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Abstract: The present report describes a three-step approach that was used to characterize and define thresholds for the Least Disturbed Condition in Mediterranean streams of four different types, regarding organic pollution and nutrients, hydrological and morphological alterations, and land use. For this purpose, a common database composed of national reference sites (929 records) from seven countries, sampled for invertebrates, diatoms and macrophytes was used. The analyses of reference sites showed that small (catchment <100km2) siliceous and non-siliceous streams were mainly affected by channelization, bank alteration and hydropeaking. Medium-sized siliceous rivers were the most affected by stressors: 25–43% of the samples showed at least slight alterations regarding channelization, connectivity, upstream dam influence, hydropeaking and degradation of riparian vegetation. Temporary streams were the least affected by hydromorphological changes, but they were nevertheless affected by alterations in riparian vegetation. There were no major differences between all permanent stream types regarding water quality, but temporary streams showed lower values for oxygenation (DO) and wider ranges for other variables, such as nitrates. A lower threshold value for DO (60%) was determined for this stream type and can be attributed to the streams' natural characteristics. For all other river types, common limits were found for the remaining variables (ammonium, nitrate, phosphate, total P, % of artificial areas, % of intensive and extensive agriculture, % of semi-natural areas in the catchment). These values were then used to select the list of reference sites. The biological communities were characterized, revealing the existence of nine groups of Mediterranean invertebrate communities, six for diatoms and five for macrophytes: each group was characterized by specific indicator taxa that highlighted the differences between groups. [Copyright &y& Elsevier]

The European Water Framework Directive establishes a framework for the protection of water resources. However, common water management tools demand common understanding of assessment methods, so quality goals are equally met. Intercalibration of methods ensures the comparability of biological elements across similar geographical areas. Many aspects can influence the outcome of intercalibration: data sampling, treatment methods, taxonomic reliability of databases, choice of metrics for ecological quality status classification, and criteria for selecting reference sites. This study describes the potentials and constraints of the intercalibration of indices using diatoms for assessment of Mediterranean rivers. Harmonisation of diatom taxonomy and nomenclature was based on a previous ring test which took place at the European level. Four diatom indices (Indice de Polluosensibilité Spécifique-IPS, Indice Biologique Diatomées-IBD 2007, Intercalibration Common Metric Italy-ICMi and Slovenian Ecological Status assessment system) were intercalibrated using data from six European Mediterranean countries (Cyprus, France, Italy, Portugal, Slovenia and Spain). Boundaries between High/Good and Good/Moderate quality classes were harmonised by means of the Intercalibration Common Metric (ICM). Comparability between countries was assured through boundary bias and class agreement. The national boundaries were adjusted when they deviated more than a quarter of a class equivalent (0.25) from the global mean. All national methods correlated well with the ICM, which was sensitive to water quality (negatively correlated to nutrients). Achnanthidium minutissimum sensu lato was the most discriminative species of Good ecological status class. Planothidium frequentissimum, Gomphonema parvulum and Nitzschia palea were the most contributive to Moderate ecological status class. Some taxa were discriminative for both Good and Moderate ecological status classes due to low indication and ecological discriminative power but also due to differences in taxonomy between countries. This intercalibration exercise allowed establishment of common water quality goals across Mediterranean Europe, which is substantiated with the ICM., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Although anthropogenic degradation of riverine systems stimulated a multi-taxon bioassessment of their ecological integrity in EU countries, specific responses of different taxonomic groups to human pressure are poorly investigated in Mediterranean rivers. Here, we assess if richness and composition of macroinvertebrate and fish assemblages show concordant variation along a gradient of anthropogenic pressure in 31 reaches across 13 wadeable streams in central Italy. Fish and invertebrate taxonomic richness was not correlated across sites. However, Mantel test showed that the two groups were significantly, albeit weakly, correlated even after statistically controlling for the effect of environmental variables and site proximity. Variance partitioning with partial Canonical Correspondence Analysis showed that the assemblages of the two groups were influenced by different set of environmental drivers: invertebrates were influenced by water organic content, channel and substratum features, while fish were related to stream temperature (mirroring elevation) and local land-use. Variance partitioning revealed the importance of biotic interactions between the two groups as a possible mechanisms determining concordance. Although significant, the congruence between the groups was weak, indicating that they should not be used as surrogate of each other for environmental assessments in these Mediterranean catchments. Indeed, both richness and patterns in nestedness (i.e. where depauperate locations host only a subset of taxa found in richer locations) appeared influenced by different environmental drivers suggesting that the observed concordance did not result from a co-loss of taxa along similar environmental gradients. As fish and macroinvertebrates appeared sensitive to different environmental factors, we argue that monitoring programmes should consider a multi-assemblage assessment, as also required by the Water Framework Directive.