Limnetica 36

In aquatic environments, especially in shaded patches (where primary production is limited by the low-light conditions), energy flow and organic-matter cycling are fundamental for maintaining a system’s metabolism. The breakdown of this organic detritus is a key process for its remobilization into the trophic chains. Our objective was to describe the temporal dynamics of leaf breakdown in a tropical stream with a riparian canopy degraded by the extraction of palm trees. The vertical input of leaves was collected monthly in a natural stream and incubated for 30 days in a stream with a degraded canopy. Leaf breakdown rates (k), and leaf associated microbial biomass, fungal sporulation and invertebrate community were estimated. Higher values of k were observed in summer most likely due to high temperatures (increased metabolic activity) and rainfall (higher physical abrasion). Aquatic invertebrates (mainly shredders) and total microorganisms showed no overall influence on leaf breakdown rates. Therefore, in this large temporal sampling, water flow, temperature and precipitation were the factors controlling k in this stream. There were no observed changes in k compared to natural environments, most likely because the canopy degradation is a structural modification and does not represent a source of pollution.