385 research outputs found
Sap flow and water transfer in the Garonne river riparian woodland, France : first results on poplar and willow
No full textThis work is the first attempt at using Granier sap sensors on Populus nigra, Populus x euramericana cv I45/51 and Salix alba for the monitoring of sap flows in an active floodplain over two consecutive years. The main characteristic of these diffuse porous trees is their capacity to use several tree rings for xylem sap transfer. Results showed that the sap flux densities remained homogeneous on the external 4 cm of the trunk, then decreased with depth. For young trees, the active sapwood can represent half of the trunk. Results indicated that in the same environment and at the same age, daily differences existed between the two major native riparian tree species, the black poplar and the white willow. Their maximal sap flux density (2.6-3.6 dm 3 dm -2 h -1) was similar to other fast growing trees. The influence of age was the third important screened factor. Sap flow measurements over several months indicated that water uptake was variable throughout the season, depending on water availability, and was more pronounced for older trees. The sap flux densities for the planted poplar (I45/51) ranged from 2.2-2.6 dm 3 dm -2 h -1 (about 90 dm 3 day -1) in the wetter spring conditions and dropped to 1.6-1.7 dm 3 dm -2 h -1 (about 60 dm 3 day -1) in less favourable conditions. Under the worst conditions, e.g., the especially long drought in the summer of 1998, these values dropped to 1.0-1.2 (about 40 dm 3 day -1), and even to 0.35 dm 3 dm -2 h -1 (about 12 dm 3 day -1) for a few days. Complementary long-term studies are needed to better understand the complex sap flow changes and to be able to relate them to significant environmental factors. Priority should be given to the long-term monitoring of sap flows at different depths for a correct estimation of actual daily water uptakes by riparian softwood trees
Interactions between groundwater and surface water at river banks and the confluence of rivers
No full textRiparian vegetation depends on hydrological resources and has to adapt to changes in water levels and soil moisture conditions. The origin and mixing of water in the streamside corridor were studied in detail. The development of riparian woodland often reflects the evolution of hydrological events. River water levels and topography are certainly the main causes of the exchange between groundwater and river water through the riverbank. Stable isotopes, such as 18O, are useful tools that allow water movement to be traced. Two main water sources are typically present: (i) river water, depleted of heavy isotopes, originating upstream, and (ii) groundwater, which comes mainly from the local rainfall. On the Garonne River bank field site downstream of Toulouse, the mixing of these two waters is variable, and depends mainly on the river level and the geographical position. The output of the groundwater into the river water is not diffuse on a large scale, but localised at few places. At the confluence of two rivers, the water-mixing area is more complex because of the presence of a third source of water. In this situation, groundwater supports the hydrologic pressure of both rivers until they merge, this pressure could influence its outflow. Two cases will be presented. The first is the confluence of the Garonne and the Ariège Rivers in the south-west of France, both rivers coming from the slopes of the Pyrénées mountains. Localised groundwater outputs have been detected about 200 m before the confluence. The second case presented is the confluence of the Ganges and the Yamuna Rivers in the north of India, downstream of the city of Allahabad. These rivers are the two main tributaries of the Ganges, and both originate in the Himalayas. A strong stream of groundwater output was measured at the point of confluence
Daily variations of water use with vapor pressure deficit in a plantation of I214 poplars.
No full textDaily rates of whole tree water use were measured in a homogeneous 7-year-old plantation over 84 days. Two trees were selected in the two most contrasting ends, i.e., with mean water table at -1.5 m and -3.5 m. Results showed that the mean tree water use was close to 80 dm3 day–1 with a small mean difference between the two sites (5.4 dm3 day–1, about 7%). Higher daily variations were observed on a single tree over the season (from 17 to 138 dm3 day–1). These fluctuations could be modeled using linear regressions on the vapor pressure deficit (VPD). Results also indicated decreasing sap flux densities with radial sapwood depth and that the whole tree water use could be estimated from the sap flux densities measured at the 0–2 cm depth
Monitoring of water from the underground to the tree: first results with a new sap extractor on a riparian woodland
No full textRiparian woodlands are characterized by variable hydrological conditions. Following the mapping of the complex underground water circulation of the wetlands, we studied the water uptake by trees. Although there are numerous analytical techniques available to monitor the water origin and water fluxes, no rapid technique for the extraction of xylem sap exists on the market. For this reason we designed and built a unique machine able to extract sap directly in the field from wood cores in a few minutes. A short description of the machine and its performance is given, prior to reporting the first experimental results obtained in a young riparian woodland along the Garonne River. The results compare the vertical water profile of the soil and the corresponding xylem sap at different roots horizons and in the trunk
Isotopic characteristics of the Garonne River and its tributaries
No full textThe Garonne is the largest river in the south-west of France, and its drainage basin stretches between
the Pyrenees and the Massif Central mountains. Until now, no water stable isotope study has been
performed on the whole Garonne river basin which is composed of different geological substrata,
and where the water resources are limited during the dry summer period. This study focuses on the
Garonne river and its tributaries from the Pyre´ne´es foothill upstream to its confluence with the Lot
River downstream. The aim of the study is to determine the origins of the surface waters using their
chemical and stable isotopic compositions (18O, D and 13C), to better understand their circulation
within the drainage basin and to assess the anthropogenic influences. The Garonne displays a
specific 18O seasonal effect, and keeps its Pyre´nean characteristics until its confluence with the Tarn
River. The difference in the dissolved inorganic carbon (DIC) comes mainly from the change in
lithology between the Pyre´ne´es and the Massif Central mountains. Agriculture activity is only
detected in the small tributaries
Variations in water use by a mature mangrove of Avicennia germinans, French Guiana
No full textIn the tropical intertidal zones, little is known on water uptake by mangroves. Transpiration rates are generally measured at leaf level, but few studies exist on water use at tree or stand levels. The objective of this study was to measure sap flow in trees of different sizes to appreciate the range of variation in water use that may exist in a site dominated by 80% mature Avicennia germinans. The results showed that from the dry to the wet season the mean water use increased from 3.2 to 5.3 dm3 d−1 in small trees (DBH ∼ 13 cm), from 11.5 to 30.8 dm3 d−1 in medium trees (∼24 cm) and from 40.8 to 64.1 dm3 d−1 in large ones (∼45 cm). Sapwood remained active up to a depth of 8 cm with radial variations within the stem. Weak correlations were obtained with VPD and net radiation. This study confirmed that transpiration was larger under low levels of salinity. Water use at stand level (∼1900 living stems ha−1) was estimated to be in the range of 5.8 to 11.8 m3 ha−1 d−1 according to the season
The Guianese paradox: How can the freshwater outflow from the Amazon increase the salinity of the Guianan shore?
