The Madre de Dios River basin of Peru: a catchment observatory across scales covering the Andes-Amazon mountain-to-floodplain transition

The transition from the eastern flank of the Andes mountains to the Amazon lowlands provides a remarkable opportunity to investigate environmental processes in the tropics - offering key information about the state of the globally important Amazon basin and its response to global change, as well as rare clues that are critical to addressing general scientific questions at the intersection of hydrology, geomorphology, biogeochemistry, ecology, and more. This region presents an elegant setting to probe the couplings and contrasts between rapid, tectonically-driven erosion in the Andes and the evolution of critical zone processes across a major floodplain. While many catchment observatories are predominantly in upland environments, the Andes-Amazon system compels us to bridge the divide to the depositional settings that make up much of Earth's surface. With these motivations in mind, over the past decade we have been leading an effort to use the Madre de Dios River basin in southeastern Peru as a critical zone observatory across the Andes-Amazon transition. This work has spanned scales from multi-year monitoring of small catchments (currently focusing at the ~1 km² area) to studies of nested catchments from ~50 to 28,000 km², as well as repeated expeditions to characterize inputs from the multiple tributaries that feed into the main stem of the Madre de Dios River. In its headwaters in the Kosñipata River Valley, puna grassland makes way to tropical montane cloud forest, and our monitoring has provided constraints to quantify the hydrological and carbon budgets of this globally important ecosystem. Across the Madre de Dios, we have learned how chemical weathering responds to erosion in a setting dominated by sulfide-rich sedimentary bedrock, where pyrite oxidation is a key process. Downstream, we have provided new information about sources and recycling of sediment, carbon, and nutrients during floodplain transit. In this contribution, we will survey and summarize these and other major scientific findings from the Madre de Dios. As the datasets from these catchments grow, we are building a repository of information that can provide a vital baseline for understanding the evolution of the Amazon system in the future, yet taking advantage of this opportunity will depend on this type of catchment observatory being sustained.