Defining Maximum Ecological Potential for heavily modified lowland streams of Northern Italy.

In relation to hydromorphological alteration the Water Framework Directive (WFD), a major piece of European legislation, has introduced the concept of Heavily Modified Water Bodies (HMWB). In water bodies falling in this category, hydromorphological modifications are permanent, significantly alter the character of the river and cannot be removed without compromising the use of the water body. In HMWBs a dedicated approach to the evaluation of their status is set, and their Ecological Potential must be assessed. Crucial to the process is the definition of Maximum Ecological Potential (MEP) as the reference conditions for HMWB. In the present paper we aim to define MEP conditions for Italian heavily modified lowland rivers, affected by strong bank protection (i.e. levees or bank reinforcement) in reason of flood protection and land drainage uses. The approach applied to identify MEP conditions follows the one considered for natural (not heavily modified) rivers in Italy and large part of Europe and bases on the identification of 'reference sites' representative for the river category and alteration. For the selection of MEP sites environmental features representing mitigation measures and/or expected natural features were considered. The ability of such features in discriminating MEP and disturbed sites was verified by multivariate analyses run on abiotic features (Principal Component Analysis) and biological communities (non-metric multidimensional scaling). We demonstrated differences both in terms of invertebrate community and biological metrics used to assess ecological status (and potential) between MEP and impaired river stretches. Finally, we recognized relevant habitat features able to clearly separate MEP reaches from nonMEP reaches with indication on the type and quantity of measures significant for benthic invertebrates and applicable in lowland Heavily Modified Water Bodies.

In-stream microhabitat mosaic depicts the success of mitigation measures and controls the Ecological Potential of benthic communities in heavily modified rivers.

The positive effect of mitigation measures on in-stream habitat conditions and the benthic community is recognised. In heavily modified rivers, though, the response of aquatic invertebrates to mitigation measures and habitat mosaic changes is scarcely documented. We used non-metric multidimensional scaling to explore the benthic community of leveed rivers in the agricultural lowlands of Northern Italy. The relevance of in-stream substrate microhabitat for the benthic community was assessed, together with the impact of mitigation measures. We proposed a straightforward approach to quantify similarity of microhabitat mosaic between sites testing its statistical significance based on Bayesian statistics. We hypothesised that changes of microhabitat mosaic would reflect the level of implementation of mitigation measures and benthic invertebrates would respond accordingly. Alpha, beta diversity and benthic metrics used to classify ecological status/potential were considered and their variation tested against different levels of measure implementation. Lastly, ecological potential classification was paralleled to both the level of measure implementation and habitat attributes. The microhabitats found at sites where measures were fully implemented differed from those observed elsewhere and they clearly mirrored morphological alteration and mitigation measures. Moreover, alongside morphological alteration, microhabitat diversity and mosaic were the main factors for benthic community structure. While benthic beta diversity strictly reflected microhabitat diversity, alpha diversity and ecological status metrics copied the mosaic gradient. Microhabitat attributes and most benthic metrics showed significant changes following measure implementation and they were accompanied by a gradual shift in ecological potential classes. We demonstrated the importance of in-stream substrate microhabitats as a bridge between mitigation measures and the benthic community. Particularly when ecological classification is under focus, microhabitat mosaic should be evaluated for achieving a better understanding of biological responses. The huge amount of data available worldwide could support a straightforward use of river mosaic information for river management.

Non-perennial Mediterranean rivers in Europe: Status, pressures, and challenges for research and management.

Non-perennial rivers and streams (NPRS) cover >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 Plans. 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.

Detecting the impact of bank and channel modification on invertebrate communities in Mediterranean temporary streams (Sardinia, SW Italy).

We hypothesized that reach-scale, bank and channel modification would impact benthic communities in temporary rivers of Sardinia, when pollution and water abstraction are not relevant. A range of variables were considered, which include both artificial structures/alterations and natural features observed in a stream reach. Multivariate regression trees (MRT) were used to assess the effects of the explanatory variables on invertebrate assemblages and five groups, characterized by different habitat modification and/or features, were recognized. Four node variables determined the splits in the MRT analysis: channel reinforcement, tree-related bank and channel habitats, channel modification and bank modification. Continuity of trees in the river corridor diverged among MRT groups and significant differences among groups include presence of alders, extent of channel shading and substrate diversity. Also, the percentage of in-stream organic substrates, in particular CPOM/Xylal, showed highly significant differences among groups. For practical applications, thresholds for the extent of channel reinforcement (40%) and modification (10%) and for bank alteration (≈30%) were provided, that can be used to guide the implementation of restoration measures. In moderately altered river reaches, a significant extent of tree-related habitats (≈5%) can noticeably mitigate the effects of morphological alteration on aquatic invertebrates. The outcomes highlight the importance of riparian zone management as an opportune, achievable prospect in the restoration of Mediterranean temporary streams. The impact of bank and channel modification on ecological status (sensu WFD) was investigated and the tested benthic metrics, especially those based on abundance data, showed legible differences among MRT groups. Finally, bank and channel modification appears to be a potential threat for the conservation of a few Sardo-Corsican endemic species. The introduction of management criteria that openly use information on endemic species seems crucial to reduce the risk of improving overall ecological status while depleting biodiversity.

