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Koh, Jasmine Su Lin

A method for the determination of concentrations and speciation of dissolved chromium in seawater was developed in this study and applied to the analysis of chromium in the waters of Saanich Inlet. A magnesium coprecipitation method was used to allow for the preconcentration and isolation of the trivalent fraction, and a reduction step employed to reduce all chromium to its trivalent form to allow for complete scavenging. Graphite furnace atomic absorption (GFAAS) and quadrupole inductively coupled plasma mass spectrometry (ICP-MS) was used for the analysis. The detection limit of the method was a minimum of 0.26 nM on the GFAAS and 1.18 nM on the ICP-MS, with an analytical precision of <1-20% (n=3) for both methods. The magnesium coprecipitation method was used to examine the seasonal variations in chromium in the Saanich Inlet – a seasonally anoxic fjord on Vancouver Island that is typically subject to renewal events that reoxygenate the bottom of the inlet and alter the dominant redox conditions of the water column. Anoxia was consistent below 100-140 m depths through the months of November 2015, January and February 2016, with the persistence of dissolved hydrogen sulfide in the bottom waters indicative of the lack of strong renewal in 2015. The chromium seasonal cycle appeared to be controlled instead by a combination of biologically-mediated reduction and removal from the surface waters, a diffusive flux of chromium driven by the strong concentration gradient of the two species across the oxycline, and a particulate export of chromium to the sediments. Chromium concentrations were observed to accumulate over the fall and winter months, culminating in a drawdown of the hexavalent fraction and the export of particle-reactive trivalent chromium on organic particulates to the sediment following the onset of a spring bloom. An examination of the speciation of dissolved chromium from the months of February to August may be necessary to provide a more comprehensive understanding of the seasonal cycle of chromium in Saanich Inlet.

Text

University of British Columbia. EOSC 449

Vancouver : University of British Columbia Library

10.14288/1.0300371

Earth and Ocean Sciences, Department of; Science, Faculty of

Unreviewed

http://creativecommons.org/licenses/by-nc-nd/4.0/