Study on hydrochemistry variation and carbon sequestration of subaquatic vegetations in karst rivers/lakes is very important for better understanding of biogeochemical processes involved in karstification, i.e. the short time scale properties it may has. Using data from high resolution monitoring data loggers and high frequency water samples, the authors analyzed the chemical daily variations in a karst lake of Huixin wetland, Guilin, as well as the impact of different subaquatic vegetations. The values of water temperature, pH, dissolution oxygen, inorganic carbon isotope show a synchronous increase during the day time, while concentrations of Ca2+ and HCO-3, values of specific conductivity decrease mainly controlled by factors of air temperature, photosynthesis and respiration. The diel amplitudes of hydrochemical parameters in submerged plant area are much higher than that in emerged plant area, the values for water temperature, pH, Ca2+, HCO-3, dissolution oxygen, inorganic carbon isotope in emerged plant area are 4.42 °C、0.65、18 mg/L、0.8 mmol/L、14.02 mg/L、-2.27‰(δ13CV PDB) respectively，and those values rise to 6.32 °C、1.43、24 mg/L、1.5 mmol/L、23.86 mg/L、-5.03‰(δ13CV PDB) respectively, reflecting higher calcium precipitation rate and carbon sequestration efficiency occurred in submerged plant area. The results could provide scientific basis for understanding karst wetland aquatic system better and carbon sink estimation caused by aquatic vegetation photosynthesis.