Abstract
Natural ecosystems present in the Pendjari watershed face a
severe degradation phenomenon due to socioeconomic and environmental factors.
Most of the researches focused on the functioning of aquatic ecosystems in the
area are solely based on hydrologic and rainfall data.
The present thesis uses a hydro-ecoregion approach in order to
bring a better understanding to the ecological and physical functioning of
natural ecosystems in the Pendjari catchment. The main goal is to identify and
map the different hydro-ecoregions of the Pendjari watershed. Afterwards,
socioeconomic and environmental drivers of the dynamic of the natural
ecosystems have been analysed.
Available data coupled with mapping have been the basis of the
methodology used to reach this goal. Two first-level hydro-ecoregions (HER)
have been identified in the study area: the Gourma HER and the Atacora HER,
using criteria like topography, geology and climate. Other criteria, among
which soils, hydrography and water physicochemical properties, have been used
to describe those HER.
Those analysis reveal four main types of drivers:
- Hydro-climatic drivers : although having the same rainfall
and hydrologic patterns and the same annual stationnarity breaks from 1960 to
2006, the two HER identified in the study area, are not affected in the same
way by hydric deficits. Rainfall deficit was 8.3 % in the Gourma HER and 12.9 %
in the Atacora HER, while the hydric deficits were 47.8 % in the two HER. The
higher deficit in water infiltration in the Atacora HER (35.9 %) is not only
related to rainfall deficit but also to the type of substratum.
- Geophysic drivers: slopes values are quite low in the Gourma
HER (0.2 to 4.3 %) with a substratum made of sand and clay deposits. In the
Atacora HER, slopes have a high value (4.3 to 77 %) and the substratum is made
of sandstone, schist, micaschist and gneiss. This is the main reason behind the
difference in the flow coefficient which is lower in the Atacora HER (5.4 %)
than in the Gourma HER (6.2 %).
- Sociocultural drivers: namely population growth, with it
corollaries, religion, history, etc.
- Economic drivers: mainly agriculture, breeding, hunting,
fishing, local and international demands in dairies products.
An analysis of adaption strategies, developed by population in
the study area, shows that endogenous adaption strategies related to climate
and water constraints, aim at the preservation and conservation of water
resources. Adaptation strategies related to soils, geology and landscape
constraints aim at improving yields. Endogenous strategies regarding water
engineering help preventing erosion and improve soils conservation. Exogenous
or modern strategies are institutional and regulatory measures regarding
sustainable management of natural ecosystems. These strategies are composed of
national and international regulations on environmental protection.
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Keywords: Hydro-ecoregions, drivers,
dynamic, natural ecosystems, Pendjari catchment.
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