Trophic state index linked to partial pressure of aquatic carbon dioxide in a typical karst plateau lake

Abstract

Trophic state index (TSI) can assess lake trophic status and trace in-situ metabolism, exhibiting a high potential in explaining autochthonous carbon dioxide (CO2) in aquatic environments. However, there remains a knowledge gap in how TSI links to the partial pressure of CO2 (pCO2) generated and consumed in lakes. Here we explored the temporal variations of lake pCO2 and TSI, as well as their linkages in a karst plateau lake. Lake pCO2 ranged from 90.1 to 7169.3 μatm and was significantly high in the post-wet period (2534.3 ± 1637.9 μatm). Over 58% of samples were found to be supersaturated in CO2 with respect to the atmospheric equilibrium (410 μatm). Biological and hydrological processes regulated lake trophic status, resulting in mesotrophic state (30 < TSI < 50) in the post-wet period and eutrophic state (TSI > 50) in the drought and initial-wet periods. Coupled carbonate dissolution and photosynthesis consumed the pCO2, whereas groundwater and respiration contributed the pCO2 in the karst lake. Our results highlighted that lake TSI could decipher trophic status and further partially explain the pCO2 dynamics and sources.