Time‐lapse electrical resistivity imaging of solute transport in a karst conduit          下载免费PDF全文

Audrey H. Sawyer  Junfeng Zhu  James C. Currens  Clay Atcher  Andrew Binley 《水文研究》2015,29(23):4968-4976

The use of electrical resistivity surveys to locate karst conduits has shown mixed success. However, time‐lapse electrical resistivity imaging combined with salt injection improves conduit detection and can yield valuable insight into solute transport behaviour. We present a proof of concept above a known karst conduit in the Kentucky Horse Park (Lexington, Kentucky). A salt tracer solution was injected into a karst window over a 45‐min interval, and repeat resistivity surveys were collected every 20 min along a 125‐m transect near a monitoring well approximately 750 m downgradient from the injection site. In situ fluid conductivity measurements in the well peaked at approximately 25% of the initial value about 3 h after salt injection. Time‐lapse electrical resistivity inversions show two broad zones at the approximate conduit depth where resistivity decreased and then recovered in general agreement with in situ measurements. Combined salt injection and electrical resistivity imaging are a promising tool for locating karst conduits. The method is also useful for gaining insight into conduit geometry and could be expanded to include multiple electrical resistivity transects. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Bottle‐green microtektites from the South Tasman Rise: Deep‐sea evidence for an impact event near the Miocene/Pliocene boundary     

D. Clay KELLY  Linda T. ELKINS‐TANTON 《Meteoritics & planetary science》2004,39(12):1921-1929

Abstract— Forty‐eight bottle‐green microtektites (BGMTs) were found in a core sample recovered from Ocean Drilling Program Site 1169, located along the western flank of the South Tasman Rise in the southeastern Indian Ocean. Biostratigraphic evidence loosely constrains the age of the Site 1169 BGMTs to an interval spanning the late‐middle Miocene to earliest Pliocene (12.1–4.6 Ma); incomplete core recovery and a major stratigraphic hiatus prevented a more precise age determination. This broad range of biostratigraphic ages indicates that these microtektites predate the Australasian strewn layer by at least 3.83 Ma, and perhaps by as much as 11.33 Ma. Furthermore, the REE signatures of the Site 1169 BGMTs are incongruent with those of typical Australasian ejecta, indicating that the Site 1169 BGMTs are not part of the larger Australasian strewn field. Among the various australite subgroups, the Site 1169 BGMTs are most similar in age to the HNa/K australites. However, numerous compositional discrepancies indicate that these two ejecta populations are also unrelated; the great distances separating Site 1169 from HNa/K australite‐bearing localities also makes a shared provenance unlikely. Therefore, we conclude that the Site 1169 BGMTs were formed by a late Miocene impact that is distinctly separate from the Australasian and HNa/K australite events, though the location of this impact is unknown.  相似文献   

Spatial and temporal changes in estuarine water quality during a post-flood hypoxic event     

Vanessa N.L. Wong  Scott G. Johnston  Richard T. Bush  Leigh A. Sullivan  Christina Clay  Edward D. Burton  Peter G. Slavich 《Estuarine, Coastal and Shelf Science》2010

A major fish kill occurred in the Richmond River estuary in January 2008 due to oxygen depletion following extensive overbank flooding. This paper examines spatial and temporal changes in the chemistry of main channel waters, thereby identifying the primary sources of deoxygenating water. Over 40 km of the mid- to lower estuary main channel was deoxygenated within seven days of the flood peak. Hypoxia was confined to downstream of the confluences with mid-estuary backswamp basins and occurred during the later phase of the flood recession. Water chemistry at key locations in the estuary indicated elevated concentrations of redox sensitive species associated with acid sulfate soils (ASS) during the hypoxic period. Peak concentrations of Fe²⁺ up to 18.2 μmol L⁻¹, dissolved Mn up to 4.3 μmol L⁻¹, chemical oxygen demand (COD) up to 2052 μmol L⁻¹, dissolved organic carbon (DOC) up to 960 μmol L⁻¹ and elemental S⁰ up to 4.7 μmol L⁻¹ were found in the backswamp discharge confluences and mid-estuary main channel locations. The geochemical signature of main channel floodwaters identifies anaerobic decomposition of floodplain vegetation in ASS backswamps as a primary process leading to generation of hypoxic waters. The transport of these hypoxic floodwaters to the estuary has been accelerated and prolonged by extensive floodplain drainage, thereby enhancing the magnitude and duration of estuarine deoxygenation.  相似文献   

