The oceanic substratum of Northern Luzon: Evidence from xenoliths within Monglo adakite (the Philippines)   总被引：2，自引：0，他引：2  

Betchaida D.  Payot  Sebastien  Jego  Rene C.  Maury  Mireille  Polve  Michel  Gregoire  Georges  Ceuleneer  Rodolfo A.  Tamayo Jr  Graciano P.  Yumul Jr  Herve  Bellon  Joseph  Cotten 《Island Arc》2007,16(2):276-290

Abstract   A 8.65 Ma adakitic intrusive sheet exposed near Monglo village in the Baguio District of Northern Luzon contains a suite of ultramafic and mafic xenoliths including in order of abundance: spinel dunites showing typical mantle-related textures, mineral and bulk rock compositions, and serpentinites derived from them; amphibole-rich gabbros displaying incompatible element patterns similar to those of flat or moderately enriched back-arc basin basalt magmas; and amphibolites derived from metabasalts and/or metagabbros of identical affinity. A single quartz diorite xenolith carrying a similar subduction-related geochemical signature has also been sampled. One amphibolite xenolith provided a whole-rock K–Ar age of 115.6 Ma (Barremian). We attribute the origin of this suite to the sampling by ascending adakitic magmas of a Lower Cretaceous ophiolitic complex located at a depth within the 30–35 km thick Luzon crust. It could represent an equivalent of the Isabela-Aurora and Pugo-Lepanto ophiolitic massifs exposed in Northern Luzon.  相似文献   

Sustained Ability of a Natural Microbial Community to Remove Nitrate from Groundwater     

Charles J. Paradis  John I. Miller  Ji-Won Moon  Sarah J. Spencer  Lauren M. Lui  Joy D. Van Nostrand  Daliang Ning  Andrew D. Steen  Larry D. McKay  Adam P. Arkin  Jizhong Zhou  Eric J. Alm  Terry C. Hazen 《Ground water》2022,60(1):99-111

Microbial-mediated nitrate removal from groundwater is widely recognized as the predominant mechanism for nitrate attenuation in contaminated aquifers and is largely dependent on the presence of a carbon-bearing electron donor. The repeated exposure of a natural microbial community to an electron donor can result in the sustained ability of the community to remove nitrate; this phenomenon has been clearly demonstrated at the laboratory scale. However, in situ demonstrations of this ability are lacking. For this study, ethanol (electron donor) was repeatedly injected into a groundwater well (treatment) for six consecutive weeks to establish the sustained ability of a microbial community to remove nitrate. A second well (control) located upgradient was not injected with ethanol during this time. The treatment well demonstrated strong evidence of sustained ability as evident by ethanol, nitrate, and subsequent sulfate removal up to 21, 64, and 68%, respectively, as compared to the conservative tracer (bromide) upon consecutive exposures. Both wells were then monitored for six additional weeks under natural (no injection) conditions. During the final week, ethanol was injected into both treatment and control wells. The treatment well demonstrated sustained ability as evident by ethanol and nitrate removal up to 20 and 21%, respectively, as compared to bromide, whereas the control did not show strong evidence of nitrate removal (5% removal). Surprisingly, the treatment well did not indicate a sustained and selective enrichment of a microbial community. These results suggested that the predominant mechanism(s) of sustained ability likely exist at the enzymatic- and/or genetic-levels. The results of this study demonstrated the in situ ability of a microbial community to remove nitrate can be sustained in the prolonged absence of an electron donor.  相似文献   

Stochastic calibration of an orographic precipitation model     

Lauren E. Hay 《水文研究》1998,12(4):613-634

In this study a stochastic approach to calibration of an orographic precipitation model (Rhea, 1978) was applied in the Gunnison River Basin of south-western Colorado. The stochastic approach to model calibration was used to determine: (1) the model parameter uncertainty and sensitivity; (2) the grid-cell resolution to run the model (10 or 5 km grids); (3) the model grid rotation increment; and (4) the basin subdivision by elevation band for parameter definition. Results from the stochastic calibration are location and data dependent. Uncertainty, sensitivity and range in the final parameter sets were found to vary by grid-cell resolution and elevation. Ten km grids were found to be a more robust model configuration than 5 km grids. Grid rotation increment, tested using only 10 km grids, indicated increments of less than 10 degrees to be superior. Basin subdivision into two elevation bands was found to produce ‘optimal’ results for both 10 and 5 km grids. © 1998 John Wiley & Sons, Ltd.  相似文献   

Integrated Hydrologic Modeling to Untangle the Impacts of Water Management During Drought     

Lauren M. Thatch  James M. Gilbert  Reed M. Maxwell 《Ground water》2020,58(3):377-391

