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The application of δ18O and δD for understanding water pools and fluxes in a Typha marsh

  • Author(s): Bijoor, NS
  • Pataki, DE
  • Rocha, AV
  • Goulden, ML
  • et al.
Abstract

The δ18O and δD composition of water pools (leaf, root, standing water and soil water) and fluxes [transpiration (T), evaporation (E)] were used to understand ecohydrological processes in a managed Typha latifolia L. freshwater marsh. We observed isotopic steady-state T and deep rooting in Typha. The isotopic mass balance of marsh standing water showed that E accounted for 3% of the total water loss, T accounted for 17% and subsurface drainage (D) accounted for the majority (80%). There was a vertical gradient in water vapour content and isotopic composition within and above the canopy sufficient for constructing an isotopic mass balance of water vapour during some sampling periods. During these periods, the proportion of T in evapotranspiration (T/ET) was between 56±17% and 96±67%, and the estimated error was relatively high (>37%) because of non-local, background sources in vapour. Independent estimates of T/ET using eddy covariance measurements yielded similar mean values during the Typha growing season. The various T/ET estimates agreed that T was the dominant source of marsh vapour loss in the growing season. The isotopic mass balance of water vapour yielded reasonable results, but the mass balance of standing water provided more definitive estimates of water losses. The δ18O and δD composition of water pools and fluxes were used to understand ecohydrological processes in a managed Typha latifolia L. freshwater marsh. Isotopic steady state transpiration and deep rooting was observed in Typha. T/ET estimates based on the isotopic mass balance of standing water, the isotopic mass balance of water vapor, and eddy covariance agreed on a dominant influence of transpiration on total ET, despite the presence of standing water. Measurements of the isotopic composition of liquid water pools in standing water, soil water, and plants provided useful information about local ecohydrology and water balance, including distinguishing between evaporation and transpiration in the isotopic composition of water vapor. © 2011 Blackwell Publishing Ltd.

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