Vegetation water sources in California's Sierra Nevada (USA) are young and change over time,a multi-isotope (δ18O, δ2H, 3H) tracer approach.     

Melissa Thaw  Ate Visser  Richard Bibby  Amanda Deinhart  Erik Oerter  Martha Conklin 《水文研究》2021,35(6):e14249

Sierra Nevada forests transpire a significant amount of California's water resources, sparking interest in applying forest management to improve California's water supply. Determining the source water of evapotranspiration enables forest managers to make informed decisions. To this end, a significant interest in critical zone science is to develop new methods to work across time scales to predict subsurface water storage and use. In this study, forest vegetation accessed young water and switched sources depending on availability, suggesting that forest drought vulnerability may depend on the range of water sources available (rain, snowmelt and deeply stored water). This finding also suggests that changes in transpiration rates may have immediate effects on water sources in close proximity to vegetation, and delayed effects on storage and runoff. New δ¹⁸O, δ²H and ³H data were used to track precipitation, runoff, evapotranspiration and storage through the critical zone seasonally, including seasons where evapotranspiration and snowmelt were in phase (winter snowmelt) and out of phase (seasonally dry summer). The main source of this headwater catchment's runoff is derived from its meadow saturated zone water, which was dominated by snowmelt. Water that originated as snowmelt contributed to transpiration, unless other sources, such as recent rain, became available. In cases where xylem δ¹⁸O and δ²H signatures matched those of deeper saturated zone water, ³H data showed that xylem water was distinctly younger than the deep saturated zone water. During 2016, which experienced relatively normal snowpack in winter and seasonally dry summer conditions, mean summer saturated zone water and vegetation water were similar in δ¹⁸O, −12.4 ± 0.04 ‰ and − 12.5 ± 0.3 ‰, respectively, but were distinctly different in ³H, 5.5 ± 0.2 pCi/L and 13.7 ± 1.1 pCi/L, respectively. While δ¹⁸O shows that vegetation and meadow saturated zone water have similar origins, ³H shows they have dissimilar ages.  相似文献   

Lumped surface and sub‐surface runoff for erosion modeling within a small hilly watershed in northern Vietnam          下载免费PDF全文

Yen Tan Bui  D. Orange  S. M. Visser  Chu Thai Hoanh  M. Laissus  A. Poortinga  Duc Toan Tran  L. Stroosnijder 《水文研究》2014,28(6):2961-2974

Developing models to predict on‐site soil erosion and off‐site sediment transport at the agricultural watershed scale represent an on‐going challenge in research today. This study attempts to simulate the daily discharge and sediment loss using a distributed model that combines surface and sub‐surface runoffs in a small hilly watershed (< 1 km²). The semi‐quantitative model, Predict and Localize Erosion and Runoff (PLER), integrates the Manning–Strickler equation to simulate runoff and the Griffith University Erosion System Template equation to simulate soil detachment, sediment storage and soil loss based on a map resolution of 30 m × 30 m and over a daily time interval. By using a basic input data set and only two calibration coefficients based, respectively, on water velocity and soil detachment, the PLER model is easily applicable to different agricultural scenarios. The results indicate appropriate model performance and a high correlation between measured and predicted data with both Nash–Sutcliffe efficiency (Ef) and correlation coefficient (r²) having values > 0.9. With the simple input data needs, PLER model is a useful tool for daily runoff and soil erosion modeling in small hilly watersheds in humid tropical areas. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Historical influence of soil and water management on sediment and carbon budgets in the United States     

Eric T. Sundquist  Katherine Visser Ackerman  Robert F. Stallard  Norman B. Bliss 《Applied Geochemistry》2011

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Mechanics of interrill erosion with wind‐driven rain     

Gunay Erpul  Donald Gabriels  L. Darrell Norton  Dennis C. Flanagan  Chi‐hua Huang  Saskia M. Visser 《地球表面变化过程与地形》2013,38(2):160-168

