Dynamics of evapotranspiration from a riparian pond complex in the Western Boreal Forest,Alberta, Canada     

R. M. Petrone  U. Silins  K. J. Devito 《水文研究》2007,21(11):1391-1401

The relative contributions to total actual evapotranspiration (AET) from pond and riparian areas in a pond‐wetland complex in the Western Boreal Plain (WBP) of northern Alberta are measured using the Bowen ratio energy balance technique. Measurements show that a pond typical of the WBP evaporates at a rate more than twice that of the adjacent riparian peatland. Relating the actual to potential evapotranspiration over both surfaces yields Priestley–Taylor α coefficients of 0·69 and 1·11 for the peatland and pond respectively. Further results demonstrate that the sheltering and turbulent influences of the adjacent forested areas must be considered in the processes governing the permanence of WBP ponds. That is, forestry practices may inadvertently enhance the evaporative losses from the ponds, over and above the controls exerted by the regional climate. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

An overview of regional land-use and land-cover impacts on rainfall   总被引：11，自引：0，他引：11  

R. A. PIELKE Sr  .  J. ADEGOKE  A. BELTRÁN-PRZEKURAT  C. A. HIEMSTRA  J. LIN  U. S. NAIR  D. NIYOGI  T. E. NOBIS 《Tellus. Series B, Chemical and physical meteorology》2007,59(3):587-601

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Comparison of Hydraulic Tomography with Traditional Methods at a Highly Heterogeneous Site          下载免费PDF全文

Steven J. Berg  Walter A. Illman 《Ground water》2015,53(1):71-89

Over the past several decades, different groundwater modeling approaches of various complexities and data use have been developed. A recently developed approach for mapping hydraulic conductivity (K) and specific storage (S_s) heterogeneity is hydraulic tomography, the performance of which has not been compared to other more “traditional” methods that have been utilized over the past several decades. In this study, we compare seven methods of modeling heterogeneity which are (1) kriging, (2) effective parameter models, (3) transition probability/Markov Chain geostatistics models, (4) geological models, (5) stochastic inverse models conditioned to local K data, (6) hydraulic tomography, and (7) hydraulic tomography conditioned to local K data using data collected in five boreholes at a field site on the University of Waterloo (UW) campus, in Waterloo, Ontario, Canada. The performance of each heterogeneity model is first assessed during model calibration. In particular, the correspondence between simulated and observed drawdowns is assessed using the mean absolute error norm, (L₁), mean square error norm (L₂), and correlation coefficient (R) as well as through scatterplots. We also assess the various models on their ability to predict drawdown data not used in the calibration effort from nine pumping tests. Results reveal that hydraulic tomography is best able to reproduce these tests in terms of the smallest discrepancy and highest correlation between simulated and observed drawdowns. However, conditioning of hydraulic tomography results with permeameter K data caused a slight deterioration in accuracy of drawdown predictions which suggests that data integration may need to be conducted carefully.  相似文献   

Examining the fate of WWTP effluent nitrogen using δ 15N–NH4 +, δ 15N–NO 3 − and δ 15N of submersed macrophytes     

Jennifer L. A. Hood  William D. Taylor  Sherry L. Schiff 《Aquatic Sciences - Research Across Boundaries》2014,76(2):243-258

The use of submersed macrophyte tissue δ ¹⁵N to quantify the level of WWTP effluent use in a highly urbanized and agricultural river was evaluated using several methods. Macrophytes, NH₄ ⁺ and NO₃ ^? were collected by canoe along two 10 km reaches of river, upstream and downstream of two major municipal WWTPs over 3 years. NH₄ ⁺ decreased in concentration while δ ¹⁵N–NH₄ ⁺ increased as a function of distance downstream of both WWTPs, changing in one survey from 13 to 31 ‰ over 1 km. This increase is attributed to the combined effects of volatilization, nitrification and uptake. While NO ₃ ^? concentrations increased downstream of the WWTP over one of the survey reaches, δ ¹⁵N–NO ₃ ^? showed no prominent trend with distance at either. Macrophyte tissue δ ¹⁵N increased with distance downstream of both WWTPs, with a slope not significantly different from that of δ ¹⁵N–NH₄ ⁺ suggesting that macrophytes incorporate effluent NH₄ ⁺ as their main N source in those areas. However, mixing models suggest that towards the end of the reach, where source separation is distinct, macrophytes may utilize background NO ₃ ^? . Our study indicates the difficulty of deriving precise estimates of effluent use by macrophytes in a system where the δ ¹⁵N of the effluent changes rapidly. It also illustrates the utility of macrophytes in describing those changes where the effluent is too attenuated to allow for direct isotopic analysis.  相似文献   

The orbital distribution of satellite galaxies     

Stéphane Herbert-Fort  Dennis Zaritsky  Yeun Jin Kim  Jeremy Bailin  James E. Taylor 《Monthly notices of the Royal Astronomical Society》2008,384(2):803-813

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Near ultraviolet–infrared colours of red-sequence galaxies in local clusters     

Timothy D. Rawle  Russell J. Smith  John R. Lucey  Michael J. Hudson  Gary A. Wegner 《Monthly notices of the Royal Astronomical Society》2008,385(4):2097-2106

We present GALEX near-ultraviolet ( NUV ) and Two-Micron All-Sky Survey J -band photometry for red-sequence galaxies in local clusters. We define quiescent samples according to a strict emission threshold, removing galaxies with very recent star formation. We analyse the NUV – J colour–magnitude relation (CMR) and find that the intrinsic scatter is an order of magnitude larger than for the analogous optical CMR (∼0.35 rather than 0.05 mag), in agreement with previous studies. Comparing the NUV – J colours with spectroscopically derived stellar population parameters, we find a strong  (>5.5σ)  correlation with metallicity, only a marginal trend with age, and no correlation with the α/Fe ratio. We explore the origin of the large scatter and conclude that neither aperture effects nor the UV upturn phenomenon contribute significantly. We show that the scatter could be attributed to simple 'frosting' by either a young or a low-metallicity subpopulation.  相似文献   

The Dakhleh Glass: Product of an impact airburst or cratering event in the Western Desert of Egypt?     

