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91.
John C. Panuska Laura Ward Good Peter A. Vadas Dennis L. Busch Asli Ozkaynak 《水文研究》2011,25(15):2329-2338
Phosphorus (P) export from agricultural lands above known threshold levels can result in adverse impacts to receiving water quality. Phosphorus loss occurs in dissolved and sediment‐bound, or particulate phosphorous (PP), forms, with the latter often dominating losses from row‐cropped systems. To target practices, land managers need good computer models and model developers need good monitoring data. Sediment monitoring data (e.g. radiometric finger printing and sediment P sorption capacity) can help identify sediment source areas and improve models, but require more sediment mass than is typically obtained by automatic sampling. This study compares a simple suspended sediment sampler developed at the University of Exeter (UE) with automatic sampling in intermittent channels draining corn and alfalfa fields. The corn field had a greater runoff coefficient (27%) than alfalfa (11%). No differences were found in enrichment ratios (sediment constituent/soil constituent) in PP (PPER) or percent loss on ignition (LOIER) between paired UE samplers on corn. The median LOIER for the UE samplers (1·9%) did not differ significantly (p > 0·13) from the automatic sampler (2·0%). The PPER from the UE samplers was on average 20% lower than the automatic samplers. A correlation (r2 = 0·75) was found between sediment PP and % LOI from automatic samplers and UE samplers for particles < 50 µm, while for > 50 µm PP concentration did not change with changes in % LOI. Sediment ammonium‐oxalate extractable metals were similarly related to LOI, with the strongest correlation for iron (r2 = 0·71) and magnesium (r2 = 0·70). Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
92.
Javier Tomasella Laura S. Borma José A. Marengo Daniel A. Rodriguez Luz A. Cuartas Carlos A. Nobre Maria C. R. Prado 《水文研究》2011,25(8):1228-1242
Severe hydrological droughts in the Amazon have generally been associated with strong El Niño events. More than 100 years of stage record at Manaus harbour confirms that minimum water levels generally coincide with intense warming in the tropical Pacific sea waters. During 2005, however, the Amazon experienced a severe drought which was not associated with an El Niño event. Unless what usually occurs during strong El Niño events, when negative rainfall anomalies usually affect central and eastern Amazon drainage basin; rainfall deficiencies in the drought of 2005 were spatially constrained to the west and southwest of the basin. In spite of this, discharge stations at the main‐stem recorded minimum water levels as low as those observed during the basin‐wide 1996–1997 El Niño‐related drought. The analysis of river discharges along the main‐stem and major tributaries during the drought of 2004–2005 revealed that the recession on major tributaries began almost simultaneously. This was not the case in the 1996–1997 drought, when above‐normal contribution of some tributaries for a short period during high water was crucial to partially counterbalance high discharge deficits of the other tributaries. Since time‐lagged contributions of major tributaries are fundamental to damp the extremes in the main‐stem, an almost coincident recession in almost all tributaries caused a rapid decrease in water discharges during the 2005 event. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
93.
Johan Holmberg Chris Flynn Laura Portinari 《Monthly notices of the Royal Astronomical Society》2006,367(2):449-453
We compile a sample of Sun-like stars with accurate effective temperatures, metallicities and colours (from the ultraviolet to the near-infrared). A crucial improvement is that the effective temperature scale of the stars has recently been established as both accurate and precise through direct measurement of angular diameters obtained with stellar interferometers. We fit the colours as a function of effective temperature and metallicity, and derive colour estimates for the Sun in the Johnson–Cousins, Tycho, Strömgren, 2MASS and SDSS photometric systems. For ( B − V )⊙ , we favour the 'red' colour 0.64 versus the 'blue' colour 0.62 of other recent papers, but both values are consistent within the errors; we ascribe the difference to the selection of Sun-like stars versus interpolation of wider colour– T eff –metallicity relations. 相似文献
94.
Young Nathan L. Lemieux Jean-Michel Locat Pascal Demers Denis Delottier Hugo Mony Laura 《Hydrogeology Journal》2022,30(4):1337-1344
Hydrogeology Journal - An extensive network of multilevel vibrating-wire piezometers (VWP) was recently created to monitor the spatial and temporal variation of pore pressure (and hydraulic head)... 相似文献
95.
Annemarie Christophersen Nicola Litchfield Kelvin Berryman Richard Thomas Roberto Basili Laura Wallace William Ries Gavin P. Hayes Kathleen M. Haller Toshikazu Yoshioka Richard D. Koehler Dan Clark Monica Wolfson-Schwehr Margaret S. Boettcher Pilar Villamor Nick Horspool Teraphan Ornthammarath Ramon Zuñiga Robert M. Langridge Mark W. Stirling Tatiana Goded Carlos Costa Robert Yeats 《Natural Hazards》2015,79(1):111-135
96.
97.
98.