The vector physics of wind‐driven rain (WDR) differs from that of wind‐free rain, and the interrill soil detachment equations in the Water Erosion Prediction Project (WEPP) model were not originally developed to deal with this phenomenon. This article provides an evaluation of the performance of the interrill component of the WEPP model for WDR events. The interrill delivery rates were measured in the wind tunnel facility of the International Center for Eremology (ICE), Ghent University, Belgium with an experimental setup to study different raindrop impact velocity vectors. Synchronized wind and rain simulations with wind velocities of 6, 10 and 14 m s^–1 were applied to a test surface placed on windward and leeward slopes of 7, 15 and 20%. Since both rainfall intensity and raindrop impact velocity varied greatly depending on differences in the horizontal wind velocity under WDRs, the resultant kinetic energy flux (KE_r, in J m^–2 s^–1) was initially used in place of the WEPP model intensity term in order to incorporate the effect of wind on impact velocity and frequency of raindrops. However, our results showed only minor improvement in the model predictions. For all research data, the model Coefficients of Determination (r²) were 0·63 and 0·71, when using the WEPP and the KE_r approaches, respectively. Alternately, integrating the angle of rain incidence into the model by vectorally partitioning normal kinetic energy flux (KE_rn, in J m^–2 s^–1) from the KE_r greatly improved the model's ability to estimate the interrill sediment delivery rates (r² = 0·91). This finding suggested that along with the fall trajectory of wind‐driven raindrops with a given frequency, raindrop velocity and direction at the point of impact onto the soil surface provided sufficient physical information to improve WEPP sediment delivery rate predictions under WDR. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Global anisotropic phase velocity maps for higher mode Love and Rayleigh waves   总被引：1，自引：0，他引：1  

K. Visser  J. Trampert  B. L. N. Kennett 《Geophysical Journal International》2008,172(3):1016-1032

It is well established that the Earth's uppermost mantle is anisotropic, but there are no clear observations of anisotropy in the deeper parts of the mantle. Surface waves are well suited to observe anisotropy since they carry information about both radial and azimuthal anisotropy. Fundamental mode surface waves, for commonly used periods up to 200 s, are sensitive to structure in the first few hundred kilometres, and therefore, do not provide information on anisotropy below. Higher mode surface waves have sensitivities that extend to and beyond the transition zone, and should thus give insight about azimuthal anisotropy at greater depths. We have measured higher mode Love and Rayleigh phase velocities using a model space search approach, which provides us with consistent relative uncertainties from measurement to measurement and from mode to mode. From these phase velocity measurements, we constructed global anisotropic phase velocity maps. Prior to inversion, we determine the optimum relative weighting for anisotropy. We present global azimuthal phase velocity maps for higher mode Rayleigh waves (up to the sixth higher mode) and Love waves (up to the fifth higher mode) with corresponding average model uncertainties. The anisotropy we derive is robust within the uncertainties for all modes. Given the ray theoretical sensitivity kernels of Rayleigh and Love wave modes, the source of anisotropy is complex, but mainly located in the asthenosphere and deeper. Our models show a good correspondence with other studies for the fundamental mode, but we have been able to achieve higher resolution.  相似文献   

Melanistic southern right‐whale dolphins (Lissodelphis peronii) off Kaikoura,New Zealand,with records of other anomalously all‐black cetaceans     

Ingrid N. Visser  Dagmar Fertl  L. Todd Pusser 《新西兰海洋与淡水研究杂志》2013,47(5):833-836

Reports of anomalously pigmented cetaceans, including melanistic (all‐black) individuals are infrequent. We observed four melanistic southern right‐whale dolphins (Lissodelphis peronii) including a calf, off Kaikoura (42°34'S, 173°50'E), New Zealand. We also compiled records of melanistic individuals from five other species of cetaceans. The ecological context of melanistic pigmentation of cetaceans is not well understood; however, it may increase heat absorption, affect ability to capture prey, impair visual/social communication, and/or increase conspicuousness to predators.  相似文献   

The impact of a severe drought on the vegetation of a subtropical estuary     

Jenneke M. Visser  Charles E. Sasser  Robert H. Chabreck  R. Greg Linscombe 《Estuaries and Coasts》2002,25(6):1184-1195

In order to document the effect of the recent drought and the resulting marine intrusion event on plant-community shifts in a Louisiana estuary, we analyzed two vegetation data sets collected in Barataria estuary in 1997 and 2000 and compared community shifts to surface salinity changes at four points along the estuarine gradient within the study area. We used the major vegetation types identified in our previous research of larger data sets and tested the use of a simple vegetation classification technique. This vegetation classification technique is based primarily on the dominant and co-dominant species, and secondarily on the number of taxa observed. To distinguish vegetation types with similar dominant species but different associated species, the vegetation classification technique used a salinity score derived from the species composition. Surface water salinity increases were reflected by a change in species composition in the mesohaline to fresh marshes. The largest species composition shift observed was the shift from oligohaline wiregrass (species rich vegetation type dominated bySpartina patens) to mesohaline wiregrass (vegetation type dominated byS. patens with few other species). Shifts in vegetation composition may have been enhanced by the presence of the major dominant species at a low abundance in other vegetation types. The vegetation classification technique used could classify over 95% of the stations. This vegetation classification technique provides a simple method to classify Louisiana's coastal vegetation based on plant species composition.  相似文献   

Techniques for simultaneous quantification of wind and water erosion in semi-arid regions   总被引：3，自引：0，他引：3  

