Paleolimnological changes during the Anthropocene in Sierra Nevada lakes

Resumen

Human-induced climate change is accelerating and is profoundly impacting remote aquatic ecosystems. In the Sierra Nevada, these climatic shifts—exacerbated by increased Saharan dust inputs—are likely driving major transformations in lake environments.

This study presents paleolimnological research reconstructing ecological and environmental trends in Sierra Nevada lakes and their catchments over the past two centuries. We analyzed multiple independent paleoindicators from high-resolution, chronologically dated sediment cores, including spectrally inferred chlorophyll-a, sedimentary ancient prokaryotic DNA, and subfossil remains of diatoms, cladocerans, and chironomids. A compilation of the paleolimnological research conducted in Sierra Nevada lakes was made, examining the effects of environmental variables on indicators of the lake structure and function, which were grouped accordingly.

Results reveal that ecological changes began subtly over a century ago, intensifying in the 1960s–1970s, coinciding with regional warming, reduced precipitation, and intensified Saharan dust deposition. Generalized linear models (GLM) and Redundancy Detrended Analyses (RDA) were applied to analyze the effects of climate variables on community assemblages. Results indicate major shifts in aquatic community composition and recent algal biomass increases, with temperature emerging as the dominant driver, and Saharan dust and precipitation as secondary factors. Species shifts indicate rising water temperature and alkalinity and greater eutrophication. Microbial communities show significant restructuring, with increased archaeal and bacterial diversity and abundance, suggesting heightened microbial activity and functional changes in biogeochemical processes.

The symchrony among proxies and climate variables across sites suggests a region-wide phenomenon. These changes are linked to prolonged ice-free seasons, elevated lake water temperatures, and reduced hydrological input—factors that influenced lake volume and water residence time. These trends reflect the increasing severity of summer droughts in the Sierra Nevada highlands over the past five to six decades.

Continued global warming, reduced precipitation, and increased Saharan dust transport are expected to intensify these ecological shifts in the future.