Over the past century, groundwater levels in California's San Joaquin Valley have dropped by more than 30 m in some areas mostly due to excessive groundwater extraction used to irrigate agricultural lands and sustain a growing population. Between 2012 and 2015, California experienced the worst drought in its recorded history, depleting surface water supplies and further exacerbating groundwater depletion in the region. Due to a lack of groundwater regulation, exact quantities of extracted groundwater in California are unknown and hard to quantify. Recent adoption of the Sustainable Groundwater Management Act has intensified efforts to identify sustainable groundwater use. However, understanding sustainable use in a highly productive agricultural system with an extremely complex surface water allocation system, variable groundwater use, and spatially extensive and diverse irrigation practices is no easy task. Using an integrated hydrologic model coupled with a land surface model, we evaluated how water management activities, specifically a suite of irrigation and groundwater pumping scenarios, impact surface water–groundwater fluxes and storage components and how those activities and the relationships between them change during drought. Results showed that groundwater pumping volume had the most significant impact on long-term water storage changes. A comparison with total water storage anomaly (TWSA) estimates from NASA's Gravity Recover and Climate Experiment (GRACE) provided some insight regarding which combinations of pumping and irrigation matched the GRACE TWSA estimates, lending credibility to these scenarios. In addition, the majority of long-term water storage changes during the recent drought occurred in groundwater storage in the deeper subsurface.  相似文献   

Improved Method for Estimating Reaction Rates During Push-Pull Tests     

Charles J. Paradis  Emma R. Dixon  Lauren M. Lui  Adam P. Arkin  Jack C. Parker  Jonathan D. Istok  Edmund Perfect  Larry D. McKay  Terry C. Hazen 《Ground water》2019,57(2):292-302

The breakthrough curve obtained from a single-well push-pull test can be adjusted to account for dilution of the injection fluid in the aquifer fluid. The dilution-adjusted breakthrough curve can be analyzed to estimate the reaction rate of a solute. The conventional dilution-adjusted method assumes that the ratios of the concentrations of the nonreactive and reactive solutes in the injection fluid vs. the aquifer fluid are equal. If this assumption is invalid, the conventional method will generate inaccurate breakthrough curves and may lead to erroneous conclusions regarding the reactivity of a solute. In this study, a new method that generates a dilution-adjusted breakthrough curve was theoretically developed to account for any possible combination of nonreactive and reactive solute concentrations in the injection and aquifer fluids. The newly developed method was applied to a field-based data set and was shown to generate more accurate dilution-adjusted breakthrough curves. The improved dilution-adjusted method presented here is simple, makes no assumptions regarding the concentrations of the nonreactive and reactive solutes in the injection and aquifer fluids, and easily allows for estimating reaction rates during push-pull tests.  相似文献   

Sedimentary processes at ice sheet grounding-zone wedges revealed by outcrops,Washington State (USA)     

Brian P. Demet  Jeffrey A. Nittrouer  John B. Anderson  Lauren M. Simkins 《地球表面变化过程与地形》2019,44(6):1209-1220

Grounding-zone wedges (GZWs) mark the grounding terminus of flowing marine-based ice streams and, in the presence of an ice shelf, the transition from grounded ice to floating ice. The morphology and stratigraphy of GZWs is predominantly constrained by seafloor bathymetry, seismic data, and sediment cores from deglaciated continental shelves; however, due to minimal constraints on GZW sedimentation processes, there remains a general lack of knowledge concerning the production of these landforms. Herein, outcrop observations are provided of GZWs from Whidbey Island in the Puget Lowlands (Washington State, USA). These features are characterized by prograded diamictons bounded by glacial unconformities, whereby the lower unconformity indicates glacial advance of the southern Cordilleran Ice Sheet and the upper unconformity indicates locally restricted ice advance during GZW growth; the consistent presence of an upper unconformity supports the hypothesis that GZWs facilitate ice advance during landform construction. Based on outcrop stratigraphy, GZW construction is dominated by sediment transport of deformation till and melt-out of entrained basal debris at the grounding line. This material may be subsequently remobilized by debris flows. Additionally, there is evidence for subglacial meltwater discharge at the grounding line, as well as rhythmically bedded silt and sand, indicating possible tidal pumping at the grounding line. A series of GZWs on Whidbey Island provides evidence of punctuated ice sheet movement during retreat, rather than a rapid ice sheet lift-off. The distance between adjacent GZWs of 10²–10³ m and the consistency in their size relative to modern ice stream grounding lines suggests that individual wedges formed over decades to centuries. © 2018 John Wiley & Sons, Ltd.  相似文献   

Mineralogical characterization of the thrusted manganese ore above the Blackridge Thrust Fault,Kalahari Manganese Field: The footprint of the Mukulu Enrichment     

Nicholas A. Vafeas  Karel S. Viljoen  Lauren C. Blignaut 《Island Arc》2019,28(1)

