1. Sources of Oxygen Demand in the Lower San Joaquin River, California
P. W. Lehman,
J. Sevier, J. Giulianotti & M. Johnson
California Department of Water Resources

2. Sacramento Stockton San Francisco Bay Antioch Mossdale
CALIFORNIA
’ W
River o e m
River c r a a S
San
Stockton
’ W
Antioch
Carquinez straight
Mossdale
San Francisco Bay

3. Current situation:
There has been little change in dissolved oxygen concentration in the channel despite enhanced management and a decrease in phytoplankton biomass

4. Frequency of values below 5 mg l-1

5. Chlorophyll a decreased over time in the channel

6. Question:
What are the primary sources of oxygen demand in the Deep Water Channel near Stockton?

7. Study Methods biweekly or monthly sampling July - November 2000 & 2001
discrete variables:
Primary productivity : in situ dissolved oxygen
light and dark bottle technique
Nutrient concentrations
chlorophyll a and phaeophytin concentration
BOD tests
continuous variables
vertical profiles with YSI 6600 sonde
continuous flow
continuous water quality

8. MD TB CP TC RR L48 San Joaquin River Deep Water Channel VN TB CP TC RR
STOCKTON
MC DONALD MD
ROBERTS
ISLAND
Rough and Ready
Island
Calaveras River TB CP TC RR
L48
San Joaquin River
Deep Water Channel N
4 km
Middle River VN 80 o 00 ’ W
121 20
Water Treatment
Plant
TC Turner Cut
RR Rough and Ready Island
L48 Navigation Light 48
TB Turning Basin
CP Channel Point
MD Mossdale
VN Vernalis
Island
Calaveras River TB CP TC RR
L48
San Joaquin River
Deep Water Channel N
4 km
121 o 20 ’ N 80 o 00 ’ W
Water Treatment
Plant
Middle River N N
4 km VN

9. Findings

10. Dissolved oxygen in DWSC

11. Dissolved oxygen upstream

12. Oxygen depletion was not caused by stratification

13. Oxygen demand was not caused by phytoplankton respiration

14. Oxygen demand was caused by nitrification

15. Pearson Correlation Coefficients (n=103)
TBOD & NBOD
NBOD & ammonia
NBOD & organic N
TBOD & ammonia
TBOD & CBOD
TBOD & chlorophyll

16. Stepwise Regression
Dissolved ammonia + carbonaceous BOD
60% %
Year n R2

17. Where does the ammonia come from ?

18. NBOD was correlated with ammonia load from treatment plant

19. NBOD at Rough and Ready varied with the ammonia load from the treatment plant

20. Total nitrogen load was higher from upstream

21. Mass Balance Model
Object: Determine the largest source of dissolved ammonia in the channel

22. Simple mass balance model
Daily dissolved ammonia load into the ship channel from the treatment plant and upstream =
1) daily load of dissolved ammonia from each source +
2) daily load of dissolved ammonia from the oxidation of the organic nitrogen load from each source +
3) daily load of dissolved ammonia from the oxidation of residual organic nitrogen from previous day from each source

23. Ammonification rate

24. Upper boundary condition:
all organic nitrogen oxidized at ammonification rate for chlorophyll (highest rate)

25. Chlorophyll was a small percent of the organic nitrogen load

26. Lower boundary condition:
only the organic matter associated with live chlorophyll was oxidized

27. Summary
Oxygen demand in the channel was primarily caused by nitrification
The treatment plant could be the primary cause of nitrification in the channel on a daily basis even though it had a small ammonia load because it was a direct source of dissolved ammonia for bacterial oxidation
The relative contribution of ammonia from the treatment plant and upstream to ammonia in the channel was a function of residence time, ammonification rate, direct loads and load composition

28. Take home message
The oxygen demand produced from the direct load of dissolved ammonia from the treatment plant could have a greater impact on daily oxygen demand in the channel than the oxidation of organic nitrogen from upstream because of the slow oxidation rate and low reactivity of upstream organic matter

30. Net transport of phytoplankton mass decreased downstream