Instream Bacteria Influences from Bird Habitation of Bridges |
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| Authors: | David Pendergrass Anne McFarland Larry Hauck |
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| Affiliation: | Texas Institute for Applied Environmental Research, Tarleton State University, Stephenville, Texas |
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| Abstract: | 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 >190 colony forming units (CFU)/100 mL, well above the state geometric mean criterion of 126 CFU/100 mL 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. |
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| Keywords: | fecal indicator bacteria environmental sampling public health avian bridge colonies surface water quality
Escherichia coli
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