Lower Po Research Articles

Dynamo action driven by precessional turbulence.

We reveal and analyze an efficient magnetic dynamo action due to precession-driven hydrodynamic turbulence in the local model of a precessional flow, focusing on the kinematic stage of this dynamo. The growth rate of the magnetic field monotonically increases with the Poincaré number Po, characterizing precession strength, and the magnetic Prandtl number Pm, equal to the ratio of viscosity to resistivity, for the considered ranges of these parameters. The critical Po_{c} for the dynamo onset decreases with increasing Pm. To understand the scale-by-scale evolution (growth) of the precession dynamo and its driving processes, we perform spectral analysis by calculating the spectra of magnetic energy and of different terms in the induction equationin Fourier space. To this end, we decompose the velocity field of precession-driven turbulence into two-dimensional (2D) vortical and three-dimensional (3D) inertial wave modes. It is shown that the dynamo operates across a broad range of scales and exhibits a remarkable transition from a primarily vortex-driven regime at lower Po to a more complex regime at higher Po where it is driven jointly by vortices, inertial waves, and the shear of the background precessional flow. Vortices and shear drive the dynamo mostly at large scales comparable to the flow system size, and at intermediate scales, while at smaller scales it is mainly driven by inertial waves. This study can be important not only for understanding the magnetic dynamo action in precession-driven flows, but also in a general context of flows where vortices emerge and govern the flow dynamics and evolution.

A Nomogram for Predicting Extubation Failure in Preterm Infants with Gestational Age Less than 29 Weeks

Introduction: How to avoid reintubations in prematurity remains a hard nut. This study aimed to develop and validate a nomogram for predicting extubation failure in preterm infants who received different modes of noninvasive ventilation as post-extubation support. Methods: This was a secondary analysis of pre-existing data from a large multicenter RCT combined with a multicenter retrospective investigation in three tertiary referral NICUs in China. The training cohort consisted of extubated infants from the RCT and the validation cohort included neonates admitted to the three NICUs in the last 5 years. The nomogram was developed through univariate and multivariate logistic regression analyses of peri-extubation clinical variables. Results: A total of 432 and 183 preterm infants (25 weeks ≤ gestational age [GA] <29 weeks) were, respectively, included in the training cohort and the validation cohort. Lower birth weight, lower Apgar 5-min score, lower postmenstrual age at extubation, lower PO₂ and higher PCO₂ before extubation, and continuous positive airway pressure rather than nasal intermittent positive pressure ventilation or noninvasive high-frequency oscillatory ventilation after extubation were associated with higher risks of extubation failure (p < 0.05), on which the nomogram was established. In both the training cohort and the validation cohort, the nomogram demonstrated good predictive accuracy (area under the receiver operating characteristic curve = 0.744 and 0.826); the Hosmer-Lemeshow test (p = 0.192 and 0.401) and the calibration curve (R² = 0.195 and 0.307) proved a good fitness and conformity; and the decision curve analysis showed significant net benefit at the best threshold (p = 0.201). Conclusion: This nomogram could serve as a good decision-support tool when predicting extubation failure in preterm infants with GA less than 29 weeks.

Elastic Critical Moment of Lateral Distortional Buckling of Castellated Composite Beams under Uniform Hogging Moment

AbstractContinuous and semicontinuous castellated composite beams can present a global buckling mode in the hogging-moment regions known as lateral-distortional buckling. In this mode, the lower po...

Psychological and Familial Factors as Predictors of First Year University Students’ Positive Orientation

This study examined the effects of psychological (life satisfaction, depression, social support) and familial factors (the size of family, family structure, education levels of parents) on first-year university students’ positive orientation. Positive orientation is an important element of life balance and expresses the positivity and attitudes of individuals towards life and themselves. A multiple regression analysis was conducted to determine the extent to which psychological and familial factors predicted PO. The results indicated that the model was significant and psychological and familial factors accounted for 44% of the variation in PO. Life satisfaction had the strongest and positive contribution to the PO. The perceived social support and depression level had the second and third highest contributions to the PO score, respectively. Findings showed that students raised in a matriarchal family had higher PO score than students raised in a patriarchal family. Also, having a single-parent family resulted in lower PO score than having a nuclear family.

