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UPWELLING EFFECTS ON THE DISTRIBUTION OF NITRATE IN YAQUINA BAY, A COASTAL OREGON ESTUARY
Citation:
Ozretich, R J. UPWELLING EFFECTS ON THE DISTRIBUTION OF NITRATE IN YAQUINA BAY, A COASTAL OREGON ESTUARY. Presented at Estuarine Research Federation meeting, Seattle, WA, September 14-18, 2003.
Description:
Coastal Oregon in the summer is dominated by northwesterly winds. Upwelling of nutrient-rich water into the nearshore is controlled by the velocity and duration of these summer winds. Yaquina Bay estuary is a mesotidal drowned river valley that is typically vertically well-mixed in the summer and stratified in the winter. Sampling the length of the estuary with CTD casts and pumped water samples at seasonally adjusted sampling frequencies (weekly to monthly) from May 1998 through September 2002 provided recurring evidence for the importance of upwelling in renewing depleted nutrients within the bay. Following cessation of the rainy season (April to May) high nitrate concentrations of the river water (>60 uM) were initially conservatively diluted with low nitrate ocean water ( 1-5 uM). As the tidal mixing continued in the lengthening daylight, nitrate concentrations in the upper reaches (10-20 km from mouth) were typically reduced to below that of the incoming seawater. When the summer wind conditions prevailed for long enough, upwelling brought cold, higher salinity water with high nitrate concentrations (10-30 uM) into the estuary. For the summer growing season upwelling can be a significant source of nitrate nitrogen to coastal estuaries of the Pacific Northwest.