HR: 16:15h
AN: B44A-04    [Abstracts]
TI: Chemical and Isotopic Variations of Three Typical End-Member Organic Materials During Aging Process: Implications for Assessment of Relative Contributions of Various Organic Inputs in Altamaha Estuary
AU: * Dai, J
EM: samdai@uga.edu
AF: Department of Marine Science, Marine Science Building, Athens, GA 30605 United States
AU: Sun, M
EM: mysun@uga.edu
AF: Department of Marine Science, Marine Science Building, Athens, GA 30605 United States
AB: To evaluate the applicability of the end-member model in assessment of relative contributions of organic matter from various sources in estuarine system, we incubated three typical end-member organic materials (C3 marine diatom, C3 land grass, and C4 salt marsh plant) in Altamaha estuarine water over two months. Chemical and isotopic parameters (bulk organic carbon/nitrogen, lipid composition, stable C/N isotopes and lipid stable carbon isotopic ratios) were analyzed for fresh and aged materials. The analytical results showed that the chemical and isotopic compositions of three organic materials varied from material to material and from compound to compound during aging process. TOC and TN contents of C3 marine diatom and C3 land grass dramatically decreased (by 40-60%) while C4 salt marsh plant reduced its TOC and TN contents by less than 13% during incubation. Lipid compositions in all materials were greatly changed by aging process, as indicated by marked drops of unsaturated/saturated fatty acid ratios (e.g., 16:1/16:0 for diatom and 18:2+3/16:0 for higher plants). Bulk δ¹³C ratios of aged materials changed in a small range (-0.17‰ to +1.99‰) while their δ¹⁵N ratios shifted more noticeably (from +3‰ to +7‰). Lipid carbon isotopic compositions of three materials changed differently during aging process: some sterols (e.g., 27Δ⁵ and 29Δ⁵) had small isotopic shifts (<±1.7‰) while most plant fatty acids showed much greater enrichment (up to +8.3‰) except 16:0 in marine diatom (-2.6‰ depletion). Bacteria-specific fatty acids [iso-15:0, anteiso-15:0 and 18:1(ω7)] became significant components during incubations of all materials and their specific carbon isotopic ratios well corresponded to those of the substrate materials. These results suggest that use of end-member model must consider the age of organic materials and the potential changes in isotopic signals. The δ¹³C ratios of bacterial-specific fatty acids also provide insights to the distributions of bioavailable organic matter in estuarine system.
DE: 4200 OCEANOGRAPHY: GENERAL
DE: 4235 Estuarine processes
DE: 4825 Geochemistry
DE: 4850 Organic marine chemistry
SC: Biogeosciences [B]
MN: 2005 Joint Assembly