The Pools, Fluxes and Residence Time of Water Across the Amazon Basin

What can ecology tell us about the hydrology of the Amazon? And what can hydrology tell us about the ecology? From a hydrological perspective, plant water storage and use contributes to determining the rate and time scales at which water is recycled from soil to the atmosphere. From an ecological perspective, plant water storage and use contributes to determining the rate and time scales at which water plants can support function. Conceptualized as residence time, the relationship between plant water storage and use can provide fundamental insights into ecohydrology. We explore the spatial variation in the aboveground storage, use, and residence time of water across the Amazon. To do so, we pair estimates of aboveground woody biomass from 413 1-ha old growth forest census plots situated across the Amazon Basin with high resolution estimates of intra- and inter- annual evapotranspiration derived from remote sensing. Aboveground water storage capacity (17.4 ± 6.3 mm) and evapotranspiration (3.7 ± 0.4 mm day-1) result in a residence time of 4.7 ± 1.5 days, equivalent to the use of ca. 24% of stored water day-1. The results indicate that residence time varies due to a predictable relationship between evapotranspiration and biomass at local, regional and landscape scales. The ecohydrology of the Amazon plays a critical role in water and carbon cycling on a global scale. We discuss how our results can help inform our understanding of both the hydrology and ecology of the Amazon Basin in the context of anthropogenic change.