Sources of Oxygen Demand in the Lower San Joaquin River, California
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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. 122 20’ N. 122 00’ N. 121 40’ N. 121 20’ N. Sacramento. CALIFORNIA. 38 20’ W. River. o. e. River. m. a. r. c. a.

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Sources of Oxygen Demand in the Lower San Joaquin River, California

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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


12220’ N

12200’ N

12140’ N

12120’ N

Sacramento

CALIFORNIA

3820’ W

River

o

e

River

m

a

r

c

a

S

San

Stockton

3800’ W

Antioch

Carquinez straight

Mossdale

San Francisco Bay


Current situation:

There has been little change in dissolved oxygen concentration in the channel despite enhanced management and a decrease in phytoplankton biomass


Frequency of values below 5 mg l-1


Chlorophyll a decreased over time in the channel


Question:

What are the primary sources of oxygen demand in the Deep Water Channel near Stockton?


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


MC DONALD

MC DONALD

o

121

20

N

ISLAND

ISLAND

Calaveras River

Calaveras River

TC

TC

o

80

00

W

STOCKTON

STOCKTON

San Joaquin River

San Joaquin River

L48

L48

TB

TB

RR

RR

Deep Water Channel

Deep Water Channel

CP

CP

Water Treatment

Plant

Rough and Ready

Rough and Ready

Island

Island

ROBERTS

ROBERTS

ISLAND

ISLAND

Middle River

N

N

MD

MD

4 km

4 km

TC Turner Cut

RR Rough and Ready Island

L48 Navigation Light 48

San Joaquin River

San Joaquin River

TB Turning Basin

CP Channel Point

MD Mossdale

VN Vernalis

VN

o

121

20

N

o

80

00

W

Water Treatment

Plant

Middle River

N

N

4 km

VN


Findings


Dissolved oxygen in DWSC


Dissolved oxygen upstream


Oxygen depletion was not caused by stratification


Oxygen demand was not caused by phytoplankton respiration


Oxygen demand was caused by nitrification


Pearson Correlation Coefficients(n=103)

TBOD & NBOD 0.86

NBOD & ammonia0.93

NBOD & organic N0.34

TBOD & ammonia 0.78

TBOD & CBOD 0.62

TBOD & chlorophyll 0.59


Stepwise Regression

Dissolved ammonia + carbonaceous BOD

60% 30%

Year n R2

2000 100 0.91

2001 85 0.73

2000 + 2001 185 0.83


Where does the ammonia come from ?


NBOD was correlated with ammonia load from treatment plant


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


Total nitrogen load was higher from upstream


Mass Balance Model

Object: Determine the largest source of dissolved ammonia in the channel


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


Ammonification rate


Upper boundary condition:

all organic nitrogen oxidized at ammonification rate for chlorophyll (highest rate)


Chlorophyll was a small percent of the organic nitrogen load


Lower boundary condition:

only the organic matter associated with live chlorophyll was oxidized


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


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


Net transport of phytoplankton mass decreased downstream


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