Abstract

 The influence of indicator bacteria in beach sands on recreational water quality has become increasingly recognized. To date, few researchers have explored anthropogenic and natural factors affecting the content of E. coli in beach sands. This study explores the influence of beach grooming on in situ populations of E. coli at two northwestern beaches of Lake Michigan: 63rd St. Beach at Chicago, IL and North Beach at Racine, WI. E. coli concentrations were monitored for two weeks before and after the placement of clean, upland sands in Chicago. Foreshore sands, offshore water, and afternoon near shore water at 45 and 90 cm depths were significantly higher before new sand placement suggesting that new sands temporarily decreased E. coli content (p<0.05). Chicago foreshore sand and lake water were monitored three days a week from May through September 2000. Foreshore and submerged sands, morning water at 45 and 90 cm depths were significantly higher during beach grooming (p<0.01). A study was subsequently conducted at North Beach, Racine, during 2001 that demonstrated professional grooming significantly increased E. coli content of foreshore sands relative to non-groomed or hand raked plots (p<0.001). These data also suggested that deeper grooming might reduce differences between groomed and non-groomed areas. In 2002, two grooming techniques were compared at Racine: groomed to a depth of 5-7 cm, leveled with finisher and groomed to a depth of 7-10 cm without leveling. E. coli content between treatments were significantly correlated (p<0.009). The density of E. coli in unfinished sands was significantly lower in visibly moist and wet but not dry sands (p=0.038). These results demonstrate that lakeshore manipulation may affect E. coli content in foreshore sands, a potential source of non-point pollution to recreational waters. Current beach management practices may need to be re-evaluated in light of these findings.