Plant litter decomposition as a tool for stream ecosystem assessment

Abstract

The decomposition of plant litter in freshwaters is an integrative process involving multiple organism groups and connecting terrestrial and freshwater ecosystems. The quantification of leaf litter decomposition has been advocated as an effective indicator of ecosystem functional integrity in the bioassessment of freshwaters. Indeed, variation in litter decomposition rates has been used to detect the impacts of a wide range of anthropogenic disturbances on the functioning of detritus-based food webs in freshwater ecosystems, particularly in streams. However, these assessments have almost exclusively been undertaken as part of research projects, and the application of litter decomposition as a tool in routine biomonitoring remains limited. We evaluate the potential for litter decomposition as a tool for ecosystem assessment by environmental agencies and managers, drawing on insights and experiences from three lines of evidence: (i) a broad selection of published research projects, (ii) an existing national-scale monitoring program and (iii) a meta-analysis comparing litter decomposition rates between nutrient-enriched and reference sites. We use this as a basis for discussing inter alia common substrates used in decomposition assays, alternatives for field protocols and sampling designs, and the use of different indices and reference conditions when arriving at an assessment of functional status.