Use of cotton strips to evaluate organic-matter decomposition in streams

Tests of leaf-litter decomposition have been instrumental in advancing understanding of organic-matter dynamics in streams and other ecosystems.  The technique is not without shortcomings, however, some of which could be overcome by using cotton fabric instead of leaves.  Advantages of cotton are that it is standardized, nutrient free, and when tensile-strength loss is used as a response variable, requires little incubation time.  To explore the potential of cotton strips as a means of evaluating decomposition in streams, we exposed strips to different environmental conditions and subsequently measured their tensile-strength loss, mass loss, and/or respiration (as consumption of dissolved oxygen).  Tensile-strength loss differed among strips incubated in different habitats of an alluvial floodplain in northern Italy, and generally tracked the mass loss of experimentally introduced leaf material.  Microbial respiration associated with cotton strips responded strongly to increases in concentrations of dissolved nutrients associated with the onset of annual salmon runs in four Alaskan streams.  Cotton-strip mass loss was less sensitive to stream conditions than either tensile-strength loss or respiration.  We conclude that, depending on research goals, the cotton-strip assay has utility as a means of assessing decomposition, especially when a highly standardized, and/or nutrient-free substrate is needed.