Tracing Causes of Hypoxia in the San Joaquin River Using Isotopic Techniques
Abstract
Fish migration through the deep-water shipping channel in the San Joaquin River near the city of Stockton CA is inhibited by periodic low dissolved oxygen (DO) concentrations during low flow conditions. There is considerable controversy regarding the relative roles of two mechanisms that can contribute to DO depletion: decomposition of algae from upstream locations and nitrification of ammonium from a nearby waste water treatment facility. Development of a successful remediation plan requires knowledge of the controls on spatial and temporal differences in oxygen-consuming mechanisms. To better understand the timing and relative importance of the mechanisms responsible for oxygen depletion, samples were collected for isotopic and chemical analysis during two intensive two-day sampling trips in August 2004. Samples were taken from a stationary houseboat in the channel, and from upstream and downstream traveling boats. Water samples at the houseboat were collected at five depths at 2-4 h intervals, and samples from 1 m were collected at about 4 h intervals from the traveling boats. All samples were analyzed for DO-d18O, seston-d15N/d13C, nitrate-d15N/d18O, DIC-d13C, water-d18O/d2H, DO, ammonium, and nitrate concentrations. Of all the measured parameters, ammonium, DO, and DO-d18O showed the strongest diurnal fluctuations, as well as significant changes with depth. Physico-chemical parameters indicated diurnal stratification and overturn of the channel. The general increase in the DO-d18O coincident with decreases in DO suggests that the night-time decrease in DO is caused largely by O2 consumption, either by respiration of organic matter or by nitrification. The DIC-d13C and nitrate-d15N data indicate that nitrification may affect DO concentrations as much or more than respiration. Preliminary principle components analysis indicates that photosynthesis is the main control over DO concentrations during this period of DO depletion, and that both nitrification and respiration are significant causes of DO depletion in this channel. Future work will focus on the transition between normal DO conditions and periods of DO depletion.
- Publication:
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AGU Spring Meeting Abstracts
- Pub Date:
- May 2005
- Bibcode:
- 2005AGUSM.H51C..06K
- Keywords:
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- 1010 Chemical evolution;
- 1045 Low-temperature geochemistry;
- 1803 Anthropogenic effects;
- 1806 Chemistry of fresh water