滩地杨树人工林皆伐后蒸发散与产流变化

目的]揭示杨树人工林皆伐对滩地蒸发散和产流的影响。方法]基于涡度相关系统对长江滩地杨树人工林皆伐前后水汽通量连续3年(2010―2012年)的观测数据,通过对比皆伐前、后气候条件相似的2个时段(1整年)的蒸发散,揭示皆伐后研究区蒸发散的变化,并基于水量平衡反推研究区产流的变化。结果]皆伐后土壤温度和水位上升,土壤表层含水量全年均值减小约0.03;研究区蒸发散皆伐前、后具有相似的日变化规律和季节动态特征,但皆伐后的全年蒸散量仅为皆伐前的66.3%;皆伐后研究区产流率(产流量/降雨量)从皆伐前的0.53上升至0.62;皆伐前、后7、8、12月的干旱指数(潜在蒸发散/降雨量)均大于1,其他时期均小于1。结论]滩地杨树人工林皆伐后滩地蒸发散减少而产流率增加,加剧夏季干旱的可能性有所降低,但洪水爆发期间削减洪峰的能力也减弱。

Variations of Evapotranspiration and Water Yield in a Post-clearcutting Riparian Poplar Plantation

Objective] To reveal the effects of clearcutting a poplar plantation at the floodplain of Yangtze River on evapotranspiration (ET) and water yield (WY). Method] Based on 3-years''consecutive observation data of water vapor flux from a poplar plantation on the floodplain of Yangtze River during the years before and after clearcutting by eddy covariance system, the variation of ET post-clearcutting was investigated by comparing the ETs in two periods (a whole year before and after clearcutting, respectively) with similar weather conditions. Then the variation of WY post-clearcutting was calculated by water balance. Result] (1) After clearcutting, both soil temperature and ground water level increased obviously while the soil water content decreased by about 0.03. (2) The ETs before and post clearcutting had the similar seasonal and diurnal dynamics; Nevertheless, the annual ET post-clearcutting was only 66.3% of that before clearcutting. (3) The WY ratio (WY/precipitation) increased from 0.53 to 0.62 after clearcutting. (4) The dryness index (potential ET/precipitation) was larger than 1 in July, August, and December, while less than 1 in other months in both before and post clearcutting period. Conclusion] Clearcutting a poplar plantation on the floodplain of Yangtze River leads to a decrease of ET and an increase of WY ratio. As a result, it is less likely to intensify regional drought in summer, but the capacity of the floodplain for flood peak clipping during flooding would also decline.