中国云南补蚌区域典型热带森林汞的空间分布特征研究

Spatial Distribution of Mercury in Bubeng Typical Tropical Forest of Yunnan Province,China

热带森林在全球汞循环中占据着重要的地位,其面积占全球森林面积的45%以上,且能够贡献全球凋落物沉降汞的50%以上。然而,关于热带森林汞的生物地球化学循环研究的匮乏导致了估算过程中最大的不确定性,全面细致的热带森林汞调查有利于构建更为精准的全球汞循环模型。本研究选取中国云南典型的热带森林——补蚌区域森林开展了5 m分辨率的土壤汞的高空间分辨率的研究,以及开展了相应的凋落物汞沉积通量的研究。研究结果表明,补蚌区域热带森林有着高达75μg/(m^(2)·a)凋落物汞沉积通量,但是土壤中汞的浓度仅为71±16 ng/g。方程模型结果指出,表层土壤汞浓度受土壤中碳含量的影响,表现出显著地正效应关系,但凋落物汞沉降输入则对表层土壤汞分布无明确效应。为了克服热带森林的高空间异质性,本研究建议凋落物采样达到14个/ha,表层土壤的采样应达到20~25个/ha时,能够有效地降低采样过程引起的不确定性。本研究结论强调了即使热带森林存在高凋落物汞输入,但其较快的物质周转促进了凋落物降解过程中汞的丢失,能够有效地减少热带森林中大气汞汇的能力。

Tropical forests play an important role in global biogeochemical mercury(Hg)cycling.Tropical forest could account for 45%of global forest-covered areas which contributes>50%of global litterfall Hg deposition.However,there is a lack of understandings of Hg biogeochemical processes in the global tropical forest,causing the great uncertainties on global calculation.In this study,we investigated spatial distribution of surface soil Hg level with the 5 m resolution and relative litterfall Hg flux in Bubeng tropical forests of Yunnan Province,China.Our results displayed the litterfall Hg deposition flux was up to 75μg/(m^(2)·a),while only 71±16 ng/g Hg concentration can be measured in surface soil.Structural equation modeling result shows soil organic carbon results in direct positive effect on surface soil Hg,but no significant effect could be attributed to litterfall Hg flux.For lowering the uncertainty caused,we suggest litterfall trap number should be greater than 14 per ha and surface soil number up to 20-25 per ha,respectively.Our study highlights the elevated nutrient turnover offsets the high litterfall Hg input in tropical forest,which is decreasing the atmospheric Hg sink.