RESUMO

BACKGROUND: Monovalent acidic pesticide sorption can be determined for any soil pH if the dissociation constant of the compound is known, and sorption coefficients are available for at least two different pH values, measured in a wide enough range to enable estimating both neutral and anionic form coefficients. Sorption estimates have also been made from a single sorption coefficient available, assuming a non-compound specific value of the anionic form sorption coefficient or considering a generic ratio between sorption coefficients of the two forms. A compound-specific procedure for adjustment of parameters of the equation for estimating sorption of monovalent acidic herbicides at different pH levels, from a single sorption coefficient, is proposed and evaluated. RESULTS: The quality of fits was good for sorption of all three herbicides studied, especially for 2,4-D and flumetsulam at pH above 5, even for diverse soils and experimental procedures and conditions. The best fits resulted in the following ratios of theoretical maximum organic-carbon sorption coefficients for neutral and anionic forms (Kocn':Koca'): 440:1 for 2,4-D; 132:1 for flumetsulam; and 55:1 for sulfentrazone. CONCLUSION: The ratios of theoretical maximum sorption coefficients for neutral and anionic forms (Kocn':Koca') are compound-specific, thus this procedure should also be applied to pH-sorption datasets for other acidic pesticides to provide the respective ratio between the theoretical maximum sorption coefficients, instead of using generic assigned values. More calibration research is recommended and validation of this approach is required to demonstrate applicability of the method. © 2020 Society of Chemical Industry.

Assuntos

Herbicidas/química , Adsorção , Concentração de Íons de Hidrogênio , Solo , Poluentes do Solo

RESUMO

Urbanization can increase sheet, rill, gully, and channel erosion. We quantified the sediment budget of the Los Laureles Canyon watershed (LLCW), which is a mixed rural-urbanizing catchment in Northwestern Mexico, using the AnnAGNPS model and field measurements of channel geometry. The model was calibrated with five years of observed runoff and sediment loads and used to evaluate sediment reduction under a mitigation scenario involving paving roads in hotspots of erosion. Calibrated runoff and sediment load had a mean-percent-bias of 28.4 and - 8.1, and root-mean-square errors of 85% and 41% of the mean, respectively. Suspended sediment concentration (SSC) collected at different locations during one storm-event correlated with modeled SSC at those locations, which suggests that the model represented spatial variation in sediment production. Simulated gully erosion represents 16%-37% of hillslope sediment production, and 50% of the hillslope sediment load is produced by only 23% of the watershed area. The model identifies priority locations for sediment control measures, and can be used to identify tradeoffs between sediment control and runoff production. Paving roads in priority areas would reduce total sediment yield by 30%, but may increase peak discharge moderately (1.6%-21%) at the outlet.