1. Acknowledgements: Astoria Field Team, CMOP Staff
High Resolution In Situ Study of Nutrient Loading and Estuarine Response in the Columbia River
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 0.4 μM 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
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