Mercury degassing from forested and open field soils in Rondônia, Western Amazon, Brazil

Abstract

A TeflonÒ dynamic flux chamber was used to characterize Gaseous Elemental Mercury (GEM) flux from forested and open field soils in a highly changing environment in Rondônia State, western Amazon. We simultaneously analyzed meteorological parameters at the soil level relating GEM fluxes to soil temper- ature, air humidity, soil moisture, solar radiation, and speed and wind direction. We also examined vari- ations of atmospheric GEM concentration. GEM fluxes during the day and night in the open field site were significantly different (17 ± 14 ng m 2 h 1 and 0.9 ± 1.9 ng m 2 h 1, for day and night, respectively), but were similar within the forest site (4.8 ± 1.4 ng m 2 h 1 and 4.4 ± 1.8 ng m 2 h 1 for day and night peri- ods, respectively). A comparison between 24-h periods averages in the two sites showed much larger emission from the open field site. GEM fluxes at the open field site were positively correlated with soil moisture, solar irradiation and soil temperature and inversely correlated with air humidity. At the forest site GEM fluxes showed no correlation with meteorological variables. At the open field site GEM concen- trations significantly correlated with GEM flux, at least during the day. At night in the open field site and during the day and night at the forest site no correlation was found between GEM fluxes and GEM con- centrations in the ambient air. Higher emissions from the open field site support earlier studies showing larger Hg remobilization following forest conversion to pasture