Modeling N transformation and removal in a duckweed pond: Model development and calibration

Based on the dynamics of total ammoniacal N (Nam), nitrate/nitrite (Nox) and organic nitrogen contained in sediment (Nsed), in water (Norg), and in hydrophyte pools (Nalgae + Ndw), respectively, a mathematical model was developed to predict N transformation processes in duckweed ponds. The availability and the sensibility of the transformation model were investigated correspondingly. The results showed that the transformation model could exactly simulate the annual variations of Nam, Nox, Nsed, Nalgae, and Ndw in a duckweed pond with the correlation coefficient ranging from 0.71 to 0.89. However, the simulated values of Norg were much lower than the measured values in windy winter, resulting in the correlation coefficient between them only being 0.61. Sensitivity analysis revealed that the model was a stable simulation system except the variable of Ndw. Further research should concentrate on a better understanding of the N transformation in duckweed, so as to make the model a more comprehensive and predictive tool.