Sediment deposition dynamics in a high-altitude lake system in the northern Ecuadorian Andes

High-altitude lakes are sensitive archives of environmental change, yet remain understudied with respect to sediment deposition dynamics. In particular, the tropical Andes of Ecuador are globally-relevant biodiversity hotspots and carbon sinks, which are highly threatened by climate change and human impacts. To learn from the past, we study the depositional history of Lake Caricocha, a high-elevation caldera lake (> 3,700 m asl) located in the Mojanda Lake region, north of Quito, Ecuador. A 72 cm-long sediment core was recovered and analyzed using a multi-proxy approach, including visual core description of the lake sediment facies, X-ray fluorescence core scanning, magnetic susceptibility, C/N and grain-size analysis. Radiocarbon dating was combined with tephra analyses to provide viable sediment accumulation rates over the last three millennia. Granulometric and geochemical data were evaluated using multivariate statistical techniques, including cluster analysis, principal component analysis, and end-member modelling analysis, to infer sediment provenance and deposition dynamics within the lake-catchment system.

The record reveals three major stratigraphic units intercalated with at least eight tephra layers and a high-energy event layer. Our analysis separates detrital sediment input from sediment input by volcanic eruptions, post-eruption reworking or catchment erosion during extreme events that activate the few existing inflows. We discuss grain-size and geochemical data as key to understand and unmix the lake-internal deposition from terrestrial erosion dynamics. This study contributes to a growing understanding of sediment dynamics in tropical high-altitude lakes, and their potential implications for local water resource management.