Vegetation controls spatial patterns of soil water isotopes in a tropical dry forest and UAV can help to predict themand

The spatial representation in studies of water stable isotopes in soils and plants is often limited. Only few studies have investigated the spatial variability of soil water isotopes. We combined spatial sampling of ten soil water isotope profiles (up to 1.5m soil depth) with an analysis of UAV (Unmanned aerial vehicle, drone)-derived vegetation indices and thermal imaging in order to investigate the relationships between spatial patterns of soil water isotopes and vegetation characteristics. We postulate and test the hypothesis that the isotopic enrichment of soil water isotopes under steady-state dry conditions is controlled by vegetation. Finally, we interpolated (external drift kriging) the soil water isotope values using the highest correlated vegetation indices in order to provide a spatially distributed map of soil water isotope depth profiles (Isoscape).

We find that i.) soil water isotopes are (highly) spatially heterogeneous, even under steady-state conditions; ii.) this heterogeneity is particularly pronounced for the near-surface soil and diminishes with soil depth; iii.) there is a significant correlation between soil water isotopes and multiple vegetation indices. Therefore, we could prove the above-stated hypothesis. Results provide opportunities for a upscaling of soil and plant water isotope data to larger area and is highly relevant for a spatially better representation of water isotope data.