Quantification of karst aquifer discharge components during storm events through end-member mixing analysis using natural chemistry and stable isotopes as tracers   总被引：1，自引：1，他引：1  

Daniel H. Doctor  E. Calvin Alexander Jr  Metka Petrič  Janja Kogovšek  Janko Urbanc  Sonja Lojen  Willibald Stichler 《Hydrogeology Journal》2006,14(7):1171-1191

Karst aquifer components that contribute to the discharge of a water supply well in the Classical Karst (Kras) region (Italy/Slovenia) were quantitatively estimated during storm events. Results show that water released from storage within the epikarst may comprise as much as two-thirds of conduit flow in a karst aquifer following rainfall. Principal components analysis (PCA) and end-member mixing analysis (EMMA) were performed using major ion chemistry and the stable isotopes of water (δ¹⁸O, δ²H) and of dissolved inorganic carbon (δ¹³C_DIC) to estimate mixing proportions among three sources: (1) allogenic river recharge, (2) autogenic recharge, and (3) an anthropogenic component stored within the epikarst. The sinking river most influences the chemical composition of the water-supply well under low-flow conditions; however, this proportion changes rapidly during recharge events. Autogenic recharge water, released from shallow storage in the epikarst, displaces the river water and is observed at the well within hours after the onset of precipitation. The autogenic recharge end member is the second largest component of the well chemistry, and its contribution increases with higher flow. An anthropogenic component derived from epikarstic storage also impacts the well under conditions of elevated hydraulic head, accounting for the majority of the chemical response at the well during the wettest conditions.  相似文献   

Sediment deposition from flow at low gradients into a buffer strip—a critical test of re-entrainment theory     

Calvin W. Rose  Bofu Yu  William L. Hogarth  Augustine E. A. Okom  Hossein Ghadiri 《Journal of Hydrology》2003,280(1-4):33-51

The spatial and size distribution of sediment deposited from short periods of overland flow due to the effect of a simulated grass buffer strip was measured for low slopes of 1.6, 3.4 and 5.1%. These data were analysed so as to critically evaluate two alternative models of the process of re-entrainment of recently deposited sediment. A model of re-entrainment, previously thought to be appropriate only for a steady-state or equilibrium situation, was found to give better agreement with experiments than did a model previously used in the literature on this subject.  相似文献   

The potential for agricultural land use change to reduce flood risk in a large watershed          下载免费PDF全文

Keith E. Schilling  Philip W. Gassman  Catherine L. Kling  Todd Campbell  Manoj K. Jha  Calvin F. Wolter  Jeffrey G. Arnold 《水文研究》2014,28(8):3314-3325

Effects of agricultural land management practices on surface runoff are evident at local scales, but evidence for watershed‐scale impacts is limited. In this study, we used the Soil and Water Assessment Tool model to assess changes in downstream flood risks under different land uses for the large, intensely agricultural, Raccoon River watershed in Iowa. We first developed a baseline model for flood risk based on current land use and typical weather patterns and then simulated the effects of varying levels of increased perennials on the landscape under the same weather patterns. Results suggest that land use changes in the Raccoon River could reduce the likelihood of flood events, decreasing both the number of flood events and the frequency of severe floods. The duration of flood events were not substantially affected by land use change in our assessment. The greatest flood risk reduction was associated with converting all cropland to perennial vegetation, but we found that converting half of the land to perennial vegetation or extended rotations (and leaving the remaining area in cropland) could also have major effects on reducing downstream flooding potential. We discuss the potential costs of adopting the land use change in the watershed to illustrate the scale of subsidies required to induce large‐scale conversion to perennially based systems needed for flood risk reduction. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Will economic growth and fossil fuel scarcity help or hinder climate stabilization?     

Elmar Kriegler  Ioanna Mouratiadou  Gunnar Luderer  Nico Bauer  Robert J. Brecha  Katherine Calvin  Enrica De Cian  Jae Edmonds  Kejun Jiang  Massimo Tavoni  Ottmar Edenhofer 《Climatic change》2016,136(1):7-22

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Managing Depleting Gold Revenues in Mali: An Assessment of Policy Options     

Fousseini Traore  Calvin Djiofack Zebaze 《Natural Resources Research》2016,25(2):183-195