Exercise Tolerance: New Insights From Single-leg Cycling Exercise

The biological factors determining the maximal exercise capacity are typically assessed during whole-body exercise (e.g. double-leg cycling), implicitly assuming that limbs contribute homogeneously to exercise tolerance. However, given the presence of limb dominance, it is possible that the dominant leg may achieve greater peak O2 uptake (V̇O2peak) and be able to sustain greater power outputs during prolonged dynamic exercise compared to the non-dominant leg. PURPOSE: To investigate peak power output (PPO), V̇O2peak, and maximal lactate steady-state (MLSS) during double-leg as well as during dominant and non-dominant and counter-weighted single-leg cycling exercise performed with the dominant and non-dominant legs. METHODS: Twelve men (30 ± 5 yrs) during 12 to 14 lab visits performed: (i) a ramp-incremental test to determine PPO, V̇O2peak, and maximal O2 extraction; and (ii) 30-min constant-load tests to determine MLSS. These tests were performed using both legs (DBL), the dominant leg only (SLd), and the non-dominant leg only (SLnd). Gas exchange variables were measured with a metabolic cart; local de-oxygenation ([HHb]) of the vastus lateralis (VL) was measured using a frequency-domain NIRS; capillary blood samples were analysed for lactate concentration ([Lac-]b). RESULTS: PPO for DBL, SLd, and SLnd was different in each condition: 329 ± 38, 181 ± 30, 168 ± 27 W, respectively (p < 0.05). V̇O2peak for DBL, SLd, and SLnd was different in each condition: 3.43 ± 0.34, 2.92 ± 0.42, 2.74 ± 0.38 L·min-1, respectively (p < 0.05). The [HHb] amplitude of the VL was greater in the dominant compared to the non-dominant leg during both DBL (18.6 ± 8.5 vs 15.4 ± 9.5 mMol) and SL (15.4 ± 9.5 vs 11.6 ± 7.7 mMol) ramp-exercise (p < 0.05). These amplitudes were highly correlated with the V̇O2peak values observed during DBL dominant and non-dominant (r = 0.86 and r=0.91, respectively), SLd (r=0.79), and SLnd (r=0.71) RI tests (p < 0.05). The PO at MLSS for DBL, SLd, and SLnd was different in each condition: 183 ± 32, 119 ± 25, and 111 ± 24 W, respectively (p < 0.05). The V̇O2, [Lac-]b, and RPE values during SLnd and SLd were similar (p > 0.05) despite this lower PO. CONCLUSIONS: These data indicate a heterogeneous exercise capacity of the exercising limbs that should be considered when evaluating exercise tolerance during double-leg exercise.

Long-term fish monitoring underlines a rising tide of temperature tolerant, rheophilic, benthivore and generalist exotics, irrespective of hydrological conditions

The invasion of exotic species is one of the main threats to worldwide biodiversity and can be aided by changes in environmental conditions. We hypothesized that a temporal trend of decreasing discharge and increasing temperature might have favored the invasion of warm-adapted, lentic exotic fish species in the lower Po River, northern Italy. We used presence/absence data over a long-term period (over 20 years) to investigate the dynamics of exotic fish invasion along water temperature and discharge gradients. Mean annual discharge and temperature did not show a clear trend and did not affect exotic fish species invasion, which progressed with time irrespective of these factors. The total number of species fluctuated without a clear trend, which underlined a progressive substitution of native species with exotic ones. Perhaps surprisingly, the community composition changed over time towards more temperature tolerant but also rheophilic, benthivore and generalist fish species. These results highlight how species interactions could be one of the main factors driving the invasion. Furthermore, our data underlines a continuously rising tide of exotics, which questions the success of past control strategies. Considering the current conservation resources limitations, priority should be given to the development of prevention strategies in order to avoid new species introductions.

