重庆铁山坪马尾松林土壤汞排放特征的现场测试

Field Measurement of Soil Mercury Emission in a Masson Pine Forest in Tieshanping,Chongqing in Southwestern China

为了研究大气汞浓度较高地区的森林土壤的汞排放特征,选取重庆铁山坪马尾松林为研究对象,应用动态通量箱与汞分析仪联用的方法,于2012年9月~2013年7月间对土壤-大气汞交换通量进行了4个季度的现场观测,并考察了辐射强度、空气温度、空气湿度、土壤温度和土壤湿度等环境因子与大气汞浓度对汞交换通量的影响.结果表明,土壤-大气汞交换通量存在明显的季节差异,夏季汞排放量为35.3 ng·(m2·d)-1,而其他季节很小,甚至在冬春两季土壤转为大气的汞汇.汞交换通量除了受辐射强度和大气/土壤温度的影响较大之外,还与大气汞浓度呈线性负相关,白天的平衡点为5.61 ng·m-3.重庆铁山坪马尾松林土壤的汞排放量为2.65μg·(m2·a)-1,较高的大气汞浓度是该值远低于较清洁地区同类森林的重要原因.

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 July2013 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)- 1in 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. 61ng·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.