FIG. 5.

Changes in E. coli NRR27 abundances in laboratory microcosms attached to periphyton-covered (▾) and bare control (•) rocks and in water overlying these rocks (periphyton-covered ▿ and bare control ○ rocks). The water in each microcosm was inoculated with E. coli NRR27 (open symbols to left of dashed line) 2 days before the experiment began and then replaced with 0.2-μm-filtered, sterile lake water at the start of the experiment (dashed line). Error bars represent standard deviations. Linear regressions indicated that the loss of E. coli from bare control rocks was almost twice as fast as that from periphyton-covered rocks. All microcosms were vigorously agitated at the end of the experiment (20 days) to simulate wave action, and E. coli concentrations in the overlying water were measured again (see arrows).