The fate of terrestrial-derived organic matter (OM) in estuaries is poorly characterized, obscuring the link between carbon cycles of land and sea. This study characterized sources of OM in the Delaware Estuary using multiple organic geochemical analyses: bulk and compound-specific stable carbon isotopes, and n-alkane and phospholipid fatty acid (PLFA) biomarkers. The spatial and temporal variations in particulate organic matter (POM) character in both surface and bottom waters were evaluated for 5 seasonal cruises in 2010-2011. Axial transects were from a marine to a riverine endmember, and geochemical analyses additionally emphasized the estuarine turbidity maxima (ETM), and chlorophyll maxima. POM characteristics were consistent with previous studies. POM was generally <10% organic carbon (OC) and the δ13C signature of POM became progressively enriched moving downstream, from -26.5 ± 2.3‰ at the riverine endmember to -22.0 ± 1.9‰ at the marine endmember. Yet, mixing of sources in the ETM and spring phytoplankton bloom signatures in Delaware Bay masked the pathway of terrestrial sources. In contrast, n-alkane and PLFA biomarkers showed the proportion of algal- and terrestrial-derived OM to be comparable in surface waters throughout the estuary and bottom waters were substantially higher in terrestrial and marsh inputs. Bottom water particulates in the ETM comprise the largest suspended OC pool in the estuary, which has a significant terrestrial component and was previously uncharacterized. Biomarker results from this study suggest that the ETM is an effective trap of terrestrial POM. The δ13C of long chain n-alkanes (C23-C33) confirmed substantial inputs from C4 marsh plant material in both September 2010 (-29.3 ± 0.9‰), and in March 2011 (-31.0 ± 2.1‰). The presence of marsh-derived OM in the main axis of the estuary and ETM suggests that lateral processes are important for OM cycling in estuaries and that the vascular plant derived OM reaching the ocean may not be sourced from upland drainage basins, but from more local inputs such as fringing wetlands. The role of marsh-derived OM in the marine OC cycle demands further attention to fully constrain its reactivity and fate in the marine environment.
Subject (authority = RUETD)
Topic
Oceanography
Subject (authority = ETD-LCSH)
Topic
Bulk solids--Sampling
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Rutgers University Electronic Theses and Dissertations
Rutgers University. Graduate School - New Brunswick
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