Abstract：
Despite the widely acknowledged public health impacts of surface water fecal contamination, there is limited understanding of seasonal effects on (i) fate and transport processes and (ii) the mechanisms by which they contribute to water quality impairment. Quantifying relationships between land use, chemical parameters, and fecal bacterial concentrations in watersheds can help guide the monitoring and control of microbial water quality and explain seasonal differences. The goals of this study were to (i) identify seasonal differences in Escherichia coli and Bacteroides thetaiotaomicron concentrations, (ii) evaluate environmental drivers influencing microbial contamination during baseflow, snowmelt, and summer rain seasons, and (iii) relate seasonal changes in B. thetaiotaomicron to anticipated gastrointestinal infection risks. Water chemistry data collected during three hydroclimatic seasons from 64 Michigan watersheds were analyzed using seasonal linear regression models with candidate variables including crop and land use proportions, prior precipitation, chemical parameters, and variables related to both wastewater treatment and septic usage. Adaptive least absolute shrinkage and selection operator (LASSO) linear regression with bootstrapping was used to select explanatory variables and estimate coefficients. Regardless of season, wastewater treatment plant and septic system usage were consistently selected in all primary models for B. thetaiotaomicron and E. coli. Chemistry and precipitation-related variable selection depended upon season and organism. These results suggest a link between human pollution (e.g., septic systems) and microbial water quality that is dependent on flow regime. IMPORTANCE In this study, a data set of 64 Michigan watersheds was utilized to gain insights into fecal contamination sources, drivers, and chemical correlates across seasons for general E. coli and human-specific fecal indicators. Results reaffirmed a link between human-specific sources (e.g., septic systems) and microbial water quality. While the importance of human sources of fecal contamination and fate and transport variables (e.g., precipitation) remain important across seasons, this study provides evidence that fate and transport mechanisms vary with seasonal hydrologic condition and microorganism source. This study contributes to a body of research that informs prioritization of fecal contamination source control and surveillance strategy development to reduce the public health burden of surface water fecal contamination.
摘要：
尽管地表水粪便污染对公众健康的影响得到了广泛认可，对（i）命运和运输过程的季节性影响以及（ii）它们导致水质损害的机制的理解有限。量化土地利用之间的关系，化学参数,和流域粪便细菌浓度可以帮助指导微生物水质的监测和控制，并解释季节性差异。这项研究的目标是（i）确定大肠杆菌和拟杆菌的季节性差异，(ii)评估基流期间影响微生物污染的环境驱动因素，融雪,和夏天的雨季，和（iii）将B.thetaiotaomicron的季节性变化与预期的胃肠道感染风险相关联。使用季节性线性回归模型分析了在三个水文气候季节从64个密歇根流域收集的水化学数据，该模型具有包括作物和土地利用比例在内的候选变量，前期降水,化学参数,以及与废水处理和化粪池使用相关的变量。自适应最小绝对收缩和选择算子（LASSO）线性回归与自举用于选择解释变量和估计系数。不管季节,在B.thetaiotaomicron和大肠杆菌的所有主要模型中，始终选择了废水处理厂和化粪池系统的使用。化学和与降水相关的变量选择取决于季节和生物。这些结果表明人类污染之间存在联系(例如，化粪池系统)和取决于流态的微生物水质。在这项研究中的重要性，一组64个密歇根流域的数据被用来了解粪便污染源，司机,以及跨季节的一般大肠杆菌和人类特异性粪便指标的化学相关性。结果重申了人类特定来源之间的联系(例如，化粪池系统)和微生物水质。虽然粪便污染和命运和运输变量的人类来源的重要性(例如，降水)在不同季节仍然很重要，这项研究提供了证据，表明命运和运输机制随季节性水文条件和微生物来源而变化。这项研究为一系列研究做出了贡献，该研究为粪便污染源控制和监测策略的制定提供了优先次序，以减轻地表水粪便污染的公共卫生负担。
