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QUANTIFYING SEASONAL SHIFTS IN NITROGEN SOURCES TO OREGON ESTUARIES. PART I: EMPIRICAL 15N MACROALGAE DATA
Citation:
KALDY, III, J. E. AND C. A. BROWN. QUANTIFYING SEASONAL SHIFTS IN NITROGEN SOURCES TO OREGON ESTUARIES. PART I: EMPIRICAL 15N MACROALGAE DATA. Presented at 19th Biennial Meeting, Estuarine Research Federation 2007, Providence, RI, November 04 - 08, 2007.
Impact/Purpose:
research presentation
Description:
“Green Tides” are typically considered to be a symptom of eutrophication associated with anthropogenic nutrient loading. In many estuaries along the Pacific Northwest (PNW), the seasonal development of macroalgal mats or “Green Tides” coincides with the initiation of coastal upwelling. We measured the 15N of attached macroalgae along a salinity gradient in 2 estuaries on a monthly basis to examine both the temporal and spatial patterns in nitrogen sources. During winter 2003 macroalgae collected from the ocean (6-7 ‰) and riverine (2-3 ‰) end-members had distinct isotope ratios with riverine samples depleted by 3-4 ‰ relative to the ocean end-member. As the seasonal wind patterns shifted to favor upwelling, the isotope ratio of the algae at the riverine end-member became more enriched eventually becoming indistinguishable from the ocean end-member indicating a change in the dominant N source. The watershed is the primary N source during winter, while coastal upwelling is the dominant summer N source. Seasonal “Green Tides” in the PNW appear to be a response to oceanographic processes and not necessarily an indicator of anthropogenic nutrient loading.
