Geormorphology, land use, and their influence on the preservation of an El Niño frequency and intensity signal in three Andean lakes

Sediment cores from Laguna Pallcacocha, a high-alpine lake in the Ecuadorian Andes, have yielded frequently cited reconstructions of Holocene ENSO variability. Intense convective storm activity during moderate to strong El Niño events generates flooding and erosion of headwalls in the catchment, which produces distinct light-colored clastic laminae in the sediment stratigraphy. However, the Holocene record of alluviation from Pallcacocha has not been reproduced. Sediment cores obtained from nearby Lagunas Martin and Fondococha each contain comparatively few laminae, representing only extreme flooding events, whereas the closely spaced laminae of Pallcacocha represent a broader range of alluvial event intensity. Tephra present in each lake, including one deposited at 2500 cal yr BP, are distinct chronostratigraphic markers that can be used to correlate the three records. Here, we examine the flood history of each lake stratigraphically above this tephra to reconstruct El Niño frequency and intensity. We use a high-resolution digital elevation model (DEM) to evaluate the geomorphic controls which lead to the deposition and preservation of clastic flood layers. Additionally, we use the Watershed Erosion Prediction Project (WEPP) model to investigate patterns of sediment erosion and their relationship to land use in order to better constrain changes in the modern sedimentary record. We find that Martin and Fondococha have clastic layer recurrence intervals of 26 and 53 years respectively, compared to 6 years for Pallcacocha, during the past 2500 years. Differences in basin sensitivity to flooding can in part be explained by the degree of channelization in the watershed, with higher order stream networks and low hypsometric integrals corresponding to increased degrees of sediment lamination.