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Attwood S.W.,Natural History Museum in London | Cottet M.,Nam Theun 2 Power Company Ltd NTPC
Hydroecologie Appliquee | Year: 2016

Malacological and parasitological observations were conducted along the Xe Bangfai River between 2010 and 2012 after a dermatitis outbreak. Mollusc populations were surveyed at 28 stations. Mollusc family and species lists were compiled. A sub-sample of 4033 snails from 10 gastropod families was screened for the presence of trematode cercariae. The findings demonstrated that mollusc populations declined after the initial operation of the Nam Theun 2 hydropower project. The species composition of the snail populations also underlined ecological changes. No definitive cause of cercarial dermatitis was found. However, cercariae resembling echinostome and xiphidiocercariae were respectively observed in one population of Bithyniidae and one population of Neotricula aperta. Further hydrobiological studies are thought to be necessary to study the succession of the molluscan community in the Xe Bangfai River until populations become stable. © EDF, 2015. Source

Som S.,Consultant for Nam Theun 2 Power Company and 216H | Cottet M.,Nam Theun 2 Power Company Ltd NTPC
Hydroecologie Appliquee | Year: 2016

The impoundment of the Nam Theun 2 (NT2) Reservoir on the Nakai Plateau resulted in the creation of a 489 km2 reservoir at its full supply level. This inundation has generated a modification of the environment e.g. in terms of geomorphology especially for the wetlands and terrestrial ecosystems. Wildlife population including six species of fresh water turtles and tortoises has been expected to be affected by the NT2 Reservoir impoundment. In order to avoid an excessive loss of these populations, a turtle conservation programme (rescue, relocation, and monitoring programmes) was conducted with two distinct phases (i) the first phase started before the reservoir impoundment (January 2008) and ended after the reservoir reached its full supply level (January 2009) and (ii) the second phase (monitoring only) was conducted from August 2008 to January 2009 and from November to December 2009. A total of 490 individuals belonging to four freshwater turtle species and three terrestrial species were rescued and relocated into different selected habitats above the full supply level. This number of rescued individuals exceeded the objectives of the rescue and relocation programme. The monitoring programme's results focused particularly on nine individuals belonging to the elongated tortoise species (Indotestudo elongata). Results showed all nine observed elongated tortoises were successfully surviving. However their annual survival rate declined from 100% during the first phase of the programme to 47% after the two monitoring phases. This annual apparent survival rate was outside the range of the natural annual survival rate of this species (88% to 96%). However, the programme found that this sharp decline might be caused by either an error of transmitters attached on individuals or external threats from poaching. This hypothesis was supported by the fact that the four individuals re-tracked showed good sign of population establishment (e.g. normal increase in body weight). © EDF, 2015. Source

Descloux S.,Electricite de France | Cottet M.,Nam Theun 2 Power Company Ltd NTPC
Hydroecologie Appliquee | Year: 2016

The zooplanktonic community of the Nam Theun 2 Reservoir, newly impounded, located in Lao PDR was monitored from 2009 to 2013. Five sampling stations distributed on the surface of the reservoir were sampled on a monthly basis. Results were interpreted to assess the spatial and temporal variability of the communities and to identify environmental factors such as physical or water chemical parameters influencing communities. The zooplanktonic community was dominated by Copepods over the study period and was characterized by low densities and biomasses reflecting low productivity conditions. The spatial heterogeneity of the zooplanktonic community observed along a longitudinal gradient disappeared rapidly after the beginning of the operational phase in 2010 and tended to stabilize. The results also highlighted a seasonal variability explained by a phytoplankton-based food chain. Zooplankton communities were significantly and negatively driven by hydraulic factors, such as the mixing period, or water quality factors, such as water temperature or the depth of the oxycline. This zooplankton community must be evaluated in order to anticipate the food availability for zooplanktivorous fish before developing a fish management plan. © EDF, 2016. Source

Tessier A.,University of Savoy | Descloux S.,University of Savoy | Descloux S.,Electricite de France | Lae R.,IRD Montpellier | And 3 more authors.
Reviews in Fisheries Science and Aquaculture | Year: 2016

To preserve ecosystem services of tropical reservoirs that provide food and income for local populations, it is necessary to monitor fish population temporal dynamics, stock, and yield fishing. The aim of this review is to provide information to who monitor fish populations in tropical reservoirs. The topics, investigative methods, observation scaling, and metrics used in publications since 1960's were inventoried. Temporal and spatial variations in fish population and fish production were the primary topics. Since 2000, studies on trophic structures and fish biological parameters have appeared. Experimental fishing with gillnets has been the technique most often used, but others include hydroacoustics for fish stock assessments and modeling to characterize trophic structures. Annual and seasonal scaling approaches dominated, as well as longitudinal/transversal gradient sampling, which permitted the characterization of fish colonization processes and the detection of halieutic resource overexploitation. For modeling approaches, the entire reservoir was considered. The calculated metrics varied depending on the investigation method. Species richness, number of individuals, and biomass per unit effort were the most common metrics for the different topics. Trophic level, effectiveness, and consumption rate were specific to trophic structure. To monitor reservoir fish populations, it is necessary to have an eco-systemic approach. © 2016 Taylor & Francis. Source

Descloux S.,Electricite de France | Guedant P.,Nam Theun 2 Power Company Ltd NTPC | Phommachanh D.,Gnommalath Office | Luthi R.,Gnommalath Office
Hydroecologie Appliquee | Year: 2016

The Nam Theun 2 hydroelectric Project is located in Lao PDR on the Nam Theun River. The reservoir impoundment started in April 2008 and hydropower generation began in March 2010. The reservoir has a total volume of 3.9 billion m3, covering an area of 489 km2 at full supply level and 86 km2 at the minimum operating level. The performance is 1070 MW and the annual production is 6 TWh. The reservoir is operated seasonally by storing water during the wet season. A system of tunnels and channels diverts the waters from the Nam Theun watershed to the Xe Bangfai watershed. An ambitious environmental monitoring programme of project sites was launched by EDF - NTPC in 2008 and remains operational. An on-site laboratory was established to ensure sampling and analysis in real time. The compartments studied are water quality, greenhouse gas emissions, phytoplankton, zooplankton, benthic macroinvertebrates and fish. A 3D numerical model was developed based on monitoring data to predict the long-term changes in water quality and greenhouse gas production of the reservoir. Additional research programmes have been launched to understand bio-chemical dynamics and processes. © EDF, 2014. Source

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