Cryptic diversity and multiple origins of the widespread mayfly species group Baetis rhodani (Ephemeroptera: Baetidae) on northwestern Mediterranean islands.

How the often highly endemic biodiversity of islands originated has been debated for decades, and it remains a fervid research ground. Here, using mitochondrial and nuclear gene sequence analyses, we investigate the diversity, phylogenetic relationships, and evolutionary history of the mayfly Baetis gr. rhodani on the three largest northwestern Mediterranean islands (Sardinia, Corsica, Elba). We identify three distinct, largely co-distributed, and deeply differentiated lineages, with divergences tentatively dated back to the Eocene-Oligocene transition. Bayesian population structure analyses reveal a lack of gene exchange between them, even at sites where they are syntopic, indicating that these lineages belong to three putative species. Their phylogenetic relationships with continental relatives, together with the dating estimates, support a role for three processes contributing to this diversity: (1) vicariance, primed by microplate disjunction and oceanic transgression; (2) dispersal from the continent; and (3) speciation within the island group. Thus, our results do not point toward a prevailing role for any of the previously invoked processes. Rather, they suggest that a variety of processes equally contributed to shape the diverse and endemic biota of this group of islands.

The European reference condition concept: A scientific and technical approach to identify minimally-impacted river ecosystems.

One objective of the European Union (EU)'s Water Framework Directive (WFD: Directive 2000/60/EC) is for all European surface waters to achieve 'good status' by 2015. In support of this objective, the EU has facilitated an intercalibration exercise to ensure harmonized definitions of the status of water bodies, reflecting the deviation of their properties (mainly biotic assemblages) from a minimally disturbed state, termed the "reference condition". One of the major challenges of the WFD has been to find common approaches for defining reference conditions and to define the level of anthropogenic intervention allowed in reference sites. In this paper we describe how river reference sites were selected in the Central-Baltic region of Europe. A list of pressure criteria was provided and 14 Member States (MSs) categorized each criterion according to the method (i.e. measured, field inspection, etc.) used for reference site screening. Additionally, reference land-use and water-chemistry thresholds were agreed among countries in order to base reference site selection on objective criteria. For land-use criteria, a reference threshold and a rejection threshold were established. Sites with all criteria below the reference threshold were considered to be reference sites; sites having most criteria below the reference threshold and only some parameters between the reference and rejection threshold were "possible reference sites". These sites were retained only after carefully checking the cumulative effects of the pressures using local expertise, and a posteriori water-chemistry evaluation was necessary. In general, the most widespread method for defining a reference site was the measurement of pressures, followed by field inspections and expert judgment. However, some major pressures (e.g. hydromorphological alteration) were evaluated in a number of different ways (e.g. measured, field inspection, expert judgment). Our meta-analyses reveal a need to reinforce standardization in the application of pressure criteria by Member States. The pressure criteria identified in this exercise should be refined and tested with biological data to help in the further validation of minimally disturbed sites (i.e. the WFD "reference condition") and to provide a firm foundation for ecological status assessment. This in turn would ensure that there is pan-European comparability when evaluating the achievement of environmental objectives.

Quality assessment of bed sediments of the Po River (Italy).

Comprehensive and contemporary evaluations of physical, chemical and toxicological endpoints have been performed on bed sediments of the Po River, the major Italian watercourse. Two extensive sampling campaigns were conducted in summer and winter low-flow conditions. Composite sediment samples were collected from ten reaches of the main river: the first was located in the upper region (ambient control), and the others downstream of the confluences of nine principal tributaries. The two sampling programs were paralleled by contemporary investigations on the macroinvertebrate community. The particle-size composition along the Po River showed a relatively uniform distribution of fine sand, a progressive downstream decrease of coarse sands and a corresponding increase of fine materials. The levels of polychlorinated biphenyls (PCB), polycyclic aromatic hydrocarbons (PAH), extractable organo halides (EOX), Cd, Cr, Cu, Hg, Ni, Pb and Zn were determined in sediment fine particles (< 63 microm), and showed marked changes across the ten river reaches. Their longitudinal trends, as those of organic carbon and total nitrogen, were very similar and largely independent of the survey season. Sediment quality benchmarks were used to evaluate sediment chemistry, and, although the overall level of contamination was from moderate to low, the reaches located downstream of the tributaries Dora Riparia, Dora Baltea, Lambro and Oglio were considered to be at risk. Sediments were tested for toxicity on Oncorhynchus mykiss, Ceriodaphnia dubia, Raphidocelis subcapitata and Vibrio fischeri. The toxicity tests were conducted both with sediment extracts and whole samples. Sediment extracts showed toxic potentials that were consistent with the spatial distribution of contaminants. Whole-sediment toxicity showed moderate/low effects which also included false positives and negatives. Alterations of the macroinvertebrate community were found for many kilometers downstream of Dora Riparia, and with a seasonal dependence, also in other reaches of the Italian river. Principal component analysis (PCA) was used to describe the longitudinal and temporal changes of the Po River, and allowed the selection of the most useful and discriminating indicators.