Determining source-specific terrigenous organic carbon contributions in sediments from the Yellow River estuary, Northeast China: A test of source apportionment models

Abstract

Molecular organic geochemistry has been used effectively to determine terrigenous organic carbon (OC) contributions from different sources in modern sediments. However, mathematic modelling using source-specific parameters could be a potentially simple-effective approach to identify the terrigenous OC signals. In this study, the Yellow River estuary was chosen to probe whether source apportionment models can determine source-specific OC contributions. The end-member mixing model suggests that terrigenous OC contributed 57.0% ± 10.2% to the sedimentary OC. n-Alkane distributions were used to perform Unmix and positive matrix factorization (PMF) to separate terrigenous and autochthonous OC into more specific sources. PMF modelling delineates the contributions of high terrigenous plants, fossil OC, macrophyte-sourced OC, and bacterial and algal-sourced OC as 22.9% ± 14.3%, 26.2% ± 19.4%, 26.5% ± 19.3%, and 24.4% ± 17.1%, respectively. In assessing terrigenous contributions, PMF results (48.7% ± 13.5%) almost agrees with the end-member mixing model (57.0% ± 10.2%), consistent and comparable with previously published data (~ 50%), while Unmix (73.9% ± 18.7%) is significantly overestimated. Interestingly, macrophyte-sourced OC from coastal wetland identified by PMF was less investigated previously and should call attention in the future study. Consequently, modelling results match well with previously published data, suggesting that mathematic modelling can be an effective approach to quantitatively evaluate source-specific terrigenous OC contributions to estuary sediments and other complex aqua-land systems. However, caution must be taken in respect to the modelling uncertainty, which could be mainly induced by sample number, diversity, and robust interpretation on chemical parameters.