Hierarchical variation in cellulose decomposition in least-disturbed reference streams: a multi-season study using the cotton strip assay

Context Decomposition of organic matter dictates productivity of headwater streams in forested biomes. However, the hierarchical structure of stream ecosystems entails that research aimed at understanding patterns and drivers of decomposition incorporate multiple spatio-temporal scales. Objectives We assessed spatio-temporal patterns of cellulose decomposition in least-disturbed streams and determined the relative distribution of variation associated with region, stream and habitat scales. We also established the environmental drivers associated with heterogeneity in cellulose decomposition. Methods We applied a hierarchical design to assess spatio-temporal patterns of cellulose decomposition in least-disturbed streams of Ontario, Canada. Cotton strips were deployed in one pool and one riffle in each of 19 streams across three regions with distinct climates and physiography. Strips were deployed in spring, summer and autumn and assessed for rate of tensile strength loss. Results Rates of tensile loss differed among regions regardless of season. Habitat differences were observed in two of three regions during the spring and summer. Season only explained a significant amount of variance when tensile loss rates were not corrected for stream temperatures. Region and stream scales were associated with twice the variance in tensile loss than habitat. Spatial variation in tensile loss was negatively associated with latitude, forest cover, nutrients and conductivity. Conclusions Our findings demonstrate the importance of the regional landscape template in explaining spatio-temporal patterns of cellulose decomposition in streams. Moreover, our study suggests application of cellulose decomposition as a biomonitoring tool requires consideration of regional landscapes, habitat and season when developing sampling protocols and bioassessment models.