whole watershed using the atmospheric fifth‐generation mesoscale model driven with the US National Center for Atmospheric Research and US National Center for Environmental Prediction reanalysis data. Using the downscaled atmospheric data as its input, the watershed environmental hydrology (WEHY) model was applied to this watershed. All physical parameters of the WEHY model were derived from the existing geographic information system and satellite‐driven data sets. By comparing the prerestoration and postrestoration simulation results under the identical atmospheric conditions, a more complete environmental assessment of the restoration project was made. Model results indicate that the flood peak may be reduced by 10–20% during the wet year and the baseflow may be enhanced by 10–20% during the following dry seasons (summer to fall) in the postrestoration condition. The model results also showed that the hydrologic impact of the land management associated with the restoration mitigates bank erosion and sediment discharge during winter storm events. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Earth observation for habitat mapping and biodiversity monitoring     

《International Journal of Applied Earth Observation and Geoinformation》2015

  相似文献   

Calc-alkaline rear-arc magmatism in the Fuegian Andes: Implications for the mid-cretaceous tectonomagmatic evolution of southernmost South America     

Mauricio González Guillot  Mónica Escayola  Rogelio Acevedo 《Journal of South American Earth Sciences》2011,31(1):1-16

The magmatic arc of the Fuegian Andes is composed mostly of Upper Mesozoic to Cenozoic calc-alkaline plutons and subordinated lavas. To the rear arc, however, isolated mid-Cretaceous monzonitic plutons and small calc-alkaline dykes and sills crop out. This calc-alkaline unit (the Ushuaia Peninsula Andesites, UPA) includes hornblende-rich, porphyritic quartz meladiorites, granodiorites, andesites, dacites and lamprophyres. Radiometric dating and cross-cutting relationships indicate that UPA is younger than the monzonitic suite. The geochemistry of UPA is medium to high K, with high LILE (Ba 500–2000 ppm, Sr 800–1400 ppm), HFSE (Th 7–23 ppm, Nb 7–13 ppm, Ta 0.5–1.1 ppm) and LREE (La 16–51 ppm) contents, along with relatively low HREE (Yb 1.7–1.3 ppm) and Y (9–19 ppm). The similar mineralogy and geochemistry of all UPA rocks suggest they evolved from a common parental magma, by low pressure crystal fractionation, without significant crustal assimilation. A pure Rayleigh fractionation model indicates that 60–65% of crystal fractionation of 60% hornblende + 34% plagioclase + 4% clinopyroxene + 1% Fe-Ti oxide, apatite and sphene (a paragenesis similar of UPA mafic rocks) can explain evolution from lamprophyres to dacites. The UPA has higher LILE, HFSE and LREE, and lower HREE and Y than the calc-alkaline plutons and lavas of the volcanic front. The HREE and Y are lower than in the potassic plutons as well. High concentrations of Th, Nb, Ta, Zr, Hf, LREE and Ce/Pb, and low U/Th, Ba/Th ratios in UPA, even in the least differentiated samples, suggest contributions from subducted sediments to the mantle source. On the other hand, relatively low HREE and Y, high LREE/HREE (La/Yb 11–38) ratios and Nb-Ta contents can be interpreted as mantle metasomatism by partial melts of either subducted garnetiferous oceanic sediment or basalt as well. Additionally, high LILE content in UPA, similar to the potassic plutons, suggests also a mantle wedge previously metasomatized by potassic parental magmas in their route to crustal levels. Therefore, UPA represents a unique suite in the Fuegian arc generated in a multiple hybridized source. UPA generation is related to a transition from normal to flat subduction which additionally caused the widening and landward migration of the magmatic arc, as well as crustal deformation. Rear-arc magmatism endured ca. 22 m.y.; afterwards, calc-alkaline magmatism remained at the volcanic front.  相似文献   

Origin and evolution of hydrothermal fluids in epithermal Pb-Zn-Cu ± Au ± Ag deposits at Koru and Tesbihdere mining districts, Çanakkale,Biga Peninsula,NW Turkey     

