Carbon dioxide concentrations in eutrophic lakes: undersaturation implies atmospheric uptake

Abstract

Understanding concentrations and contributions of carbon dioxide (CO2) in aquatic ecosystems is an important part of a comprehensive global carbon budget. Current dogma suggests that world lakes are important emitters of CO2 to the atmosphere. We estimated the partial pressure of carbon dioxide (ρCO2) in 131 agriculturally eutrophic lakes over a 7 year sampling period. Values of ρCO2 in these lakes ranged from 0.1 to 40 392 μatm with a median of 322 μatm (n = 3049). In contrast to previous analyses of CO2 in lakes, 60% of the eutrophic lake samples were undersaturated with CO2. Correlation analysis implied that nutrient-driven primary production, reflected by high oxygen concentrations, drives CO2 concentrations below atmospheric equilibrium. Multiple regression analysis showed several limnological and catchment characteristics that explained a statistically significant amount of variability in ρCO2 (R2 = 0.32). Important variables included chlorophyll a concentration and the ratio of total nitrogen to total phosphorus. Our estimated ρCO2 values were significantly (p < 0.0001) lower than a previously published dataset of world lake ρCO2 values derived primarily from oligotrophic–mesotrophic lakes. High-nutrient lakes, especially those that are small and rich in oxygen from primary production, could act as net atmospheric CO2 uptake sites.