Initial mass of leaf litter influences mass loss and invertebrate assemblages in two mountain streams

Abstract

Leaf litter that enters to rivers and streams generates leaf packs of diverse mass, but it is not clear if increasing litter mass of these accumulations modifies their decomposition rates and invertebrate assemblages associated. We tested whether greater initial leaf litter masses (3, 5, or 7 g) modified the breakdown rates and colonization of alder litterbags by invertebrates in two Iberian mountain streams. Similar to most previous experimental studies that compared leaf litter masses of 5 g or less in streams, higher initial masses reduced the percentage of lost leaf litter, but only when compared with litterbags that had the lowest mass (3 g). We found that greater initial mass did not hinder large invertebrates accessing the leaf litter, and it did not increase the ability of litterbags to provide refuges from predators. Higher initial mass was positively related to invertebrate diversity and total invertebrate abundance (animals/litterbag), but negatively related to invertebrate density (animals/g of litter remaining), possibly due to the geometry of leaf litter packs because a greater leaf mass (i.e., greater volume) reduces the surface area:volume ratio in a non-uniform manner, as well as decreasing the fraction of the leaf litter that is exposed directly to water flow.