5 years of monitoring of zooplankton community dynamics in a newly impounded sub-tropical reservoir in Southeast Asia (Nam Theun 2, Lao PDR)

Abstract

5 years of monitoring of zooplankton community dynamics in a newly impounded sub-tropical reservoir in Southeast Asia (Nam Theun 2, Lao PDR) Abstract -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.Key words -sub-tropical reservoir, Southeast Asia, Copepods, spatial heterogeneity, mixing

Fish catch and fishing practices in the Nam Theun 2 Reservoir and watershed (Lao PDR)

“…The NT2 Reservoir evolved to an oligotrophic status after the trophic upsurge period (Martinet et al . ; Descloux & Cottet ).…”

A Case Study of Fisheries Governance and Management in a Reservoir of Lao PDR: Perspectives for Improvement

“…The Nam Theun 2 hydropower dam is a 1070 MW trans-basin project releasing the turbined water from the Nam Theun 2 Reservoir into the Xe Bangfai River through a 27 km long downstream channel (Figure 1) [20]. The Nam Theun 2 reservoir impounded in 2008 is shallow (8 m depth on average) and its surface area varies between 489 km 2 at full supply level to 86 km 2 in the dry season.…”

“…The environment of the reservoir has been subject to multiple studies [20], starting with a hydrodynamic and water quality model based on the monitoring of 15 parameters [37]. A 3D model allows assessing the impact of watershed management on the primary productivity of the reservoir [38,39].…”

“…A 3D model allows assessing the impact of watershed management on the primary productivity of the reservoir [38,39]. Plankton monitoring indicates the trophic status of the reservoir [20,40], but results have not been used to predict the evolution of fish stock. Despite the remaining terrestrial vegetation (mainly hard wood, the labile organic matter was decomposed in the first five years after impoundment) the reservoir is meso-oligotrophic, with a limited nutrient concentration, in particular in phosphorus.…”