Sources of particulate organic matter in surface waters of the York River, VA estuary

Estuaries play an important role in the global carbon cycle as sites of removal and transformation for carbon derived from terrigenous and anthropogenic sources and as sites of high primary production. In this study, C:N ratios, bulk stable carbon isotopes (δ13C), and fatty acid and sterol biomarker compounds were used to identify seasonal variations in the sources of particulate organic matter (POM) in surface waters of a temperate estuary, the York River, VA. Surface water samples were collected seasonally from six sites along the York River between June 1998 and April 1999. Lipid biomarker compounds (sterols and fatty acids) were analyzed to evaluate the sources of POM to the estuary. With the exception of a site located in the freshwater region, POM was dominated by autochthonous sources and exhibited little temporal variability. Compounds reflecting zooplankton and phytoplankton sources of POM dominated fatty acid and sterol biomarkers. Similarly, isotopic and molecular biomarkers were dominated by algal signatures throughout most of the estuary. However, the freshwater portion of the estuary was unique in its biomarker and isotopic signatures, reflecting contributions from local marshes and/or terrigenous vascular plant sources. Overall, despite the relatively pristine condition of the York River, biomarker signatures and concentrations were similar to those found in the nearby, but more impacted, Chesapeake Bay.