In stream ecosystems, chemical composition of particulate organic matter (POM) greatly depends on its origin, and affects its decomposition rate and nutritional availability for organisms. At any point in a stream, POM is assumed to be affected quantitatively and qualitatively by material transport from upstream and by local processes, such as primary production and material input from riparian areas. However, the relative contributions of advective transport from upstream or local processes in governing site-specific chemical properties of POM in streams have not been examined. Under low-flow conditions (<0.23 m³ s^-1) in summer 2007, we examined longitudinal variations in chemical signatures (e.g. C/N, δ¹³C, δ¹⁵N) of POM (suspended fine POM, sediment fine POM, biofilm) as well as benthic invertebrates in three forested streams of southwestern British Columbia, Canada. Results showed that in general, the chemical signatures of POM and invertebrates significantly varied between stations in each stream, and had discontinuous longitudinal trends. The δ¹⁵N signatures were positively related between biofilm, sediment POM and some invertebrate species. This linkage of the chemical signatures between these POM components suggests that local processes were important controls of the chemical signatures, and contributed to their longitudinal heterogeneity.