Leaf litter breakdown and benthic invertebrate colonization affected by seasonal drought in headwater lotic systems of Andean Patagonia

We aimed to establish the effect of seasonal drought on leaf litter breakdown and invertebrate communities. Differences in breakdown rates of Nothofagus pumilio were experimentally compared using the litter bag method (coarse and fine mesh size bags) in two first-order streams, one intermittent and one perennial, during two different hydrological periods. Colonizing fauna found in coarse mesh bags was quantified, identified and compared with benthic biota from the same streams. Leaf litter decay rates in low flow conditions revealed that breakdown was principally a consequence of microbial action in the intermittent stream. In contrast, breakdown in high flow conditions was caused by invertebrate feeding in both streams. Collector–gatherers constituted most of the abundance and biomass in bags from the intermittent stream, due to their rapid benthic recolonization. Shredders peaked at approximately 50% remaining leaf litter mass in both streams only during high flow, which coincided with general models of detritus breakdown in streams. Considering global warming scenarios, with drought and water temperature increases expected for many regions of the world, these studies on the consequences for the biota and ecological processes of small streams will allow the prediction of negative effects on such vulnerable ecosystems.