Environmental history recorded in estuarine sediment describes water quality regimes through the use of geochemical and biological proxies. We collected sediment cores from two locations in the Coos Estuary, Oregon, at South Slough and Haynes Inlet, spanning from ~ 1680 AD to the present. To reconstruct the historical water column oxygen in the estuary, we measured geochemical proxies including organic matter, magnetic susceptibility, and elemental composition, and we constructed sediment chronologies using the Pb210 profile and radiocarbon dates. Correlation of geochemical proxies and a detailed 15-year record of dissolved oxygen observations supports the inference of dissolved oxygen (DO) history from these sediment cores: a novel finding for small, seasonal Pacific Northwest estuaries. Geochemical evidence suggests that over the last 300 years, annually or semi-annually averaged dissolved oxygen stress has been increasing at South Slough, while remaining stable or even decreasing at Haynes inlet. This history was explained by changing climatic and land-use effects on erosion and organic matter as well as the role of shipping channel maintenance in providing a dissolved oxygen reservoir at Haynes Inlet relative to the more isolated South Slough.

Authors: Johnson, Geoffrey M.; Sutherland, David A.; Roering, Josh J.; Mathabane, Nathan; Gavin, Daniel G.

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Estuaries and Coasts, July 2019, Volume 42, Issue 5, pp. 1211-1225
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15 pages