Paired O₂–CO₂ measurements provide emergent insights into aquatic ecosystem function

Abstract

Scientific Significance StatementMetabolic stoichiometry predicts that dissolved oxygen (O2) and carbon dioxide (CO2) in aquatic ecosystems should covary inversely; however, field observations often diverge from theoretical expectations. Here, we propose a suite of metrics describing this O2 and CO2 decoupling and introduce a conceptual framework for interpreting these metrics within aquatic ecosystems. Within this framework, we interpret cross‐system patterns of high‐frequency O2 and CO2 measurements in 11 northern lakes and extract emergent insights into the metabolic behavior and the simultaneous roles of chemical and physical forcing in shaping ecosystem processes. This approach leverages the power of high‐frequency paired O2–CO2 measurements, and yields a novel, integrative aquatic system typology which can also be applicable more broadly to streams and rivers, wetlands and marine systems.

Drought alters the biogeochemistry of boreal stream networks

“…Similarly, high-frequency data from paired O 2 and CO 2 sensors in the surface stream revealed a shift toward higher ΔCO 2 :ΔO 2 domains as WRT increased throughout the experiment (Fig. 4b) 36 . Finally, the total dispersion around the ΔCO 2 :ΔO 2 relationship for discrete samples also increased in both the stream surface and hyporheic water during drought ( Fig.…”

“…The observed chemical patterns suggest that drought in boreal streams can induce shifts in the relative dominance of aerobic versus anaerobic metabolic processes. While measuring whole ecosystem rates of anaerobic metabolism in streams remains a challenge 35 , one way to explore the relative significance of these processes is to evaluate the departures of CO 2 and O 2 from atmospheric equilibrium (ΔCO 2 :ΔO 2 ) [36][37][38] . Briefly, theory predicts that CO 2 and O 2 should inversely covary if aerobic mineralization of organic matter dominates the flux of both gases, and deviations from this relationship can reveal CO 2 production through anaerobic processes 36,37 .…”

“…We also used the CH 4 :O 2 ratio to provide a synthesis of the full range of terminal electron-accepting processes in the sample. Low values of the CH 4 :O 2 ratio indicate that aerobic pathways dominate the metabolic balance, while increases of CH 4 :O 2 ratios represent a shift toward a dominance of anaerobic over aerobic metabolic processes 36,37 . To examine whether drought drove similar redox responses under experimental and natural conditions, we compared the relationship between stream WRT and surface water CH 4 :O 2 molar ratios along the experimental stream reach during summers 2017 (experimental drought) and 2018 (severe natural drought).…”

“…Equilibrium concentrations were calculated from temperature and barometric pressure 72 . Different statistical analyses on ΔCO 2 :ΔO 2 observations were used to test the treatment effects on the central tendency and dispersion of these data 36 .…”

A simplified approach to detect a significant carbon dioxide reduction by phytoplankton in lakes and rivers on a regional and global scale

“…To assess the role of CO 2 uptake by primary production more accurately on a global scale, the growing amount of metabolism data might be used (e.g., Appling et al 2018). Quantifying primary production using metabolism calculations (Odum 1956;Vachon et al 2020) has the advantage of integrating all forms of primary production, not only considering CO 2 uptake by phytoplankton in the pelagic zone. However, when using aquatic metabolism data, a higher measuring frequency than is typically used for phytoplankton biomass may be necessary, because metabolism is more variable on short time scales (Wetzel 2001).…”