Fine mesh and course mesh screening enclosing experimental leaves allows researchers to determine the importance of insect and other macro-invertebrates on the decomposition of the leaves. Fine mesh screens allow just microbes to colonize and decompose the leaves, while coarse screens also allow the larger organisms in to feed on the material. The leaf packs are placed in the stream for several weeks to measure the weight loss and chemical changes of the leaves. In this case, only punched disks of leaves are being used to help standardize the experiment. Photo, Tagliamento River, Italy, March 2006.