Temporal variability in terrestrially-derived sources of particulate organic carbon in the lower Mississippi River and its upper tributaries

In this study, we examined the temporal changes of terrestrially-derived particulate organic carbon (POC) in the lower Mississippi River (MR) and in a very limited account, the upper tributaries (Upper MR, Ohio River, and Missouri River). We used for the first time a combination of lignin-phenols, bulk stable carbon isotopes, and compound-specific isotope analyses (CSIA) to examine POC in the lower MR and upper tributaries. A lack of correlation between POC and lignin phenol abundances (Lambda(8)) was likely due to dilution effects from autochthonous production in the river, which has been shown to be considerably higher than previously expected. The range of delta C-13 values for p-hydroxycinnamic and ferulic acids in POC in the lower river do support that POM in the lower river does have a significant component of C-4 in addition to C-3 source materials. A strong correlation between delta C-13 values of p-hydroxycinnamic, ferulic, and vanillyl phenols suggests a consistent input of C3 and C4 carbon to POC lignin while a lack of correlation between these same phenols and POC bulk delta C-13 further indicates the considerable role of autochthonous carbon in the lower MR POC budget. Our estimates indicate an annual flux of POC of 9.3 x 10(8) kg y(-1) to the Gulf of Mexico. Total lignin fluxes, based on As values of POC, were estimated to be 1.2 x 10(5) kg y(-1). If we include the total dissolved organic carbon (DOC) flux (3.1 x 10(9) kg y(-1)) reported by [Bianchi T. S., Filley T., Dria K. and Hatcher, P. (2004) Temporal variability in sources of dissolved organic carbon in the lower Mississippi River. Geochim. Cosmochim. Acta 68, 959-967.], we get a total organic carbon flux of 4.0 x 10(9) kg y(-1). This represents 0.82% of the annual total organic carbon supplied to the oceans by rivers (4.9 x 10(11) kg). (C) 2007 Elsevier Ltd. All rights reserved.