《Ore Geology Reviews》2016

The Koru and Tesbihdere mining districts in Biga Peninsula, Northwestern Turkey, consist of twelve deposits covering approximately 12 km². The epithermal Au-Ag enriched base metal veins and associated low-grade breccia and stockwork at Koru and Tesbihdere are hosted by Oligocene subaerial and calc-alkaline volcanic rocks including basaltic andesite lavas, dacitic lava-tuffs, rhyolitic lava-domes and tuffs. NW- to N-trending strike-slip faults and E- and NE-trending faults constitute the most important ore-controlling structures in the Koru and Tesbihdere districts respectively. In the Koru mining district, galena is the dominant ore mineral in barite-quartz veins containing sphalerite, chalcopyrite, pyrite, bornite, enargite and tennantite. According to base metal content, the Tesbihdere mining district can be subdivided into sphalerite-galena dominated Tesbihdere mineralization and chalcopyrite-pyrite dominated Bakır and Kuyu Zones mineralization. Gold is present in small quantities with maximum 3.14 g/t Au values either as free grains in quartz or as micro inclusions in pyrite and galena. The most widespread silver minerals are polybasite, pearceite, argentite and native silver which commonly occur as replacements of galena, sphalerite and pyrite, and other sulfides, or as fillings of microfractures in sulfides and quartz.Microthermometric measurements of primary liquid-rich fluid inclusions in sphalerite, barite and quartz in Koru indicate that the veins were formed at temperatures between 407 and 146 °C from fluids with salinities between 0.7 and 12.5 wt.% equiv. NaCl. Barite from the Tahtalıkuyu, Kuyutaşı and 5^th Viraj mineralization show the highest homogenization temperatures. Fluid inclusion data for ore-stage quartz and sphalerite from the Tesbihdere mining district, indicate that these minerals were deposited at temperatures between 387 and 232 °C from more diluted fluids with moderate salinities between 0.2 and 10.6 wt.% NaCl equiv. Tahtalıkuyu and 5^th Viraj mineralization show only boiling trends while Kuyutaşı, Tesbihdere, Bakır and Kuyu Zones mineralization show both boiling and isothermal mixing trends. The O and H isotope compositions of ore fluids from the Tahtalıkuyu (δ¹⁸O = − 1.40 to 0.25‰; δD = − 72.49 to − 52.68‰) and Kuyutaşı (δ¹⁸O = − 2.29 to 3.59‰; δD = − 90.70 to − 70.93‰) mineralization indicate that there was a major contribution from a magmatic component to ore genesis. Based on 9 quartz samples associated with orebodies at the Tesbihdere mining district, the relatively higher δ¹⁸O and lower δD isotope compositions from hydrothermal fluids could be attributed to a relatively dilute fluid derived by the mixing with meteoric water. The Pb isotope compositions also reveal that most of the lead in both mining districts is derived from the Oligocene-Miocene magmatic rocks, possibly with smaller contributions from the Eocene magmatic rocks.  相似文献   

Nonhumans in the practice of development: Material agency and friction in a small-scale energy program in Indonesia     

《Geoforum》2016

We develop the outlines of a new approach to study the role of nonhumans in constituting ‘implementation’ and calculative–discursive practices in development projects and programs. Developing a framework around the concept of friction (material resistance or recalcitrance encountered in processes of transformation), we analyze an Energy Self-sufficient Village program in Indonesia. Focusing on specific projects and episodes within this program, we identify multiple distinctive instances of friction. These were driven by nonhumans’ (and humans’) resistance, as remolding of development beneficiaries’ practices was attempted by project administrators, government officials, entrepreneurs and by the (scientific) calculations embedded in their policies, strategies and models. In concluding, we distill four ways in which nonhumans relationally shape development practices: (a) by resisting representations and calculations produced by human actors, (b) by re-directing planned/expected courses of action, (c) through biophysical change to their weight or textures as they move in space and time, and (d) by mediating competition for resources. Overall, nonhumans play a central role in making and unmaking asymmetric relations of power in practice and by constituting practices that diverge from prior expectations, problematize linear understandings of ‘policy implementation’. Their material and discursive agency is multiple, manifesting differently in different relational settings, which highlights the importance of broadening the range of spokespersons who speak on behalf of nonhumans and whose voices can be considered reliable and true. Our study thus provides support to calls for pluralizing and democratizing development ‘expertise’ beyond the usual suspects in science, government and civil society.  相似文献   

