Figure 3. Changes in productivity (carbon fixation rate) of periphyton (top panel), phytoplankton (middle panel) and epipelon (bottom panel) in replicated control (solid lines) and nutrient spiked (dotted lines) enclosures in the Blind Channel. Vertical solid bars indicate the N+P additions on 20 June and 2 August 1993. Errors bars are the standard deviation of six replicate substrata from each of two replicated enclosures.