Combined effect of climate and vegetation on soil-landscape development in volcanic ecosystems (Galapagos, Ecuador)

Understanding the spatial variation of rock-derived weathering products across heterogeneous landscapes is important to constrain ecosystem processes. Few quantitative data exist on soil-landscape development in pristine volcanic ecosystems, as most of these ecosystems are prone to intensive land use and management. By working in the Galapagos Islands, a UNESCO World Heritage Site, we aim to constrain physical erosion and weathering over millennial timescales from empirical data in pristine ecosystems. Our monitoring sites on the island of Santa Cruz cover a ~10 km long NW-SE stretch with a 10-fold increase in precipitation rates and associated changes in vegetation cover. In five ecosystems, we monitor two sites: one that is developed on basaltic lava flows and a second one on basaltic scoriae. By controlling for the age and composition of the basaltic parent material, we focused on the unique natural soil landscapes that developed along the sharp hydroclimatic gradient. We determined weathering extent, and rates of physical erosion based on geochemical proxies and meteoric ¹⁰Be isotopes (¹⁰Be_m). These data were then related to time-series of precipitation, air, and soil temperature to explore the relationship between soil development, climate, and parent material. Along the hydroclimatic gradient, the empirical data on chemical weathering and physical erosion show a nonlinear relationship with the precipitation rate.