阿特拉津在饱和砂质壤土中非平衡运移的模拟

SIMULATION OF NONEQUILIBRIUM TRANSPORT OF ATRAZINE IN SATURATED SANDY LOAM UNDER STEADY-STATE WATER FLOW CONDITION

针对农药阿特拉津在稳定流场饱和砂质壤土中的运移 ,根据平衡与非平衡假设条件下对流—弥散方程数学模型的解析解 ,基于易混合置换实验获得的阿特拉津和示踪溶质Br- 的穿透曲线及批量平衡法求得的阻滞因子 ,应用CXTFIT 2 0软件 ,通过拟合土柱实验中溶质的出流浓度变化 ,估算了模型的有关参数 ,在此基础上模拟分析了实验土柱不同埋深处阿特拉津的出流浓度和累积淋溶量动态 ,结果表明 。

Nonequilibrium transport of pesticides is frequently reported to greatly affect their transport and mobility in soil. Atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) is a kind of herbicide that is widely used for selective control of grassy weeds in corn production but poses potential danger to the quality of ground water in China. Consequently,there is interest in predicting its mobility in agricultural soils. The objective of the present study was to apply the one-dimensional convection-dispersion equation based on the local equilibrium assumption model (LEA model) and nonequilibrium assumption model (NEA model,including the two-site model and two-region model) for describing nonequilibrium sorption characteristics of atrazine during miscible displacement in water-saturated homogeneous soil. Soil column experiments were conducted in duplicate with a sandy loamy soil under steady-state flow at a specific pore water velocity. A nonlinear least-squares optimization approach (CXTFIT 2.0) was used to fit breakthrough curves (BTCs) for bromide and atrazine in Exp. 1. The symmetrical BTC for tracer bromide was best described by the LEA model,indicating that there were no significant effects of immobile water on transport of bromide (i.e.,no significant physical nonequilibrium in this system). The asymmetrical shape and tailing of atrazine BTC showed that atrazine was mainly influenced by chemical nonequilibrium during transport and the best fit to observed atrazine BTC was obtained with the two-site model. Model verification procedures were based on best-fit parameters optimized from the first displacement experiment (Exp.1),and then these fitted parameters were used to simulate the transport of atrazine in the duplicate experiment (Exp.2) by the chemical nonequilibrium model. The results showed that there was a good agreement between measured and simulated concentration variations for atrazine leaching in this soil column. In addition,dynamics of the flux concentration and the cumulative leaching quantity of atrazine at different depths of the soil column in Exp. 2 were simulated. This study suggests that the two-site model based on the nonequilibrium theory can be used as a useful approach to better quantifying environmental fate of atrazine in a given scenario.