The public trust doctrine and critical legal geographies of water in California     

《Geoforum》2016

Legal processes shape how water resources are allocated, regulated, distributed, and governed. This paper examines the public trust doctrine, a legal principle that addresses the state’s role in governing natural resources by requiring states to manage certain bodies of water and their shorelines for the good of the public. The paper focuses on how the public trust doctrine has been used—with varying degrees of success—to protect water bodies by contesting the diversion and transfer of water in California. The paper compares how the doctrine was applied in two cases: Mono Lake and the Salton Sea, two California lakes that have been threatened by water diversions and transfers. Advocates at Mono Lake successfully used the public trust doctrine for environmental protection, while public trust was an unsuccessful strategy at the Salton Sea. The paper examines issues of nonequilibrium ecosystems, natural versus artificial ecosystems, and wasteful versus reasonable uses of water.By investigating why one case was deemed eligible for public trust protections while the other was not, this paper examines how discursive constructions of nature are embedded in and enacted by legal institutions and how these constructions of nature impact the implementation of legal protections of natural resources. In examining the use of the public trust doctrine in California, the paper examines both the potential and the limitations of the public trust in practice, showing how legal processes and institutions can be used to protect public interests in natural resources but also how particular environmental narratives are reinforced through these institutions.  相似文献   

Isotopic analysis of the super-large Shuangjianzishan Pb–Zn–Ag deposit in Inner Mongolia,China: Constraints on magmatism,metallogenesis, and tectonic setting     

《Ore Geology Reviews》2016

The super-large Shuangjianzishan Pb–Zn–Ag deposit is a newly discovered deposit located in the Huanggang–Ganzhuermiao polymetallic metallogenic belt of Inner Mongolia, NE China. The deposit's resource includes 0.026 Mt Ag, 1.1 Mt Pb, and 3.3 Mt Zn. The deposit is controlled by a NW-trending ductile shear zone and NE- and NW-trending faults in black pelite assigned to the lower Permian Dashizhai Formation. LREE enrichment, HREE depletion, Nb, Ta, P, and Ti depletion, and Zr and Hf enrichment characterize felsic magmatic rocks in the Shuangjianzishan Pb–Zn–Ag district. The ages of porphyritic monzogranite, rhyolitic crystal–vitric ignimbrite, and porphyritic granodiorite are 254–252, 169, and 130 Ma, respectively. Pyrite sampled from the mineralization has Re–Os isochron ages of 165 ± 7 Ma, which suggest the mineralization is associated with the ca. 169 Ma magmatism in the Shuangjianzishan district.Zircons extracted from the porphyritic granodiorite yield ε_Hf(t) values of − 11.34 to − 1.41, with t_DM2 dates of 1275–1901 Ma. The ε_Hf(t) values of zircons in the rhyolitic crystal–vitric ignimbrite and the ore-bearing monzogranite porphyry are 7.57–16.23 and 10.18–15.96, respectively, and their t_DM2 ages are 177–733 and 257–632 Ma, respectively. Partial melting of depleted mantle resulted in the formation of the ca. 254–252 Ma ore-bearing porphyritic monzogranite and the ca. 169 Ma rhyolitic crystal–vitric ignimbrite; dehydration partial melting of subducted oceanic crust resulted in the formation of the ca. 130 Ma porphyritic granodiorite. The porphyritic monzogranite was emplaced during the late stages of closure of the Paleo-Asian Ocean during the transformation from a collisional to extensional tectonic setting. The ca. 170 and ca. 130 Ma magmatism and mineralization in the Shuangjianzishan district are related to subduction of the Mongolia–Okhotsk Ocean and subduction of the Paleo-Pacific Ocean Plate, respectively.  相似文献   

