CPWF Volta Science Workshop: Management of Small Reservoirs for Multiple Purposes

1. CPWF‐V3
Ecological externalities
Ph. Cecchi (IRD G-eau)
S. Sanogo (Univ. Bobo)
(logos to be added)

2. 1. Lakes monitoring (water level)
Level and temperature loggers installation (June 2011)
Usable?
? By whom
4.2 Mm3 => Conflicts?
? Hydro.
=> Filing up?
1.2 Mm3 ≈ 30%
Andes • Ganges • Limpopo • Mekong • Nile • Volta

3. 1. Lakes monitoring (temperatures)
Mean depth = 2.1 m
Vertical Mixing sensitivity
Mechanical Buffer?
Andes • Ganges • Limpopo • Mekong • Nile • Volta

4. 2. Ceratophyllum submersum
Proliferation since a couple of years
1/ Strong LOCAL preoccupation:
‐ Infrastructures
‐ Fishery
2/ METABOLISM consequences
‐ Quality & productivity
3/ SCIENTIFIC priority
‐ causes & impacts
From an ecosystem perspective, the simultaneous dominance of cyanobacteria
in the phytoplankton pool (> 60%) and the invasion of water masses
by huge amounts of macrophyte do point out without ambiguity
the advanced eutrophication status of the Boura reservoir.
Andes • Ganges • Limpopo • Mekong • Nile • Volta

5. Both states are
RESILIENT
NOW BEFORE
WHEN?
MACROPHYTES PHYTOPLANKTON
(clear) (turbid)
WHY?
Andes • Ganges • Limpopo • Mekong • Nile • Volta

6. ? Pesticides Algae Turbidity
? Agri. practices
? Allelopathy
Cerato
? Origins Nutrients ? Hydrodynamics
Sediment
Fish Resuspension
? Structure
Diagnose: realized by V3 project
Remediation: support to local communities
Andes • Ganges • Limpopo • Mekong • Nile • Volta

7. 3. Allelopathy?
Preliminar experiments have confirmed the allelopathic potential of
Ceratophyllum submersum.
Andes • Ganges • Limpopo • Mekong • Nile • Volta

8. 4. Pesticides?
Macro‐invertebrates communities exhibited contrasted patterns in
agriculture‐impacted versus reference stations
Andes • Ganges • Limpopo • Mekong • Nile • Volta

9. 4. Pesticides?
Tee shirt distributed Commercial formulation
by an agrochemical (paraquat‐based)
company in Ghana found in fields
(Binaba, April 2011). (Boura, March 2012).
Andes • Ganges • Limpopo • Mekong • Nile • Volta

10. 5. Perspectives: towards chemical ecology
1/ What could be the cumulative effects (antagonism / synergy / others)
of both allelopathic metabolites and phytosanitary by‐products
on the aquatic productivity and diversity?
2/ What could be the effects on the growth performances
of irrigated cultures?
3/ Implementation of dedicated experiments using pesticides collected
by passive samplers (in situ), pure molecules (paraquat) and allelopathic
metabolites
4/ Impacts on aquatic food web structure and on selected irrigated crops.
Output: better understanding of the nexus linking
‘Agricultural Intensification’ & ‘Ecosystem Resilience’…
Andes • Ganges • Limpopo • Mekong • Nile • Volta