Abstract
Chronological changes in heavy metal concentrations were investigated by chemical analysis of core sediments from Manko tidal land, downstream area of the Kokuba and Noha rivers in Naha city. It is located in a densely-populated area, and the soil has been contaminated with heavy metals from development upstream flowing into the tidal land. The sedimentation rate of cores measured using the 210 Pb ex method was estimated to be 1.1-1.9cmy-1 (2.1-3.7gcm-2y-1), a relatively rapid rate. Depth profiles of the aluminum content in the sediment showed only a small variation, whereas the calcium content tended to increase. Lead also showed a tendency to increase through the 1980s, but has decreased ever since likely influenced by the popularization of unleaded gasoline. Other heavy metals such as Ni, Cu and Hg showed a low concentration downstream of the Noha river but showed a high concentration in the confluence area of the two rivers. This result suggests that these elements in the sediment likely originated from the Kokuba river.
