Litter Input

Abstract

Food webs in forested streams are largely fuelled by plant litter of terrestrial origin. Litter enters streams directly from the canopy (vertical inputs), laterally as material initially fallen on the ground (lateral inputs) and as material transported longitudinally from upstream. This chapter describes how to estimate these three components of input in small streams. The last pathway is the most difficult to quantify, as it is highly variable over time, depending on rates of litter fall and on discharge. Litter traps are constructed from 1 mm-mesh on a wooden or metallic frame and deployed over the stream channel, along the banks and in the channel upstream of a selected reach to collect vertical and lateral inputs as well as litter transported downstream. The collected litter is regularly retrieved, sorted into categories such as leaves, wood, etc., and dried and weighed. Subsamples are ashed and re-weighed to determine ash-free dry mass. Longitudinal transport traps can only be deployed for short periods. Therefore, transport during periods without traps in the channel needs to be estimated based on transport-discharge relationships computed from multiple short-term measurements. This requires continuous discharge records. The collected input data provide essential information to construct energy budgets for streams.