No full textFrench Guiana is notable for the extent of its rain forests, which occupy 97% of the country, and the influence of the Amazon along its shores. In fact, the shores and estuaries support a mangrove forest typical of saline conditions. This paper reports the chemical characteristics, conductivity and salinity and the stable isotopes (oxygen and deuterium) of the rivers and shores between the Cayenne area and the border with Surinam. The results show a quite homogenous freshwater pool over the country. However, the low slope of the coast, a result of the wide mud banks deposited by the Amazonian plume, have turned the mouths of the smaller rivers to the northwest, creating large salty areas where mangroves grow several kilometers inland. Despite the large amount of Amazonian water, the Guianan coast exhibits high salinity. In fact, the freshwater itself remains far from the shore, following the north Brazilian current, while only the mud plume arrives at the coast, creating this paradox
Who is going to save the final girl? the politics of representation in the films halloween and the silence of the lambs
No full textTese (doutorado) - Universidade Federal de Santa Catarina, Centro de Comunicação e Expressão, Programa de Pós-Graduação em Inglês: Estudos Linguísticos e Literários, Florianópolis, 2014Abstract: This dissertation aims at analyzing female representations in two film productions of the North American horror cinema, specifically of its subgenre slasher films, namely Halloween, directed by John Carpenter (1978) and The Silence of the Lambs, directed by Jonathan Demme (1991). My main theoretical framework is film, representation, gender, feminist and queer theories (Butler, 1990, 1993; Clover, 1989; Dika, 1985, Halberstam, 1995; Hall 1973, 1997; Mulvey, 1975, 1981; 2006; Rockoff, 2006; Weedon, 1995). My hypothesis is that the figure of the final girl, in the two films selected for analysis, is not progressive as suggested by the author Carol Clover in her work Men, Women and Chainsaws (1989). On the contrary, the two female characters are represented, in the narrative, as subjugated by the patriarchal system that has been conventionalized in the slasher subgenre. In order to provide arguments for my hypothesis, I analyze general aspects of both form and content of the two films, as well as specific scenes, using the cinematic elements of mise-en-scène, props, characterization, editing and lighting in order to obtain relevant results for my research.Esta tese de doutorado objetiva analisar as representações femininas em duas produções cinematográficas do cinema de horror Norte-americano, especificamente do seu subgênero slasher films, intituladas Halloween, dirigido por John Carpenter (1978) e The Silenceof the Lambs, dirigido por Jonathan Demme (1991). Para tal análise, eu utilizo como referencial teórico as teorias de estudos de cinema, representação, gênero, feministas e queer (Butler, 1990, 1993; Clover, 1989; Dika, 1985; Halberstam, 1995; Hall, 1973, 1997; Halberstam, 1995; Mulvey, 1975; 1981; 2006; Rockoff, 2006; Weedon, 1995) para compor os meus argumentos. A minha hipótese consiste no fato de que a figura da final girl não é inovadora como sugere a autora Carol Clover em sua obra Men, Women and Chainsaws (1989). Ao contrário, a personagem feminina é representada na narrativa como subjugada pelo sistema patriarcal que se convencionou em filmes do gênero. Para a investigação da minha hipótese, foram feitas análises gerais dos filmes propostos, tanto considerando suas formas quanto conteúdos, bem como a de cenas específicas, utilizando-se dos elementos de cinema tais como mise-èn-scene, elementos de cena, caracterização de personagens, edição e luz a fim de obter resultados relevantes para a minha pesquisa
Mangrove trees growing in a very saline condition but not using seawater
No full textMangrove trees, which develop along tropical coasts, are known to use saline water uptake. In French Guiana, the high salinity condition is the result of seawater evaporation on mud banks formed from the Amazon sediment flumes. In the back mangrove a few kilometres inland, groundwater, soil water and the xylem sap uptake in the trees remain highly salty, and only very tolerant plants like Avicennia germinans can flourish, whereas the less salt-tolerant Rhizophora mangle is more difficult to find. Curiously, the same Avicennia trees propagate on the seafront. However, stable isotope ratio mass spectrometry (IRMS) measurements and ion analysis (high-performance liquid chromatography (HPLC) and inductively coupled plasma atomic emission (ICP-AES) spectroscopy reveal that the origin of the water in the back mangrove is not seawater. It is freshwater percolating into the sand bars from the inland marshes and rainwater during the wet season that redissolves a marine evaporite and gives a saline groundwater. The absence of barren saltine areas (‘tanne’) in French Guiana could be explained by this freshwater inflow, the aquifer being no longer linked with the ocean
Bulletin No. 073 - Ration Experiments with Lambs, 1905-06
No full textBulletin No. 073 - Ration Experiments with Lambs, 1905-0
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