Atmospheric nitrogen deposition in a subtropical hydroelectric reservoir (Nam Theun II case study, Lao PDR)

Adon1, C. Galy-Lacaux2, D. Serça2, F. Guerin3, P. Guedant4, A. Vonghamsao4, W. Rode4.

1 Laboratoire de Physique de l’Atmosphère et de Mécanique des Fluides, Université Félix Houphouët-Boigny, Abidjan, Côte d’Ivoire, E-mail : [email protected]

2 Laboratoire d’Aérologie, Université de Toulouse, CNRS, UPS, France

3 GET (Geosciences Environnement Toulouse), UMR 5563, Toulouse, France

4 Nam Theun 2 Power Company Limited (NTPC), Environment & Social Division – Water Quality and Biodiversity Dept. – Gnommalath Office, P.O. Box 5862, Vientiane, Lao PDR

Abstract

This study presents an estimation of the atmospheric inorganic nitrogen deposition into the NT2 hydroelectric reservoir, in the subtropical region of the Lao PDR, based on a two-year monitoring (June 2010 to July 2012) including gas concentrations and precipitation. Dry deposition fluxes are calculated from monthly mean surface measurements of NH3, HNO3 and NO2 concentrations (passive samplers) together with simulated deposition velocities. Wet deposition fluxes are calculated from NH4+ and NO3- concentrations determined in single event rain samples (automated rain sampler). Annual rainfall depth was 2502 mm and 3162 mm in 2010 and 2011, respectively. The average nitrogen deposition flux is estimated at 1.26 kg N ha-1 yr-1 from dry processes and 5.01 kg N ha-1 yr-1 from wet ones, i.e., an average annual total nitrogen flux of 6.3 kg N ha-1 yr-1 deposited into the NT2 reservoir with 80% from wet deposition.