San Joaquin River DOTMDL -- Technical Working Group

Algal Dynamics - Nitrification Mechanisms

Project Contact Information

Gary Litton, PhD
Associate Professor
University of the Pacific
(209) 946-3070

Project Description

Dissolved oxygen (DO) concentrations in the Stockton Deep Water Ship Channel (DWSC) respond rapidly to changes in flow under conditions that are poorly understood. For example, the DO declined from 8 mg/L on January 1, 2003 to 0 mg/L in early February. The DWSC at Rough and Ready Island remained anoxic throughout most of February. More recently in May, 2004, the DO fell from 8 mg/L to 3 mg/L immediately after VAMP inputs ceased, causing the net flow to fall from 2500 to 400 cfs. Other extreme events are also well documented, but poorly understood and problematic to model accurately.

Preliminary data suggest that high ammonia concentrations, exacerbated by low net flows in the San Joaquin River, are the primary cause of the acute hypoxia observed in the DWSC during the winter months. Research is continuing to verify this hypothesis by monitoring the recovery of this river reach and contributing factors. Kinetic rate studies of oxygen demanding substances are being performed in the laboratory and will be compared with analyses of field observations. Early kinetic rates investigation results suggested that ammonia and nitrite oxidizing bacteria population dynamics play an important role. As such, identification and enumeration of these microorganisms was added to the investigation.

This study investigates the causes for extreme dissolved oxygen deficits that were common in 2003 and 2004. Some of the mechanisms responsible for these severe episodes have been quantified. Quantification of important parameters necessary to describe and predict the DO response in the DWSC have also been performed.

Project Documents

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