Historic and recent patterns of dissolved oxygen in the Yaquina Estuary (Oregon, USA): Importance of anthropogenic activities and oceanic conditions

Abstract

Spatial and temporal patterns of dissolved oxygen (DO) in Yaquina Estuary, Oregon (USA) are examined using historic and recent data. There was a significant increasing trend in DO in the upstream portion of the estuary during the years 1960e1985. Historically, minimum dry season (MayeOctober) DO levels occurred about 20 km from the estuary mouth at warm water temperatures, near both point source discharges and where extensive log rafting occurred. Presently, there is a trend of increasing dry season DO with increasing distance from the mouth of the estuary. Minimum DO levels occur at cool water temperatures (w8 deg C), suggesting that recently upwelled oceanic water from the shelf is the source of the low DO water. Recent time-series data (2001e2007) demonstrates that the water advected into the estuary from the coastal ocean has DO levels < 5 mg l À1 about 13% of the time during the dry season and that water temperature is a good indicator of the oceanic source. Similarity in the flood-tide DO and water temperature relationship between recent time-series data in Yaquina and in historic data from other estuaries suggests that the hypoxic conditions observed off the Oregon coast since 2002 may have occurred previously, especially during the 1950'se1960's. It is important to characterize the natural background DO levels for estuaries in the region to be able to separate anthropogenic from natural influences on DO.

Hydrographic and dissolved oxygen variability in a seasonal Pacific Northwest estuary

“…7), a result that indicates either 1) water properties in Coos Bay were strongly coupled to shelf processes where a similar temporal signal is observed, or 2) biological processes drew down ambient DO levels during summer. The coupling between shelf waters and the estuarine waters has been previously documented for Coos Bay (Czielsa, 1999;Roegner and Shanks, 2001), and other, similar small Pacific Northwest estuaries (Roegner et al, 2002;Brown and Ozretich, 2009;Brown and Power, 2011). However, the higher incidence of lower DO levels late in the dry season coincides with longer residence times as the dry season progresses, potentially allowing biological processes to decrease DO.…”

“…The well-mixed conditions and weak exchange flow in Coos Bay in late summer implies that, even if hypoxic shelf waters existed offshore, they could only enter the estuary through tidal dispersion processes. Indeed, previous work in Yaquina Bay, a slightly smaller estuary north of Coos Bay, shows similar flood-tide propagation of low-DO waters into the estuary (Brown and Power, 2011).…”

“…To put the CTD and recent time series data into historical context, we obtained a fifty-year record of temperature, salinity, and oxygen in Coos Bay from the Oregon Department of Environmental Quality (DEQ) LASAR database (Brown and Power, 2011). Latitude, longitude, station, date, time, and sampling matrix (surface water or bay/estuary/ocean) were recorded along with DO, salinity, temperature, and percent saturation DO.…”

“…In general, though, much less attention has been given to the vulnerability of smaller coastal estuarine environments in the CCS (Roegner et al, 2002;O'Higgins and Rumrill, 2008;Brown and Power, 2011).…”

In situ 13C tracer experiments elucidate carbon translocation rates and allocation patterns in eelgrass Zostera marina

“…These differences may reflect the change in isotopic composition of the DIC pool available to the plants due to freshwater inflow or ocean upwelling rather than any physiological change in carbon acquisition and use. Recent work shows close coupling of ocean and estuarine water column dissolved and particulate constituents, with seasonal shifts during summer and winter conditions (Brown & Ozretich 2009, Brown & Power 2011. Riverine δ 13 C-DIC tends to be isotopically depleted relative to oceanic DIC (Chanton & Lewis 1999, Kaldy et al 2005.…”