A Geophysical Investigation to Image the Critical Zone Architecture in a High Andean Puna Grassland

Communities in the Peruvian Andes are dependent on water derived from non-glaciated upland basins that lie within the seasonally wet montane grassland ecoregion known as puna . Understanding the critical zone architecture and quantifying the dynamic water storage capacity of these landscapes is crucial for developing long-term sustainable water usage plans for nearby agricultural communities that rely on the water yield of the puna grasslands. Geophysical data— seismic refraction tomography, electrical resistivity tomography (ERT), and nuclear magnetic resonance (NMR)—were collected in the Ramaschaka watershed (elevation 4400 masl) above the community of Zurite, Perú. Seismic refraction tomography and ERT transects were collected along four transects across the Ramaschaka watershed. The seismic images revealed the subsurface geologic structure and were used to identify the base of the critical zone. Low electrical resistivity regions in ERT images were associated with bofedales , high-altitude peatlands with large water storage capacity; high electrical resistivity regions were associated with lower water content hillslope soils. Borehole NMR data collected in augered and drilled holes along the ERT and seismic transects allowed the direct in situ quantification of water content and porosity within the different soil and rock types. In future work, the geophysical data will contribute to a hydrogeologic model that will be used to improve and extend the irrigation network, allowing for sustainable year-round agricultural development in the community of Zurite, Perú.