Temporal Changes in Dissolved Organic Carbon Composition in Tempe Town LakeMegan Kelly and Hilairy HartnettApril 19, 2008

Conceptual DiagramTempe Town LakeSalt RiverRainRun-offEvaporationOutput toSalt RiverInfiltrationRecharge WellsDams Lowered31 Dec 2004W. Dam Raised18 Feb 2005E. Dam Raised4 Apr 2005Monsoon begins18 Jul 2005Monsoon ends10 Sep 20052004: significant Winter rainfall

Dissolved Organic CarbonProduced by photosynthesisAltered or removed by microbial respiration Photosynthesis CO2 + H2O CH2O + O2 RespirationAltered or removed by photo-degradationAdsorbs to particlesRemoved by flocculation

MethodsSampling:2005 - daily2006 & 2007 - bimonthlyMeasurements:pH, conductivity, temperature, dissolved O2DOC analysis:Bulk concentrationMolecular level composition

Conductivity (S)

Conductivity (S)

Electrospray Ionization Mass SpectrometrySoft ionization using electric fieldTwo modes:Positive mode Negative modeIn: Sample diluted with methanol and waterOut: Abundance of peaks of nominal masses 30-1500 corresponding to masses of compounds

High Flow PeriodRainy Period

# of compounds presentin high-flow period

High-flow periodEvaporative period

High-flow periodEvaporative periodRainy period

ConclusionsWater chemistry indicates evaporation and primary production are dominant processesBulk DOC concentration indicates microbial respiration or photo-degradationESI-MS data suggest that different processes may dominate over time

Future WorkComparison of mass spectrometry data before and after winter and summer rain events and algaecide applicationsExperiments to determine individual compounds produced by photosynthesis, microbial degradation, and photo degradation

Thanks to:Brad Brown, Katie Mayer, Nic Dionisio, Hilary Waterman, Jessie Shipp for samplingKatie Alexander for discussionsPeggy Nelson and students of COURS 2007 for insightsBarrett 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-0423704, 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).