<?xml version="1.0" encoding="UTF-8"?><xml><records><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>17</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Dubbert, Maren</style></author><author><style face="normal" font="default" size="100%">Cuntz, Matthias</style></author><author><style face="normal" font="default" size="100%">Piayda, Arndt</style></author><author><style face="normal" font="default" size="100%">Máguas, Cristina</style></author><author><style face="normal" font="default" size="100%">Werner, Christiane</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">Partitioning evapotranspiration – Testing the Craig and Gordon model with field measurements of oxygen isotope ratios of evaporative fluxes</style></title><secondary-title><style face="normal" font="default" size="100%">Journal of Hydrology</style></secondary-title></titles><keywords><keyword><style  face="normal" font="default" size="100%">Craig and Gordon</style></keyword><keyword><style  face="normal" font="default" size="100%">evaporation</style></keyword><keyword><style  face="normal" font="default" size="100%">Evapotranspiration</style></keyword><keyword><style  face="normal" font="default" size="100%">Kinetic fractionation</style></keyword><keyword><style  face="normal" font="default" size="100%">Laser spectroscopy</style></keyword><keyword><style  face="normal" font="default" size="100%">Stable oxygen isotopes</style></keyword></keywords><dates><year><style  face="normal" font="default" size="100%">2013</style></year><pub-dates><date><style  face="normal" font="default" size="100%">2013///</style></date></pub-dates></dates><urls><web-urls><url><style face="normal" font="default" size="100%">http://www.sciencedirect.com/science/article/pii/S0022169413004083</style></url></web-urls></urls><volume><style face="normal" font="default" size="100%">496</style></volume><pages><style face="normal" font="default" size="100%">142 - 153</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">su mmary Stable oxygen isotopes of water provide a valuable tracer for water movements within ecosystems and are used to estimate the contribution of transpiration to total ecosystem evapotranspiration (ft). We tested the Craig and Gordon equation against continuous field measurements of isotopic composition of evaporation and assessed the impact for partitioning evapotranspiration. Therefore, evaporation (E) and its isotopic signature (d18OE) on bare soil plots, as well as evapotranspiration (ET) and its correspond- ing isotopic composition of (d18OET) of an herbaceous layer was measured with a cavity ring-down spec- trometer connected to a soil chamber on a field site in central Portugal. We quantified the variation in d18OE arising from uncertainties in the determination of environmental input variables to the Craig and Gordon equation: the isotope signature (d18Oe) and the temperature at the evaporating site (Te), and the kinetic fractionation factor (ak). We could hence quantify ft based on measured d18OET, modeled d18OE from observed soil water isotopic composition at the evaporating site (d18Oe), and modeled d18O of transpiration (d18OT) from observed total soil water isotopic composition. Our results demonstrate that predicting d18OE using the Craig and Gordon equation leads to good agree- ment with measured d18OE given that the temperature and 18O isotope profiles of the soil are thoroughly characterized. However, modeled d18OE is highly sensitive to changes in Te and d18Oe as well as ak. This markedly affected the partition results of transpiration and evaporation from the total ET flux: The frac- tion of transpiration (ft) varied strongly using different formulations for ak and assuming steady or non- steady state transpiration. These findings provide a first comparison of laser-based and modeled isotopic compositions of evaporation based on the Craig and Gordon equation under field conditions. This is of special interest for studies using stable isotopes to separate soil evaporation and plant transpiration fluxes and highlights the need for a thorough characterization of the micrometeorological and isotopic constitution of the upper soil layer to locate the evaporating front with a resolution of a few cm soil depths. We also call on a better characterization of the kinetic fractionation factor of soil evaporation.</style></abstract></record><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>17</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Baldocchi, Dennis D.</style></author><author><style face="normal" font="default" size="100%">Xu, Liukang</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">What limits evaporation from Mediterranean oak woodlands – The supply of moisture in the soil, physiological control by plants or the demand by the atmosphere?</style></title><secondary-title><style face="normal" font="default" size="100%">Advances in Water Resources</style></secondary-title></titles><keywords><keyword><style  face="normal" font="default" size="100%">ecohydrology</style></keyword><keyword><style  face="normal" font="default" size="100%">evaporation</style></keyword><keyword><style  face="normal" font="default" size="100%">quercus douglasii</style></keyword><keyword><style  face="normal" font="default" size="100%">savanna</style></keyword><keyword><style  face="normal" font="default" size="100%">Transpiration</style></keyword></keywords><dates><year><style  face="normal" font="default" size="100%">2007</style></year><pub-dates><date><style  face="normal" font="default" size="100%">2007///</style></date></pub-dates></dates><urls><web-urls><url><style face="normal" font="default" size="100%">http://linkinghub.elsevier.com/retrieve/pii/S0309170807000577</style></url></web-urls></urls><volume><style face="normal" font="default" size="100%">30</style></volume><pages><style face="normal" font="default" size="100%">2113 - 2122</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">The prediction of evaporation from Mediterranean