High Resolution In Situ Study of Nutrient Loading and Estuarine Response in the Columbia River

1. 1,2Melissa Gilbert, 1,2Needoba, J., 3Koch, C., 3Barnard, A., 2Baptista, A. 1Oregon Health and Science University 2The Center for Coastal Margin Observation and Prediction 3WET Labs Results: Research Question What are the dominant process in the lower Columbia River and the Columbia River estuary affecting nutrient biogeochemistry during the summer of 2010? • Methods: • The estuary station: • Physical parameters such as salinity and • temperature data are acquired • APNA collects hourly nitrate & ammonium data • Cycle-PO4 collects hourly phosphate data • The river station: • Nitrate/phosphate ratios are calculated based • on grab samples run in the laboratory on an • auto analyzer (data not shown) • Figure 5. Nitrate/phosphate ratios in the estuary (gray circles) and nitrate/phosphate ratios of the river water just before it becomes saline (pink squares) • Average river signal in the estuary • nitrate/phosphate ratio is 6.4 • The decrease in the nitrate/ • phosphate ratio from the river to • the estuary (24.8→6.4) could be • caused by: • Decrease in nitrate • Increase in phosphate • Figure 6. River nitrate and estuary end member nitrate data • Note: 1 day offset of data to • account the for time it takes the • river water to reach the estuary • Average loss of 1.3 μM(only • decreases ratio to 20) • Figure 7. River phosphate and estuary end member phosphate data • Average gain of 0.4 μM • According to Redfield ratio of • 16/1 N/P a gain of 0.4μM P • should be accompanied by a • gain of 6.4 μM reactive N • (either nitrate or ammonium) • Figure 8. Ammonium concentrations observed • 6.4 μM can be accounted for • through the Redfield ratio gain • in phosphate • Large amounts of ammonium • are seen in the estuary that are • not in the river APNA • Introduction: • It is vital we understand if the Columbia river fresh water tidal flats (red oval below) and estuary are • decreasing or increasing the coastal nutrient load • Excess nutrient loading to coastal zones is known to cause harmful algal blooms and coastal hypoxia • Nitrogen/Phosphorus are taken up by primary producers at a ratio of 16/1 • > 16/1 = Phosphate limited system • < 16/1 = Nitrogen limited system • Hourly data allows for the calculation of N/P in the estuarine environment High Resolution In Situ Study of Nutrient Loading and Estuarine Response in the Columbia River Cycle-PO4 The Data: SATURN-05 Figure 1. All of the phosphate and nitrate data for 2010 Washington Small Loss in Nitrate River SATURN-03 Large Gain in Phosphate Pacific Ocean Oregon Estuary Figure 2. Nitrate/ phosphate ratios of intermediate salinities Large Gain in Ammonium Estuary River Denitrification Decrease in nitrate 6.4- Remineralization Phosphate Limited • Conclusions: • High resolution in situ nutrient data yields evidence for an overwhelming remineralization signal in the Columbia River fresh water tidal flats during the summer • During summer months MORE reactive N may be leaving the Columbia River • and estuary in the form of ammonium than in nitrate • The Columbia River and estuary may not remove large quantities of • anthropogenic nitrate via denitrification during the summer months • Lower NO3-N/PO4-P ratios in the estuary than the river Nitrate Limited Figure 3. High frequency tidal data Remineralization Increase in ammonium Increase in phosphate Figure 4. Phosphate concentration versus salinity Zero salinity/ intercept is the river concentration in the estuary River End Member: The concentration of the nutrient in fresh water just before it mixes with salty ocean water Acknowledgements: Astoria Field Team, CMOP Staff