Spatial variation of stable isotopic composition in surface waters of the Huai River basin, China and the regional hydrological implication

Oxygen (delta O-18) and hydrogen (delta D) stable isotopes in the surface waters of the Huai River basin were analyzed in this study. Results indicated the northern waters had higher delta O-18 and delta D than the southern waters, the water delta O-18 and delta D increased along the water flow directions. These variations mostly resulted from the spatial differences of precipitation and evaporation. Comparing with published different continents' river water delta O-18 data, this study suggests that evaporation effect is a more plausible interpretation than altitude effect as the cause of delta O-18 increasing from upriver to downriver waters. This region's local surface water line (LSWL, delta D = 5.36 delta O-18 - 18.39; r(2) = 0.84) represents one of the first presented LSWLs in eastern China. The correlation between d-excess and delta O-18 demonstrates this region is dominated by the Pacific oceanic moisture masses in summer. Comparing the various LSWLs from eastern China and eastern United States river waters, this study proposes a hypothesis that the water LSWLs slopes of lower latitude regions may be less than those of higher latitude regions within similar topographic areas. This hypothesis may be tested in other geographically comparable coupled areas in the world if corresponding large-scale data can be found.