Stable isotopes reveal linkages among ecohydrological processes in a seasonally dry tropical montane cloud forest

Abstract

Despite their critical role as freshwater resources and their vulnerability to anthropogenic pressures, our knowledge of the ecohydrology of tropical montane cloud forests remains limited. Here, we use a dual stable isotope approach (δ2H and δ18O) to trace water inputs, fluxes, and pools through a seasonally dry tropical montane cloud forest in central Veracruz, Mexico. We found strong seasonal variation in the isotope composition of precipitation inputs (δ2H ~130‰ and δ18O ~18‰), with significantly more depleted wet‐season values as compared with dry‐season values. These seasonal differences are subject to inter‐annual variation, as reflected by shifts in the local meteoric water line. Even at the peak of the dry season, stable isotope values of plant xylem water from six different deciduous and evergreen species occurring in the understory and canopy of mature and secondary forests were all consistent with the use of shallow soil water (20–60 cm). Alternative limiting factors, such as nutrient distribution along the soil profile, may be strongly contributing to plant rooting patterns. Stable isotope values of soil water were evaporatively enriched compared with precipitation inputs, whereas stream values plotted with precipitation on the local meteoric water line. In contrast to current hydrologic models, this indicates the presence of two distinct soil water pools, one highly mobile pool of precipitation that contributes to streams and a second less mobile pool of soil water that contributes to plant fluxes. This comprehensive perspective can provide the basis for generating process‐based models of ecohydrology in the future. Copyright © 2011 John Wiley & Sons, Ltd.

Importance of vegetation, topography and flow paths for water transit times of base flow in alpine headwater catchments

“…The seasonality of precipitation and its stable isotope signals and the seasonality of transpiration could produce different water pools (i.e. soil water vs. groundwater) with different isotopic characteristics, analogous to the findings of Brooks et al (2010) and Goldsmith et al (2012). Brooks et al (2010) found that evaporation changed stable isotope values of soil water.…”

Effects of climatic seasonality on the isotopic composition of evaporating soil waters

“…Ehleringer and Dawson, 1992;Dawson et al, 2002;Volkmann et al, 2016;Rothfuss and Javaux, 2017), and identifying plant water sources (e.g. Brooks et al, 2010;Dawson and Ehleringer, 1991;Dawson and Simonin, 2011;Goldsmith et al, 2012;Evaristo et al, 2015;Hervé-Fernández et al, 2016;McCutcheon et al, 2017). A recent review by Sprenger et al (2016) 5 provides an extensive overview of isotope-based studies in the unsaturated zone.…”

Oxygen isotope ratios of plant available phosphate in lowland tropical forest soils

“…To detect whether isotopic variations occurred between different rain events during the study period (as reported in tropical forest elsewhere (Goldsmith et al, 2012)), rain samples were taken twice, at the 15th of September and at the 5th of October. No isotopic variations were observed between the two samples.…”