Environmental History of Estuarine Dissolved Oxygen Inferred from Trace-Metal Geochemistry and Organic Matter
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Environmental history recorded in sediments can reconstruct estuarine water quality metrics, such as dissolved oxygen, through the use of geochemical and biological proxies. I collected sediment cores from two locations in the Coos Bay Estuary, at South Slough and Haynes Inlet, spanning from ~1680 AD to the present. To address the historical record of water column oxygen in the estuary I measured a suite of geochemical proxies including organic matter, magnetic susceptibility, and redox-sensitive metals to calibrate against a detailed 15-year record of dissolved oxygen. High visual correlation of these proxies and recent water quality supports the interpretation of long-term water quality from sediment cores. Finally, my semi-quantitative analysis describes a complex history where potential low water quality has increased at South Slough, while decreasing or staying stable at Haynes inlet over the last 300 years, though erosion indicators profoundly increase at both sites across the Euro-Amercian settlement horizon. This history was explained in terms of changing land use (logging, splash dams) effects on erosion and organic matter loading, oceanic vs terrestrial water sources, and the role of the dredged Coos Bay channel affecting the replenishment of estuary water.