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Simulation of the fate and seasonal variations of α-hexachlorocyclohexane in Lake Chaohu using a dynamic fugacity model.

Kong XZ, He W, Qin N, He QS, Yang B, Ouyang H, Wang Q, Yang C, Jiang Y, Xu F - ScientificWorldJournal (2012)

Bottom Line: Seasonal patterns in various media were successfully modeled and factors leading to this seasonality were discussed.Sensitivity analysis found that parameters of source and degradation were more important than the other parameters.Uncertainty analysis showed that the model uncertainty was relatively low but significantly increased in the second half of the simulation period due to the increase in the gas-water diffusion flux variability.

View Article: PubMed Central - PubMed

Affiliation: MOE Laboratory for Earth Surface Processes, College of Urban and Environmental Sciences, Peking University, Beijing 100871, China.

ABSTRACT
Fate and seasonal variations of α-hexachlorocyclohexane (α-HCH) were simulated using a dynamic fugacity model in Lake Chaohu, China. Sensitivity analyses were performed to identify influential parameters and Monte Carlo simulation was conducted to assess model uncertainty. The calculated and measured values of the model were in good agreement except for suspended solids, which might be due to disregarding the plankton in water. The major source of α-HCH was an input from atmospheric advection, while the major environmental outputs were atmospheric advection and sediment degradation. The net annual input and output of α-HCH were approximately 0.294 t and 0.412 t, respectively. Sediment was an important sink for α-HCH. Seasonal patterns in various media were successfully modeled and factors leading to this seasonality were discussed. Sensitivity analysis found that parameters of source and degradation were more important than the other parameters. The sediment was influenced more by various parameters than air and water were. Temperature variation had a greater impact on the dynamics of the model output than other dynamic parameters. Uncertainty analysis showed that the model uncertainty was relatively low but significantly increased in the second half of the simulation period due to the increase in the gas-water diffusion flux variability.

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Related in: MedlinePlus

Coefficients of sensitivity of the calculated concentrations of the environmental compartments to the input static parameters with (Cn) (a) and without (Cs) (b) CV normalization.
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fig6: Coefficients of sensitivity of the calculated concentrations of the environmental compartments to the input static parameters with (Cn) (a) and without (Cs) (b) CV normalization.

Mentions: For the static parameters, the sensitivity coefficients changed significantly after correction with the coefficients of variation (Figure 6). Thus, despite the high sensitivities regarding Koc, r23, r43, Bps, BH,A2, and Sc, the corrected sensitivity coefficients for those parameters with lower variability were significantly reduced, such that these eight parameters were considered to be insensitive. The sensitivity reductions in Koc and A2 were also observed by Cao et al. [2]. In contrast, due to higher variability, the sensitivity coefficients of h4, km4, km2, and L4 increased after correction, and they were found to be important parameters. h4 is related to sediment volume, and sediment is found as the sink for α-HCH in lakes; km4 is directly related to the degradation of α-HCH in the sediments, which has been found to be the most important degradation process in the environment (Section 3.2). Thus, the two static parameters exerted considerable influence on the model results. L4 and km2 become more important parameters due to their high variability. Other parameters, including C02t, O23, O43, X43, Ps25, and H25, had relatively similar high sensitivity coefficients before and after correction. C02t strongly affects the α-HCH content in the water and suspended matter. O23 and O43 determine the adsorption capacity of the particles in the suspended solids and sediments, while X43 is related to the amount of sediment adsorption. Therefore, these parameters exert a great influence on the model output. Ps25 determines the fugacity capacity of the atmospheric particulates [33], and H25 plays a decisive role in the fate of POPs in the environment [34]. Although the variability of these two parameters is negligible, the collected values in this study are based on the results from different time periods using different methods. Therefore, the sensitivities of these two parameters remain high after the correction.


Simulation of the fate and seasonal variations of α-hexachlorocyclohexane in Lake Chaohu using a dynamic fugacity model.

Kong XZ, He W, Qin N, He QS, Yang B, Ouyang H, Wang Q, Yang C, Jiang Y, Xu F - ScientificWorldJournal (2012)

Coefficients of sensitivity of the calculated concentrations of the environmental compartments to the input static parameters with (Cn) (a) and without (Cs) (b) CV normalization.
© Copyright Policy - open-access
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3539339&req=5

fig6: Coefficients of sensitivity of the calculated concentrations of the environmental compartments to the input static parameters with (Cn) (a) and without (Cs) (b) CV normalization.
Mentions: For the static parameters, the sensitivity coefficients changed significantly after correction with the coefficients of variation (Figure 6). Thus, despite the high sensitivities regarding Koc, r23, r43, Bps, BH,A2, and Sc, the corrected sensitivity coefficients for those parameters with lower variability were significantly reduced, such that these eight parameters were considered to be insensitive. The sensitivity reductions in Koc and A2 were also observed by Cao et al. [2]. In contrast, due to higher variability, the sensitivity coefficients of h4, km4, km2, and L4 increased after correction, and they were found to be important parameters. h4 is related to sediment volume, and sediment is found as the sink for α-HCH in lakes; km4 is directly related to the degradation of α-HCH in the sediments, which has been found to be the most important degradation process in the environment (Section 3.2). Thus, the two static parameters exerted considerable influence on the model results. L4 and km2 become more important parameters due to their high variability. Other parameters, including C02t, O23, O43, X43, Ps25, and H25, had relatively similar high sensitivity coefficients before and after correction. C02t strongly affects the α-HCH content in the water and suspended matter. O23 and O43 determine the adsorption capacity of the particles in the suspended solids and sediments, while X43 is related to the amount of sediment adsorption. Therefore, these parameters exert a great influence on the model output. Ps25 determines the fugacity capacity of the atmospheric particulates [33], and H25 plays a decisive role in the fate of POPs in the environment [34]. Although the variability of these two parameters is negligible, the collected values in this study are based on the results from different time periods using different methods. Therefore, the sensitivities of these two parameters remain high after the correction.

Bottom Line: Seasonal patterns in various media were successfully modeled and factors leading to this seasonality were discussed.Sensitivity analysis found that parameters of source and degradation were more important than the other parameters.Uncertainty analysis showed that the model uncertainty was relatively low but significantly increased in the second half of the simulation period due to the increase in the gas-water diffusion flux variability.

View Article: PubMed Central - PubMed

Affiliation: MOE Laboratory for Earth Surface Processes, College of Urban and Environmental Sciences, Peking University, Beijing 100871, China.

ABSTRACT
Fate and seasonal variations of α-hexachlorocyclohexane (α-HCH) were simulated using a dynamic fugacity model in Lake Chaohu, China. Sensitivity analyses were performed to identify influential parameters and Monte Carlo simulation was conducted to assess model uncertainty. The calculated and measured values of the model were in good agreement except for suspended solids, which might be due to disregarding the plankton in water. The major source of α-HCH was an input from atmospheric advection, while the major environmental outputs were atmospheric advection and sediment degradation. The net annual input and output of α-HCH were approximately 0.294 t and 0.412 t, respectively. Sediment was an important sink for α-HCH. Seasonal patterns in various media were successfully modeled and factors leading to this seasonality were discussed. Sensitivity analysis found that parameters of source and degradation were more important than the other parameters. The sediment was influenced more by various parameters than air and water were. Temperature variation had a greater impact on the dynamics of the model output than other dynamic parameters. Uncertainty analysis showed that the model uncertainty was relatively low but significantly increased in the second half of the simulation period due to the increase in the gas-water diffusion flux variability.

Show MeSH
Related in: MedlinePlus