Evaluating the Resilience of Andean Lakes to Climatic and Anthropogenic Impacts on Varying Temporal and Spatial

Contemporary and subfossil diatoms were used to investigate Andean lake response and resilience to local and regional stressors on varying spatial and temporal scales. First, the modern diatoms from a group of lakes in the Ecuadorian Andes were described, and the physico-chemical gradients influencing their distribution were evaluated. Interandean lakes are warm water, high nutrient, high pH, and high conductivity, whereas pàramo lakes are cold water, low nutrient, lower pH, and low conductivity. Conductivity, pH, and Secchi transparency significantly influence diatom species distribution. Lakes with high connectivity in the southern pàramo have higher relative abundances of Discostella stelligera, suggesting connectivity also plays a role in the distribution of this species. After the modern diatom assemblages were characterized, a subset of lakes were selected to compare to those collected from the same lakes in the 1980s. The diatom assemblages of interandean and pàramo lakes differ from one another, both in the 1980s and present day. Yet, in general, the species composition of individual lakes was not substantially different between the 1980s in comparison to 2017, suggesting that ii lacustrine diatom assemblages are resilient to local and regional changes over the past ~40 years, during a period of documented increases in air surface temperature and diverse human influences. Two lakes, from the northern and southern Ecuadorian Andes were chosen for paleolimnological analysis spanning the last 2 millennia. Subfossil diatom assemblages showed multiple shifts in composition throughout the last ~2500 cal. yr. BP in each lake; however, these shifts did not occur simultaneously. The diatoms from Laguna Fondococha responded to shifting lake-level caused by regional climate changes, whereas Laguna Piñan diatoms responded to local changes in catchment geochemistry, likely as a result of volcanism and human influence. Finally, the paleoenvironment of a 5.4 Ma paleo-lake