Fluxes and Transport of Organic Carbon and Trace Metals in the Tropical Tsengwen Estuary,Southwestern Taiwan

Distributions of organic carbon and trace metals were investigated in the tropical Tsengwen river end-member and in the estuary to better understand thoroughly the riverine fluxes and estuarine transports of constituents into the sea. Experimental results indicated that riverine fluxes of organic carbon and trace metals possessed a highly temporal variability, attributed primarily to temporal variation in river water discharge and suspended load. More than 70% of annual fluxes of dissolved constituents and >90% of particulate constituents arose from river floods caused by summer typhoons. the flushing time of fresh water in the estuary varied from a half month in the dry season to a half day in the flood period. Dissolved organic carbon (DOC) and nutrienttype metals (Cd, Cu, Zn) were conservatively transported through the estuary. Dissolved particle-reactive metals (Mn, Pb), however, were apparently transported non-conservatively through the estuary. Particulate organic carbon (POC) and trace metals (PTM) were transported non-conservatively by following the transport mode of total suspended matter (TSM) in the estuary. DOC slightly dominates the transport of organic carbon while particle-reactive PTM predominates the transport of trace metals through the estuary. Total organic carbon (TOC) in estuarine sediment was progressively enriched with ¹³C downstream, as derived by mixing the overlying TSM between terrestrial and marine end-members. Distributions of trace metals in sediment were subsequently controlled by sedimentary TOC and particle size. Based on results presented here, we believe that enrichments of trace metals in the estuary are attributed primarily to the natural processes of transport and sedimentation of fluvial TSM