PERIPHYTON REACTIONS TO DIFFERENT LIGHT AND NUTRIENT LEVELS AND THE RESPONSE OF BACTERIA TO THESE MANIPULATIONS

We determined the extent of seasonal light and nutrient limitation of algae in open and closed canopy sections of a second order stream. By artificially shading portions of the open and closed canopied sections , we were able to manipulate algal densities and thus observe the effe cts of these algal manipulations on bacterial abundance. Furthermore, by using clay diffusion pots, we also determined the extent of nutrien t limitation of both attached algae and bacteria. Algal abundance was reduced by 40 % or more in natural and artificially shaded sections su ggesting that light was the primary limiting resource in shaded sectio ns. Limitation of algae by nitrogen and phosphorus was observed only d uring October in the open and closed canopy sections (after leaf absci ssion). Bacterial abundance was positively correlated with algal abund ance and thus suggests a possible interaction between the two. Bacteri a also were nutrient-limited but only when algal abundance was very lo w (artificially shaded site under a naturally closed canopy). Our resu lts suggest that bacteria within the biofilm may rely on algal exudate s for an energy source and possibly inorganic nutrients as well for gr owth.