Rinehart, Amanda J. (2007-08). Dissolved organic matter discharge in the six largest arctic rivers-chemical composition and seasonal variability. Master's Thesis. Thesis uri icon

abstract

  • The vulnerability of the Arctic to climate change has been realized due to disproportionately large increases in surface air temperatures which are not uniformly distributed over the seasonal cycle. Effects of this temperature shift are widespread in the Arctic but likely include changes to the hydrological cycle and permafrost thaw, which have implications for the mobilization of organic carbon into rivers. The focus of this research was to describe the seasonal variability of the chemical composition of dissolved organic matter (DOM) in the six largest Arctic rivers (Yukon, Mackenzie, Ob, Yenisei, Lena and Kolyma) using optical properties (UV-Vis Absorbance and Fluorescence) and lignin phenol analysis. We also investigated differences between rivers and how watershed characteristics influence DOM composition. Dissolved organic carbon (DOC) concentrations followed the hydrograph with highest concentrations measured during peak river flow. The chemical composition of peak-flow DOM indicates a dominance of freshly leached material with elevated aromaticity, larger molecular weight, and elevated lignin yields relative to base-flow DOM. During peak flow, soils in the watershed are still frozen and snowmelt water follows a lateral flow path to the river channels. As the soils thaw, surface water penetrates deeper into the soil horizons leading to lower DOC concentrations and likely altered composition of DOM due to sorption and microbial degradation processes. The six rivers studied here shared a similar seasonal pattern and chemical composition. There were, however, large differences between rivers in terms of total carbon discharge reflecting the differences in watershed characteristics such as climate, catchment size, river discharge, soil types, and permafrost distribution. The large rivers (Lena, Yenisei), with a greater proportion of permafrost, exported the greatest amount of carbon. The Kolyma and Mackenzie exported the smallest amount of carbon annually, however, the discharge weighted mean DOC concentration was almost 2-fold higher in the Kolyma, again, indicating the importance of continuous permafrost. The quality and quantity of DOM mobilized into Arctic rivers appears to depend on the relative importance of surface run-off and extent of soil percolation. The relative importance of these is ultimately determined by watershed characteristics.
  • The vulnerability of the Arctic to climate change has been realized due to
    disproportionately large increases in surface air temperatures which are not uniformly
    distributed over the seasonal cycle. Effects of this temperature shift are widespread in
    the Arctic but likely include changes to the hydrological cycle and permafrost thaw,
    which have implications for the mobilization of organic carbon into rivers. The focus of
    this research was to describe the seasonal variability of the chemical composition of
    dissolved organic matter (DOM) in the six largest Arctic rivers (Yukon, Mackenzie, Ob,
    Yenisei, Lena and Kolyma) using optical properties (UV-Vis Absorbance and
    Fluorescence) and lignin phenol analysis. We also investigated differences between
    rivers and how watershed characteristics influence DOM composition.
    Dissolved organic carbon (DOC) concentrations followed the hydrograph with
    highest concentrations measured during peak river flow. The chemical composition of
    peak-flow DOM indicates a dominance of freshly leached material with elevated
    aromaticity, larger molecular weight, and elevated lignin yields relative to base-flow
    DOM. During peak flow, soils in the watershed are still frozen and snowmelt water
    follows a lateral flow path to the river channels. As the soils thaw, surface water
    penetrates deeper into the soil horizons leading to lower DOC concentrations and likely
    altered composition of DOM due to sorption and microbial degradation processes. The
    six rivers studied here shared a similar seasonal pattern and chemical composition.
    There were, however, large differences between rivers in terms of total carbon discharge
    reflecting the differences in watershed characteristics such as climate, catchment size, river discharge, soil types, and permafrost distribution. The large rivers (Lena, Yenisei),
    with a greater proportion of permafrost, exported the greatest amount of carbon. The
    Kolyma and Mackenzie exported the smallest amount of carbon annually, however, the
    discharge weighted mean DOC concentration was almost 2-fold higher in the Kolyma,
    again, indicating the importance of continuous permafrost. The quality and quantity of
    DOM mobilized into Arctic rivers appears to depend on the relative importance of
    surface run-off and extent of soil percolation. The relative importance of these is
    ultimately determined by watershed characteristics.

publication date

  • August 2007