Location: Water Management ResearchTitle: Simulation of fumigant transport and volatilization from tarped broadcast applications Author
Submitted to: Vadose Zone Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2013
Publication Date: 8/8/2013
Citation: Spurlock, F., Johnson, B., Tuli, A., Gao, S., Tao, J., Sartori, F., Qin, R., Sullivan, D., Stanghellini, M., Ajwa, H. 2013. Simulation of fumigant transport and volatilization from tarped broadcast applications. Vadose Zone Journal. 12(3):1-10. Interpretive Summary: Mechanistic models capable of simulating complex physico-chemical pesticide fate and transport processes can improve estimates of potential environmental impacts and exposures, thereby helping to guide regulatory decision making. However, historically there has been a lack of suitable models, particularly for fumigants. The ability of the HYDRUS 2D/3D model to simulate fate and transport of chloropicrin and 1,3-dichloropropene after application to soil under a low permeability tarp was evaluated. These fumigants are important alternatives to methyl bromide. The model accurately described the basic fate, transport and volatilization processes for both fumigants, as well as heat transport, and soil-water dynamics. Simulated fumigant flux densities and cumulative emission losses for both pre- and post-tarp cut time periods were within the range of uncertainty of conventional field-based flux estimates. These latter estimates were derived using the standard procedure of inverse modeling of off-site fumigant air concentrations. The ability of The HYDRUS 2D/3D model to accurately simulate individual processes increases confidence in modeled flux predictions, and advances the use of modeling as an additional tool for evaluating fumigant volatilization in the field.
Technical Abstract: We evaluated the ability of the HYDRUS 2D/3D model to simulate chloropicrin and 1,3-dichloropropene fate, transport and volatilization. Three fields with similar soil conditions were broadcast fumigated under a totally impermeable film (TIF). One field was used to calibrate HYDRUS by adjusting fumigant degradation rates, soil sorption coefficients and TIF tarp resistance factors. In comparisons of simulated and measured soil gas concentrations, soil temperature, soil-water contents, and inverse-modeled estimates of fumigant volatilization flux, the model accurately simulated the basic individual processes of fumigant partitioning and degradation, heat transport, and soil-water dynamics in the calibration field. Subsequent flux simulations of the remaining two fields were performed using only measured, independently estimated or calibrated inputs with no further adjustments. The magnitudes of simulated cumulative fluxes, and both pre- and post-tarpcut discrete flux densities were within the estimated range of uncertainty (factor of ~ 2) of conventional inverse-modeled field-based flux estimates. However, the timing of maximum discrete flux densities was delayed by 1 – 2 days relative to inverse-modeled estimates. While HYDRUS provided reasonably accurate flux estimates, it was also evident that parameterization – particularly for TIF tarp permeability properties - generally requires field-based calibration due to a lack of representative field effective permeability data.