Contribution of transparent exopolymeric particles (TEP) to estuarine particulate organic carbon pool

Transparent exopolymer particles (TEP) contribute to carbon export and can represent a significant fraction of the carbon pool, most notably in estuarine systems. This study investigates, for the first time, TEP seasonal variability, vertical distribution and contribution to the carbon pool in the Lower St. Lawrence Estuary (LSLE), a highly productive subarctic estuary. TEP variability was investigated on a weekly basis at a fixed station (IML-4) from May to October 2011. TEP remained relatively low (15 mu g GX eq l(-1)) during spring, but increased markedly in summer and fall, with surface concentrations reaching up to 1548 mu g GX eq l(-1). TEP concentrations were positively correlated with the phytoplankton biomass in surface waters. No significant relationship between TEP and other biological and physico-chemical factors was found. TEP-C content represented the second most important contributor to the particulate organic carbon pool after phytoplankton-C (41 and 54%, respectively) in the surface layer. The TEP-C contribution decreased in the cold intermediate and bottom layers over the summer and fall (ranging between 24 and 35%). However, this contribution was particularly high during the spring (>94%) in the cold intermediate and bottom layers, possibly due to the colloidal organic carbon fraction contributing to TEP-C in deep waters. Our results suggest that TEP-C combined with phytoplankton-C are major contributors to the carbon pool and could significantly contribute to the subsequent export of macro-aggregates, and probably contribute to the decrease in oxygen concentration and pH in the bottom layer of the LSLE by respiration/remineralisation processes.