Reconstructing productivity changes in Lake Tota (Boyacá) through the study of its sedimentary record

• Autores: Claudia Liliana Muñoz-López
• Directores de la Tesis: Carlos A. Rivera Rondón (dir. tes.)
• Lectura: En la Pontificia Universidad Javeriana ( Colombia ) en 2025
• Idioma: inglés
• Enlaces
  • Tesis en acceso abierto en: hdl.handle.net
• Resumen

  • High mountain lakes are exceptional systems for detecting environmental changes at different scales. The objective of this thesis was to identify the effect of anthropic activities on the productivity of Lake Tota (Boyacá), through the study of diatoms and biogeochemical indicators, in a paleolimnological multi-proxy approach. Likewise, the response of diatoms to environmental gradients in mountain lakes was studied to determine their potential to indicate conditions of the aquatic environment and thus be used in reconstruction. Two sediment cores from this lake were analyzed using Pb dating and cluster analysis. Changes in organic matter, carbon and nitrogen isotope ratios, C:N ratios, diatoms and elemental fraction were studied as productivity indicators. pH changes were reconstructed using transfer functions based on a training set composed of diatoms and environmental variables collected from 60 mountain lakes, including Tota. Water samples were collected for physical and chemical characterization, and diatoms were sampled from the bottom sediment. The results showed that alkalinity and pH emerged as reliable models for diatom reconstruction and prediction, with high correlation values and low mean error, emphasizing robust reconstruction and prediction capabilities. Sediment proxies indicated two periods of environmental change: (1) a large pre-eutrophication period prior to 1960 A.D. dominated by alkaline conditions, mesotrophic diatoms and inorganic sediment accumulation by erosion; and (2) an accelerated anthropogenic eutrophication period (1960-2021 A.D.) associated with human population growth, rapid land-use change, and organic accumulation in the sediments. Analysis of Lago Grande and Lago Chico identified two distinct diatom zones, consistent with shifts in biogeochemical proxies. These zones indicated changes from well-oxygenated and moderately productive period to hypoxic conditions and highly productive conditions as reflected by changes in the S/Fe ratio. In particular, a progressive increase in sediment organic matter and diatom concentrations was observed after 1960 A.D. The study showed that increases in δ¹⁵N values due to agricultural runoff indicate increased nitrogen inputs that stimulate primary productivity and alter nutrient dynamics. In addition, shifts in δ¹³C values indicate changes in organic carbon sources, associated with nutrient enrichment and high terrestrial inputs due to erosion. These isotopic shifts reflect ecological changes in response to human influence, affecting processes such as primary productivity, nutrient availability, and food web dynamics.