Continuous isotope signal of water balance in a northeastern forest in the United States

In this paper, continuous stable water isotopes of various ecosystem components of a temperate forest were measured in order to quantify water movement between vegetation and the atmosphere. Being that the tracing atmospheric water vapor to its source is a challenging topic in isotope hydrology, few studies on continuous 18O/16O measurement over the full growing season have been reported. We monitored the 18O/16O ratios of stem flow, soil water, rain, stream water and groundwater with a mass spectrometer and compared the results with realtime continuous measurement of 18O/16O ratios of water vapor and canopy transpiration with a tunable diode laser (TDL) analyzer over the 2005 growing season. We found that rain input was the most crucial factor in determining the isotope ratios of stream and soil water. We concluded that, however, the isotope ratios of stem flow were in sensitive to summer precipitation. The isotope ratios of stem flow are almost consistent over growing season despite variation of rain input which had large isotope signal variations.