The spatial patterns and impact factors of stable oxygen and hydrogen isoscapes in pond water: A case study on the water-source forests of the Hani terraced fields in Yunnan, China

Abstract

Isoscapes are useful tools for studies concerned with hydroclimatic processes, at multiple scales, and their effects on water resources. However, few studies have been conducted on the application of landscape ecology methods for the characterization of isoscape patterns and their impact factors. In this work, measurements of stable hydrogen and oxygen isotope composition were performed on 112 pond-water samples from the water-source forest of the Hani terraced fields. The spatial gradients of pond-water isotope compositions, and the altitude factor of these gradients, were then analysed according to the topography of the study area, using spatial interpolation and gradient analysis methods. It was found that: 1) The pond-water evaporation line (PWEL) of the study area was δD = 6.28δ18O − 5.5 (R2 = 0.96, n = 112). The gradient and intercept of the PWEL were lower than those of the global meteoric water line (GMWL) and local meteoric water line (LMWL), indicative of intense evaporation. 2) Inverse distance weighting (IDW) interpolation, natural neighbourhood interpolation, spline interpolation, Kriging and Co-Kriging (with altitude as an auxiliary variable) were compared, and IDW interpolation was demonstrated to be the most precise of these methods. IDW interpolation demonstrated that pond-water δ18O values generally increased with decreased altitude, in E-W, S-N and SE-NW directions across the study area. 3) Gradient analysis demonstrated that δ18O generally decreased with increased altitude across the whole-region and at watershed-scales. The δ18O was significantly correlated with altitude on virtually all transects. Therefore, altitude is one of the key factors for the spatial pattern in the stable isotope compositions of the study area’s pond water. This was less pronounced in the E-W transect across the study area, as its isotope compositions were affected by watershed-level patterns. In summary, this work has established a new approach for the analysis of water-body isoscapes and their altitude factor by adopting methods of pattern analysis from landscape ecology.