woodland ecosystems is complicated by an array of climate, soil and plant factors. To provide a mechanistic and process-oriented understanding, we evaluate theoretical and experimental information on water loss of Mediterranean oaks at three scales, the leaf, tree and woodland. We use this knowledge to address: what limits evaporation from Mediterranean oak woodlands – the supply of moisture in the soil, physiological control by plants or the demand by the atmosphere? The Mediterranean climate is highly seasonal with wet winters and hot, dry summers. Consequently, available sunlight is in surplus, causing potential evaporation to far exceed available rainfall on an annual basis. Because the amount of precipitation to support woody plants is marginal, Mediterranean oaks must meet their limited water supply by a variety of means. They do so by: (1) constraining the leaf area index of the landscape by establishing a canopy with widely spaced trees; (2) reducing the size of individual leaves; (3) by adopting physiological characteristics that meter the use of water (e.g. regulating stomatal, leaf nitrogen/photosynthetic capacity and/or hydraulic conductance); (4), by tapping deep supplies of water in the soil; (5) and/or by adopting a deciduous life form, which reduces the time interval that the vegetation transpires.</style></abstract><issue><style face="normal" font="default" size="100%">10</style></issue></record><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>17</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Baldocchi, Dennis D.</style></author><author><style face="normal" font="default" size="100%">Xu, Liukang</style></author><author><style face="normal" font="default" size="100%">Kiang, Nancy</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">How plant functional-type, weather, seasonal drought, and soil physical properties alter water and energy fluxes of an oak–grass savanna and an annual grassland</style></title><secondary-title><style face="normal" font="default" size="100%">Agricultural and Forest Meteorology</style></secondary-title></titles><keywords><keyword><style  face="normal" font="default" size="100%">Biosphere–atmosphere interactions</style></keyword><keyword><style  face="normal" font="default" size="100%">ecohydrology</style></keyword><keyword><style  face="normal" font="default" size="100%">evaporation</style></keyword></keywords><dates><year><style  face="normal" font="default" size="100%">2004</style></year><pub-dates><date><style  face="normal" font="default" size="100%">2004///</style></date></pub-dates></dates><urls><web-urls><url><style face="normal" font="default" size="100%">http://linkinghub.elsevier.com/retrieve/pii/S0168192303002739</style></url></web-urls></urls><volume><style face="normal" font="default" size="100%">123</style></volume><pages><style face="normal" font="default" size="100%">13 - 39</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">Savannas and open grasslands often co-exist in semi-arid regions. Questions that remain unanswered and are of interest to biometeorologists include: how do these contrasting landscapes affect the exchanges of energy on seasonal and annual time scales; and, do biophysical constraints imposed by water supply and water demand affect whether the land is occupied by open grasslands or savanna? To address these questions, and others, we examine how a number of abiotic, biotic and edaphic factors modulate water and energy ﬂux densities over an oak–grass savanna and an annual grassland that coexist in the same climate but on soils with different hydraulic properties. The net radiation balance was greater over the oak woodland than the grassland, despite the fact that both canopies received similar sums of incoming short and long wave radiation. The lower albedo and lower radiative surface temperature of the transpiring woodland caused it to intercept and retain more long and shortwave energy over the course of the year, and particularly during the summer dry period. The partitioning of available energy into sensible and latent heat exchanged over the two canopies differed markedly. The annual sum of sensible heat exchange over the woodland was 40% greater than that over the grassland (2.05 GJ m−2 per year versus 1.46 GJ m−2 per year). With regards to evaporation, the oak woodland evaporated about 380 mm of water per year and the grassland evaporated about 300 mm per year. Differences in available energy, canopy roughness, the timing of physiological functioning, water holding capacity of the soil and rooting depth of the vegetation explained the observed differences in sensible and latent heat exchange of the contrasting vegetation surfaces. The response of canopy evaporation to diminishing soil moisture was quantiﬁed by comparing normalized evaporation rates (in terms of equilibrium evaporation) with soil water potential and volumetric water content measurements. When soil moisture was ample normalized values of latent heat ﬂux density were greater for the grassland (1.1–1.2) than for the oak savanna (0.7–0.8) and independent of moisture content. Normalized rates of evaporation over the grassland declined as volumetric water content dropped below 0.15 m3 m−3 , which corresponded with a soil water potential of −1.5 MPa. The grassland senesced and quit transpiring when the volumetric water content of the soil dropped below −2.0 MPa. The oak trees, on the other hand, were able to transpire, albeit at low rates, under very dry soil conditions (soil water potentials below −4.0 MPa). The trees were able to endure such low water potentials and maintain basal levels of metabolism because ecological forcings kept the tree density and leaf area index of the woodland low, physiological factors forced the stomata to close progressively and the trees were able to tap deeper water sources (below 0.6 m) than the grasses.</style></abstract><issue><style face="normal" font="default" size="100%">1-2</style></issue></record></records></xml>