Derivation and application of a parameter for denitrification rates in the Taihu Lake model based on an isotope-labeled denitrification experiment

In recent years, the total nitrogen concentration in Taihu Lake has decreased significantly. Denitrification, as the main nitrogen removal process, is the key reason for the decrease. Here, the denitrification parameter values in the Environmental Fluid Dynamic Code (EFDC) model were calculated based on isotope-labeled denitrification experiment instead of selecting the recommended values directly. This study further focused on EFDC denitrification parameter derivation with an experimental denitrification rate (D_tot) to reduce simulation errors. According to the EFDC nitrate deposition flux mechanism, the conversion equation between the denitrification rate of the first sediment layer ( \({\kappa }_{1,N{O}_{3}}\) ${\kappa }_{1,N{O}_3}$ ) in EFDC and D_tot was successfully derived. The results revealed a linear correlation between \({\kappa }_{1,N{O}_{3}}\) ${\kappa }_{1,N{O}_3}$ and (D_tot)^1/2. The \({\kappa }_{1,N{O}_{3}}\) ${\kappa }_{1,N{O}_3}$ values of sampling points ranged from 0.25 to 0.27 m·day⁻¹, within the range of model parameters. After substituting \({\kappa }_{1,N{O}_{3}}\) ${\kappa }_{1,N{O}_3}$ into the Taihu Lake EFDC model, the average percentage bias and determination coefficient of total nitrogen were 16.25% and 0.87, respectively. The average total nitrogen concentration reduction caused by denitrification at water quality calibration points ranged from 0.027 to 0.305 mg·L⁻¹.