【作者】 张钊；

【导师】 孙新超；

【作者基本信息】 天津大学 ， 地质学， 2020， 硕士

【摘要】 准确理解森林生态系统大气水文化学的穿冠输入过程机制是更好地评估大气沉降的生态效应以及生态系统营养元素状态和平衡的关键环节。在不同树种和不同气候条件下,大气化学组分穿过树冠后的浓度和通量改变的程度和方向并不相同。大气化学组分穿冠输入的地球化学行为特征及其过程机制并不十分清楚。因此,本研究以我国华北地区代表性人工油松林为研究对象,详细分析大气降雨、穿透雨和树干流化学组分浓度和通量在不同降雨事件和降雨事件过程下的特征和差异,解析大气降雨化学组分穿过树冠到达地表的时空变化性,量化大气干沉降和冠层交换对净穿透通量的相对贡献,以及评估冠层对大气酸沉降的影响,为深入理解森林生态系统大气沉降的穿冠过程机制和准确量化土壤营养元素的外源输入提供科学依据,同时为该区域森林生态系统管理和生态环境建设也具有实践意义。结果表明:（1）研究期间大气降雨量为1121.8 mm,穿透雨、树干流和冠层截留占到大气降雨量的69.2%,2.6%和27.9%;树干流漏斗比为6.18,并与降雨量和降雨强度存在显著负幂指数关系;穿透雨空间变异系数为25.26%,并随着降雨量的增加而减小。（2）大气降雨化学组分穿冠后浓度表现出富集,但各离子浓度富集程度不同。其中,穿透雨中K⁺富集比（3.17）最大,而NH₄⁺-N富集比（1.36）最小;树干流中SO₄^2-富集比（3.75）最大,Mg²⁺富集比（1.02）最小。此外,大多数离子(如NH₄⁺-N、NO₃^--N、Cl^-、K⁺、Ca²⁺、Mg²⁺)均表现出较大的空间变异性和较低的时间稳定性,而SO₄^2-和Na⁺时间稳定性相对较好。（3）穿透雨NH₄⁺-N、SO₄^2-、K⁺、Ca²⁺、Na⁺和Mg²⁺浓度在降雨过程中呈显著负幂指数下降趋势。此外,穿透雨NH₄⁺-N富集程度呈现先贫化再富集的现象,而NO₃^--N表现出相反的趋势。相对于无机氮素,穿透雨碱性阳离子(除Ca²⁺外)富集情况无明显变化。（4）冠层淋溶是K⁺和Mg²⁺净穿透通量的主要组成部分,分别占到72%和73%;而大气干沉降是Ca²⁺净穿透通量的主要组成成分,占到56%。穿透雨和树干流酸性中和能力和碱度值小于大气降雨,说明华北人工油松林冠层增强了大气降雨穿过冠层到达地表的雨水酸性水平,对土壤酸化产生潜在的负面影响。更多还原

【Abstract】 Better understanding of the mechanisms of atmospheric hydro-chemical input processes through the forest canopy is a key component to assess the ecological effects of atmospheric deposition as well as the state and balance of nutrient elements in forest ecosystems.However,the magnitude and direction of changes in concentrations and fluxes of acidic and alkaline atmospheric chemistry components after passing through the canopy varies between tree species and climatic conditions.The characteristics of geochemical behavior of atmospheric chemical component input through the canopy and its process mechanism are not well understood.Therefore,in this study,Pinus tabuliformis Carr.forest in North China is used to analyze the characteristics and differences in the concentrations and fluxes of bulk precipitation,throughfall and stemflow chemical components under different rainfall events and within rainfall event,analyze the spatial and temporal variability of bulk precipitation chemical components during canopy passage,quantify the relative contributions of atmospheric dry deposition and canopy exchange to the net throughfall fluxes,and assess the canopy effects on atmospheric acidic deposition.The results can provide a scientific basis for understanding the mechanisms of atmospheric deposition through the canopy and quantifying the external inputs of soil nutrients in forest ecosystems,and have practical implications for forest ecosystem management and ecosystem construction in the region.The results showed that:（1）The rainfall during the study period was 1121.8 mm,with throughfall,stemflow and canopy interception accounting for 69.2%,2.6%and 27.9%of the rainfall amount.The funnel ratio was 6.18 and had a significant negative exponential relationship with rainfall and rainfall intensity.The spatial coefficient of variation for throughfall was 25.26%and decreased with increasing precipitation.（2）The chemical components of atmospheric precipitation were enriched after passing through the canopy,but the enrichment degree of each ion concentration was different.Among them,the K⁺enrichment ratio（3.17）was the largest in throughfall,while the NH₄⁺-N enrichment ratio（1.36）was the smallest;the SO₄^2-enrichment ratio（3.75）was the largest in stemflow and the Mg²⁺enrichment ratio（1.02）was the smallest.In addition,most of the ions(e.g.,NH₄⁺-N,NO₃^--N,Cl^-,K⁺,Ca²⁺,Mg²⁺)exhibited greater spatial variability and lower temporal stability,while SO₄^2-and Na⁺had relatively better temporal stability.（3）The concentrations of NH₄⁺-N,SO₄^2-,Cl^-,K⁺,Ca²⁺,Mg²⁺in the throughfall showed a significant negative exponential decrease during rainfall processes.In addition,the enrichment of NH₄⁺-N in throughfall showed a depletion followed by enrichment,while NO₃^--N showed the opposite trend.Relative to inorganic nitrogen,the enrichment of base cations(except Ca²⁺)in throughfall did not change significantly,but was influenced by the rainfall intensity.（4）Canopy leaching is the main component of the net throughfall flux for K⁺and Mg²⁺,accounting for 72%and 73%,respectively,while atmospheric dry deposition is the main component of the net throughfall flux for Ca²⁺,accounting for 56%.The values of acid neutralizing capacity and alkalinity of throughfall and stemflow were smaller than those of bulk precipitation,indicating that the canopy of Pinus tabuliformis Carr.in North China enhanced the acidity level of rainfall during rainwater passing through the canopy,which had a potential negative impact on soil acidification.更多还原