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International Institute for Geo-Information Science and Earth Observation (ITC) 2010

Estimating tree groundwater transpiration in La Mata catchment, Spain

Agbakpe, B.A. (Benjamin Asigbui)

Titre : Estimating tree groundwater transpiration in La Mata catchment, Spain

Auteur : Agbakpe, B.A. (Benjamin Asigbui)

Etablissement de soutenance : University of Twente International Institute for Geo-Information Science and Earth Observation (ITC)

Grade : Master of Science in Geo-Information Science and Earth Observation 2009

Résumé
Understanding of vegetation activity in an ecological setting provides insight on water balance prediction of a catchment. This study focuses on groundwater sources of tree transpiration because this issue is vital in catchment groundwater balances. Multiple approaches were used to determine and analyze groundwater transpiration in La Mata Catchment of Sardon Watershed . Stable isotope tracing , soil matric potential and sap flow measurements were combined to determine contributions of saturated and unsaturated zone in the tree transpiration. The sap flux density was monitored using two methods (TDP and HFD) for the whole of the dry season making it possible to determine the dynamics of the transpiration process in the catchment. Whilst TDP was used to monitor stem circumferential and axial variation in sap flux density the HFD was used to monitor radial variations of sap flux density with sap wood depth. The mean daily canopy transpiration determined for the dry season 2009 was 1.46 mm/day for Q.i. and 1.03 mm/day for Q.p. The transpiration was upscaled using biometric upscaling functions based on the biometric data collected within the study period. For partitioning of the sap flow measured at the tree stems, groundwater was enriched by deuterium isotope and consequently the deuterium was analyzed in groundwater, in moisture along the soil profiles and in the stem water . Two compartment mixing model based on analyses of the results of soil matric potential was used to analyze the deuterium data in establishing the sources of the water used in the transpiration process. The result showed 69% and 76% water uptake from the groundwater by Quercus ilex and Quercus pyrenaica respectively. The total transpiration was partitioned into groundwater transpiration T g and unsaturated zone transpiration T u based on the contribution from each zones established through the deuterium isotope analysis. The mean transpiration based on the 50x50m grid is 0.016 mm/day with 0.014mm/day and 0.002 mm/day from Tg and Tu

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