The lateral transport of carbon across the landscape is an area of research that lags behind other aspects of global carbon cycle science. Smaller in magnitude than net primary production, the transport of organic and inorganic carbon represents a 2.7 Pg C yr−1 flux into the world's major rivers of which 1.0 Pg C yr−1 is exported to the ocean and 1.1Pg C yr −1 is degassed across the rivers and estuarine surface. Riverine carbon represents a net flux of carbon from the terrestrial biosphere.
In chapter 2 I utilize chemical measurements in rivers and high resolution spatial data on river morphology to estimate the contribution of carbon in CO2 degassed from streams and rivers in the US. Streams and rivers in the US are super-saturated in CO2 averaging ∼2400 µatm and emit 97 ± 32 Tg C yr−1 to the atmosphere. I report a strong correlation between regional stream CO2 evasion and precipitation which I suggest is due to the climatic regulation of watershed geomorphology and CO2 flushing from soils. This estimate for the U.S. scales to ∼0.5 Pg of carbon emitted annually from northern temperate rivers between 25°N and 50°N.
In chapter 3 I show that the Δ14C of DOC varies across 15 large river basins in the coterminous United States from a low of −92.9‰ in the Colorado River to 73.4‰ in the Altamaha River for the year 2009. Average Δ14C of DOC for all rivers in the US is −1.3–1.2‰). This variation correlates to indices of the aromaticity of the DOC measured by the specific UV absorbance at 254nm (SUVA254; r2 = 0.6, p<0.001) as well as differences in annual river discharge. I then explain the variation in SUVA254 by differences in the watershed vegetation characteristics measured by the Enhance Vegetation Index derived from the NASA Moderate Resolution Imaging Spectrometer (MODIS). I suggest that basins with high discharge, high proportions of vegetation cover, and low population densities export organic material this is enriched in aromatic plant material that corresponds to recently fixed atmospheric CO2.
In Chapter 4 I present a systematic analysis of both the variation in organic matter quality and biologically available DOC (BDOC) for 15 large temperate river systems in North America from 2009–2010. I evaluate the ability of optical properties and develop a Parrallel Factor Analysis Model (PARAFAC model) to explore differences in organic matter quality and BDOC. DOC concentrations ranged from 1.8–15.8 mg C 1−1 . Specific UV absorbance at 254nm ranged from 1 – 4.9 L/(mg C * m) and the hydrophobic organic acid fractions (HPOA) varied from 29% – 50% across all 15 basins. In contrast to the chemical variation, BDOC as a percentage of the DOC pool averaged 4.1 ± 2% across all basins. Results from a PARAFAC model suggest that intermediate organic matter components are present in large river basins as a result of in-situ processing including photo-oxidation. The proportion of the total DOC pool represented by each component of the PARAFAC model showed remarkable uniformity suggesting that in-stream processing greatly affects the final composition of organic matter exported from large temperate river systems.
In chapter 5 I evaluate 3 common analytical methods for the determination of DOC, High Temperature platinum catalyzed combustion (HTC), UV promoted persulfate digestion, and High energy UV-Oxidation. I find that both the UV-Oxidation and persulfate digestion produce the highest recoveries of dissolved organic carbon. I show the effect of freezing and use of HTC can results in a systematic loss of up to 18% of the total DOC and suggest that freezing as a method of preservation should be used when no other option is available. I emphasize caution when evaluating DOC concentration and trends across research studies as there can be significant systematic differences between dissolved organic carbon determination methods. (Abstract shortened by UMI.)
|Advisor:||Raymond, Peter Alexander|
|School Location:||United States -- Connecticut|
|Source:||DAI-B 73/12(E), Dissertation Abstracts International|
|Keywords:||Carbon-14 isotope, Coastal water, Organic carbon, Radio carbon|
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