Spatial and temporal variation of benthic macroinvertebrates in the Nam Gnom Basin receiving discharged waters from the Nam Theun 2 Reservoir (Lao PDR)

In order to assess the impact of water release in the downstream area of the Nam Theun 2 Reservoir (Lao PDR), the spatial and temporal variation of benthic macroinvertebrates was explored. Between 2010 and 2012, five sites were monitored in the Nam Gnom Basin, a tributary of the Xe Bangfai River, receiving the turbinated waters. Repeated-time collections revealed the presence of 109 taxa mainly identified to the family level, attesting to a rich biota. Preliminary results did not show shifts in diversity, population composition, and feeding metrics. Redundancy Analysis indicated that the altitudinal gradient ( i.e . altitude and altitude-related variables) remained the major environmental factor influencing the macroinvertebrates distribution before water discharge. The presence of a tributary downstream of the release point, and the respect of the natural river inflow can explain the preservation of natural conditions. More samples and a strengthened ecological knowledge of Southeast Asian macroinvertebrates are still required to confirm these preliminary results.