Inter‐ and Intra‐Regional Variability of Leaf Litter Breakdown in Reference Headwater Streams of Northern Spain: Atlantic versus Mediterranean Streams

The main goal of this study was to examine the natural variability of alder (Alnus glutinosa (L.) Gaertn.) leaf processing and explore its potentiality as a functional indicator to assess the ecological status of Spanish headwater streams. Breakdown of leaf litter was studied during autumn‐winter in reference headwater streams of two regions of northern Spain: the Basque Country (on the Atlantic) and Catalonia (on the Mediterranean). Spring experiments were also carried out in the Atlantic region in order to study seasonal changes. Leaf mass loss rates were slightly higher in Catalonian streams. Temperature was not the main factor for explaining differences between the two regions. In the Atlantic one, however, water temperature determined the spatial and seasonal variability of leaf litter processing. Because of the high natural variability in breakdown rates, our results highlight the difficulty in detecting moderate impairments on stream functioning through the analysis of leaf litter decomposition if this process is not accompanied by the study of other factors affecting it. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)