Direct dating of folding events by 40Ar/39Ar analysis of synkinematic muscovite from flexural-slip planes     

《Journal of Structural Geology》2016

Timing of folding is usually dated indirectly, with limited isotopic dating studies reported in the literature. The present study investigated the timing of intracontinental, multi-stage folding in Upper Proterozoic sandstone, limestone, and marble near Beijing, North China, and adjacent regions. Detailed field investigations with microstructural, backscattered electron (BSE) images and electron microprobe analyses indicate that authigenic muscovite and sericite crystallized parallel to stretching lineations/striations or along thin flexural-slip surfaces, both developed during the complex deformation history of the study area, involving repeated compressional, extensional and strike-slip episodes. Muscovite/sericite separates from interlayer-slip surfaces along the limbs and from dilatant sites in the hinges of folded sandstones yield muscovite ⁴⁰Ar/³⁹Ar plateau ages of ∼158–159 Ma, whereas those from folded marble and limestone samples yield ages of 156 ± 1 Ma. Muscovite from thin flexural-slip planes on fold limbs and hinges yields ages within analytical error of ∼155–165 Ma. Further muscovite samples collected from extensionally folded limestone and strike-slip drag folds yield younger ages of 128–125 Ma with well-defined plateaus. To assess the potential influence of the detrital mica component of the host rock on the age data, two additional muscovite samples were investigated, one from a folded upper Proterozoic–Cambrian sandstone outside the Western Hills of Beijing and one from a folded sandstone sampled 20 cm from folding-related slip planes. Muscovite separates from these samples yield significantly older ages of 575 ± 2 Ma and 587 ± 2 Ma, suggesting that the timing of folding can be directly determined using the ⁴⁰Ar/³⁹Ar method. This approach enables the identification and dating of distinct deformation events that occur during multi-stage regional folding. ⁴⁰Ar/³⁹Ar dating can be used to constrain the timing of muscovite and sericite growth at moderate to low temperatures (<400 °C) during folding, yielding well-defined plateau ages and thereby the age of deformation in the upper crust.  相似文献   

Weakness and mechanical anisotropy of phyllosilicate-rich cataclasites developed after mylonites of a low-angle normal fault (Simplon Line,Western Alps)     

《Journal of Structural Geology》2016

The Simplon Fault Zone is a late-collisional low-angle normal fault (LANF) of the Western Alps. The hanging wall shows evidence of brittle deformation only, while the footwall is characterized by a c. 1 km-thick shear zone (the Simplon Fault Zone), which continuously evolved, during exhumation and cooling, from amphibolite facies conditions to brittle-cataclastic deformations. Due to progressive localization of the active section of the shear zone, the thermal-rheological evolution of the footwall resulted in a layered structure, with higher temperature mylonites preserved at the periphery of the shear zone, and cataclasites occurring at the core (indicated as the Simplon Line). In order to investigate the weakness of the Simplon Line, we studied the evolution of brittle/cataclastic fault rocks, from nucleation to the most mature ones. Cataclasites are superposed on greenschist facies mylonites, and their nucleation can be studied at the periphery of the brittle fault zone. This is characterized by fractures, micro-faults and foliated ultracataclasite seams that develop along the mylonitic SCC′ fabric, exploiting the weak phases mainly represented by muscovite and chlorite. Approaching the fault core, both the thickness and frequency of cataclasite horizons increase, and, as their thickness increases, they become less and less foliated. The fault core itself is represented by a thicker non-foliated cataclasite horizon. No Andersonian faults or fractures can be found in the footwall damage zone and core zone, whilst they are present in the hanging wall and in the footwall further from the fault. Applying a stress model based on slip tendency, we have been able to calculate that the friction coefficient of the Simplon Line cataclasites was <0.25, hence this fault zone is absolutely weak. In contrast with other fault zones, the weakening effect of fluids was of secondary importance, since they accessed the fault zone only after an interconnected fracture network developed exploiting the cataclasite network.  相似文献