Global Change Abstracts The Swiss Contribution - SCNAT

114
08.1-199
Effect of climate and vegetation on soil
organic carbon, humus fractions, allophanes,
imogolite, kaolinite, and oxyhydroxides in
volcanic soils of Etna (Sicily)
Egli M, Alioth L, Mirabella A, Raimondi S, Nater M,
Verel R
Switzerland, Italy
Agriculture, Soil Sciences , Geology , Geochemistry
& Geophysics
A soil sequence along an elevational gradient ranging
from to subalpine climate zones in the Etna region
(Sicily, southern Italy) investigated with respect
to organic C, kaolinite, and crystalline noncrystalline
Al and Fe phases. Special emphasis was given
to stabilization of soil organic carbon (SOC) and its
interaction with inorganic phases. The soils were
variations of Vitric Andosols developed on a trachybasaltic
lava flow with an age of 15,000 years. main
vegetation systems dominated the sites: at the lower
sites, it mainly maquis vegetation and, at the higher
elevated sites, predominantly coniferous forest. The
concentration of SOC in the topsoil, SOC stocks in
the profiles, the humus fractions such as humic
and acids, functional groups and substances of organic
matter, type materials (ITM), and oxyhydroxides
were found to be related to elevation and, thus,
climate (precipitation and temperature) and vegetation.
The C/N ratio in the topsoil was especially
indicative the vegetation type. The amount of SOC,
ITM, and crystalline oxyhydroxides decreased with
increasing altitude. Weathering, as to the proportion
of crystalline Fe-oxyhydroxides or the kaolinite
centration in the clay fraction, seemed to be greater
at the lower sites. At these sites, maquis vegetation
led to a higher accumulation SOC as compared with
the coniferous trees at the higher sites. activity, as
indicated by aromatic compounds in the humic
acids and the presence of charcoal in the soil, has
most probably influenced important soil processes.
The identification and radiocarbon dating charcoal
revealed evidence that repeated bush fires had
played a significant role in soil formation. The better
stabilization of SOC at altitudes might be due to
the specific climatic conditions with a pronounced
change in periods of humidity alternating with periods
droughts and resultant fire activity. The positive
correlation mean annual temperature and SOC
content supports such a hypothesis. The climate-
and vegetation-dependent stabilization of organic
matter the soil can be ascribed to the proportion
of aromatics in the humic acids, to the presence
of noncrystalline Al and Fe phases, to the kaolinite
concentration, to the amount of clay, and to a lesser
extent to the fraction.
Soil Science, 2007, V172, N9, SEP, pp 673-691.
Global Change Abstracts – The Swiss Contribution | Soil and Lithosphere
08.1-200
Soil moisture - Atmosphere interactions during
the 2003 European summer heat wave
Fischer E M, Seneviratne S I, Vidale P L, Lüthi D,
Schär C
Switzerland, England
Modelling , Meteorology & Atmospheric Sciences ,
Agriculture, Soil Sciences
The role of land surface-related processes and feedbacks
during the record-breaking 2003 European
summer heat wave is explored with a regional climate
model. All simulations are driven by lateral
boundary conditions and sea surface temperatures
from the ECMWF operational analysis and 40-yr
ECMWF Re-Analysis (ERA-40), thereby prescribing
the large-scale circulation. In particular, the
contribution of soil moisture anomalies and their
interactions with the atmosphere through latent
and sensible heat fluxes is investigated. Sensitivity
experiments are performed by perturbing spring
soil moisture in order to determine its influence
on the formation of the heat wave. A multiyear
regional climate simulation for 1970-2000 using a
fixed model setup is used as the reference period.
A large precipitation deficit together with early
vegetation green-up and strong positive radiative
anomalies in the months preceding the extreme
summer event contributed to an early and rapid
loss of soil moisture, which exceeded the multiyear
average by far. The exceptionally high temperature
anomalies, most pronounced in June and August
2003, were initiated by persistent anticyclonic circulation
anomalies that enabled a dominance of
the local heat balance. In this experiment the hottest
phase in early August is realistically simulated
despite the absence of an anomaly in total surface
net radiation. This indicates an important role
of the partitioning of net radiation in latent and
sensible heat fluxes, which is to a large extent controlled
by soil moisture. The lack of soil moisture
strongly reduced latent cooling and thereby amplified
the surface temperature anomalies. The evaluation
of the experiments with perturbed spring
soil moisture shows that this quantity is an important
parameter for the evolution of European heat
waves. Simulations indicate that without soil moisture
anomalies the summer heat anomalies could
have been reduced by around 40% in some regions.
Moreover, drought conditions are revealed to influence
the tropospheric circulation by producing
a surface heat low and enhanced ridging in the
midtroposphere. This suggests a positive feedback
mechanism between soil moisture, continentalscale
circulation, and temperature.
Journal of Climate, 2007, V20, N20, OCT 15, pp
5081-5099.