Summary 1. The efficacy of leaf‐litter decomposition, sediment respiration, biofilm biomass, growth, chlorophyll a concentration and the autotrophic index (biofilm ash‐free dry mass/chlorophyll a) and fungal biomass for detecting human‐induced change was evaluated using 24 references and 15 disturbed stream sites located in central Portugal. 2. Decomposition rates of alder (Alnus glutinosa) and oak (Quercus robur) leaves and sediment respiration rates were effective in discriminating impairment. Decomposition was negatively correlated with abiotic factors, such as ammonium and nitrite concentrations, connectivity and alterations in the hydrological regime, and positively correlated with nitrate concentration and oxygen concentration. Sediment respiration rates were correlated with organic contamination, land use and morphological changes. 3. Growth rates of biofilm, concentration of chlorophyll a and the autotrophic index, although 41–73% higher at disturbed compared to reference sites, were not significantly different. These three variables were significantly correlated with total organic carbon, oxygen concentration, pH, nitrite and the presence of dams. Fungal biomass on leaves and biofilm biomass on natural substrata did not differ between reference and disturbed sites. 4. Our findings lend support to the use of functional variables like decomposition and sediment respiration in monitoring and when used together with structural variables should give a more holistic measure of stream health.

Please cite this article in press as: Alvim, E.A.C.C., et al., Small leaf breakdown in a Savannah headwater stream. Limnologica (2014), http://dx. a b s t r a c tThe chemical nature and nutritional quality of leaves influence microbial colonization, microbial activity and consequently leaf breakdown rates. In the present study, we compared the decomposition of Baccharis concinna and Baccharis dracunculifolia leaves and the influence of leaf quality on the microbial activity during the decomposition process. This investigation was conducted in a Brazilian savanna headwater stream with a riparian zone composed predominantly of herbaceous and shrubs. The breakdown coefficient was higher in B. dracunculifolia than in B. concinna; for both species, increases in leaf mass were observed after the 60th day. The secondary compounds were quickly leached in the first seven days, but the structural compounds persisted longer and served as the main carbon source for the detritus-associated microorganisms. The highest values of ergosterol were observed in the final stages of leaf breakdown and indicated the difficulty of colonization on the detritus; these values were related to the increase in leaf mass. The ATP content increased without corresponding increase in ergosterol content, suggesting a biofilm formation during leaf breakdown. These results indicated that the total microbial biomass can assimilate organic compounds released from detritus by the enzymatic action of fungi, demonstrating the importance of this group for releasing the energy stored in small leaves.