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| Titel |
Quantification and analysis of deuterium and oxygen-18 isotope composition of precipitation at the southern foothills of Mt. Kilimanjaro (Tanzania) |
| VerfasserIn |
Insa Otte, Florian Detsch, Tim Appelhans, Thomas Nauss |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250112555
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| Publikation (Nr.) |
 EGU/EGU2015-12718.pdf |
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| Zusammenfassung |
| Tropical rainforest are important ecosystems for cycling water at local, regional and global
scales. A number of studies have emphasized the increasing trend of extreme seasonal and
inter-annual variability of precipitation and hydrology in the Kilimanjaro region. So
far, only a limited number of observations have been available for water budget
quantification.
For quantifying atmospheric water input at the southern foothills of Mt. Kilimanjaro,
rainfall, fog and throughfall were measured for two years along an elevation and
disturbance gradient ranging from 950 m a.s.l. to 3,880 m a.s.l.. Measurements
were conducted at eight research plots, equipped with one accumulating rainfall
bucket, one accumulating standard mesh fog collector and a sampling network of 29
accumulating throughfall buckets. The bimodal rainfall distribution is shaped by a "short"
(October to December) and "long" (March to May) rainy season. Maximum annual
rainfall is denoted in the midmontane zone between 2,200 m a.s.l. and 2,490 m a.s.l.
(approximately 3,300 mm). In higher elevations precipitation amounts declines, reaching
55% of the maximum at 3,880 m a.s.l., while fog water deposition ranges from 2%
of rainwater input in the lower montane forest (1,800 m a.s.l.) to 8% at 3,880 m
a.s.l..
Stable isotope composition of volume-weighted samples from eight of the 29
throughfall accumulation buckets, the fog mesh grid and the rainfall accumulation
gauge were measured in a weekly interval from November 2012 to November 2014
on each of the eight research plots. To get insights into the importance of local
vs. remote water sources, two additional rainfall gauges were installed in eastern
direction (Same, Mkomazi National Park, Tanga) to get isotope characteristics of the
approaching rainfall systems. During one transition from dry to wet (December 2013) and
wet to dry (April 2014) season, the sampling interval was increased to a sub-daily
resolution to account for amount and elevation effects in the analysis. Variations in
isotopic content were noted. The 24 month weekly dataset for the entire research
area gives the following regression: δ2H = 7.55 δ18O + 15.41, altering to δ2H =
7.20 δ18O + 12.76 during the intensive campaign in December 2013 and to δ2H
= 7.31 δ18O + 15.74 during the second intensive campaign in April 2014. The
isotopic composition between mean fog water deposition and mean rainfall samples
shows variations along the elevation gradient with 7oÂδ18O and 34oÂδ2H for
lower montane forest (1,800 m a.s.l.) and 18oÂδ18O and 32oÂδ2H in 3,800 m
a.s.l..
Furthermore, deuterium & oxygen-18 isotope composition will be used to interpret the
importance of local evaporation as a significant resource for fog and rainfall (recycling
hypothesis) to analyse if local land-cover change will likely have a negative effect on
the atmospheric water input. If fog and rainfall is primarily fed by remote water
sources, local land-cover changes might enhance rainfall (convection hypothesis). |
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