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Elucidating Temporal Variability in Organic Matter Sources and Cycling in Tropical Rivers

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dc.contributor.advisor Ingalls, Anitra E en_US Ellis, Erin Elizabeth en_US 2012-09-13T17:20:19Z 2012-09-13 2012 en_US
dc.identifier.other Ellis_washington_0250E_10628.pdf en_US
dc.description Thesis (Ph.D.)--University of Washington, 2012 en_US
dc.description.abstract Tropical rivers are large sources of carbon to the atmosphere and the ocean. The composition of riverine organic matter (OM) affects the size of these fluxes by governing how much carbon will be returned to the atmosphere while in transit versus exported to the ocean, where carbon can be permanently buried in marine sediments. Carbon isotopes coupled with biomarker measurements are powerful tools to elucidate the sources and cycling of OM in rivers, yet few studies have employed them in the tropics. Here I use carbon isotopes (stable and radiocarbon) and biomarker measurements of higher plants and soils to address the following topics: sources of organic carbon respired in rivers; terrestrial OM sources to rivers; the age of riverine OM. In the Amazon Basin, in situ respiration rates are high enough to support the high carbon dioxide gas evasion rates occurring in many white-water rivers. C<sub>4</sub> grasses, C<sub>3</sub> plants, and phytoplankton fuel respiration, with phytoplankton being important during the low-water season. On the mainstem, C<sub>4</sub> grasses are an important substrate for respiration during the rising-water stage, but other sources dominate during falling water. In the Mekong Basin, vascular plants contribute to 15-76 percent of the particulate organic carbon (POC) exported by the river, with phytoplankton and higher plants dominating OM composition during the dry and rainy seasons, respectively. The age of lignin exported by the Mekong is consistently young (produced within the last 15 years), and it cycles amidst POC of varying ages, ranging from contemporary during the rainy season, to over 3,000 years old during the rising-water period. The aged signal observed during the dry period is likely due to the increasing influence from carbon derived from the Upper Basin (the Chinese mountains and the Tibetan Plateau), whereas the young rainy-season values reflect carbon derived from the Lower Basin. Seasonal variability in the composition of particulate lignin corroborates these findings. Finally, the highest concentrations of branched tetraether lipids were found in floodplains and lake beds, suggesting that anaerobic environments may be a significant source of these biomarkers to the river, with production likely occurring within the river. en_US
dc.format.mimetype application/pdf en_US
dc.language.iso en_US en_US
dc.rights Copyright is held by the individual authors. en_US
dc.subject Amazon; carbon; Mekong; organic matter; river; Tropics en_US
dc.subject.other Biogeochemistry en_US
dc.subject.other Hydrologic sciences en_US
dc.subject.other Chemical oceanography en_US
dc.subject.other Oceanography en_US
dc.title Elucidating Temporal Variability in Organic Matter Sources and Cycling in Tropical Rivers en_US
dc.type Thesis en_US
dc.embargo.terms Delay release for 2 years -- then make Open Access en_US
dc.embargo.lift 2014-09-03T17:20:19Z

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