Sources of oxygen demand in the lower San Joaquin River,California |
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| Authors: | Email author" target="_blank">P?W?LehmanEmail author J?Sevier J?Giulianotti M?Johnson |
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| Institution: | (1) Lamont-Doherty Earth Observatory, Columbia University, 61 Route 9W, Palisades, NY 10964, USA;(2) Department of Earth and Environmental Sciences, Columbia University, New York, NY 10027, USA;(3) Department of Oceanography, University of Hawaii, Honolulu, HI 96822, USA;(4) Department of Earth and Environmental Engineering, Columbia University, 500 West 120th Street, New York, NY 10027, USA;(5) Department of Earth Science, University of California at Santa Barbara, Santa Barbara, CA 93106, USA;(6) Department of Civil and Environmental Engineering, University of California at Davis, Davis, CA 95616, USA |
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| Abstract: | Dissolved oxygen concentration below 5 mg 1−1 has characterized the lower tidal portion of the San Joaquin River downstream of Stockton, California, during the summer
and fall for the past four decades. Intensive field research in 2000 and 2001 indicated low dissolved oxygen concentration
was restricted to the first 14 km of the river, which was deepened to 12 m for shipping, downstream of Stockton. The persistent
low dissolved oxygen concentration in the shipping channel was not caused by physical stratification that prevented aeration
from vertical mixing or respiration associated wigh high phytoplankton biomass. The low dissolved oxygen concentration was
primarily caused bynitrification that produced up to 81% of the total oxygen demand. Stepwise multiple regression analysis
isolated dissolved ammonia concentration and carbonaceous oxygen demand as the water quality variables most closely associated
with the variation in oxygen demand. Between these two sources, dissolved ammonia concentration accounted for 60% of the total
variation in oxygen demand compared with a maximum of 30% for carbonceous oxygen demand. The Stockton wastewater treatment
plant and nonpoint sources upstream were direct sources of dissolved ammonia in the channel. A large portion of the dissolved
ammonia in the channel was also produced by oxidation of the organic nitrogen load from upstream. The phytoplankton biomass
load from upstream primarily produced the carbonaceous oxygen demand. Mass balance models suggested the relative contribution
of the wastewater and nonpoint upstream load to the ammonia concentration in the shipping channel at various residence times
was dependent on the cumulative effect of ammonification, composition of the upstream load, and net downstream transport of
the daily load. |
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