Water storage capacity and hydrological role of andean peatlands in the semi-arid Chile

In a main tributary of the semi-arid Elqui valley called the Estero Derecho in North-Central Chile, peatlands role is essential because vegetation that grow on is a key resource for biodiversity and livestock, especially at the end of the summer where the only water source is rock glaciers and aquifers connecting glaciers to streams. Thus, characterizing the structure and functioning of the peatlands, called bofedales there, is important for vegetation development as well as improving the understanding of its hydrogeological role. The subterranean geometry and stratigraphy of one peatland at about 3000masl elevation was characterized in north-central Chile using Electrical Resistivity Tomography (ERT), Ground Penetrating Radar (GPR) and core extraction. Two sounding locations, two transversal and one longitudinal profile allowed a 3D interpretation of the bofedal’s internal structure. A conceptual model of the current bofedal system is proposed. Geophysical results combined with porosity measurements were used to estimate the bofedal water storage capacity.  The second objective is to better understand the water exchanges between the peatland and the streamflow using discharge measurements and water stable isotopes. Water and isotopes budgets highlight a streamflow loss towards the peatland groundwater reservoir at the end of spring season. In addition, ten δ¹⁸O and δ²H surveys were used to characterize the distinct wetland water sources and their temporal variations. Using hydrological data at the watershed scale, implications regarding the hydrological role of bofedales in the semiarid Andes were then briefly assessed. At the catchment scale, bofedal water storage capacity, evapotranspiration losses and annual streamflow are on the same order of magnitude. High-altitude peatlands are therefore storing a significant amount of water and their impact on basin hydrology should be investigated further.

Figure 1. Topography of the Estero Derecho valley following the Elqui River from the ocean to the highest point at the headwaters.

Figure 2. Inclined aerial photography with vertical exaggeration. Yellow stars correspond to watersample locations. P1–P4 are the geophysical profiles.

Figure 3. Schematic cross-section of the studied peatland showing water surface fluxes , groundwater fluxes , and atmospheric fluxes