This document summarizes monitoring and research from the CPWF-V3 project on the Boura reservoir in Ghana. It finds that: 1) Water levels decreased by 1.2 billion cubic meters (30%) from June to March, and temperatures varied daily more at the surface than bottom. 2) The macrophyte Ceratophyllum submersum has proliferated in recent years, raising concerns about infrastructure, fisheries, and ecosystem impacts. 3) Preliminary experiments confirmed Ceratophyllum's allelopathic potential, and macroinvertebrate communities varied between agricultural and reference sites, indicating pesticide impacts. 4) Future work aims to understand cumulative effects of allelopathy and pest

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
=> Conflicts?
Relative Variations of Water Level (cm)
550
500
4.2 Mm3
450
? Hydro.
=> Filing up?
400
350
300
250
15/6
1.2 Mm3 ≈ 30%
15/7
15/8
15/9
15/10
Andes • Ganges • Limpopo • Mekong • Nile • Volta
15/11
15/12
15/1
15/2
15/3

3. 1. Lakes monitoring (temperatures)
Daily Variations of Temperatures (°C)
25
20
15
10
dT (air)
5
dT (Bottom of the Lake)
0
15/6
15/7
15/8
15/9
15/10
15/11
15/12
15/1
15/2
15/3
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
(clear)
PHYTOPLANKTON
(turbid)
WHY?
Andes • Ganges • Limpopo • Mekong • Nile • Volta

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

7. 3. Allelopathy?
Y (%)
A
F= 41.643; P< 0.001
A
100%
AB
BC
90%
C
80%
70%
60%
D
50%
40%
REF
PICK1
PICK2
PICK3
PICK4
PICK5
Preliminar experiments have confirmed the allelopathic potential of
Ceratophyllum submersum.
Andes • Ganges • Limpopo • Mekong • Nile • Volta

8. 4. Pesticides?
70%
60%
50%
40%
Dytiscidae
30%
Hydrophylidae
20%
10%
0%
Agri
Ref
Macro-invertebrates communities exhibited contrasted patterns in
agriculture-impacted versus reference stations
Andes • Ganges • Limpopo • Mekong • Nile • Volta

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

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