Hydrologic - Biogeochemical Connections Across the Terrestrial - Aquatic Interface in Tropical Andean Watersheds

A rapidly growing body of work recognizes inland waters as fundamental players in the carbon and nutrient cycles. In particular, headwater streams have been the focus of recent scientific investigations because they connect terrestrial and aquatic ecosystems, having a higher proportion of stream water volume in direct contact with adjacent soils. This paper evaluates the grand challenge of understanding hydrologic and biogeochemical connections across the terrestrial - aquatic interface in tropical montane watersheds in the face of climate and land-use change. First, we assess how the metabolic regimes of high-elevation streams might vary in the Tropical Andes where active geology, extremely rich soil carbon stores, and complex topography, might impose a different set of constraints on stream ecosystem function. Second, we examine how land-use and climate changes may affect stream functioning and, as a result, the availability and export of nutrients such as C, N, and P. Finally, we explore how these changes in nutrient availability and export may in turn affect the biota, including primary producers and consumers. We conclude by synthesizing potential strategies to address this grand challenge, including the extrapolation of the limited, existing observations across greater spatial and temporal scales, and the identification of immediate priorities and research opportunities for advancing the hydrologic sciences and biogeosciences of tropical montane streams.