Effects of different precipitation on the runoff-lake library carbon cycle process in the Three Gorges Reservoir

Precipitation significantly affects the carbon cycle of reservoirs. We regarded the reservoir as a biochemical reactor to investigate the impact of precipitation on the external carbon content of the CO2 (CO2-C) load and internal CO2-C cycle. Detailed descriptions of the reservoir carbon-cycle models under different rainfall conditions are provided. The field monitoring data collected literature parameters, and the calculation formulas of each part of the carbon-cycle mass balance model were integrated. Many ecological mathematical models were used in this study, including the thin boundary layer (TBL) equation, the pH sub-model equation system, the two-component exponential model, the algal synthetic carbon fixation equation, and the bacterial respiratory equation. Our study reveals that different rainfall levels in the backwater area of the Three Gorges Reservoir (TGR) would affect the dynamic balance of the reservoir carbon budget. In the discharge period of the reservoir, 10 mm·d-1 rainfall is the critical point of the transformation of CO2 source and sink flux at the water-air interface. When the rainfall exceeds 24 mm·d-1, the surface runoff begins to disturb the carbon budget. Our research provides a biochemical and physical model of the impact of rainfall events on reservoir CO2 budgets.