This paper analyzes the impact of medium-term policy options in the context of gold resources depletion in Mali. Using a recursive-dynamic computable general equilibrium model calibrated to a 2006 Malian Social Accounting Matrix, we assess the impact of gold resources depletion in Mali and two policy options: the adoption of the permanent income hypothesis (PIH) and a “borrow and invest” scenario consisting at boosting public investment by 5% points of GDP. The depletion of gold resources in Mali would cause a substantial fall in GDP growth, and lead to unsustainable fiscal path if the government were to keep its current pattern of spending. Adopting either the “borrow and invest” fiscal approach or the PIH is likely to generate higher growth and a more sustainable fiscal framework compared to the status quo.  相似文献   

The Quaternary Lancaster Sound trough‐mouth fan,NW Baffin Bay     

Gang Li  David J.W. Piper  D. Calvin Campbell 《第四纪科学杂志》2011,26(5):511-522

The development of the Lancaster Sound Trough Mouth Fan (TMF) and glacial history in Arctic Canada were studied using a high‐resolution seismic profile across the entire fan and two piston cores. Stacked tills separated by erosion surfaces on the shelf pass seaward through till deltas into thick transparent glacigenic debris flow (GDF) deposits on the slope, separated by thin, well‐stratified glaciomarine layers. An age model was built by ties to the Ocean Drilling Program Site 645. The deepest GDF on the seismic profile was indicative of the onset of shelf‐crossing glaciation in the Early Pleistocene. The transition of the growth of Lancaster Sound TMF from an aggradational sequence (unit M) to an aggradational–progradational sequence (unit F) occurred at the Middle Pleistocene transition in glacial cyclicity. In the most recent glacial cycle, GDF sheets were deposited during Heinrich events 4 and 2 according to the correlation of the main detrital carbonate beds in two piston cores. The outmost till wedge reflects the maximum advance of the grounding glacier, far seaward of previously proposed Last Glacial Maximum ice extent. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Southern Westerlies during the last glacial maximum   总被引：1，自引：0，他引：1  

Calvin J. Heusser 《Quaternary Research》1989,31(3)

Vegetation and climate over approximately the past 13,000 yr are reconstructed from fossil pollen in a 9.4-m mire section at Caleta Róbalo on Beagle Channel, Isla Navarino (54°56′S, 67°38′W), southern Tierra del Fuego. Fifty surface samples reflecting modern pollen dispersal serve to interpret the record. Chronologically controlled by nine radiocarbon dates, fossil pollen assemblages are: Empetrum-Gramineae-Gunnera-Tubuliflorae (zone 3b, 13,000–11,850 yr B.P.), Gramineae-Empetrum-assorted minor taxa (zone 3a, 11,850-10,000 yr B.P.), Nothofagus-Gramineae-Tubuliflorae-Polypodiaceae (zone 2, 10,000–5000 yr B.P.), Nothofagus-Empetrum (zone 1b, 5000-3000 yr B.P.), and Empetrum-Nothofagus (zone 1a, 3000-0 yr B.P.). Assemblages show tundra under a cold, dry climate (zone 3), followed by open woodland (zone 2), as conditions became warmer and less dry, and later, with greater humidity and lower temperatures, by closed forest and the spread of mires (zone 1). Comparisons drawn with records from Antarctica, New Zealand, Tasmania, and the subantarctic islands demonstrate broadly uniform conditions in the circumpolar Southern Hemisphere. The influences of continental and maritime antarctic air masses were apparently considerable in Tierra del Fuego during cold late-glacial time, whereas Holocene climate was largely regulated by interplay between maritime polar and maritime tropical air.  相似文献   

Petrology of Peter I Øy (Peter I Island), West Antarctica     

Tore Prestvik  Calvin G. Barnes  Bjrn Sundvoll  Robert A. Duncan 《Journal of Volcanology and Geothermal Research》1990,44(3-4)

