Records of Lead and Other Heavy Metal Inputs to Sediments of the Ala Wai Canal, O'ahu, Hawai'i

Abstract

In this paper we present depth profiles of selected transition metals and major constituents in four sediment cores recovered from the Ala Wai Canal, a small drainage estuary in Honolulu, Hawai'i. Our study documents the advent, increase in use, and subsequent phasing out of Pb-alkyl fuel additives in Honolulu over the past 60 yr. Sedimentary Pb concentrations increase from < 10 ppm in the oldest (deepest) portions of the cores to a maximum of about 750 ppm in sediments corresponding to the mid-1970s; subsequently Pb contents decrease to a range of 100-300 ppm in the most recent deposits. Other metals, including Cd, Cu, and Zn, reveal patterns that are also consistent with an increasing flux of metals to the sediments attributable to anthropogenic inputs. However, unlike Pb, these metals do not exhibit clear maxima in sediments deposited during the mid-1970s. Rather, there appears to be a continued input of these metals from the watershed likely associated with ever-increasing anthropogenic activity in Honolulu. Approximately 25-75%, depending on the depth within the core, of the Cu and Zn contents of the sediments can be attributed to natural inputs of soils formed by weathering of the O'ahu volcanic edifices. Elements such as Co and Ni are found in concentration ranges consistent with the dominant mineralogy of the sediments and do not appear to exhibit an anthropogenic signal.