Source-age dynamics of estuarine particulate organic matter using fatty acid delta C-13 and Delta C-14 composition

This study used a multiproxy approach to elucidate the source and age composition of estuarine particulate organic matter (POM) using bulk stable isotopes (C-13(POC)), fatty acid (FA) biomarkers, and compound specific isotopic analyses in surface waters along the Delaware River and Bay (Delaware Estuary, hereafter). C-13 values of FA (C-13(FA)) ranged more widely (-30.9 parts per thousand to -21.8 parts per thousand) than C-13(POC) (-27.5 parts per thousand to -23.5 parts per thousand), providing greater insight about POM sources along the estuary. C-13 values of C-16:0 phospholipid FA (primarily, aquatic sources) increased along the salinity gradient (-29.8 parts per thousand to -23.4 parts per thousand), while C-13(FA) values of long-chain neutral fatty acid (terrestrial sources) decreased (-28.6 parts per thousand to -30.9 parts per thousand). C-13(FA) values for C-18's FA indicated the importance of marsh-derived organic matter within Delaware Estuary. Compound specific radiocarbon analysis showed the heterogeneous age structure of FA associated with POM (FA(POM)). C-14 ages of FA ranged from modern (postbomb) to 1790BP; aged FA (120BP to 1700BP) derived primarily from the watershed, whereas modern FA were produced within Delaware Estuary. C-14 ages of short-chain FA (aquatic sources) reflected differences in the age of dissolved inorganic carbon along the estuary and had older C-14 ages at the river end-member. C-14 ages of FA from terrigenous sources were older than water and sediment residence times indicating this source derived from the watershed. This study is the first to document the complex age distribution of FA(POM) along the estuarine salinity gradient and shows that inorganic carbon sources, watershed inputs and autochthonous production contribute to variation in the ages of POM.