S. M. Visser  G. Sterk  O. Ribolzi 《Journal of Arid Environments》2004,59(4):699-717

Wind and water erosion are usually studied as two separate processes. However, in semi-arid zones both processes contribute significantly to soil degradation. Whereas for water erosion the direction of sediment transport is controlled by topography, in wind erosion the direction of transport is controlled by the wind direction. Furthermore, the spatial pattern of erosion and deposition for wind erosion is determined by the spatial distribution of source material, soil erodibility factors and non-erodible roughness elements. Given this difference in dependence on topography, different approaches are needed to determine the mass balance for a given area. For water erosion, the research area has to be defined such that no input of sediment occurs, whereas in wind erosion the input and output fluxes of sediment should be measured, or a non-eroding boundary should be created.In semi-arid regions, wind erosion events are often followed immediately by heavy rain. As wind and water erosion occur almost simultaneously at the same site, the effect of wind and water erosion at a given site should be studied concurrently. To do so, a number of measurement techniques with different spatial and temporal scales are necessary. The research should be started at the scale of a Sahelian field. For a complete insight into the processes at a site, the research should include measurement techniques that quantify the impact of wind and water erosion separately and techniques that quantify their combined effect.  相似文献   

A Pan-African core complex in the Sinai,Egypt     

Blasband  B.  Brooijmans  P.  Dirks  P.  Visser  W.  White  S. 《Geologie en Mijnbouw》1997,76(3):247-266

In the late Precambrian history of the Wadi Kid area in the Sinai, Egypt, two deformation phases are clearly recognized. The first phase, D₁ (pre-620 Ma), produced a steep regional foliation, axial planar to upright F₁ folds, in rocks of a lower-greenschist grade. This compressional phase of deformation is interpreted in terms of subduction in an island-arc setting. The second phase, D₁ (post-620 Ma), is mainly expressed by the widespread development of sub-horizontal mylonitic zones with a total thickness of 1.5 km. Shear sense indicators give a consistent regional transport direction to the northwest, with local indications of reversal to the southeast. This event is associated with regional LP/HT metamorphism, indicative of high thermal gradients. Because of the LP/HT metamorphism, the change in geochemical nature of the granitoids, and the orientation of the dykes, we interpret the mylonitic zones as low-angle normal shear zones related to core-complex development during an extensional event with the transport reversal being induced by doming. We postulate that orogenic collapse was responsible for the transition from the D₁ compressional phase to the D₁ extensional phase.  相似文献   

Fluorine-bearing hydrogarnets from Blengsvatn,Bamble Sector,south Norway     

Dr. D. Visser 《Mineralogy and Petrology》1993,47(2-4):209-218

Summary Hydrograndites (grossular-andradite) with up to 1.60 weight percent fluorine occur in altered parts of andesine-garnet-biotite-cummingtonite-hornblende rocks, Blengsvatn, Bamble Sector, south Norway. The garnets occur intergrown with secondary prehnite, pumpellyite, epidote and chlorite along biotite cleavage planes and formed through retrogradation of nearby plagioclase, almandine-rich garnet and hornblende. The conditions of formation are estimated at about 300°C and 1–2 kbar. The observed F/OH distribution at 300°C and calculated relatively low fHF/fH₂O ratios of 10^–5.84 to 10^–7.32 indicates that fluorine is more strongly partitioned relative to OH in hydrogarnet than coexisting biotite and cummingtonite. The low fHF/fH₂O ratios suggest that fluorinebearing hydrogarnets could be very common.

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Fluorhaltige Hydrogranate von Blengsvatn, Bezirk Bamble, Südnorwegen

Zusammenfassung Fluorhaltige Hydrograndite (Grossular-Andradit) mit bis zu 1,60 Gew.% Fluor kommen in umgewandelten Teilen von Andesin-Granat-Biotit-Cummingtonit-HornblendeGesteinen von Blengsvatn, Bezirk Bamble, Südnorwegen, vor. Die Granate treten verwachsen mit sekundärem Prehnit, Pumpellyit, Epidot und Chlorit längs Biotitspaltflächen auf und bildeten sich durch retrograden Abbav von benachbartem Plagioklas, Almandin-reichem Granat und Hornblende. Die Bildungsbedingungen werden auf ungefähr 300°C und 1–2 kbar geschätzt. Die beobachtete F/OH-Verteilung und die relativ niedrigen berechneten fHF/fH₂OQuotienten von 10^–5.84 bis 10^–7.32 weisen darauf hin, daß Fluor relativ zu OH stärker in Hydrogranat als in koexistierendem Biotit und Cummingtonit angereichert ist. Die fHF/fH₂O-Verhältnisse lassen vermuten, daß fluorhaltige Hydrogranate sehr verbreitet sein könnten.

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With 5 Figures  相似文献