Reconstructing carbon dynamics of alpine and temperate zone lakes using stable isotopic analysis

Research output: ThesisPhD Thesis

Abstract

Lake sediments integrate signals from the catchment, atmosphere and water column, offering a unique window through which to view changes in the carbon cycle. Carbon dynamics in lakes are changing due to nitrogen loading and anthropogenic climate warming (ACW), threatening the water quality of lakes. This thesis identifies how the carbon dynamics of lakes have responded to anthropogenically-driven forcings by comparing pre- and post- AD 1850 records preserved in lake sediments. First, the carbon dynamics of Barry Lake (Ontario, Canada), a low-elevation temperate lake, are investigated. Effective moisture (the net of water inputs and evaporation) is reconstructed using the carbon and oxygen isotope compositions of marl, carbon isotope compositions of total organic carbon and hydrogen isotope compositions of the n-alkane C17. The isotope compositions and abundances of biomarkers are used to reconstruct changes in organic matter (OM) source and methane oxidation. These reconstructions reveal that current levels of primary production in Barry Lake are unprecedented during the last ~900 years, likely due to land use change and, perhaps, ACW. Furthermore, inferred methane oxidation and OM source, but not primary production, are closely tied to changes in effective moisture. This finding suggests that future changes in aridity driven by anthropogenic climate change may alter the sources of carbon to sediments and affect how methane is recycled by temperate lakes. A second goal of this thesis is to characterize sources of organic matter to four cold, high-elevation alpine lakes (Uinta Mountains, Utah, United States). Analyses of modern terrestrial and aquatic samples provide a baseline to improve interpretations of stable isotopes in alpine lake sediments. A database of carbon and hydrogen isotope compositions of n-alkanes extracted from vegetation surrounding the lakes is used to estimate the carbon isotopic composition of ancient carbon dioxide (δ13CCO2) and hydrogen isotopic composition of ancient precipitation (δ2Hprecip). Finally, a comparison of Barry Lake with the Uinta Mountain lakes reveals that both systems have become more productive in the last 50-100 years. In summary, this thesis identifies recent changes in the carbon dynamics at Barry Lake and advances the ability of researchers to interpret proxies in alpine environments.
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • Western University
Award date26 Feb 2021
Publication statusPublished - 23 Dec 2020

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