The thrusted manganese ore above the Blackridge Thrust Fault is a predominantly unstudied ore‐type and as such, there is an urgent need to petrographically characterize it. A total of 80 samples were collected from the thrusted lower manganese ore bed of six boreholes on Mukulu in the north of the Kalahari Manganese Field. Each sample underwent a range of optical and electron petrographic analyses in order to effectively characterize three dominant stages of alteration, namely Stages 1, 2 and 3. Similar to the hydrothermally‐altered Wessels‐type manganese ore, braunite II is the predominant mineral phase present during Stage 1 alteration, and alters to bixbyite with increasing proximity to normal faults at the onset of Stage 2 alteration. The final stage of alteration is exhibited by the development of hausmannite and jacobsite adjacent to the ferruginised zone at the normal fault plane. Apatite precipitation, in abundances previously undocumented in the Kalahari Manganese Field, is a hallmark feature of the newly identified Mukulu Enrichment. This supergene‐related enrichment process contributed to the significant abundance of arsenic‐bearing apatite in the ore, whilst residually enriching the ore‐hosted Fe and Mn oxides.  相似文献   

Building resilience through interlocal relations: Case studies of polar bear and walrus management in the Bering Strait     

Chanda L. Meek  Amy Lauren Lovecraft  Martin D. Robards  Gary P. Kofinas 《Marine Policy》2008,32(6):1080-1089

Arctic coastal communities in the Bering Strait region of Alaska (USA) and Chukotka (Russia) share a close relationship with their natural environments that can be characterized as a social–ecological system. This system is complex, featuring changing ecosystem conditions, multiple jurisdictions, migratory animal populations, and several cultures. We argue that linkages between communities in both countries enhance the effectiveness of transborder polar bear and walrus conservation. We find that locally embedded bilateral institutions can provide effective management venues that persist despite slow or lacking processes of international law because they provide a better fit between rules for managing and the true system state.  相似文献   

Evaluating spatiotemporal variation in water chemistry of the upper Colorado River using longitudinal profiling     

Robert T. Hensley  Margaret J. Spangler  Lauren F. DeVito  Paul H. Decker  Matthew J. Cohen  Michael N. Gooseff 《水文研究》2020,34(8):1782-1793

Stream water chemistry is traditionally measured as variation over time at fixed sites, with sparse sites providing a crude understanding of spatial heterogeneity. An alternative Lagrangian reference frame measures changes with respect to both space and time as water travels through a network. Here, we collected sensor-based measurements of water chemistry at high spatial resolution along nearly 500 km of the Upper Colorado River. Our objective was to understand sources of spatiotemporal heterogeneity across different solutes and determine whether longitudinal change manifests as smooth gradients as suggested by the River Continuum Concept (RCC) or as abrupt changes as suggested by the Serial Discontinuity Concept (SDC). Our results demonstrate that Lagrangian sampling integrates spatiotemporal variation, and profiles reflect processes that vary in both space and time and over different scales. Over each day of sampling, water temperature (T) and dissolved oxygen (DO) varied strongly in response to diel solar cycles, with most of the variation driven by sampling time rather than sampling location. Equilibration of T and DO with the atmosphere limited small scale spatial heterogeneity, with variation at the entire profile scale driven by regional climate gradients. As such, T and DO profiles more closely approximated the smooth gradients of the RCC (though including temporal sampling artefacts). Conversely, variation in specific conductance and nitrate (NO₃-N) was largely driven by spatial patterns of lateral inflows such as tributaries and groundwater. This resulted in discrete shifts in the profiles at or downstream of discontinuities, appearing as the profiles expected with the SDC. The concatenation of spatiotemporal variation that produces observed Lagrangian profiles presents interpretive challenges but also augments our understanding of where, how, and critically why water chemistry changes in time and space as it moves through river networks.  相似文献   

A new flow for Canadian young hydrologists: Key scientific challenges addressed by research cultural shifts     

Caroline Aubry-Wake  Lauren D. Somers  Haley Alcock  Aspen M. Anderson  Amin Azarkhish  Samuel Bansah  Nicole M. Bell  Kelly Biagi  Mariana Castaneda-Gonzalez  Olivier Champagne  Anna Chesnokova  Devin Coone  Tasha-Leigh J. Gauthier  Uttam Ghimire  Nathan Glas  Dylan M. Hrach  Oi Yin Lai  Pierrick Lamontagne-Hallé  Nicolas R. Leroux  Laura Lyon  Sohom Mandal  Bouchra R. Nasri  Nataša Popović  Tracy E. Rankin  Kabir Rasouli  Alexis Robinson  Palash Sanyal  Nadine J. Shatilla  Brandon Van Huizen  Sophie Wilkinson  Jessica Williamson  Majid Zaremehrjardy 《水文研究》2020,34(8):2001-2006

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