Landscape Development and spatio-temporal Variation in Soil Erosion Rates: Impact of Man, Climate or Neo-tectonics?

Landscape Development and spatio-temporal Variation
in Soil Erosion Rates: Impact of Man, Climate or Neo-tectonics?

E. Cammeraat (1), V. Castillo (2), S.-H. Chung (1) and B. Schuett (3)

(1) Institute for Biodiversty and Ecosystem Dynamics, University of Amsterdam, The
Netherlands, (2) CEBAS-CSIC, Murcia, Spain, (3) Institut für Geographische Wissenschaften,
FU Berlin, Germany, lcammera@science.uva.nl / Fax : +31 20 5257431

In the region of SE Spain soil erosion processes affecting soils and changing landscapes
are widespread. The question arises whether soil erosion processes driven by
the impact of man only, as a direct result of land use change, or that climate change and
tectonics are also important. Especially the high variability in precipitation makes the
interpretation of erosion data from plots extremely difficult. It is well known that upscaling
also involves thresholds in runoff generation and that sediment yield declines
with increasing catchment size.
A case study will be presented, comparing erosion rates in a small semi-natural 12
km2 catchment in the Guadalentin basin (Murcia, Spain) at different spatio-temporal
scales. Soil erosion rates were estimated in four different ways: A 10 year erosion dataset
was obtained using classical open erosion plots, for 3 different cover types; a time
series comparison of landscape metrics derived from detailed aerial photography; by
determination of deposition rates in a small 70 year old retention basin and by incision
rates determined over the last 650 years. For each of the different methods different
erosion rates were estimated. The rates found, showed a large variation in erosion
rates, ranging from very low erosion rates (<0.1 ton ha−1) up to an extremely high
incisionrate of approximately 6mm yr−1over thelast 650 years, although deposition
also occurred in the same channel.
The area under study does currently not have any agricultural activity, nor grazing,
and only a few agricultural hectares have been abandoned over 50 years ago. Hence
direct impact of grazing and agriculture can be excluded to have affected the upstream
catchment itself. There might be an impact of changed precipitation regimes, but from
the local precipitation data available this is not clear. However from historical data
it can be derived that there have been periods with much higher flood levels in the
most important regional rivers, and that commonly are related to land use changes and
climate transitions (little ice age). A final discussion will be related to the possible
impact of stream rejuvenation, as the basin is part of a neo-tectonically active area.
However the impact of this last factor is strongly influenced by human agricultural
and engineering activity such as terracing and reservoir building. The data discussed
show that soil erosion has important impacts on landscape evolution and that different
measurement methods contain spatio-temporal scale effects that affect processes and
their respective rates.