Carbon dioxide partial pressure and its diffusion flux in karst surface aquatic ecosystems: a review.

Carbon dioxide (CO2) emissions from aquatic ecosystems are an important component of the karst carbon cycle process and also a key indicator for assessing the effect of karst carbon sinks. This paper reviewed the CO2 partial pressure (pCO2) and its diffusion flux (FCO2) in karst surface aquatic ecosystems, mainly rivers, lakes, and reservoirs, and their influencing factors summarized the methods for monitoring CO2 emissions in karst aquatic ecosystems and discussed their adaptation conditions in karst areas. The pCO2 and FCO2 decreased in the order of rivers > reservoirs > lakes, and the values in karst lakes were eventually significantly lower than those in global lakes. The pCO2 and FCO2 of karst aquatic ecosystems had patterns of variation with diurnal, seasonal, water depth and hydrological cycles, and spatial and temporal heterogeneity. The sources of CO2 in karst waters are influenced by both internal and external sources, and the key spatial and temporal factors affecting the CO2 emissions from karst rivers, lakes, and reservoirs were determined in terms of physicochemical indicators, biological factors, and biogenic elements; additionally, the process of human activity interference on CO2 emissions was discussed. Finally, a conceptual model illustrating the impacts of urban development, agriculture, mining, and dam construction on the CO2 emissions at the karst surface aquatic ecosystem is presented. Meanwhile, based on the disadvantages existing in current research, we proposed several important research fields related to CO2 emissions from karst surface aquatic ecosystems. [ABSTRACT FROM AUTHOR]