Program

Spectral analysis have been widely used to characterize the quantitative and qualitative variation of dissolved organic matter (DOM) in various aquatic environments, including the estuaries which are the major link between land and ocean carbon cycles. Particulate organic matter (POM) was also an important role of estuarine carbon pool. However, the spectral analysis of estuarine POM are still very limited. In this study, absorption and three-dimensional fluorescence spectroscopy were utilized to reveal the optical properties of POM (i.e. chromophoric particulate organic matter, CPOM) in the turbid macrotidal Jiulong River Estuary, China. Surface suspended particles along the estuarine transects were collected during eight cruises between 2014-2015. Time-series POM samples were also collected from the fixed stations of the estuarine turbidity maximum (ETM) zone in May and July, 2015. CPOM absorption coefficient (a₃₅₀p) and fluorescence intensities of the six PARAFAC components generally decreased with the increasing salinity. However, obvious removal and addition of CPOM signals were observed in the river-estuary interface, indicated the active processes (e.g. flocculation, desorption, adsorption) occurred in this dynamic land-sea transitional zone. Such result was further supported by the significant changes of the qualitative and quantitative properties of CPOM in ETM zone within the tidal cycle. The intensity ratio of protein-like to humic-like fluorescence components (P/H) generally increased with salinity along the estuarine transect, consistent with the change of the POM sources in the estuary from terrestrial-dominated into marine-dominated. The comparison of the P/H ratio of CPOM with δ¹³C of POC demonstrated that spectral analysis is a powerful tool to study the sources and quality of suspended and sediment organic matter in estuarine environments.

Keywords: Chromophoric particulate organic matter; absorption and fluorescence spectroscopy; estuary; estuarine turbidity maximum; ¹³C isotope