Non-perennial rivers and streams (NPRS) cover N 50% of the global river network. They are particularly predominant in Mediterranean Europe as a result of dry climate conditions, climate change and land use development. Historically, both scientists and policy makers underestimated the importance of NRPS for nature and humans alike, mainly because they have been considered as systems of low ecological and economic value. During the past decades, diminishing water resources have increased the spatial and temporal extent of artificial NPRS as well as their exposure to multiple stressors, which threatening their ecological integrity, biodiversity and ecosystem services. In this paper, we provide a comprehensive overview of the structural and functional characteristics of NPRS in the European Mediterranean, and discuss gaps and problems in their management, concerning their typology, ecological assessment, legislative and policy protection, and incorporation in River Basin Management Contents lists available at ScienceDirect Science of the Total Environment j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / s c i t o t e n vPlans. Because NPRS comprise highly unstable ecosystems, with strong and often unpredictable temporal and spatial variability -at least as far as it is possible to assess -we outline the future research needs required to better understand, manage and conserve them as highly valuable and sensitive ecosystems. Efficient collaborative activities among multidisciplinary research groups aiming to create innovative knowledge, water managers and policy makers are urgently needed in order to establish an appropriate methodological and legislative background. The incorporation of NPRS in EU-Med River Basin Management Plans in combination with the application of ecological flows is a first step towards enhancing NPRS management and conservation in order to effectively safeguard these highly valuable albeit threatened ecosystems.

The generalization of ecological results from temporary streams needs the study of those ecosystems across a broad scale of running waters, covering the geographical ecological constraints involved (e.g., precipitation, temperature and geology). For the particular situation of Mediterranean streams in Southern Europe, high changes in water level, with unpredicting flood events, represent an important factor determining the structure and function of Mediterranean streams. This variability, inducing accentuated changes in the macroinvertebrate community, tends to influence the assessment methodologies. A set of metrics commonly used in Europe to assess organic degradation (Shannon-Wiener index, evenness, richness, BBI, IBE, BMWP , ASPT , DSFI, EPT, number of Trichoptera families, percentage of Gasteropoda, Oligochaeta and Diptera) and a multimetric index (IM9) developed to assess organic degradation in southern siliceous Portuguese basins were tested to evaluate quality at two contrasting sites (one unimpaired and another impaired by an identified point source of pollution). The multimetric index (IM9) composed by: ASPT (average score per taxon); GOLD (one minus percentage of Gasteropoda, Oligochaeta and Diptera); and TRICF (number of Trichoptera families), was the most suitable assessment methodology. IM9 presented a quite stable temporal pattern from February in late winter until June in early summer, even under the effect of episodic floods. A stepwise regression showed that most of tested metrics were significantly related to environmental variables (soluble reactive phosphorous, dissolved inorganic nitrogen and dissolved oxygen). Only richness, IBE and BMWP were not significantly influenced by environmental variables. Future research must be done covering the complete gradient of organic degradation, including the extension of multimetric assessment methodologies to temporary streams located in other regions under different geological and climatic conditions.

The potential importance of benthic diatoms in Mediterranean watercourses has received limited academic attention historically. This study sought to provide baseline information for this poorly studied group. Temporary and permanent watercourses in Portugal differ in catchment characteristics, climatic variables and water chemistry. The benthic diatom communities were characterized in terms of ecological preferences and conservation status for taxa with relative abundance above 1% in at least one site covering 39 temporary sites (109 taxa) and 53 permanent sites (130 taxa). The low-profile guild dominated both temporary and permanent watercourses, followed by the high-profile and motile guilds. Indicator value analysis indicated that Amphora copulata, Cocconeis placentula, Diploneis separanda, Encyonopsis subminuta, Fragilaria radians, Gomphonema olivaceum, Gomphonema truncatum, Halamphora veneta, Navicula radiosa, Navicula veneta, Sellaphora seminulum and Ulnaria acus were indicators of temporary watercourses, whereas Encyonema minutum, Eunotia minor, Fragilaria rumpens, Fragilaria cf. socia and Navicula rhynchocephala were characteristic of permanent watercourses. Ecological preferences of indicator taxa were inferred on the basis of environmental variables that differed significantly between temporary and permanent watercourses. The importance of temporary watercourses for the maintenance of diatom biodiversity is discussed and explored.

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A sampling programme was developed in three stream types, of siliceous geology, from the south of Portugal (small and mid-sized lowland streams and small-sized median altitude streams). The samples were taken according to the AQEM site protocol procedure, keeping transport and depositional habitats samples separated. In each stream type, at least 13 sites were studied over a gradient of organic pollution (pre-classification). The benthic macroinvertebrates were identified to the lowest possible taxonomic level. A Detrended Correspondence Analysis of macroinvertebrate communities identified a gradient of organic pollution strongly related to the first axis. This ordination allowed the establishment of classes of organic pollution using the Kmeans software (post-classification). Metrics based on the macroinvertebrate communities (tolerance, richness, composition and trophic structure) were computed and tested for correlation with the gradient of organic pollution (first axis of DCA). Most of the selected metrics were able to discriminate the four quality classes (high, good, moderate and poor) of ecological status. A multimetric index, integrating ASPT index, Trichoptera families and percentage of Gasteropoda, Oligochaeta and Diptera, is proposed to assess the ecological status of Portuguese southern siliceous basins.