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Instream Bacteria Influences from Bird Habitation of Bridges

机译：桥梁鸟类栖息地对河内细菌的影响

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The representativeness of ambient water samples collected from bridge crossings has occasionally been challenged because critics contend birds nesting on bridges elevate fecal indicator bacteria concentrations over samples collected from river reaches not spanned by bridges. This study was designed to evaluate the influence, if any, of bridge-dwelling bird colonies on instream bacteria concentrations. Three bridges in central Texas were sampled under dry-weather conditions for instream Escherichia coli. Two bridges were inhabited by migratory cliff swallows and one was devoid of birds. Numerous samples were collected from locations upstream, at the upstream bridgeface, and downstream of each bridge to determine whether significant increases in E.coli occurred in a downstream direction when birds were present. E.coli values increased significantly at bridgeface and downstream locations compared to upstream locations throughout the nesting season. During peak bird activity in May, bacteria geometric mean concentrations at bridgeface and downstream locations jumped from background levels <50 to >190colony forming units (CFU)/100mL, well above the state geometric mean criterion of 126CFU/100mL for primary contact recreation use. Results confirmed that under dry-weather conditions bird colonies can have a significant impact on bacteria concentrations in the vicinity of the bridges they inhabit and therefore, to avoid this impact, monitoring should occur upstream of bridges.
机译：偶尔会从桥梁过境处收集的环境水样品的代表性受到挑战，因为批评家认为，筑巢在桥梁上的鸟类会提高粪便指示菌的浓度，而不是从桥梁未跨越的河段采集。这项研究旨在评估桥栖鸟类群体对河床细菌浓度的影响（如果有的话）。在干燥天气条件下，对德克萨斯州中部的三座桥梁进行了采样，以采集大肠杆菌。迁徙的燕子栖息着两座桥，没有鸟儿。从每个桥梁的上游，上游桥面和下游位置收集了许多样品，以确定当有禽类出现时，大肠杆菌是否在下游方向发生了显着增加。与整个筑巢季节的上游位置相比，桥面和下游位置的大肠杆菌值显着增加。在五月份鸟类活动高峰期间，桥面和下游位置的细菌几何平均浓度从背景水平<50跃升至> 190菌落形成单位（CFU）/ 100mL，远高于主要接触娱乐用途的国家126CFU / 100mL几何平均标准。结果证实，在干燥的天气条件下，鸟类的殖民地会对栖息地附近的细菌浓度产生重大影响，因此，为避免这种影响，应在桥梁上游进行监测。

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