Soil characteristics and soil erosion by water in a semi-arid catchment (Wadi Drâa, South Morocco) under the pressure of global change [Elektronische Ressource] / Anna Klose

Anna Klose

Informations

• Publié par: rheinische_friedrich-wilhelms-universitat_bonn
• Publié le: 01 janvier 2009
• Nombre de lectures: 41
• Langue: English
• Poids de l'ouvrage: 21 Mo

Extrait

Soil characteristics and soil erosion by water in a
semi-arid catchment (Wadi Drâa, South Morocco)
under the pressure of global change
Dissertation
zur
Erlangung des Doktorgrades (Dr. rer. nat.)
der
Mathematisch-Naturwissenschaftlichen Fakultät
der
Rheinischen Friedrich-Wilhelms-Universität Bonn
vorgelegt von
Anna Klose
aus
Bad Neuenahr - Ahrweiler
Bonn, im August 2009Angefertigt mit Genehmigung der Mathematisch-Naturwissenschaftlichen Fakultät der
Rheinischen Friedrich-Wilhelms-Universität Bonn
1. Gutachter: Prof. Dr. Bernd Diekkrüger
2. Gutachter: PD Dr. Martin Kehl
Tag der Promotion: 16.10.2009For my parents and my husbandi
Acknowledgements
This work is conducted in the framework of the IMPETUS project, and was support ed by
the Federal German Ministry of Education and Research (BMBF) under grant No. 01 LW
06001B and by the Ministry of Innovation, Science, Research and Technology (MIWFT) of
the federal state of Northrhine-Westfalia under grant No. 313-21200200.
This work was only possible through the contribution of many people. First of all I express
my gratitude to my supervisor Prof. Dr. B. Diekkrüger, who was always re ady for
discussion and support. I would like to thank my co-supervisor PD Dr. M. Kehl as well as
Prof. Dr. B. Reichert and Prof. Dr. H. Goldbach for their interest in my work and for the
pleasant cooperation.
I am further grateful to the laboratory staff, E. Mainz, E. Oettershagen and A. Schä fermeier
for all the work on my soil samples and the methodological discussion. I extend my th anks
to B. Irvine and M. Kirkby for answering all my PESERA questions. I would like to thank all
my colleagues who provided data for this work, namely K. Born, H. Busche, M. F inckh, P.
Fritzsche, S. Klose, H. Paeth, A. Roth and O. Schulz. I am grateful to our Moro ccan
partners who provided me with data and personal experience, namely the Serv ice Eau
Ouarzazate, the Office Régionale de Mise en Valeur Agricole Ouarzazate and the Haut
Commissariat aux Eaux et Forêts et la Lutte Contre la Desertifiation. I further t hank the
IMPETUS head office for the support and cooperativeness. Furthermore I am grateful to all
the student assistants who contributed to this study, namely B. Ambeck, L. Deno ux, M.
Hees, E. Lampe, S. Olbrisch, D. Prangenberg, F. Tonhauser, H. Voigt and M. Wargenau.
During my field work in Morocco many people have contributed to the unique expe riences
I was able to make there. Representative of those I would like to mention Jamal Ait El
Hadj, Abdallah, Abdessalam, Nour-Eddine, Fatima, Mohamed Bayach, Mohamed Tazi,
Mustafa El Sabbar, Fadna Syam, Omar Abdellaoui, Mohamed Ait Richa, Lahcen Ait
Ahmed, Ali, Redouan and Aziz.
Especially H. Busche, K. de Vries, S. Klose and O. Schulz spend a lot of time on
discussions on my subjects. They improved this work substantially – I am very gratef ul for
that! K. de Vries, A. Haveresch and S. Klose sacrificed a lot of time to proof-read thi s work,
thank you! I thank G. Braun for translating the abstract to latin and A. Kocher for proof-ii
reading the french abstract.
It was a pleasure for me to work together with the colleagues from the IMPE TUS project.
Special thanks to A. Bossa, K. Born, H. Busche, M. Finckh, P. Fritzsche, S. Giertz, C.
Heidecke, C. Hiepe, B. Höllermann, H. Hölzel, S. Klose, C. Rademacher-Schulz, A. Roth,
O. Schulz, G. Steup and A. Waidosch for the fantastic working atmosphere, the fru itful
discussions and all the fun we had together in Bonn and Morocco. You are friends, not
colleagues.
Last but not least, I express my deep gratitude to my parents, Inge and Rudi Zeyen, and
my husband, Stephan Klose for their patience and their unconditional support.iii
ABSTRACT
Soil characteristics and soil erosion by water in a semi-arid catchment (Wad i Drâa,
South Morocco) under the pressure of global ch ange
Soil resources are crucial for the well-being of man and the environment. The resul ts of the
firstG lobal Assessment of Human-induced Soil Degradation (GLASOD) indicate that 13%
of the world’s soils are degraded; thereof 55% suffer from soil erosion by w ater. Drylands
are especially vulnerable due to the sparse protecting vegetation cover, soils that fea ture a
low organic matter content and rare but intense rainfall events. Soil erosion in dry lands is
likely to intensify as a result of climate change and human activities, such as forest
