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| Titel |
Modification of rainfall stable isotopes by throughfall and stemflow. The case of Scots pine and downy oak forest under Mediterranean conditions. |
| VerfasserIn |
Carles Cayuela, Pilar Llorens, Elisenda Sánchez-Costa, Jérôme latron |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250138095
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| Publikation (Nr.) |
 EGU/EGU2017-1014.pdf |
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| Zusammenfassung |
| In forested ecosystems the isotopic composition of rainfall that reaches the soil either as
throughfall or stemflow is modified by processes that take place in the tree canopies. The
known factors that can cause a change in the isotopic composition are evaporation,
exchange between liquid and atmospheric vapor, and selective canopy storage for
isotopically temporal varying rainfall. These processes are still poorly understood, but
they have important implications on the heterogeneities of the input water at the
catchment scale. Recent advances suggest that equilibrium exchange and selective
canopy storage are the dominant processes, even though there is a lack of data to
unambiguously identify them. Here, we present the results of an experiment focused on the
characterization of the spatio-temporal variability of the isotopic composition of
rainfall, throughfall and stemflow in order to identify the main factors affecting its
modification.
The study was carried out between May 2015 and June 2016 in a Downy oak (Quercus
pubescens) forest and a Scots pine (Pinus sylvestris) forest located in the Vallcebre
research catchments (NE Spain, 42º 12’N, 1º 49’E), under Mediterranean climate
conditions. The sampling design for isotopic analysis of each stand consisted of one
automatic sampler and 10 throughfall collectors distributed within the stand to
collect throughfall, and 4 stemflow collectors to collect stemflow. Bulk rainfall was
collected with automatic samplers and bulk collectors in two open areas near each
forest stand. At each stand, isotopic sampling was combined with hydrometric
measurements that consisted of 20 tipping buckets to measure throughfall and 7
stemflow rings connected to tipping buckets to measure stemflow. Moreover, rainfall
depth was measured in the two open areas and meteorological variables in the two
stands by means of towers located above canopies. In total 36 rainfall events were
analyzed.
Our results revealed a high heterogeneity on the isotopic composition of the open rainfall
during the studied period. Enrichment occurred for 74% of the throughfall samples and for
91% of the stemflow samples. In general, enrichment was higher for those rainfall events with
a more depleted isotopic composition and of lower magnitude, and stemflow was more
enriched than throughfall. Despite the structural differences in the canopy and bark of the
species, small differences were found in the 18O enrichment between species. Likewise,
small differences were found between winter and summer events. Mean differences
between δ18O of rainfall and throughfall were 0.3 ± 0.3‰ for oaks and 0.5 ±
0.5‰ for pines; rainfall and stemflow differences were 1.2 ± 0.7‰ for oaks and 0.9 ±
1‰ for pines. Even there was a persistence of temporal patterns of throughfall and
stemflow volumes in both stands, there was not a clear persistence on the isotopic
enrichment.
These results show the complexity of differentiating the processes controlling
the isotopic changes of water when passes through the canopies. The analysis of
sub-event scale rainfall and throughfall isotopic composition, combined with detailed
meteorological data will give us some light on the role of each controlling factor. |
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