Reconstructing the Late Holocene History of Human Activity and Climate from a Costa Rican Diatom Record

This project expands on the 4200-year history of Laguna Los Mangos by adding diatom analysis to existing records of pollen, charcoal, elemental composition, and stable light isotope analysis. Diatoms were counted in peroxide-treated samples, and data were analyzed using cluster analysis, PCA, CCA, and Pearson correlation. Diatom variability was correlated with nitrogen and organic material. Before 3430 cal yr BP, diatoms reflect landscape instability with higher lake levels and macrophyte cover. This period was followed by a period of agriculture-induced nutrient pollution, reduced pH, and increased precipitation until about 2450 cal yr BP. Peaks in A. granulata may indicate periods of increased mixing driven by precipitation. Diatom composition reflects reduced agricultural activity and lake desiccation during the TCD and increased precipitation and agricultural collapse during the LIA. Overall, this record reflects a history of slightly alkaline, eutrophic conditions, increasing salinity, and human disturbance from maize agriculture and deforestation.