Source apportionment of sediment organic material in a semi-enclosed sea using Bayesian isotopic mixing model

Abstract

To determine sources of organic material in semi-enclosed Bohai Sea, samples of marine surface sediments, suspended particulates in adjacent rivers and atmospheric deposition were collected and analyzed for grain size composition, total organic carbon(TOC and POC), total nitrogen (TN and PN), and stable isotopic composition (δ¹³C and δ¹⁵N). Measured bulk C/N ratio (5.50-12.28), δ¹³C (-23.59~-19.54‰), and δ¹⁵N (2.80-8.07‰) values of surface sediment organic materials indicated a mixed source of marine and terrestrial contributions. Spatial distribution of organic C, N and their stable isotope composition indicated a land-sea gradient of organic material content and source combination. Using MixMIR model with dual isotopes, it was estimated that relative contributions of marine, riverine, and atmospheric sources to sediment mixture were 69.0%, 9.6%, and 21.4%, respectively. Our results demonstrated the advantage of Bayesian isotope mixing models over the conventional end-member mixing models for source apportionment in coastal seas with complex source origins.

Keywords: Atmospheric deposition; MixSIR Carbon budget; Particulate organic carbon; Stable isotopes.