Solar and temporal effects on Escherichia coli concentration at a Lake Michigan swimming beach

Applied and Environmental Microbiology
By: , and 



Studies on solar inactivation of Escherichia coli in freshwater and in situ have been limited. At 63rd St. Beach, Chicago, Ill., factors influencing the daily periodicity of culturable E. coli, particularly insolation, were examined. Water samples for E. coli analysis were collected twice daily between April and September 2000 three times a week along five transects in two depths of water. Hydrometeorological conditions were continuously logged: UV radiation, total insolation, wind speed and direction, wave height, and relative lake level. On 10 days, transects were sampled hourly from 0700 to 1500 h. The effect of sunlight on E. coliinactivation was evaluated with dark and transparent in situ mesocosms and ambient lake water. For the study, the number of E. coli samples collected (n) was 2,676. During sunny days, E. coli counts decreased exponentially with day length and exposure to insolation, but on cloudy days, E. coli inactivation was diminished; the E. coli decay rate was strongly influenced by initial concentration. In situ experiments confirmed that insolation primarily inactivated E. coli; UV radiation only marginally affected E. coliconcentration. The relationship between insolation and E. coli density is complicated by relative lake level, wave height, and turbidity, all of which are often products of wind vector. Continuous importation and nighttime replenishment of E. coli were evident. These findings (i) suggest that solar inactivation is an important mechanism for natural reduction of indicator bacteria in large freshwater bodies and (ii) have implications for management strategies of nontidal waters and the use of E. coli as an indicator organism.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Solar and temporal effects on Escherichia coli concentration at a Lake Michigan swimming beach
Series title Applied and Environmental Microbiology
DOI 10.1128/AEM.70.7.4276-4285.2004
Volume 70
Issue 7
Year Published 2004
Language English
Publisher American Society for Microbiology
Contributing office(s) Great Lakes Science Center
Description 10 p.
First page 4276
Last page 4285
Online Only (Y/N) N
Additional Online Files (Y/N) N