Dissolved and Particulate Organic Matter Dynamics Relative to Sediment Resuspension Induced by the Tidal Cycle in Macrotidal Estuaries, Kyushu, Japan

Abstract

The tide-induced resuspension of sediments plays important roles in the efflux of particulate organic carbon (POC) from rivers to the coastal sea. Although dissolved organic carbon (DOC) comprises more than half of the riverine flux of organic carbon to the ocean, the influence of sediment resuspension induced by the tidal cycle on DOC dynamics is largely unknown. This study examined the dynamics of POC, particulate organic nitrogen (PON), DOC, humic-like and protein-like fluorescent dissolved organic matter (DOM) in relation to the tidal cycle in the Chikugo and Hayatsue River Estuaries, Kyushu, Japan. This study is the first to show both the particulate organic matter (POM) and DOM dynamics in relation to the tidal cycle in the macrotidal estuaries. We found that the turbidity changed with the tidal cycle and that there were significant positive correlations of turbidity with POC and PON in the Chikugo River mouth, suggesting that tide-induced sediment resuspension supplied POM to the water column. The DOC concentration, humic-like and protein-like fluorescent DOM were not correlated with turbidity but were negatively correlated with salinity. These results suggest that POM efflux, but not DOM efflux, can be accelerated by tide-induced sediment resuspension in the macrotidal estuaries.