The aim of this paper is to investigate different aspects of the seasonal-to-interannual temperature variability in Eastern Patagonia, the southernmost area of South America, east of the Andes Cordillera. Homogenous regions of seasonal variability and the atmospheric circulation patterns associated with warm and cold conditions in each of them are described in this study. Relationships between temperature in Eastern Patagonia and that registered in other areas of southern South America are also addressed. Results show that the northern and southern areas of Eastern Patagonia have different temperature variability in summer and autumn whereas the temperature variability tends to be more homogeneous within the region during winter and spring. Warm (cold) conditions in the northern areas are associated with reinforced (weakened) westerlies in summer, winter and spring whereas northerly (southerly) advections of warm (cold) air toward the region produce such conditions in autumn. Temperature in the southern portion of Eastern Patagonia is affected by anticyclonic (cyclonic) anomalies that enhance (reduce) the incoming solar radiation and induce reinforced (weakened) westerlies promoting warm (cold) conditions in the region. Furthermore, cyclonic (anticyclonic) anomalies at subpolar latitudes hinder (favor) outbreaks of cold air increasing (decreasing) the temperature over areas of Eastern Patagonia. The circulation anomalies associated with warm (cold) conditions in Eastern Patagonia also promote cold (warm) conditions over areas of northern Argentina, Paraguay and southern Brazil. Consequently, a dipole of temperature is detected in southern South America with centers of opposite sign over these regions. 相似文献
99.
Javier Tomasella Patrícia F. Pinho Laura S. Borma José A. Marengo Carlos A. Nobre Olga R. F. O. Bittencourt Maria C. R. Prado Daniel A. Rodriguez Luz A. Cuartas 《Climatic change》2013,116(3-4):723-746
It is well known that most of the severe droughts in Amazonia, such as that of 1997, are El Niño-related. However, in 2005, the Amazon was affected by a severe drought that was not El Niño-related, as most of the rainfall anomalies that have happened in southwestern Amazonia are driven by sea surface temperature anomalies in the tropical North Atlantic. Earlier studies have analyzed both droughts in terms of their meteorological causes and impacts in terra firme (non-flooded) forests. This study compares the hydrological effects of both droughts on the Amazonian floodplain and discusses their potential ecological and human impacts based on an extensive literature review. The results revealed that the effects of the 2005 drought were exacerbated because rainfall was lower and evaporation rates were higher at the peak of the dry season compared to the 1997 drought. This induced a more acute depletion of water levels in floodplain lakes and was most likely associated with higher fish mortality rates. Based on the fact that the stem growth of many floodplain species is related to the length of the non-flooded period, it is hypothesized that the 1997 drought had more positive effects on floodplain forest growth than the 2005 drought. The fishing community of Silves in central Amazonia considered both droughts to have been equally severe. However, the 2005 drought was widely broadcasted by the press; therefore, the governmental mitigation efforts were more comprehensive. It is suggested that the availability of new communication technology and greater public awareness regarding environmental issues, combined with the new legal framework for assessing the severity of calamities in Brazil, are among the primary factors that explain the difference in societal response between the two droughts. 相似文献
100.
Osvaldo M. Rabbia Laura B. Hernández David H. French Robert W. King John C. Ayers 《Mineralium Deposita》2009,44(8):849-866
Mineralogical, textural, and chemical analyses (EPMA and PIXE) of hydrothermal rutile in the El Teniente porphyry Cu–Mo deposit
help to better constrain ore formation processes. Rutile formed from igneous Ti-rich phases (sphene, biotite, Ti-magnetite,
and ilmenite) by re-equilibration and/or breakdown under hydrothermal conditions at temperatures ranging between 400°C and
700°C. Most rutile nucleate and grow at the original textural position of its Ti-rich igneous parent mineral phase. The distribution
of Mo content in rutile indicates that low-temperature (∼400–550°C), Mo-poor rutile (5.4 ± 1.1 ppm) is dominantly in the Mo-rich
mafic wallrocks (high-grade ore), while high-temperature (∼550-700°C), Mo-rich rutile (186 ± 20 ppm) is found in the Mo-poor
felsic porphyries (low-grade ore). Rutile from late dacite ring dikes is a notable exception to this distribution pattern.
The Sb content in rutile from the high-temperature potassic core of the deposit to its low-temperature propylitic fringe remains
relatively constant (35 ± 3 ppm). Temperature and Mo content of the hydrothermal fluids in addition to Mo/Ti ratio, modal
abundance and stability of Ti-rich parental phases are key factors constraining Mo content and provenance in high-temperature
(≥550°C) rutile. The initial Mo content of parent mineral phases is controlled by melt composition and oxygen fugacity as
well as timing and efficiency of fluid–melt separation. Enhanced reduction of SO2-rich fluids and sulfide deposition in the Fe-rich mafic wallrocks influences the low-temperature (≤550°C) rutile chemistry.
The data are consistent with a model of fluid circulation of hot (>550°C), oxidized (ƒO2 ≥ NNO + 1.3), SO2-rich and Mo-bearing fluids, likely exsolved from deeper crystallizing parts of the porphyry system and fluxed through the
upper dacite porphyries and related structures, with metal deposition dominantly in the Fe-rich mafic wallrocks. 相似文献