Physicochemical and biological processes characterizing suspended particulate organic matter in a temperate estuarine bay exposed to a low-turbidity river discharge

Abstract

Estuaries are characterized by great seasonal and spatial variations of biogeochemical and hydrological processes and act as a continuum between the terrestrial environment and the coastal ocean. Suspended particulate organic matter (SPOM) in estuaries derived from autochthonous (in situ production) and allochthonous (terrestrial) sources. To better understand the sources, physicochemical and biological processes regulating particulate organic matter (POM) and phytoplankton community composition, spatial and temporal patterns of environmental conditions and their relation to the phytoplankton community were studies. Different multivariate analysis techniques identified regional differences corresponding to salinity, turbidity (SPM), and seasonal riverine nutrient inputs from Seomjin River. The phytoplankton community of Gwangyang Bay was dominated by diatoms and dinoflagellates. Particulate organic matter (POC) and nitrogen (PN) amount, POC:Chla , C:N ratio and isotopic signatures (δ13CPOM and δ15NPOM) showed that POM was mainly autochthonous phytoplankton-derived with negligible terrestrial inputs and was greatly influenced by seasonal community composition. Further biochemical composition of seston i.e., carbohydrates (CHO), proteins (PRT), lipids (LIP) and proxies like PRT:CHO and CHO:LIP highlighted that phytoplankton physiological status and seasonal succession of community composition regulate the quality of POM. Hence autochthonous biological production leads to high nutritive value POM available to consumers based on fatty acids profiles of source and consumers and consumers diets reflecting POM ingestion and diatoms and dinoflagellates accounting for major portion of consumers diets.