1. Megan Kelly and Hilairy Hartnett April 19, 2008
Temporal Changes in Dissolved Organic Carbon Composition in Tempe Town Lake
Megan Kelly and Hilairy Hartnett
April 19, 2008

2. Conceptual Diagram Evaporation Salt River Output to Salt River Rain
Tempe Town Lake
Output to
Salt River
Rain
Run-off
2004: significant
Winter rainfall
Infiltration
Recharge Wells
Dams Lowered
31 Dec 2004
W. Dam Raised
18 Feb 2005
E. Dam Raised
4 Apr 2005
Monsoon begins
18 Jul 2005
Monsoon ends
10 Sep 2005

3. Dissolved Organic Carbon
Produced by photosynthesis
Altered or removed by microbial respiration
Photosynthesis 
CO2 + H2O  “CH2O” + O2
 Respiration
Altered or removed by photo-degradation
Adsorbs to particles
Removed by flocculation

4. Methods Sampling: 2005 - daily 2006 & 2007 - bimonthly Measurements:
pH, conductivity, temperature, dissolved O2
DOC analysis:
Bulk concentration
Molecular level composition

10. Conductivity (μS)

11. Conductivity (μS)

12. Electrospray Ionization Mass Spectrometry
Soft ionization using electric field
Two modes:
Positive mode
Negative mode
In: Sample diluted with methanol and water
Out: Abundance of peaks of nominal masses corresponding to masses of compounds

13. High Flow Period
February +
February -
Rainy Period
August +
August -

15. # of compounds present
in high-flow period

16. High-flow period
Evaporative
period

17. High-flow period
Evaporative
period
Rainy period

18. Conclusions
Water chemistry indicates evaporation and primary production are dominant processes
Bulk DOC concentration indicates microbial respiration or photo-degradation
ESI-MS data suggest that different processes may dominate over time

19. Future Work
Comparison of mass spectrometry data before and after winter and summer rain events and algaecide applications
Experiments to determine individual compounds produced by photosynthesis, microbial degradation, and photo degradation

20. Thanks to:
Brad Brown, Katie Mayer, Nic Dionisio, Hilary Waterman, Jessie Shipp for sampling
Katie Alexander for discussions
Peggy Nelson and students of COURS 2007 for insights
Barrett Honors College, CAP-LTER, and ASU/NASA Space Grant for funding
This material is based upon work supported by the National Science Foundation under Grant No. DEB , Central Arizona - Phoenix Long-Term Ecological Research (CAP LTER). Any opinions, findings and conclusions or recommendation expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation (NSF).