California has one of the largest systems of surface water reservoirs in the world, providing irrigation water to California's agriculturally productive Central Valley. Irrigation water is recognized as a vehicle for the microbial contamination of raw produce and must be monitored according to new federal regulation. The purpose of this study was to further understanding of the variability of fecal indicator bacteria (Escherichia coli and fecal coliforms) and pathogens (E. coli O157:H7, Non-O157 shiga toxin-producing E. coli and Salmonella) along both horizontal and vertical profiles within California reservoirs. Monthly sampling was conducted in six reservoirs located in the foothills of the Western Sierra Nevada during the summer irrigation season and extreme drought conditions of 2014 (n = 257). Concentrations of fecal indicator bacteria were highly variable between reservoirs (p < 0.05) and along the horizontal profile (p < 0.001) from upstream to downstream, with higher concentrations typically found outside of the reservoirs than within. Though many of the reservoirs were thermally stratified, bacterial concentrations were not associated with water temperature (p > 0.05) or any one particular depth strata (p < 0.05). However, prevalence of Salmonella and non-O157 STEC (16/70 and 9/70 respectively) was higher in the deep strata than in mid or surface layers. Water quality outcomes were We found no statistical association between samples collected downstream of reservoirs and those from the reservoirs themselves. Continued monitoring and modeling of both bacterial indicators and enteric pathogens are critical to our ability to estimate the risk of surface irrigation water supplies and make appropriate management decisions.

加利福尼亚拥有世界上最大的地表水系统之一，为加利福尼亚农业生产性的中央谷地提供灌溉水。灌溉水被公认为是对农产品微生物污染的媒介，必须根据新的联邦法规进行监控。这项研究的目的是进一步了解粪便指示菌（大肠杆菌和粪便大肠菌）和病原体（大肠杆菌O157：H7，产生非O157志贺毒素的大肠杆菌和沙门氏菌）的变异性）沿着加利福尼亚水库内的水平和垂直剖面。在夏季灌溉季节和2014年的极端干旱条件下（n = 257），在内华达山脉西部山麓的六个水库进行了每月采样。粪便指示菌的浓度在储层之间（p <0.05）和沿水平剖面（p <0.001）从上游到下游变化很大，通常在储层外部比在内部更高。尽管许多储层是热分层的，但细菌浓度与水温（p> 0.05）或任何一个特定深度地层（p <0.05）都不相关。然而，沙门氏菌的流行和非O157 STEC（分别为16/70和9/70）在深层中高于中层或表层。我们发现水质结果与水库下游收集的样本和水库本身收集的样本之间没有统计关联。对细菌指标和肠道病原体的持续监控和建模对于我们评估地表灌溉水供应风险和做出适当管理决策的能力至关重要。