Coupling Between the Coastal Ocean and Yaquina Bay,Oregon: Importance of Oceanic Inputs Relative to Other Nitrogen Sources |
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| Authors: | Cheryl A Brown Robert J Ozretich |
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| Institution: | (1) Pacific Coastal Ecology Branch, Western Ecology Division, U.S. Environmental Protection Agency, 2111 S.E. Marine Science Center Drive, Newport, OR 97365, USA;(2) Western Ecology Division, U.S. Environmental Protection Agency, 200 SW 35th, Corvallis, OR 97333, USA |
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| Abstract: | Understanding of the role of oceanic input in nutrient loadings is important for understanding nutrient and phytoplankton
dynamics in estuaries adjacent to coastal upwelling regions as well as determining the natural background conditions. We examined
the nitrogen sources to Yaquina Estuary (Oregon, USA) as well as the relationships between physical forcing and gross oceanic
input of nutrients and phytoplankton. The ocean is the dominant source of dissolved inorganic nitrogen (DIN) and phosphate
to the lower portion of Yaquina Bay during the dry season (May through October). During this time interval, high levels of
dissolved inorganic nitrogen (primarily in the form of nitrate) and phosphate entering the estuary lag upwelling favorable
winds by 2 days. The nitrate and phosphate levels entering the bay associated with coastal upwelling are correlated with the
wind stress integrated over times scales of 4–6 days. In addition, there is a significant import of chlorophyll a to the bay from the coastal ocean region, particularly during July and August. Variations in flood-tide chlorophyll a lag upwelling favorable winds by 6 days, suggesting that it takes this amount of time for phytoplankton to utilize the recently
upwelled nitrogen and be transported across the shelf into the estuary. Variations in water properties determined by ocean
conditions propagate approximately 11–13 km into the estuary. Comparison of nitrogen sources to Yaquina Bay shows that the
ocean is the dominant source during the dry season (May to October) and the river is the dominant source during the wet season
with watershed nitrogen inputs primarily associated with nitrogen fixation on forest lands. |
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