Assessing source contributions to particulate organic matter in a subtropical estuary: A biomarker approach

Assessing the sources and quantifying the contributions of particulate organic matter (POM) in estuaries is a challenge. Here we apply source-specific biomarkers to assess POM sources in an estuary receiving suspended material from freshwater wetlands, fringe mangroves and coastal environments. A three end-member mixing model, including terrestrial, estuarine and marine end-member contributions was developed and successfully validated to assess general OM dynamics and hydrologic processes that control POM distributions within the Shark River estuary in South Florida. Low tide and wet season conditions coincided with an enhanced signal of the freshwater end-member biomarker abundance, while high tide and dry season conditions resulted in enhanced POM input of marine origin. Incoming tide was observed to be an important factor in the re-suspension and tidal pumping of mangrove-derived POM, which seems to be the dominant source of particulate organic carbon (POC) in the estuary. The three end-member conceptual model was tested to obtain a rough estimate of POC source strength, with the ultimate goal of constraining carbon budgets in this sub-tropical estuary. Mangrove-derived POC flux of ca. 5.3 × 105 to 1.0 × 106 kg/yr POC from the Shark River to the Gulf of Mexico were estimated, but end-member values used in the assessment need to be better constrained to reduce the degree of variability.