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The d 18 O of DO reflects the ratio of productivity to respiration in the water column

We piggybacked on Fleenor’s 2 August DWSC experiments and obtained water samples every 2-4 hours from the houseboat, and low/high tide samples from the traveling boats. Analyses: Nitrate d15N/d18O (done) POM d15N/d13C (in progress) DOC-d13C (done) DIC-d13C (done) DO-d18O (almost done)

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The d 18 O of DO reflects the ratio of productivity to respiration in the water column

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  1. We piggybacked on Fleenor’s 2 August DWSC experiments and obtained water samples every 2-4 hours from the houseboat, and low/high tide samples from the traveling boats. • Analyses: • Nitrate d15N/d18O (done) • POM d15N/d13C (in progress) • DOC-d13C (done) • DIC-d13C (done) • DO-d18O (almost done) • Water-d18O/d2H (not done yet) • Ammonium (archived)

  2. The d18O of DO reflects the ratio of productivity to respiration in the water column Respiration (consumption) dilution Photosynthesis (addition) (from Len Wassenaar, 2001)

  3. 48-Hour Diel Cycle of DO concentrations and d18O • Typical pattern found in small lakes and streams: • 140 % range in O2 saturation in 24 hours • 17 ‰ range in d18O of DO over 24 hours (are currently giving this a try at a few USGS studies in CA, OR, WA) (from Len Wassenaar, 2001)

  4. How to tease out the main controls on DO levels in the DWSC (and elsewhere): • Photosynthesis (P) • Respiration (R) • Nitrification (N) R N d18O P DO P N d13C These processes will probably also cause diagnostic changes in the d18O/d15N of nitrate and the d15N/d13C of POM R DIC

  5. Cartoon showing how isotopic compositions of O2, NO3, and POM can be used to separate the effects of nitrification of ammonium vs respiration of algae as BOD reactions d15NNO3 = 12‰ d15NPOM = 11‰ d15NNO3 = 15‰ d15NPOM = 10‰ d18OO2 = 23‰ d18OO2 = 25‰ O2 = 1.0 O2 = 0.9 d18OO2 = 27‰ O2 = 0.7 d18OO2 = 29‰ flow O2 = 0.6 Treatment plant Water samples would be collected along a grid, and at several depths

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