Using deuterium excess to determine the sources of high-altitude precipitation: Implications in hydrological relations between sub-alpine forests and alpine meadows

Summary: Alpine meadows in the upper catchments of the Yangtze River, China provide critical amounts of water to maintain regional water resources, but little is known about the hydrological processes in these alpine ecosystems. In this paper, we analyzed the sources of precipitation in an alpine meadow using the deuterium excess in rain, fog, soil water, shallow groundwater and stream water. Rain and fog in the alpine meadow had high deuterium excess, 35‰ and 38‰ compared to 10‰ of precipitation brought by monsoon at lower elevation. These high values suggested that a large part of rain at the alpine meadow derived from secondarily evaporated water and that fog derived from the evaporated water produced shortly after rain events. However, averaged evaporation rate calculated by an isotopic mass balance model of soil water was only 0.26mm/d, about 3.6% of the rainfall and 7.57‰ of the average deuterium excess value of rain. The contribution from evaporated water to precipitation in the alpine meadow therefore had to be mainly from sub-alpine vegetations in the region. This eco-hydrological relation between sub-alpine and alpine ecosystems can partly explain the high water yield of the alpine meadow and should be considered for regional resource management. [Copyright &y& Elsevier]