缙云山常绿阔叶林湿沉降过程中不同空间层次水质变化特征

为全面调查森林生态系统各层次降水水质状况以及对降水中各离子的截留特征,于2013年9月至2014年8月对重庆市缙云山常绿阔叶林大气降雨、林内降雨、地表枯透水、土壤渗滤液进行了持续1a的水质效应研究.结果表明,缙云山大气降雨偏酸性(pH=4.75);土壤层和林冠层均能调升降雨的pH值,其中土壤层对pH值的调升幅度最大,其次为森林林冠层.森林林冠层对NO_3~-、Na~+有一定的吸附净化作用,降雨能够淋溶森林林冠层的NH_4~+、SO_4~(2-)、PO_4~(3-)、Mg~(2+)、Ca~(2+)和K~+.另外,枯枝落叶的降解导致构成植物组织的有机物降解为无机物,进而促使各离子质量浓度在地表枯透水中增加.森林土壤中的官能团以及胶体能够吸附并中和渗滤液中的NO_3~-、SO_4~(2-)、NH_4~+、PO_4~(3-)、K~+和Mg~(2+),同时长期处于酸性条件下的土壤层也释放出部分Na~+、PO_4~(3-)和Ca~(2+).该森林生态系统对大气降水中各离子具有较强的截留作用,但各层次对降水中的各离子表现出的截留特征不尽相同,其中以林冠层的截留作用最强.

Dynamics of the Water Quality in a Broad-leaf Evergreen Forest at Different Spatial Levels on Jinyun Mountain

A typical forest stand on the subtropical Jinyun Mountain in China was selected to investigate water quality and interception characteristics for several important ions at different levels in the subtropical forest ecosystem. Based on field and laboratory experiments, the effect of precipitation, throughfall, litterfall, and soil percolation on water quality and ionic interception were investigated from September 2013 to August 2014. Results indicated that the rainfall on Jinyun Mountain was obviously acidic, with an average pH of 4.75. The soil and canopy can elevate the pH of rainfall, while the soil had a greater capability for adjusting pH than did the forest canopy. In addition, the concentrations of NH₄⁺, SO₄^2-, PO₄^3-, Mg²⁺, Ca²⁺, and K⁺ in the litterfall increased with litterfall tissue disintegration, while the other ions decreased. Moreover, functional groups and colloids in the soil can bind or neutralize many ions, such as NO₃^-, SO₄^2-, NH₄⁺, PO₄^3-, K⁺, and Mg²⁺. However, some ions were released from the soil by erosion from acid rain over a long time. Generally, the forest ecosystem is a sink for ions found in precipitation with diverse functions for different layers, and the forest canopy has the highest interception capacity for the ions found in precipitation.