[Field measurement of soil mercury emission in a Masson pine forest in Tieshanping, Chongqing in Southwestern China].

To investigate soil mercury emission characteristics in areas with high atmospheric mercury concentration, the soil-air exchanging flux of gaseous elemental mercury (Hg0) was measured for four seasons from September 2012 to July 2013 in a Masson pine forest of Tieshanping, Chongqing in Southwestern China using a dynamic flux chamber and a LUMEX RA-915+ mercury analyzer. The effects of ambient air mercury concentration and environmental factors, such as radiation intensity, air temperature, air humidity, soil temperature, and soil water content, on exchanging flux were also studied. Results showed that there was obvious seasonal variation of the Hg0 exchanging flux, with the highest value of 35.3 ng · (m2 · d)(-1) in the summer and very low values in other seasons, even negative in spring and winter. In addition to radiation intensity and air/soil temperature, ambient air mercury concentration was an important impacting factor, which was negatively correlated with the Hg0 exchanging flux, with the equilibrium concentration at 5.61 ng · m(-3). The total soil emission of Hg0 was estimated to be 2.65 μg · (m2 · a)(-1), which was much lower than that in similar forests in cleaner areas. High ambient air Hg0 concentration in Tieshanping was the main reason for the difference.