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Manganese chemistry in the Fraser estuary

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Title: Manganese chemistry in the Fraser estuary
Author: De Mora, Stephen John
Degree Doctor of Philosophy - PhD
Program Oceanography
Copyright Date: 1981
Subject Keywords Manganese -- Environmental aspects; Fraser River Estuary (B.C.)
Abstract: The Fraser Estuary was investigated five times under varying flow regimes. The surface distribution of dissolved manganese consistently exhibited a maximum value at a salinity ranging from 4 to 12 ppt. Experimental results and field data suggest this peak does not result from the desorption nor dissolution of riverborne suspended particulate manganese. The excess metal is derived from the estuarine bottom sediments. Desorption or dissolution of manganese from the estuarine bottom sediments resuspended due to the advancing salt wedge enhances the dissolved manganese concentration in the bottom waters, especially in the toe of the salt wedge. This manganese enrichment may also be influenced to a lesser extent by the concurrent release of some interstitial water with enriched dissolved manganese concentrations due to the in situ reduction of amorphous manganese oxides. The subsequent entrainment and mixing of water from the toe of the salt wedge into the outflowing river water causes a downstream increase in the dissolved manganese content, and eventually determines the peak manganese concentration and salinity. Further downstream mixing with saline waters having relatively low manganese levels causes surface concentrations to decrease. Thus, the dissolved manganese distribution can be explained in terms of two conservative dilution curves which intersect at the manganese peak. The dissolved oxygen generally behaves conservatively in both the surface and bottom waters of the Fraser Estuary. The removal of alkalinity may occur at low salinity, however, alkalinity exhibits conservative behaviour through most of the salinity range. The surface distribution of pH can be replicated theoretically only when mixing in the surface is considered as a two step process. The alkalinity behaves conservatively in the surface waters of the Strait of Georgia. The pH and dissolved oxygen display seasonal variations related to primary productivity and mixing processes. The distribution of dissolved manganese in surface waters of the Strait of Georgia is determined mainly by the dilution of Fraser River water. Bottom waters have enhanced dissolved manganese concentrations due to reductive remobi1ization of manganese from the sediments. Concentrations of dissolved manganese at mid-depths are determined by seasonal variations in the stability of the water column. Depth profiles of suspended particulate manganese indicate increasing concentrations with depth. This may result from the oxidative precipitation of manganese and/or the resuspension of bottom sediments.
URI: http://hdl.handle.net/2429/22730
Series/Report no. UBC Retrospective Theses Digitization Project [http://www.library.ubc.ca/archives/retro_theses/]
Scholarly Level: Graduate

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