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Mercury gas exchanges over selected bare soil and flooded sites in the bay St. François wetlands (Québec, Canada)

Poissant, L. et Pilote, M. et Constant, P. et Beauvais, C. et Zhang, H.H. et Xu, X. (2004). Mercury gas exchanges over selected bare soil and flooded sites in the bay St. François wetlands (Québec, Canada). Atmospheric Environment , 38 (25). p. 4205-4214. DOI: 10.1016/j.atmosenv.2004.03.068.

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In order to evaluate and understand the mercury gas exchange processes in fluvial wetlands, related researches were initiated in a St. Lawrence River wetland (Bay St. François, Qué., Canada). Mercury fluxes were measured using dynamic flux chamber methods, coupled with an automatic mercury vapor analyzer (namely, Tekran, Model 2537A). Mercury air–surface gas exchanges as well as meteorological conditions were measured during two intensive field campaigns from August to September, 1999 and May, 2000, respectively. The field studies in 1999 were performed under bare soil (unvegetated portions) dry wetland conditions whereas the studies in 2000 were conducted under flooded conditions. Both field measurements were performed at the same location in the aim to study the impact of the water levels on the mercury fluxes. The water-level effect was simply to provide either a dry or a flooded site. Water-level fluctuations in fluvial wetland can result in a conversion between a standing water environment and an environment in which sediments are exposed to air. Mercury flux dynamics and processes would alter accordingly to changing environmental conditions. The average concentration of total Hg in the soil and water were ∼0.06 ng mg−1 (dry weight basis) and ∼1 ng l−1, respectively. The predominant flux of Hg° over both bare soil and water was emission. Median Hg flux under dry conditions was 0.83 ng m−² h−1 in comparison with 0.50 ng m−² h−1 under flooded conditions. Correlations between Hg flux, net radiation and temperature (bare soil or water) indicated that the main process involved in air–soil gas exchange under dry conditions is the enthalpy of volatilization; whereas photoreduction predominates under flooded conditions. This paper discusses the Hg flux results under both conditions in the perspective of water-level fluctuations and their impacts on the air–surface exchange of mercury.

Type de document: Article scientifique
Statut du texte intégral: Autre
Mots-clés libres: Mercury, Air–surface exchange, Volatilization, Deposition, Wetland
Sujets: 1. Laboratoire de développement durable > 1.7. Environnement, écologie, écosystème
2. Milieu physique > 2.3. Climatologie
3. Végétation, milieux humides
8. Impacts et monitoring > 8.1. Qualité de l’eau
Date de dépôt: 08 avr. 2017 18:11
Dernière modification: 27 oct. 2017 20:25

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