clearing or overstocking. This study aims at understanding and describing the spa tial
distribution of soil characteristics as well as the current extent and distribution o f soil
erosion by water. Based on these findings, the impact of global change on soil erosion risk
is assessed.
Soil characteristics in the semi-arid upper and middle Drâa catchment (30 000 km², Sou th
Morocco) are examined by investigating soil profiles that are arranged alo ng
toposequences that cover the main geological units. Soil properties are regionalised base d
on their relationship to environmental factors by using multiple linear regression including
dummy variables. The physically-based, distributed soil erosion model, PESERA (Pa n
European Soil Erosion Risk Assessment), is used to assess the current and future soil
erosion risk for five periods between 1980 and 2050. Climate change scenarios that are
simulated with the regional climate model REMO are applied together with the scenarios o f
socio-economic change, which have been defined in the IMPETUS project.
Typical semi-arid soil properties are found: high skeleton content, high CacCoOntent ,
3
high pH values, low organic matter content and partially strong salinity. The most commo n
soil types are Calcisols, Regosols and Leptosols. Between 22 and 89% of the variance of
the soil characteristics can be explained depending on the parameter. The resulting maps
reflect the identified relationships to the environmental factors well and pro vide a
reasonable view of the distribution of soil properties in the Drâa catchment.
A mean erosion rate of 19.2 t/ha/a is simulated under the current conditions. E rosion
hotspots are identified in the high mountain zones, more precisely in the western (Tizi-n-
Tichka), central (Skoura Mole) and eastern (M'Goun chain) part of the Central High Atlas.
Rainfall reduction and higher temperatures that are expected following the climate ch ange
scenarios lead to a decrease in vegetation cover. Together with more intense precipit ation
events, this will cause an increase in soil erosion by up to 31%. Due to further
marginalisation, people are forced to satisfy their energy demand by enhanced extract ion
of firewood that further degrades vegetation cover. This results in an increase in the
erosion rate of 27%. In contrast, rural development brings about a loss of the nomadiciv
lifestyle and, consequently, a reduction in the animal numbers and grazing pressure. Th us,
the soil loss is reduced by 54%. Combining the impact of climate and socio -economic
changes shows that human activity can aggravate (+64%) or mitigate (-25%) soi l erosion
risk. The “Mansour Eddahbi” reservoir that is located at the outlet of the upper ca tchment
is endangered by upstream soil loss. Its simulated capacity in 2050 varies between 0 and
46% of the initial storage volume, depending on the scenario. The efficiency of anti-erosive
measures is analysed by simulating two intervention scenarios that consider afforestatio n
(6300 ha) and grazing exclusion (75 000 ha). Efficiency depends on the spat ial scale that
is under consideration. At the local scale (i.e., the intervention zone), soil loss is reduced
by 36-99% up to 2050; afforestation is more efficient. At the scale of th e upper Drâa
catchment, i.e., the relevant scale for reservoir siltation, erosion is reduced by 1 to 13%.
Pasture exclusion is more efficient due to the larger intervention zone. This work presents
a comprehensive study on the risk of soil erosion by water in the Drâa catchment an d can
serve as a scientific basis for local decision making processes.
KURZFASSUNG
Bodeneigenschaften und Bodenerosion durch Wasser in einem semi-a riden
Einzugsgebiet (Wadi Drâa, Süd-Marokko) unter dem Einfluss des globalen Wandels
Die Ressource Boden ist von immenser Bedeutung für Mensch und Umwelt. Die erste
globale Abschätzung der durch den Menschen verursachten Bodendegradierung (Global
Assessment of Human-induced Soil Degradation GLASOD) ergab dass 13% de r
weltweiten Böden degradiert sind, davon 55% durch Bodenerosion durch Wasser.
Trockengebiete sind aufgrund der geringen Vegetationsbedeckung, des geringen Geha lts
an organischer Substanz im Boden und den seltenen aber intensiv en
Niederschlagsereignissen besonders betroffen. Eine weitere Intensivierung der
Bodenerosion in Trockengebieten aufgrund von Klimawandel und menschlich er
Beeinflussung, z.B. durch Abholzung oder Überweidung, ist wahrscheinlich. Zie l der
vorliegenden Arbeit ist die Analyse der räumlichen Verteilung von Bodeneigenschaf ten
sowie des aktuellen Ausmaßes und der Verbreitung von Bodenerosion. Basierend au f
diesen Erkenntnissen wird der Einfluss des globalen Wandels auf die Bodenero sion
simuliert.
Die Bodeneigenschaften im semi-ariden oberen und mittleren Dr