The capture efficiency map: the capture zone under time-varying flow   总被引：3，自引：0，他引：3  

Festger AD  Walter GR 《Ground water》2002,40(6):619-628

The capture zone or contributing area of a ground water extraction well can be defined as that portion of the aquifer from which the well draws its water. Accurate delineation of capture zones is important in many ground water remediation applications and in the definition of wellhead protection areas. Their mathematical delineation is often simplified by using quasi-steady-state models based on time-weighted average pumping rates and background hydraulic gradients. We present a new semianalytic approach for the definition of capture zones under transient-flow conditions. We then use this approach to evaluate the effects of time variations in the direction of the background hydraulic gradient on capture. Results are presented in the form of capture efficiency maps (CEMs). Although the area contributing to a given well is found to generally expand relative to the steady-state average capture zone when the gradient direction varies, the zone of 100% capture may expand or contract depending on site-specific conditions. We illustrate our CEM approach by applying it to the design of a plume containment system.  相似文献   

Tar ball frequency data and analytical results from a long-term beach monitoring program     

Owens EH  Mauseth GS  Martin CA  Lamarche A  Brown J 《Marine pollution bulletin》2002,44(8):770-780

Following the spill of fuel oils from the New Carissa in February 1999, approximately 300 km of beaches on the Pacific coast of North America were surveyed. A long-term observation program focused on the documentation of stranded tar balls in the vicinity of the spill site. Systematic beach surveys which were conducted over the period March 1999 to April 2001 and semi-logarithmic scale, time-series plots proved the most useful format for identifying trends. Beach monitoring continued through to August 2001. by which time 212 tar balls had been analyzed by GC/MS for their chemical characteristics. The samples of tar balls collected between February 1999 and August 2001 were qualitatively compared with New Carissa source oils (NCSO) and 101 (48%) were not consistent with NSCO. The presence of tar balls that are not related to an incident can confound attempts to define cleanup or endpoint criteria and to assess possible injury to natural resources.  相似文献   

Editorial     

John Wilson  Stewart Fotheringham  Gary Hunter  Jochen Albrecht 《Transactions in GIS》2006,10(2):153-153

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Ten Years On . . .     

John Wilson  Stewart Fotheringham  Gary Hunter  Jochen Albrecht 《Transactions in GIS》2006,10(3):333-333

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Scale-dependent influences on water quality, habitat, and fish communities in streams of the Kalamazoo River Basin, Michigan (USA)     

Ashley H. Moerke  Gary A. Lamberti 《Aquatic Sciences - Research Across Boundaries》2006,68(2):193-205

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Infinite uncertainty,forgotten feedbacks,and cost-benefit analysis of climate policy   总被引：1，自引：1，他引：1  

Richard S. J. Tol  Gary W. Yohe 《Climatic change》2007,83(4):429-442

Tol (2003) questioned the applicability of expected cost-benefit analysis to global mitigation policy when he found evidence that the uncertainty surrounding estimates of the marginal damage of climate change could be infinite even if total damages were finite. Yohe (2003) suggested that this problem could be alleviated if international development aid were directed at eliminating the source of the problem – climate induced negative growth rates in a few regions along a handful of troublesome scenarios. The hypothesis about adding a second policy lever to the climate policy calculus is shown to hold, though perhaps not as robustly as originally thought. A portfolio of international policies with at least two independent tools can avoid infinite uncertainty on the margins and the associated implications for global mitigation policy at a reasonable price even in the relatively unlikely event that climate change causes negative economic growth in a region or two. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

Environmental change recorded in sediments from the Marmes rockshelter archaeological site, southeastern Washington state, USA     

Gary Huckleberry  Cynthia Fadem 《Quaternary Research》2007,67(1):21-32

The Marmes Rockshelter archaeological site in southeastern Washington state contains a > 11 kyr stratigraphic record that was excavated in the 1960s but only recently analyzed in detail. We present the results of physical, chemical, and isotopic analyses of archived Marmes sediments from rockshelter, hillslope, and floodplain locations. Multiple lines of evidence including éboulis production, soil chemistry, and δ¹³C and δ¹⁸O signatures in soil organic matter and calcium carbonate suggest that relatively cool, moist conditions 10,600 to 9700 ¹⁴C yr BP were followed by relatively warm and dry conditions as early as 9000 ¹⁴C yr BP. Warm and dry conditions extended to the late Holocene, followed by a return to cooler and moister climate. The limited range of δ¹³C and δ¹⁸O values in Marmes paleosols suggests that the magnitude of moisture and temperature shifts was locally buffered in the lower Snake River Canyon but adequate to generate significant changes in sedimentation and soil formation, possibly due to nonlinear geological and pedological processes. These buffered canyon environments were well suited for establishing residential bases associated with foraging and logistical collecting strategies and may have minimized the influence of climate changes in food resource abundance.  相似文献   

Fe-Ni and Mn-Cr isotopic systems in sulfides from unequilibrated enstatite chondrites     

