ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

JOSE MANUEL SAYAGO
Geomorphic indicators of present and former
environmental changes in the sub-tropical region of
Northwestern Argentina
Instituto de Geociencias y Medio Ambiente, Tucuman University,
M. Lillo 205, 4000 Tucuman, Argentina
The perspective of future climatic changes generated by
the greenhouse effect have increase the importance of
landform as key indicators of the future environmental
changes. Present geomorphic processes and the tendencies
in relief evolution would be a valuable information on the
prediction of the global changes effects.
In this paper an overview of geomorphological processes
and its relationship with the future changes in the pre-Andean
sub-tropical region of Argentina is presented. Geomorphological
indicators are analyzed from different environmental
condition: a) Natural region in which anthropogenic
influences are incipient allowing the permanence of
the primitive landscape organization. b) Regions in which
the anthrogenic disturbance is so high (as for instance the
agrarian ecosystems) that the primitive landscape structure
have been strongly changed, and c) Urban regions in which
the geomorphological processes play an important rol
on its present and future evolution.
As a conclusion and recommendation some comments are
included (based in regional case study) about the perspective
(spatial and temporal) in which geomorphological indicators
would be integrated into predictive models of the
future landscape changes. Finally, a proposal for the inventory
of geomorphological indicators and trends in environmental
change at regional and macro-regional level is ineluded.
DANIEL SCHAUB, CHRISTOPH WUTHRICH
& CHRISTOPH SEIBERTH
How landscape features influence sediment yields
(a comparison of two investigaton areas
in North West Switzerland)
Department of Geography, University of Basel, Spalenring 145,
CH-4055 Basel, Switzerland
A long-term investigation on nonpoint-source pollution of
water courses due to soil erosion has been conducted in
two intensively used agricultural areas of north west Switzerland,
the loess covered quaternary hill country of the
High Rhine valley (Hrv) and the Swiss Jura Plateau (Sjp)
with clay-rich soils. Rainfall erosivity is almost equal for
both landscapes, and similar crop rotations are practised.
The field investigations have been carried out at three sea­
1es: the test plot scale, the field scale, and the catchment
scale. Soil losses from bounded runoff plots in clean -tilled
continuous fallow were in the same range for both areas.
On farmer-managed fields, however, the rates were higher
in the Hrv. Moreover, the contribution of soil erosion to
the sediment yield remains low in the Sjp catchments, whereas
in the Hrv a considerable proportion of the eroded
soil is removed from the arable land. Thus on the catchment
level, there is an even greater difference in the significance
of soil erosion processes between the two test regions.
The low soil erosion sediment delivery ratio of the
Sjp is surprising because here landforms such as thalwegs
cause concentrated flow erosion which should result in
longer flow distances. Moreover, the low permeability of
the underground entails a high natural drainage density.
Both factors are supposed to favour a close link between
fields and receiving stream. On the other hand the high sediment
yield in the Hrv is astonishing because there are no
perennial streams.
The explanation of this unexpected behaviour starts from
the fact that for single soil loss events the sediment concentration
in surface runoff is generally higher in the SJP than
in the Hrv because runoff generation is determined by higher
thresholds of rainfall intensity, and frequently intact
aggregates, i.e. coarser particles, are transported. Decreasing
flow velocity due to lower slope steepness causes the
exceeding of the transport capacity at the footslope and
thus to the deposition of the eroded sediment within the
same field. The typical Sjp topography with concave slopes
(and thus level footslopes) enhances this effect of short
transport distances, compared to the linear slopes in the
Hrv. Moreover, the land use pattern in the Sjp contains
considerably more elements (grass strips, buffer zones)
which impede or intercept runoff. The land use pattern is
determined by the extension, shape and areal distribution
of single fields, drainage ditches, paved roads, sealed surfaces,
and the presence of linear elements such as hedgerows.
Based on these results a simple Gis-incorporated model is
being developed. It describes sediment and nutrient fluxes
in the catchment scale with the help of statistical relationships
between weather conditions, geomorphological features,
soil properties, as well as land use and sediment retention
functions of different landscape elements. In Swiss
cultural landscapes which have a long history of human activities,
the land use pattern has an important function in
determining the range of lateral sediment movement.
Changes of the land use pattern thus offer opportunities
for erosion control measures. In a recent report of the
Swiss government on «Agronomic Policy 2002», direct
payments for alternative tillage systems and nature conservation
measures have been announced. It is expected that
the vast majority of Swiss farmers will have shifted to such
programs by the turn of the millennium. The eligibility depends
on the observance of several quality aspects, e.g. the
reduction of soil erosion. Our model can therefore be used
as a planning tool to identify areas at higher risks of water
erosion and to select the best locations for the above-mentioned
conservation measures, such set-asides, vegetative
filter strips or grassed waterways to mitigate effects of runoff
and erosion on water quality.
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