[Emission Estimation and Fate Simulation of Dichlorvos in the Dongjiang River Watershed]

The application of pesticides and their constant inputs have resulted in the universal contamination of the environments within watersheds, and it is essential to assess the level of contamination. Compared with traditional monitoring methods, models coupled with GIS show more obvious advantages. However, the difficult access to application scenarios and emission data of pesticides hinder the modeling and assessment of the pesticides used in watersheds. We established an emission estimation method of pesticides, which was based on the planting scenarios and pesticide application standards of different crops in administered regions and by situational analysis and mathematical deduction, the usage of each sub-basin was able to be derived. Then, by using the aforementioned results as source input data, a semi-distributed watershed hydrological, SWAT (soil and water assessment tool) model, was used to simulate the fate of dichlorvos in the Dongjiang River watershed as an example. The verification results show that the comparisons of magnitude between the simulation and the observations were almost within 1, indicating that the SWAT model, which is based on a source input estimation, was able to assess the environmental fate of pesticides in watershed effectively. Also, the modeling results indicated that the annual emission load of the dichlorvos in the watershed accounted for 3.72% of the usage. Moreover, the losses due to degradation and other reactions within the channels reach 2.35%. Most reaches of the Dongjiang River watershed have mass concentrations over 0.1 μg·L^-1, demonstrating that certain safety concerns exist.