Seasonal variations in concentration and lability of dissolved organic carbon in Tokyo Bay

[摘要] Concentrations of recalcitrant and bioavailable dissolved organic carbon(DOC) and their seasonal variations were investigated at three stations inTokyo Bay, Japan, and in two freshwater sources flowing into the bay. Onaverage, recalcitrant DOC (RDOC), as a remnant of DOC after 150 days ofbottle incubation, accounted for 78% of the total DOC in Shibaura sewagetreatment plant (STP) effluent, 67% in the upper Arakawa River water,66% in the lower Arakawa River water, and 78% in surface bay water.Bioavailable DOC (BDOC) concentrations, defined as DOC minus RDOC, were lowerthan RDOC at all stations. In freshwater environments, RDOC concentrationswere almost constant throughout the year. In the bay, RDOC was higher duringspring and summer than in autumn and winter because of freshwater input andbiological production. The relative concentration of RDOC in the bay derivedfrom phytoplankton, terrestrial, and open-oceanic waters was estimated to be8–10, 21–32, and 59–69%, respectively, based on multiple regressionanalysis of RDOC, salinity, and chl a. In addition, comparison withprevious data from 1972 revealed that concentrations of RDOC and BDOC havedecreased by 33 and 74% at freshwater sites and 39 and 76% in TokyoBay, while the ratio of RDOC to DOC has increased. The change in DOCconcentration and composition was probably due to increased amounts of STPeffluent entering the system. Tokyo Bay exported mostly RDOC to the openocean because of the remineralization of BDOC.

[学科分类] 地球化学与岩石