Saltwater sport fishing for food or income in the Northeastern US: Statistical estimates and policy implications     

Scott Steinback  Kristy Wallmo  Patricia Clay 《Marine Policy》2009

In the Northeast US fishery managers have attempted to control marine recreational fishing mortality through annual adjustments to the number and/or size of fish that can be kept. These measures, with a few exceptions, have generally failed to prevent recreational fishing mortality rates from exceeding annual target levels. In this study, we show that one of the reasons why keep limits may have failed is that a substantial number of anglers obtain little value from being able to keep self-caught fish. Our findings are based on a telephone survey administered to marine anglers in all of the coastal counties in the Northeast US in 2004/2005. To evaluate the importance of keeping self-caught fish, we provide estimates of the size of the marine angling population in the Northeast US that keeps fish for food or income and also for those that fish primarily for recreation and place little or no value on keeping fish. Demographic characteristics of the two groups of anglers are compared statistically and differences related to consumption of self-caught marine resources and to health warning advisories are discussed. We also estimate the size of the Northeast US angling population that relies on their self-caught marine resources as a cost-saving food source or as a supplement to household income. This information could improve the effectiveness of fisheries regulations and the ability of policy analysts to predict how anglers might be affected by proposed fishery management actions.  相似文献   

High resolution acoustic structure of fish     

Nash  Richard D. M.; Sun  Ying; Clay  C. S. 《ICES Journal of Marine Science》1987,44(1):23-31

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Hydrological alteration along the Missouri River Basin: A time series approach   总被引：1，自引：0，他引：1  

Mark A. Pegg  Clay L. Pierce  Anindya Roy 《Aquatic Sciences - Research Across Boundaries》2003,65(1):63-72

Human alteration of large rivers is commonplace, often resulting in significant changes in flow characteristics. We used a time series approach to examine daily mean flow data from locations throughout the mainstem Missouri River. Data from a pre-alteration period (1925-1948) were compared with a post-alteration period (1967-1996), with separate analyses conducted using either data from the entire year or restricted to the spring fish spawning period (1 April-30 June). Daily mean flows were significantly higher during the post-alteration period at all locations. Flow variability was markedly reduced during the post-alteration period as a probable result of flow regulation and climatological shifts. Daily mean flow during the spring fish spawning period was significantly lower during the post-alteration period at the most highly altered locations in the middle portion of the river, but unchanged at the least altered locations in the upper and lower port ions of the river. Our data also corroborate other analyses, using alternate statistical approaches, that suggest similar changes to the Missouri River system. Our results suggest human alterations on the Missouri River, particularly in the middle portion most strongly affected by impoundments and channelization, have resulted in changes to the natural flow regime.  相似文献   

A search for very high energy bursts     

A. G. K. Smith  R. W. Clay  R. T. Pace  R. J. Protheroe  P. G. Edwards 《Astrophysics and Space Science》1995,231(1-2):319-322

Of great importance in distinguishing between models for gamma-ray bursts (GRBs) is the experimental determination of the highest energy gamma rays associated with bursts. The EGRET detection of a 15 GeV gamma ray indicates that the spectra of at least some bursts extend well beyond the several MeV limit of the BATSE detectors (Hurleyet al., 1994). The low expected flux means that the collecting area of the present generation of satellite-based detectors is too small to detect gamma rays much above this energy efficiently, and such searches are currently undertaken with ground based detectors. In this paper searches made for very high energy GRBs with a southern hemisphere air shower particle array are described.  相似文献