TABLE 4

Average total E. coli concentrations in air samples collected at the north edge of the feedlot pens and at each of the leafy green plots

Sample dateFeedlot pen surface conditionsWind direction; avg wind speed/avg high wind speeda (mph)Avg. E. coli concentrations (CFU/m3 of air) in air at:
Edge of feedlot (0 m)Leafy green plots
60 m120 m180 m
15 August 2011MuddySE; 10.3/16.842.2 Ab7.2 B3.0 B2.2 B
18 August 2011Moderately dustySSE; 10.7/20.22.3 A2.7 A2.7 A0.8 A
22 August 2011DustyS; 12.7/22.910.2 A4.0 B4.0 B2.2 B
26 August 2011Very dustySSE; 7.5/14.841.7 A5.8 B2.5 B1.7 B
1 September 2011MuddySSW; 8.5/15.43.7 A1.0 B0.2 B0.0 B
6 June 2012Moderately dustySE; 11.1/19.426.5 A5.7 B2.2 B1.7 B
7 June 2012Moderately dustySSE; 10.9/19.615.3 A2.2 B0.8 B0.8 B
22 June 2012Moderately muddySSE; 11.3/19.49.3 A3.3 B0.7 B0.3 B
26 June 2012DrySE; 11.7/19.14.7 A1.8 B1.5 B0.3 B
27 June 2012DrySW; 13.7/22.41.8 A0.7 AB1.3 AB0.2 B
6 July 2012Very dustySSW; 6.8/12.84.0 A4.5 A2.0 A3.5 A
17 July 2012Moderately dustyS; 6.1/11.53.4 A1.5 B0.5 B0.8 B
25 July 2012Moderately dusty; freshly scrapedcSSW; 8.8/15.80.0 A0.0 A0.0 A0.2 A
15 August 2012Very dustyS; 9.5/16.516.0 A3.0 B3.2 B1.2 B
24 August 2012Very dustySSE; 11.2/20.1837.2 A16.7 B10.0 B5.3 B
  • a Dominant wind direction, average wind speed, and average high wind gust speed during the approximately 2.5-h air sampling periods are given. Wind data were recorded at 15-min intervals by an on-site weather station. SSW, south-southwest.

  • b The sample date-by-distance interaction was significant (P < 0.0001), so total E. coli concentrations on each sample date were analyzed separately across distance. Within a row, values followed by different capital letters (A and B) are significantly different (P ≤ 0.05).

  • c In the week preceding 25 July 2012, the 10 adjacent feedlot pens were scraped clean of accumulated manure before placement of new cattle.