Emerging patterns of CO2 : O2 dynamics in rivers and their link to ecosystem carbon processing

Aquatic metabolism is reflected in the dynamics of dissolved oxygen (O2) and carbon dioxide (CO2) concentrations. Thus, paired measurements of CO2 and O2 concentrations can capture the metabolic characteristics of an ecosystem, with promising results in lakes. Yet, for rivers, hydrological, chemical, and biological processes all influence CO2 and O2 concentrations, complicating how paired measurements can be used to infer ecosystem processes. Here we combine a data synthesis with a simple mechanistic model of river metabolism, gas exchange, groundwater inputs and carbonate equilibrium to assess how each imprints upon CO2 : O2 patterns. Among the physicochemical processes considered, groundwater inputs substantially influenced CO2 : O2 relationships. Regardless, analysis of paired CO2 : O2 data resolved predictable differences in ecosystem function across rivers with variable productivity and disturbance, as well as along the river continuum. Results indicate that paired CO2 : O2 data can aid in assessments of river metabolism, provided that we account for the dynamic physical environment.