On the Relationship Between Aquatic CO₂ Concentration and Ecosystem Fluxes in Some of the World's Key Wetland Types

To understand patterns in CO2 partial pressure (P-CO2) over time in wetlands' surface water and porewater, we examined the relationship between P-CO2 and land-atmosphere flux of CO2 at the ecosystem scale at 22 Northern Hemisphere wetland sites synthesized through an open call. Sites spanned 6 major wetland types (tidal, alpine, fen, bog, marsh, and prairie pothole/karst), 7 K & ouml;ppen climates, and 16 different years. Ecosystem respiration (R-eco) and gross primary production (GPP), components of vertical CO2 flux, were compared to P-CO2, a component of lateral CO2 flux, to determine if photosynthetic rates and soil respiration consistently influence wetland surface and porewater CO2 concentrations across wetlands. Similar to drivers of primary productivity at the ecosystem scale, P-CO2 was strongly positively correlated with air temperature (T-air) at most sites. Monthly average P-CO2 tended to peak towards the middle of the year and was more strongly related to R-eco than GPP. Our results suggest R-eco may be related to biologically driven P-CO2 in wetlands, but the relationship is site-specific and could be an artifact of differently timed seasonal cycles or other factors. Higher levels of discharge do not consistently alter the relationship between R-eco and temperature normalized P-CO2. This work synthesizes relevant data and identifies key knowledge gaps in drivers of wetland respiration.