Sources and Areal Distribution of Trace Metals in Recent Sediments of Middle Loch, Pearl Harbor (Hawaii).

摘要

The primary objective of this project was to determine whether current operations of the Naval Inactive Ships Maintenance Facility contribute significant trace metal contamination to Middle Loch of Pearl Harbor. Secondary objectives were (1) to identify and quantify all major sources of trace metal contamination in Middle Loch and (2) to determine if trace metal concentrations in Middle Loch have declined following termination of direct discharges from the Pearl City Sewage Treatment Plant. Sediment samples from ten locations within Middle Loch and from two locations in each of the two major streams entering the loch were analyzed for radioisotopes and metals. Major elements (aluminum and calcium) as well as organic and inorganic carbon were used to help characterize sediment composition and source. High aluminum-to-calcium ratios and high organic carbon concentrations are associated with terrigenous material carried into Middle Loch by the streams. The presence of the natural, short-lived (53-d half-life) radioisotope (7)Be was used to identify sites where the sedimentary material was recently deposited (i.e., within the past 3 months) and to identify patterns of recent sediment accumulation. Beryllium-7 was detected at eight of the ten sample sites within Middle Loch and in all stream samples. High (7)Be inventories beneath the ships and at the mouths of the streams suggest that these are areas of rapid sediment accumulation, or sediment focusing. The concentrations of (7)Be closely match the expected input based on rain-bucket data. This suggests that Middle Loch effectively traps all the (7)Be through adsorption onto suspended matter and deposition to the sediments. 14 refs., 10 figs., 8 tabs.