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Extreme temperatures have increased in intensity, duration and frequency in the last century, with potential consequences on key ecological processes such as organic matter breakdown. Many stream ecosystems are fueled by the breakdown of terrestrial leaf litter, which is exposed to atmospheric conditions for certain periods of time before entering the stream. Thus, extreme warming or freezing events may affect the litter physicochemical structure, which could translate into altered breakdown within the stream. The above prediction was tested by exposing litter of common riparian tree species in southern Chile to freezing (−20 ºC; dry or wet litter) or heating (40 ºC) and comparing breakdown with control litter exposed to room temperature (20 ºC), separating the effects of different breakdown agents (i.e., leaching, microorganisms and detritivores). The greatest effects were found in wet litter subjected to freezing; this treatment significantly increased leaching in the short term (48 h) and slowed down breakdown in the long term (30 days), mostly due to the inhibition of microbial breakdown. Heating also retarded microbial breakdown, but the effect was smaller. Our results suggest that short-term extreme temperatures—particularly cold ones—have the potential to slow down litter breakdown in streams, which will most likely impact global biogeochemical cycles where streams play a key role. [ABSTRACT FROM AUTHOR]

Intermittent streams comprise the majority of stream length in many parts of the world, particularly dry regions. Many dry regions are expected to experience longer and more intense dry periods as the global climate changes. The response of benthic macroinvertebrate communities in intermittent streams to current variability in dry-period duration and intensity may predict their future response to climate change, but such responses require quantification in different stream types and climate zones. I compared the macroinvertebrate community among drier and wetter years from 2008 to 2012 in intermittent forested and pasture streams in a relatively warm, dry region of New Zealand. I predicted that macroinvertebrate communities would decline in density and taxonomic richness with increasing dryness, and that drought-sensitive Ephemeroptera, Plecoptera and Trichoptera (EPT) taxa would show a stronger response than Diptera and non-insects. EPT richness and density did decline with increasing dry period duration, whereas total macroinvertebrate density and richness, and Diptera richness, showed weak and/or non-significant relationships. I predicted that loss of remnant pools (a potential dry-season refuge) would cause a decline in macroinvertebrate richness and density, but found no significant difference between years with and without pools. I predicted that years when flow resumed late in the autumn (when temperatures are too cool for insect flight) would have lower EPT richness and density than years when flow resumed early, and results confirmed this. Intermittent pasture stream communities showed a weaker response to dry period duration than communities in intermittent forested streams, as taxa relatively tolerant of agricultural stressors are also relatively tolerant of drying. Results suggest that global climate change will cause a loss of drought-sensitive species from intermittent streams in this region. [ABSTRACT FROM AUTHOR]

Temporary streams on the island of Mallorca support unique fauna that differ from other temporary streams on the mainland. It comprises many poor-dispersing endemics as well as more ubiquitous species with better dispersal abilities. To determine the importance of spatial and temporal drivers, this study assesses on the composition and biological traits of macroinvertebrate assemblages, and their variation among 26 non impaired streams corresponding to 3 temporary stream types (mountain, canyon and lowland) during two hydrological phases (flow and disconnected pools) sampled seasonally between 2005 and 2008. Mountain and canyon streams showed longer water permanence, and higher biodiversity than lowland streams, which were characterized by higher drying impact. Significant differences (PERMANOVA and PERMDIST) in species and biological traits composition were found among hydrological phases and stream types, indicating the high spatial and temporal heterogeneity of these temporary systems. The lack of desiccation-resistant forms was dominant in the temporary streams community, suggesting that taxa may survive and persist over the summer in other refugia, such as the hyporheic zone and/or groundwater springs. The environmental variables (physico-chemical, hydromorphological and basin land uses) explained only 40% of the distribution of macroinvertebrate composition (dbRDA analysis), leaving spatial characteristics and temporal variables the highest percentages of variance. Moreover, a significant influence of distance on the macroinvertebrate dispersion (within the surrounding 5 km) was found. Therefore, both neutral (dispersal processes) and niche explanations (local environmental conditions) contribute to patterns of local diversity. Our study highlights the importance of determining the spatio-temporal drivers which influence the ecology and composition of aquatic communities of temporary streams. Such improvement on our knowledge is highly needed for the appropriate design of monitoring programs, being urgently required in the lowlands streams, as they are the most vulnerable to climate change (longer seasonal and supra-seasonal droughts) and human impacts. [ABSTRACT FROM AUTHOR]