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| Titel |
Analysis of runoff sources and water uptake by trees using isotopic data in a small forested catchment |
| VerfasserIn |
N. Mantese, D. Penna, G. Zuecco, M. Borga, T. Anfodillo, V. Carraro, G. Dalla Fontana |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250063714
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| Zusammenfassung |
| Plant transpiration is an important component of the hydrological cycle. Particularly, in
densely vegetated areas, climatic and land-use changes might have significant hydrological
(and ecological) implications. This leads to the need to identify the main water sources for
tree transpiration and to evaluate how the flux exchanges between soil, vegetation and
atmosphere possibly affect the runoff response of forested watersheds. Specifically,
this study took advantage of the natural presence of water stable isotopes in the
hydrological cycle to assess: i) the sources of water uptake by trees, and ii) the origin of
water contributing to runoff in a small and densely forested catchment in the Italian
Pre-Alps.
Field surveys were carried out during late summer and early autumn of 2011 in the Ressi
catchment (1.9 ha, North-Eastern Italy, mean elevation of 660 m a.s.l.). Beeches, chestnuts,
maples and hazels represent the main tree species in the area, with sparse presence of
hornbeams and ashes. Stream water stage, soil moisture at 0-30 cm depth at four
locations, and water table level at three locations were continuously recorded. Bulk
precipitation was collected from plastic bottles sealed with mineral oil and weekly manual
sampling of stream water, soil water (by means of suction cups), groundwater and
water in the xylem conduits (sap) from six beeches was performed for isotopic
analyses. Sap was extracted in situ from beech twigs by using a pressure bomb. The
isotopic composition of liquid samples (δ2H and δ18O) was determined by laser
absorption spectroscopy. Additionally, water electrical conductivity was measured in the
field (only for stream water, groundwater and rainfall) by a portable conductivity
meter.
Preliminary results showed a marked difference in the tracer concentration among the
various water components in the catchment. Particularly, the average isotopic signal of tree
water (-38.1 per mil δ2H and -5.95 δ18O) was statistically similar to soil water (-36.9 per mil
δ2H and -6.60 δ18O), but significantly different from streamflow and groundwater (-58.1 per
mil δ2H and -8.96 δ18O, -58.5 per mil δ2H and -8.89 δ18O, respectively). This suggested that
vegetation (at least in the study period and during the inter-storm spells) might use the
water available in the shallow soil, rather than the water stored in the saturated
zone. Moreover, rainfall in the study period (-41.0 per mil δ2H and -7.20 δ18O)
was isotopically similar to soil water and sap but more enriched in heavy isotopes
compared to groundwater and stream water. This indicated a possible groundwater
recharge in wintertime and springtime by precipitation likely mixed with snowmelt.
Finally, the isotopic composition of sap was similar among the different beeches,
even if located in different areas of the catchment, suggesting similar patterns of
water uptake. Future investigations will be extended to the entire vegetative season,
approximately from April to October 2012, in order to better assess the spatial and
seasonal patterns of water utilization, including also sampling during specific rainfall
events.
Keywords: stable water isotopes, sap flow, water uptake, water sources. |
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