title: Dynamics of dissolved oxygen isotopic ratios: a transient model to quantify primary production, community respiration, and air-water exchange in aquatic ecosystems.
abstract: Dissolved O(2) is an important aquatic ecosystem health indicator. Metabolic and gas exchange (G) rates, which control O(2) concentration, are affected by nutrient loading and other environmental factors. Traditionally, aquatic metabolism has been reported as primary production:community respiration (P:R) ratios using diel measurements and interpretations of dissolved O(2) and/or CO(2) concentrations, and recently using stable isotopes (delta(18)O, Delta(17)O) and steady state assumptions. Aquatic ecosystems, such as rivers and ponds, are not at steady state and exhibit diel changes, so steady state approaches are often inappropriate. A dynamic O(2) stable isotope model (photosynthesis-respiration-gas exchange; PoRGy) is presented here, requiring a minimum of parameters to quantify daily averaged P, R, and G rates under transient field conditions. Unlike steady state approaches, PoRGy can address scenarios with 100% O(2) saturation but with delta(18)O-O(2) values that are not at air equilibrium. PoRGy successfully accounts for isotopic G when applied to an oxygen isotope equilibration laboratory experiment. PoRGy model results closely matched the diel O(2) and delta(18)O-O(2) data from three field sites with different P:R:G ratios and various P, R and G rates. PoRGy provides a new research tool to assess ecosystem health and to pose environmental impact-driven questions. Using daily averaged rates was successful and thus they can be used to compare ecosystems across seasons and landscapes.
authors.affiliation: Department of Earth Sciences, University of Waterloo, 200 University Avenue W, Waterloo, ON N2L 3G1, Canada. jjvenkit@uwaterloo.ca
authors.forename: Jason J
authors.initials: JJ
authors.lastname: Venkiteswaran
authors.forename: Leonard I
authors.initials: LI
authors.lastname: Wassenaar
authors.forename: Sherry L
authors.initials: SL
authors.lastname: Schiff
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism*; D019069:Cell Respiration / Q000502:physiology; D002940:Circadian Rhythm / Q000502:physiology; D017753:Ecosystem; D005618:Fresh Water / Q000737:chemistry; D008954:Models, Biological; D010100:Oxygen / Q000032:analysis / Q000378:metabolism*; D010103:Oxygen Isotopes / Q000032:analysis / Q000378:metabolism; D010788:Photosynthesis / Q000502:physiology*
chemical_list: D010103:Oxygen Isotopes; D002245:Carbon Dioxide; D010100:Oxygen