Yunbin Guan  Gary R. Huss  Laurie A. Leshin 《Geochimica et cosmochimica acta》2007,71(16):4082-4091

In situ measurements of ⁶⁰Fe-⁶⁰Ni and ⁵³Mn-⁵³Cr isotopic systems with an ion microprobe have been carried out for sulfide assemblages from unequilibrated enstatite chondrites (UECs). Evidence for the initial presence of ⁶⁰Fe has been observed in nine sulfide inclusions from three UECs: ALHA77295, MAC88136, and Qingzhen. The inferred initial (⁶⁰Fe/⁵⁶Fe) [(⁶⁰Fe/⁵⁶Fe)₀] ratios show a large variation range, from ∼2 × 10⁻⁷ to ∼2 × 10⁻⁶. The sulfide inclusions with high Fe/Ni ratios yield (⁶⁰Fe/⁵⁶Fe)₀ ratios of ∼(2-7) × 10⁻⁷, similar to most of the (⁶⁰Fe/⁵⁶Fe)₀ values of troilite and pyroxene observed in unequilibrated ordinary chondrites (UOCs). Inclusions with high inferred (⁶⁰Fe/⁵⁶Fe)₀ ratios (∼1-2 × 10⁻⁶) have low Fe/Ni ratios and the magnitude of the ⁶⁰Ni excesses is similar in two MAC88136 assemblages in spite of a difference of a factor of two in their Fe/Ni ratios. The inferred high (⁶⁰Fe/⁵⁶Fe)₀ ratios were probably the result of Fe-Ni re-distribution in the sulfides during later alteration processes.The ⁵³Mn-⁵³Cr system was measured in five of the sulfide assemblages that were examined for their ⁶⁰Fe-⁶⁰Ni systematics. The ⁵³Mn-⁵³Cr isochrons yielded variable initial (⁵³Mn/⁵⁵Mn) [(⁵³Mn/⁵⁵Mn)₀] ratios from ∼(2-7) × 10⁻⁷. There is no obvious correlation between the (⁶⁰Fe/⁵⁶Fe)₀ and (⁵³Mn/⁵⁵Mn)₀ ratios. The variable ⁵³Mn-⁵³Cr isochrons probably also indicate later disturbance to the isotopic systems in these sulfides. Even though no chronological information can be extracted from the ⁶⁰Fe-⁶⁰Ni and ⁵³Mn-⁵³Cr systems in these UEC sulfides, our results indicate that ⁶⁰Fe was present in the enstatite chondrite formation region of the early Solar System.  相似文献   

Elevated marine deposits in Bermuda record a late Quaternary megatsunami     

Gary M. McMurtry  David R. Tappin  Peter N. Sedwick  Ian Wilkinson  Jan Fietzke  Bruce Sellwood   《Sedimentary Geology》2007,200(3-4):155-165

Deposits of coral-bearing, marine shell conglomerate exposed at elevations higher than 20 m above present-day mean sea level (MSL) in Bermuda and the Bahamas have previously been interpreted as relict intertidal deposits formed during marine isotope stage (MIS) 11, ca. 360–420 ka before present. On the strength of this evidence, a sea level highstand more than 20 m higher than present-day MSL was inferred for the MIS 11 interglacial, despite a lack of clear supporting evidence in the oxygen-isotope records of deep-sea sediment cores. We have critically re-examined the elevated marine deposits in Bermuda, and find their geological setting, sedimentary relations, and microfaunal assemblages to be inconsistent with intertidal deposition over an extended period. Rather, these deposits, which comprise a poorly sorted mixture of reef, lagoon and shoreline sediments, appear to have been carried tens of meters inside karst caves, presumably by large waves, at some time earlier than ca. 310–360 ka before present (MIS 9–11). We hypothesize that these deposits are the result of a large tsunami during the mid-Pleistocene, in which Bermuda was impacted by a wave set that carried sediments from the surrounding reef platform and nearshore waters over the eolianite atoll. Likely causes for such a megatsunami are the flank collapse of an Atlantic island volcano, such as the roughly synchronous Julan or Orotava submarine landslides in the Canary Islands, or a giant submarine landslide on the Atlantic continental margin.  相似文献   

双差定位法在地震丛集精确定位中的应用   总被引：4，自引：0，他引：4       下载免费PDF全文

刘劲松  Kin-Yip Chun  刘福田  郝天珧 《地球物理学进展》2007,22(1):137-141

应用双差定位方法(hypodd)对北美Loma Prieta 地区的分属于3个地震丛集的47个地震进行了精确定位.采用交叉谱法精确求取信号的走时差；同时采用人机联做方式在时域调整、修正按自动方式无法准确提取时差的信号，确保每个事件对的走时差精度.重定位后，在几百米的范围内，原来相互重叠的震源位置聚集为三个明显分离的丛集;水平方向的相对位置平均误差为8.5米，震源深度方向的平均误差为23.4 m.  相似文献