Engle Mark A, Sexauer Gustin Mae, Johnson Dale W, Murphy James F, Miller Wally W, Walker Roger F, Wright Joan, Markee Melissa
Department of Natural Resources and Environmental Science, Mail Stop 370, University of Nevada, Reno, Nevada, 89557, USA.
Sci Total Environ. 2006 Aug 15;367(1):222-33. doi: 10.1016/j.scitotenv.2005.11.025. Epub 2006 Jan 9.
Mercury (Hg) concentration, reservoir mass, and Hg reservoir size were determined for vegetation components, litter, and mineral soil for two Sierran forest sites and one desert sagebrush steppe site. Mercury was found to be held primarily in the mineral soil (maximum depth of 60 to 100 cm), which contained more than 90% of the total ecosystem reservoir. However, Hg in foliage, bark, and litter plays a more dominant role in Hg cycling than the mineral soil. Mercury partitioning into ecosystem components at the Sierran forest sites was similar to that observed for other US forest sites. Vegetation and litter Hg reservoirs were significantly smaller in the sagebrush steppe system because of lower biomass. Data collected from these ecosystems after wildfire and prescribed burns showed a significant decrease in the Hg pool from certain reservoirs. No loss from mineral soil was observed for the study areas but data from fire severity points suggested that Hg in the upper few millimeters of surface soil may be volatilized due to exposure to elevated temperatures. Comparison of data from burned and unburned plots suggested that the only significant source of atmospheric Hg from the prescribed burn was combustion of litter. Differences in unburned versus burned Hg reservoirs at the forest wildfire site demonstrated that drastic reduction in the litter and above ground live biomass Hg reservoirs after burning had occurred. Sagebrush and litter were absent in the burned plots after a wildfire suggesting that both reservoirs were released during the fire. Mercury emissions due to fire from the forest prescribed burn, forest wildfire, and sagebrush steppe wildfire sites were roughly estimated at 2.0 to 5.1, 2.2 to 4.9, and 0.36+/-0.13 g ha(-1), respectively, with litter and vegetation being the most important sources.
测定了两个内华达山脉森林站点和一个沙漠蒿属植物草原站点的植被成分、凋落物和矿质土壤中的汞（Hg）浓度、汞储量和汞库大小。结果发现，汞主要存在于矿质土壤中（最大深度为60至100厘米），该土壤中汞含量占整个生态系统汞库总量的90%以上。然而，树叶、树皮和凋落物中的汞在汞循环中所起的作用比矿质土壤更为显著。内华达山脉森林站点生态系统各成分中的汞分配情况与美国其他森林站点的观测结果相似。由于生物量较低，蒿属植物草原系统中的植被和凋落物汞库明显较小。野火和规定火烧后从这些生态系统收集的数据显示，某些汞库中的汞含量显著下降。研究区域未观察到矿质土壤中的汞流失，但火灾严重程度数据表明，表层土壤上部几毫米的汞可能因温度升高而挥发。对比火烧和未火烧地块的数据表明，规定火烧产生的大气汞的唯一重要来源是凋落物的燃烧。森林野火站点未火烧与火烧汞库的差异表明，火烧后凋落物和地上活体生物量汞库大幅减少。野火后火烧地块中没有蒿属植物和凋落物，这表明这两个汞库在火灾期间都被释放了。森林规定火烧、森林野火和蒿属植物草原野火站点因火灾产生的汞排放量大致估计分别为2.0至5.1、2.2至4.9和0.36±0.13克·公顷-1，其中凋落物和植被是最重要的来源。
