Department of Civil & Environmental Engineering, Michigan State University, East Lansing, MI, USA.
Environ Sci Technol. 2010 Feb 1;44(3):1010-6. doi: 10.1021/es902232a.
Escherichia coli (EC) concentrations at two beaches impacted by river plume dynamics in southern Lake Michigan were analyzed using three-dimensional hydrodynamic and transport models. The relative importance of various physical and biological processes influencing the fate and transport of EC were examined via budget analysis and a first-order sensitivity analysis of model parameters. The along-shore advective flux of EC (CFU/m(2).s) was found to be higher compared to its cross-shore counterpart; however, the sum of diffusive and advective components was of a comparable magnitude in both directions showing the importance of cross-shore exchange in EC transport. Examination of individual terms in the EC mass balance equation showed that vertical turbulent mixing in the water column dominated the overall EC transport for the summer conditions simulated. Dilution due to advection and diffusion accounted for a large portion of the total EC budget in the nearshore, and the net EC loss rate within the water column (CFU/m(3).s) was an order of magnitude smaller compared to the horizontal and vertical transport rates. This result has important implications for modeling EC at recreational beaches; however, the assessment of the magnitude of EC loss rate is complicated due to the strong coupling between vertical exchange and depth-dependent EC loss processes such as sunlight inactivation and settling. Sensitivity analysis indicated that solar inactivation has the greatest impact on EC loss rates. Although these results are site-specific, they clearly bring out the relative importance of various processes involved.
采用三维水动力和输运模型分析了受密西根湖南部河川羽流动力影响的两个海滩的大肠杆菌（EC）浓度。通过预算分析和对模型参数的一阶敏感性分析，研究了影响 EC 归宿和输运的各种物理和生物过程的相对重要性。EC 的沿岸平流通量（CFU/m(2).s）高于其横向通量；然而，在两个方向上扩散和平流分量的总和具有相当的大小，表明 EC 输运中横向交换的重要性。EC 质量平衡方程中各单项的研究表明，在模拟的夏季条件下，水柱中的垂直湍动混合主导着 EC 的整体输运。由于平流和扩散导致的稀释占近岸 EC 总预算的很大一部分，并且水柱内 EC 的净损失率（CFU/m(3).s）与水平和垂直输运率相比小一个数量级。这一结果对娱乐海滩 EC 模型的评估具有重要意义；然而，由于垂直交换与依赖深度的 EC 损失过程（如阳光失活和沉降）之间的强耦合，EC 损失率的评估变得复杂。敏感性分析表明，阳光失活对 EC 损失率的影响最大。尽管这些结果是特定于地点的，但它们清楚地说明了所涉及的各种过程的相对重要性。
