Stable isotope record of contrasting lake systems: Analysis of the Peruvian Andes and Adirondack Mountains

Lake sediments preserve valuable records of past environmental and climatic change, making them important archives for reconstructing hydroclimate variability and ecosystem responses through time. This study compared sediment cores from two different lake systems, Laguna Capilla in the Peruvian Andes and Lower St. Regis Lake in the Adirondack Mountains, to investigate how stable isotope records reflect environmental processes across different climate regimes. Stable isotope analysis was conducted on lacustrine carbonate from Laguna Capilla (𝛿18O and 𝛿13C) and on bulk organic matter from Lower St. Regis Lake (𝛿15N and 𝛿13C) to evaluate hydroclimate variability, lake productivity, and watershed influences. The Laguna Capilla record indicates variability in precipitation associated with fluctuations in the South American Summer Monsoon, with lower 𝛿18O values suggesting periods of increased precipitation and higher 𝛿13C values indicating enhanced lake productivity. Magnetic susceptibility data also suggest periods of increased metal-rich sediment input, potentially linked to regional mining activities documented in nearby Lake Junin. In contrast, the Lower St. Regis Lake record primarily reflects changes in watershed nutrient inputs and lake productivity associated with nineteenth-century development around the lake. The establishment and expansion of the Paul Smith Hotel, beginning in the 1850s, brought increased tourism, shoreline development, logging, and wastewater discharge to the watershed, likely contributing to increased 𝛿15N values. Towards the surface, decreasing 𝛿15N and 𝛿13C values combined with increasing organic carbon and nitrogen concentrations indicate a shift toward greater aquatic productivity. Together, these records demonstrate how lake sediments capture different environmental signals depending on regional climate and watershed processes, highlighting the value of lacustrine isotope archives for reconstructing environmental changes across distinct environments.