Gordon R. OSINSKI  Johanna KIENIEWICZ  Jennifer R. SMITH  Mark B. E. BOSLOUGH  Mark ECCLESTON  Henry P. SCHWARCZ  Maxine R. KLEINDIENST  Albert F. C. HALDEMANN  Charles S. CHURCHER 《Meteoritics & planetary science》2008,43(12):2089-2107

Abstract— Impact cratering is a ubiquitous geological process on the terrestrial planets. Meteorite impact craters are the most visible product of impact events, but there is a growing recognition that large aerial bursts or airbursts should occur relatively frequently throughout geological time. In this contribution, we report on an unusual impact glass‐the Dakhleh Glass (DG)–which is distributed over an area of ?400 km ²of the Dakhleh Oasis, Egypt. This region preserves a rich history of habitation stretching back to over 400,000 years before the emergence of Homo sapiens. We report on observations made during recent fieldwork and subsequent analytical analyses that strengthen previous suggestions that the DG formed during an impact event. The wide distribution and large size of DG specimens (up to ?50 cm across), the chemistry (e.g., CaO and Al₂O₃ contents up to ?25 and ?18 wt, respectively), the presence of lechatelierite and burnt sediments, and the inclusion of clasts and spherules in the DG is inconsistent with known terrestrial processes of glass formation. The age and other textural characteristics rule out a human origin. Instead, we draw upon recent numerical modeling of airbursts to suggest that the properties of DG, coupled with the absence of a confirmed crater, can best be explained by melting of surficial sediments as a result of a large airburst event. We suggest that glass produced by such events should, therefore, be more common in the rock record than impact craters, assuming that the glass formed in a suitable preserving environment.  相似文献   

Quasi-periodic patterns coupling the Sun,solar wind and the Earth     

《Journal of Atmospheric and Solar》2008,70(17):2112-2117

The spectrum of velocity and magnetic fields in the solar wind is self-similar (power-law type) in the frequency range greater than >1/day indicating well-mixed turbulence. But it loses self-similarity for lower frequencies indicating the presence of large-scale patterns, which are intermittently generated inside the Sun and propagate from the Sun to the Earth.Here we discuss the spatia–temporal characteristics and origin of the 1.3-year quasi-periodic pattern found inside the Sun by helioseismic methods and detected in the solar wind. To identify and characterize this pattern on the Sun we use time series of solar magnetic Carrington maps generated at the Wilcox Solar Observatory and independent component data analysis. This analysis shows the latitudinal distribution of the pattern, its variable frequency and intermittent appearance.  相似文献   

The mobility of radium-226 and trace metals in pre-oxidized subaqueous uranium mill tailings     

《Applied Geochemistry》2003,18(7):1095-1110

The exchange of ²²⁶Ra and trace metals across the tailings-water interface and the mechanisms governing their mobility were assessed via sub-centimetre resolution profiling of dissolved constituents across the tailings–water interface in Cell 14 of the Quirke Waste Management Area at Rio Algom's Quirke Mine, near Elliot Lake, Ontario, Canada. Shallow zones (<1.5 m water depth) are characterized by sparse filamentous vegetation, well-mixed water columns and fully oxygenated bottom waters. Profiles of dissolved O₂, Fe and Mn indicate that the tailings deposits in these areas are sub-oxic below tailings depths of ∼3 cm. These zones exhibit minor remobilization of Ra in the upper 5 cm of the tailings deposit; ²²⁶Ra fluxes at these sites are relatively small, and contribute negligibly to the water column activity of ²²⁶Ra. The shallow areas also exhibit minor remobilization of Ni, As, Mo and U. The release of these elements to the water cover is, however, limited by scavenging mechanisms in the interfacial oxic horizons. The presence of thick vegetation (Chara sp.) in the deeper areas (>2 m water depth) fosters stagnant bottom waters and permits the development of anoxia above the benthic boundary. These anoxic tailings are characterized by substantial remobilization of ²²⁶Ra, resulting in a relatively large flux of ²²⁶Ra from the tailings to the water column. The strong correlation between the porewater profiles of ²²⁶Ra and Ba (r²=0.99), as well as solubility calculations, indicate that the mobility of Ra is controlled by saturation with respect to a poorly ordered and/or impure barite phase [(Ra,Ba)SO₄]. In the anoxic zones, severe undersaturation with respect to barite is sustained by microbial SO₄ reduction. Flux calculations suggest that the increase in ²²⁶Ra activity in the water cover since 1995 (from <0.5 to 2.5 Bq l⁻¹) can be attributed to an increase in the spatial distribution of anoxic bottom waters caused by increased density of benthic flora. The anoxic, vegetated areas also exhibit minor remobilization with respect to dissolved As, Ni and Zn. The removal of trace metals in the anoxic bottom waters appears to be limited by the availability of free sulphide. Collectively, the data demonstrate that while the water cover over the U mill tailings minimizes sulphide oxidation and metal mobility, anoxic conditions which have developed in deeper areas have led to increased mobility of ²²⁶Ra.  相似文献   

Evidence for scavenging by the marine crocodile Metriorhynchus on the carcass of a plesiosaur     

《Proceedings of the Geologists' Association. Geologists' Association》2003

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