Peter I Øy is located in the Bellinghausen Sea, 400 km NE of Thurston Island, West Antarctica. It is a Pleistocene volcanic island situated adjacent to a former tranform fault on the continental rise of the presently passive margin between the Pacific and Antarctica. New K-Ar age determinations ranging from 0.1 to 0.35 Ma show that the volcanism responsible for this island took place at the same time as post-subduction, rift-related volcanism occurred in the nearby Marie Byrd Land and the Antarctic Peninsula. The rocks of the island are alkalic basalt and hawaiite, benmoreite and trachyte. The basic tocks typically contain phenocrysts of olivine (Fo_61–84), diopsidic augite, and plagioclase (ca. An₆₀). Small xenoliths are present and consist of mantle-type spinel lherzolite, cumulate clinopyroxenite and gabbro and felsic inclusions that consist of medium-grained strained quartz, plagioclase, and abundant colorless glass. Chemically, the basic rocks are characterized by rather high MgO (7.8–10.2 wt.%) and TiO₂ (3.1–3.7 wt.%) and relatively low CaO (8.4–9.5 wt.%) contents. They have steep REE patterns, [(La/Yb)_N = 20] with HREE only 5 x chrondrite. Y and Sc are almost constant at relatively low levels. Compatible trace elements such as Ni and Cr show considerable variation (190–300 and 150–470 ppm, respectively.), whereas V shows only little variation. Sr and Nd isotope ratios vary slightly with ⁸⁷Sr/⁸⁶Sr averaging 0.70388 and ¹⁴³Nd/¹⁴⁴Nd 0.512782, both typical for ocean island volcanism. Lead isotope ratios are consistently high in basalts; ²⁰⁶Pb/²⁰⁴Pb = 19.194, ²⁰⁷Pb/²⁰⁴Pb = 15.728 and ²⁰⁸Pb/²⁰⁴Pb = 39.290, whereas benmoreïte is somewhat less radiogenic. Oxygen isotope analyses average δ¹⁸O = +6.0‰. Incompatible trace elements vary by a factor of 1.5–2.0 within the range of the basic rocks. It is proposed that the incompatible trace-element variations represent different degrees (<10%) of partial melting, and that these melts were later modified by minor (<15‰) olivine and spinel fractionation. The very small variation in Y (and Sc) and the very fractionated REE pattern indicate that the source had an Y- and HREE-rich residual phase, most probably garnet. Furthermore, it is suggested that the source was slightly hydrous and that melting took place at 18–20 kbar. Trachyte was derived by multiphase fractionation of ne-normative basalts, and benmoreite from hy-normative parental liquids. The rocks of Peter I Øy are generally of the same type and age as those outcropping in extensional regimes on the nearby continent, and therefore, these occurrences may be related to each other in some way. However, the Peter I Øy rocks are considerably more radiogenic in strontium and less radiogenic in neodymium than the rocks of the Antarctic Peninsula and Marie Byrd Land. Possible explanations are that Peter I Øy represent asthenospheric hot spot activity, or transtensional rifting as subduction ceased.  相似文献   

Geochemistry of the Sweetwater Wash Pluton,California: Implications for “anomalous” trace element behavior during differentiation of felsic magmas   总被引：1，自引：0，他引：1  

David W. Mittlefehldt  Calvin F. Miller 《Geochimica et cosmochimica acta》1983,47(1):109-124

Field relations, mineralogy and major and trace element data for the very felsic, peraluminous Sweetwater Wash pluton establish a differentiation sequence dominantly controlled by fractional crystallization processes. Elements Ba and Sr show depletion by factors of 50–60X from the earliest granite unit analyzed to the late-stage pegmatites and aplites. The strong Ba depletion is largely due to the partitioning behavior of this element in K-feldspar, while the Sr depletion is due to the combined effects of the two feldspars. The 4-fold increase in Rb during crystallization is also predictable from mineral/ melt partition coefficients.Coefficients for the light rare-earth elements (LREE) in major mineral species predict that these elements should behave incompatibly during crystallization and increase with fractionation. In fact, the LREE abundances decrease by a factor of 10–20X during crystallization. This anomalous behavior is commonly observed in felsic plutonic and volcanic sequences. In the Sweetwater Wash pluton monazite occurs in minute quantities, but it is sufficiently abundant to govern the partitioning of LREE and Th during crystallization. Petrographic observations indicate that monazite was on the liquidus throughout most of the crystallization. Analyses of silicate mineral separates suggest that the monazite contains more than 75% of the LREE in the whole rocks.Fractionation of REE-rich accessories (in particular monazite) from felsic magmas may be the general cause of REE depletion during differentiation of these melts. Monazite can easily be mistaken for zircon and, because it typically contains 50% LREE, extremely minute and easily overlooked quantities of monazite can control LREE abundances.  相似文献   

Sydney's Ethnic Geography: New approaches to analysing patterns of residential concentration     

Ron Johnston  James Forrest  Michael Poulsen 《The Australian geographer》2001,32(2):149-162

Most studies of ethnic residential segregation in Australian cities have used single-measure indices of dissimilarity and segregation, which access the degree of unevenness between two maps. Segregation is a multi-dimensional concept, however, and in this paper we introduce an alternative way of measuring residential concentration which incorporates several of the key dimensions. The procedure is illustrated using birthplace and language-used-at-home data for collection districts in metropolitan Sydney in 1996. Results show no evidence of extreme spatial concentration of ethnic groups.  相似文献