STATE-OF-THE-ART LAND-SEA OBSERVATION FOR COLORED DISSOLVED ORGANIC MATTER (CDOM) IN NANAO WEST BAY AND KUMAKI RIVER

Abstract

 River plumes forming in coastal oceans significantlly impact on the marine environment because they contain large amounts of dissolved organic matter and nutrients. Since their dynamics vary greatly in space and time, high-resolution observations in the coastal oceans shouled be essential. This study investigated the spatio-temporal variation on colored dissolved organic matter (CDOM), a bio-refractory substance, as an indicator of terrestrial loads from the watershed of Kumaki River into the coastal sea located around the west bay of Nanao Bay, Ishikawa Prefecture, to capture the land-sea material dynamics. We conducted the integrated observations over the land and ocean using a CDOM logger and a automated vessel. As a result, the CDOM concentration was low in the upstream of Kumaki River mostly covered by the forest, and the concentration increased in the middle watershed retaining the large area of rice paddy fileds. Finally, the concentration in the downstream tidal areas decreased as salinity increased due to seawater dilution. Our marine observations using the automated vessel indicated that the water mass characterized by the low salinity and the low CDOM concentration was transported by the tidal flow and ocean currents from the estuary of Kumaki River to the oyster aquaculture and offshore areas, suggesting the the advection-diffusion process of river plume and its dilution.