Application of a chemical leach technique for estimating labileparticulate aluminum, iron, and manganese in the ColumbiaRiver plume and coastal waters off Oregon and Washington

摘要

In order to determine the total concentration of bioavailable trace metals in seawater,measurement of both the dissolved and labile particulate fractions is necessary.Comparison of labile particulate metal concentrations from various researchers is limitedbecause of differing definitions of the fraction that is potentially available tophytoplankton on a time frame of generations. A comparison experiment was conductedon coastal and riverine suspended particulate matter to determine the difference betweenseveral commonly used techniques that operationally define the labile particulate tracemetal fraction. Furthermore, we compared two leach techniques for surface transectsamples from within the Columbia River plume and water offshore of Oregon andWashington, United States. The particulate trace metal concentration in the leachate wasdetermined by high-resolution inductively coupled plasma–mass spectrometry. From thiscomparison, one chemical leach was chosen to best define the labile particulate fractionof Al, Fe, and Mn: a weak acid leach (25% acetic acid at pH 2) with a mild reducingagent (0.02 M hydroxylamine hydrochloride) and a short heating step (10 min 90-95°C).This leach was applied to three surface transects within the Columbia River plume. Thesecoastal waters were found to be rich in labile particulate trace metals that are directlydelivered from the Columbia River and indirectly supplied via resuspension fromupwelling over a broad continental shelf.