鼎湖山季风常绿阔叶林水相沉积元素分布及其相关性研究

2001年2月~ 2002年3月在鼎湖山季风常绿阔叶林对大气降水、穿透水、土壤水 (30和 80cm层 ) 和溪水中的沉积元素进行监测, 拟通过不同水相元素浓度的比较及相关关系分析, 揭示系统的营养循环功能状况以及对区域化学条件变化的响应, 阐明因素在环境中的迁移转化规律。结果表明 :林冠与大气间强烈的相互作用, 极大地提高穿透水中Mn2 + 、Sr2 + 、K+ 、Mg2 + 、Ca2 + 浓度。水与土壤作用后, 极大地提高水相中Al3 + 的浓度。 30cm土壤溶液和溪水中的Al3 + 浓度分别是大气降水 (0.32 9mg·L-1) 的 4.8和 3.7倍。溪水中的Al3 + 主要来源于土壤的淋溶。大气降水平均Pb2 + 浓度为 0.0 6 2mg·L-1, 存在着一定程度的Pb2 + 污染, 其浓度分别是穿透水和溪水的 5倍和 10倍。林冠吸收和土壤过滤吸附是森林生态系统净化Pb2 + 等重金属污染物的主要过程。大气降水、穿透水、土壤水和溪水中Na+的浓度逐步增加, 但增幅不大。元素浓度的变异系数在 5 1.1%~ 2 36.7%之间。水相中的离子浓度与雨量有关, 大气降水、穿透水、土壤水中的沉积元素浓度大部分是干季大于湿季, 而溪水中是干季小于或近等于湿季。元素相关分析发现, 与元素Mg相关的元素最多, 穿透水所含相关元素对最多, 不同水相间元素相关状况差异与其元素的来源和外部环境条件有关系。Pb与金属元素Al、Mn在大气降水中极显著相关, Mn_Al、Mn_Mg、Mg_K在所有水相中显著相关, Al_Sr、Mn_Sr、Ca_K、Ca_Mg在除溪水外的所有水相中显著相关, Na_K、Na_Mg在除大气降水外的所有水相中显著相关, 而Pb_Na、Pb_K在所有水相中都无相关关系。结果说明, 季风常绿阔叶林系统已经遭受一定的外界环境压力, 但是其物质循环功能依然稳定。

CHANGES IN SOLUTION CHEMISTRY OF EIGHT INORGANIC ELEMENTS IN A MONSOON EVERGREEN BROAD-LEAVED FOREST IN DINGHUSHAN

The monsoon evergreen broad-leaved forest (MEBF) in Dinghushan Biosphere Reserve, Guangdong Province, China, is considered climax forest vegetation in this climatic zone. Studies of its ecological processes, including the hydrology and inorganic solution chemistry, are important for understanding ecosystem function and to direct ecological restoration efforts in this region. In order to understand the response of nutrient cycles to environmental impacts and characterize the nutrient element cycles in this ecosystem, water samples of precipitation, throughfall, soil water at 30 and 80 cm depth and runoff in MEBF were collected weekly and the concentrations of eight inorganic elements measured from February 2001 to March 2002. The elements Al3+, Mn2+, Sr2+ and Pb2+ were measured by ICP (ps-1000AT, USA), Ca2+ and Mg2+ were analyzed using Atomic Absorption Spectrometer, and K+ and Na+ were determined using Flame Atomic Absorption Spectrometer. The results showed that the average concentration of Al3+ in throughfall (0.393 3 mg·L－1) was slightly higher than that in precipitation (0.329 mg·L－1). The average concentrations of Al3+ soil solutions were much higher than in precipitation and were about 4.7 times and 3.8 times higher in soil water collected at 30 cm depth and runoff, respectively. Al3+ in runoff was derived primarily from soil leaching. Average concentrations of Mn2+, K+ and Mg2+ were lowest in precipitation and Sr2+and Ca2+ concentrations were lowest in runoff. The average concentrations of Mn2+, Sr2+, K+, Mg2+ and Ca2+ in throughfall were much higher than in precipitation as a result of strong interactions with the tree canopy. The average concentration of Pb2+ in precipitation was as high as 0.062 mg·L－1, indicating some Pb2+ pollution, and it was about 5 times and 10 times higher than that in throughfall and runoff, respectively. This indicated that the Pb2+ in precipitation could be largely absorbed by the tree canopy and soil. The average concentration of Na+ gradually increased as it passed through the ecosystem from precipitation (0.320 2 mg·L－1) to throughfall (0.524 7 mg·L－1), soil water at 30 cm (0.627 3 mg·L－1) and 80 cm (0.639 1 mg·L－1) depth and finally as runoff (0.629 6 mg·L－1). Coefficients of variation of the elemental concentrations in the different solutions ranged from 51.1% and 236.7%. The average concentrations of those elements in precipitation, throughfall, soil water at 30 and 80 cm depth were higher during the dry season than during wet season, but their concentrations in runoff during the dry season were lower than or close to that during the wet season. The element Mg had the highest element-couple correlation as compared to all other elements. The greatest element-couple correlations were found in throughfall. Correlations among other elements were highly variable. The results show that element nutrient cycles in this forest ecosystem are stable even though under environmental stress.