Evaluating Water and Suspended Sediment Fluxes from a Headwater River in the Tropical Andes: Insights for evaluating ecosystem condition and degradation.

Abstract:

Land clearing, rapid development of hydropower, and new and improved road networks, have resulted in swift changes in land-use and land cover in Ecuador’s tropical Andes, underscoring the need for detailed information on ecosystem condition in this setting. National and regional payment for the protection of ecosystem services (PES) programs seek to target critical areas, such as these, for watershed conservation, but are often informed by minimal information on sustainable flows and impacts of land use activities. As part of a program to assess riverine ecosystem condition, provide a baseline for evaluating ecosystem degradation with development, and inform conservation efforts, we established a hydrological monitoring program in the southern Ecuadorian Andes in 2013, using high frequency monitoring and sampling techniques. Our site, the Mazar River, is a tributary of the Paute River Basin, situated on the eastern Andean cordillera. The station is equipped with sensors to continuously monitor stream stage and turbidity and an automated sampler for event-based collection of stream water samples. Our observations to date provide new insights into the highly variable flow and sediment transport conditions in this high elevation setting. Runoff varies from less than 3 m³/s during baseflow conditions to nearly 80 m³/s during the flood of record. During measured storm events, suspended sediment concentrations exceeded 1000 mg/l with maximum measured concentrations exceeding 13 g/l during storm peaks. More than 75% of the annual estimated sediment load occurred in short duration storm events during the four-month wet period in 2015. We compare our results to other montane rivers in the tropical Andes and comment on the value of baseline information for evaluating riverine ecosystem condition in the face of rapid change in the tropical Andes.