DMS project: Primary and fish production report
by Jorma Koponen, Dirk Lamberts, Juha Sarkkula, Arto Inkala, Wolfgang Junk, Ashley Halls and Mrigesh Kshatriya (2010)
Summary on hydropower development impacts on nutrients, productivity and fisheries
- Habitats, biodiversity and native species will suffer from changing flow and sediment regimes.
- The sediment trapping will decreased bioavailable phosphorus input to the Cambodian floodplains and Delta by 10'000 - 18'000 tonnes/y.
- Tonle Sap primary productivity will decrease 50% or more in large areas in the lake proper and in the floodplains; this will have significant impact on the Tonle Sap fisheries.
- Soil fertility and primary productivity will decrease in the Delta resulting in significant agricultural losses.
- Freshwater fisheries will decline significantly due to decreasing primary productivity and dam barrier effects on migratory fish.
- Depending on their location the possible mainstream dams can destroy migratory fisheries (Halls et. al. 2009); the barrier impacts can't be mitigated with current technologies.
- Coastal fisheries will decrease significantly due to reduced sediment and nutrient input to the sea.
- Increased fertiliser use in the basin will not necessarily compensate for the loss of trapped nutrients; increased chemical fertiliser use is not sustainable in the long run and fertiliser prices have experienced sharp increase lately.
Knowledge Gaps and Additional Considerations
Current knowledge on Mekong nutrients and productivity have following gaps:
- Delta flood flow, water quality, salinity intrusion, sediment, productivity, morphological etc. processes are poorly understood; there is need for systematic and comprehensive modelling and monitoring effort.
- Tonle Sap productivity modelling needs to be verified and developed.
- Basin-wide productivity needs to be assessed and modelling initiated.
- Coastal areas need to modelled for erosion, water quality and productivity.
- Detailed reservoir modelling is required for impact analysis, economic evaluation, fisheries production, guidance for sediment management, multi-purpose optimal operation etc.
- Sediment sources, especially the 3S, need to be verified.
- Sediment nutrient sources and fates need to be clarified with field studies and modelling.
- Nutrient cycles need to be understood.
- Systematic research effort is needed to clarify fisheries functioning and improve impact analysis.
- MRC fisheries valuation work should be continued.
- Linkage between socio-economic analysis and modelling need to be strengthened.
- Economics of hydropower development require comprehensive and critical approach.
In addition to the above list, some of the issues and considerations not directly linked to sediments but relevant for the BDP2 process can be listed as:
- Combined impact of climate change, land use change and hydropower development need to be analysed.
- Assumed diversion and irrigation water use decrease dry season flows in the hydropower scenarios and produce too low water levels; this has consequences on for instance habitat destruction analysis.
- In the hydrological analysis extreme years are more important than analysis of averages; especially in dry years hydropower impacts are more pronounced and the Mekong system is stressed.
- Related to critical conditions, changes in variability and tipping points should be analysed instead of focusing on average changes only.
- Short and medium term flow fluctuations are missing from the analysis.
- Salinity intrusion needs to be checked with 3D model which is able to describe the saline intrusion process (density, turbulence, stratified flow, channel morphology impacts).
This ‘primary and fish production report’ has five companion reports: DMS final report, capacity building, sediments, IWRM (integrated water resource management) and socio-economics.