Seasonal water storage in peat-forming bofedales sustains baseflow in the Andes

Abstract

Humid punaBofedales, or low gradient peat-forming wetlands, are a characteristic feature of thehumid puna - a high elevation, seasonally dry grass- and shrub-land found throughoutthe Central Andes. Despite the importance of the humid puna in supplying water todownstream communities, and the inference that bofedales may play an important role,few studies have explored the hydrology of the humid puna, and none have quantifiedthe amount of water bofedales contribute to streamflow. We designed a 3-year study inthe Upper Ramuschaka Watershed (URW), a 2.12 km 2 humid puna catchmentsustaining a perennial stream used for irrigation. We monitored precipitation,subsurface moisture, bofedal groundwater, and streamflow, measured discharge in 19nested subbasins through the wet and dry seasons, and investigated the structure andhydraulic properties of bofedales.We discovered a positive relationship between unit runoff and the percent of bofedal cover across subbasins. Bofedales collect groundwater from areas 4-12 times their size, store large volumes in high porosity peat, and release water to streams through lower conductivity layers. Bofedales cover 11.6% of the URW, dynamically store105,000 m^3 of water and yield 49 mm at the catchment scale, accounting for 20 –98% of dry season runoff. Bofedales regulate drainage from the humid puna todownstream communities and are therefore vital to local and regional water security.