Isotopic analysis of water cycle elements in different land covers in a small headwater watershed

In this study, comparisons of isotopic variation of rainfall, throughfall, surface water, and groundwater were conducted in the Meilin watershed, which represents two different land uses, chestnut wood and bamboo. Also, isotopic differences between rainfall and throughfall were identified in these sub-watersheds. The results showed that the isotopic value of incremental rainfall, incremental throughfall and surface water exhibited a marked temporal variation in the selected sub-watersheds. The throughfall isotopic variation range was smaller than that of rainfall, which may result from the different production process between rainfall and throughfall. However, the isotopic composition difference between rainfall and throughfall resulting from different land uses was insignificant. The range of isotopic composition variation of surface water was not the same as that of rainfall, indicating that surface water came from a mix of precipitation and water stored before the rainfall event. The temporal variation of the isotopic composition of groundwater was small, implying that the influence of different land uses on groundwater isotopic composition was insignificant. The total variation range of δ²H and δ¹⁸O of groundwater was smaller than that of surface water and sequential incremental rainfall, which means the δ¹⁸O of groundwater can be replaced by that of base flow before the event in the hydrograph separation.