摘要
利用2002年1月-2003年12月在西双版纳热带季节雨林观测样地收集的林冠截留滴落雾水、雨水、浅层土壤水和地下水水样，对其氢、氧稳定性同位素比率δD和δ^18O的测定结果进行了分析，研究了林冠截留雾水对土壤水和地下水的影响。干季（11-翌年4月份），热带雨林林冠截留雾水的稳定性同位素比率、过量氘（d-excess）值明显高于雨水的相应值，表明雾水水汽中包含了区域森林植被蒸发、蒸腾的再循环水汽。林下地表浅层土壤水的稳定性同位素比率介于雾水和雨水的同位索比率之间，表明浅层土壤水来源于雾水和雨水的补给，但是干季浅层土壤水包含更多的雾水。在降雨稀少的干季，浅层土壤水主要来自雾水的补给，表明了林冠滴落的雾水是林下幼树和耐阴树种生长和生存的重要环境因子。干季和雨季（5-10月份）地下水的稳定性同位素比率与雨水的均没有显著差别，表明雾水对地下水的补给没有贡献，其水分补给仅仅来自雨水。
Intercepted fog water （fog drip） by forest canopy, rainwater, shallow soil water and groundwater were collected during January 2002 and December 2003 for stable isotopic analysis at a tropical seasonal rain forest site in Xishuangbanna, Southwest Ch/na. The object of the study is to determine whether the fog interception has influence on soil water and groundwater. Bottlefunnel collectors were used to determine daily amount of intercepted fog water during fog-only events in the rain forest, and fog drip samples were collected monthly interval. Rainwater samples were collected monthly interval on an event basis, by using a collector consisting of a stainless steel funnel mounted on the top of a 72 m high meteorological tower. Rainwater sample was also collected at each rain event when rainfall exceeded 10 mm at the weather station. Shallow soil samples were obtained randomly within the forest site from cores collected to a depth of 20 cm beneath the canopy on each sampling day. Groundwater was collected monthly from the hand-dug wells located in the forest. The stable hydrogen （δD） and oxygen isotope composition （δ^18 O） of fog drip, rainwater, shallow soil water and groundwater was determined from an isotope ratio mass spectrometer. The results indicated that the fog drip water was thought to contain water that has been evaporated and recycled terrestrial meteoric water （ evaporation of nearby surface waters and canopy interception）. Tile rain was isotopically more depleted. The fog drip was consistently more enriched than the rain during both the dry season and rainy season. The shallow soil water commonly had composition between the fog drip and rain, suggesting that the shallow soil water is a mixture of the two waters. However, the soil water collected in dry season appeared to contain more fog drip water than that collected in rainy season. The detection of fog drip water in the shallow soil indicates that fog drip may in dry season be an important factor in growth and survivability of understory species and seedlings. Therefore, neglect of the contribution from horizontal precipitation （ibg drip） will make calculations of the water balance inaccurate in the forest. The groundwaters in both seasons were characterized by an isotopic composition similar to that of rain. The stable isotopic compositions of groundwater collected during both seasons also showed little seasonal variations, indicating that the groundwater has a constant and homogeneous source. These waters mainly located on the LMWL （Local Meteoric Water Line） and plotted in the rain isotopic field, suggesting that they were not affected by evaporation during infiltration in the recharge area and were recharged by rainwater. The groundwaters also displayed less fluctuation in isotopic compositions than the rain and fog drip, indicating a long residence time for these groundwaters. These variations in isotopic compositions of groundwater are probably the result of local recharge events since groundwater is believed to be recharged only by rainwater. Comparison of the δ^18O of groundwater with rainwater indicated that the seasonal response of groundwater lags behind the seasonal change in rainwater because the groundwater has a greater residence time than soil water. For example, the rainwater reached its greatest δ^18 O value in April 2003 when the 81So value of groundwater was still near their minimum values for the year, and reached its lowest δ^18O value in the September when the groundwater was near their maximum. This isotopic pattern suggests fog drip water does not play a significant role as a source of recharge for the groundwater. This groundwater was thought to be recharged solely by rainwater. Our results also demonstrate the importance of understanding the impacts of climate factors, and have important implications for ecologists and hydrologists interested in fog-inundated ecosystems and the plants which inhabit them. Further detailed studies which should cover the entire water cycle and water use by plants in this ecosystem are warranted to investigate the importance of the fog drip to the forest. The Xishuangbanna area is suitable for these studies since dense fog almost occurs every day and little rainfall falls during dry season （November to April）.
出处
《生态学报》
CAS
CSCD
北大核心
2006年第1期9-15,共7页
Acta Ecologica Sinica
基金
国家自然科学基金资助项目(30570308
30100019)
国家重点基础发展计划资助项目(2003CB415100)~~
关键词
辐射雾
雾水截留
地下水
土壤水
稳定性同位素
热带季节雨林
radiation fog
fog interception
groundwater
soil water
stable isotopes
tropical seasonal rain forest