Economic Impacts of Irrigation-Constrained Agriculture in the Lower Po Basin

Climate change, increasing demand for water, higher environmental standards and inelastic water supply suggest that future drought response in Southern Europe would require more efficient management of water use. In this context, there is a pressing need for a better understanding of the economic impacts of irrigation restrictions, including their microeconomic and broad economic repercussions. This paper connects a multi-attribute Revealed Preference Model working at an agricultural district level with a regionally calibrated supply and use model that combines nonlinear programming and input-output modeling techniques to address water allocation issues. To the best of our knowledge, this is the first time these two modeling approaches are combined in this fashion. Methods are illustrated with an application to the Lower Po River Basin (LPRB) in the Emilia Romagna Region, Italy. Results show that irrigation restrictions generate rising incremental losses in the agricultural districts of the LPRB, which are amplified through negative inter-sectorial feedbacks at a regional level. Contraction of production in Emilia Romagna results in an excess demand situation that propels the production of substitute goods elsewhere in Italy, partially but not fully compensating economic losses in the region. Methods and results offer a basis for assessing tradeoffs in irrigation restrictions and related adaptations, for climate change included.

The Po di Adria, Frattesina and the Po Delta between the Middle-Recent Bronze Age and the Early Iron Age

The Po di Adria, Frattesina and the Po Delta between the Middle-Recent Bronze Age and the Early Iron Age

Nutrient mobilization by plasmodium of myxomycete Physarum rigidum in deadwood

Abstract To assess the nutrient mobilization ability of myxomycete plasmodia in deadwood, a microcosm experiment was conducted. Alive or dead plasmodia of a common lignicolous myxomycete, Physarum rigidum , were inoculated on field-collected crushed wood powder of white-rot or brown-rot pine wood and incubated for 24 d. The activity of living plasmodia led to increased concentrations of Ca 2+ , K + , Mg 2+ , Na + , and Cl − , but lower PO 4 3– concentrations in the wood powder. For NO 3 − concentration, the effect of living plasmodia was negative in white-rotted wood but positive in brown-rotted wood. These results suggest that the plasmodium of P. rigidum has the ability to mobilize nutrients in deadwood.

Effects of levee cover strength on flood mapping in the case of levee breach due to overtopping

ABSTRACTThe reliability of a levee system is a crucial factor in flood risk management. In this study we present a probabilistic methodology to assess the effects of levee cover strength on levee failure probability, triggering time, flood propagation and consequent impacts on population and assets. A method for determining fragility curves is used in combination with the results of a one-dimensional hydrodynamic model to estimate the conditional probability of levee failure in each river section. Then, a levee breach model is applied to calculate the possible flood hydrographs, and for each breach scenario a two-dimensional hydrodynamic model is used to estimate flood hazard (flood extent and timing, maximum water depths) and flood impacts (economic damage and affected population) in the areas at risk along the river reach. We show an application for levee overtopping and different flood scenarios for a 98 km reach of the lower Po River in Italy. The results show how different design solutions for the levee cover can influence the probability of levee failure and the consequent flood scenarios. In particular, good grass cover strength can significantly delay levee failure and reduce maximum flood depths in the flood-prone areas, thus helping the implementation of flood risk management actions.EDITOR D. KoutsoyiannisASSOCIATE EDITOR A. Viglione

An ecosystem model of the lower Po river for use in ecological risk assessment of xenobiotics

Ecological modelling has the potential to increase the realism of chemical risk assessment for better informed risk management and decision making meeting the protection goals and requirements of the EU's chemicals- and water-related regulations. We developed a food web model of the final lowland section of the longest Italian river (Po) to assess the importance of ecological interactions in setting protective thresholds for river ecosystems exposed to chemicals discharged via wastewater. An integrated 14 compartment model was setup using AQUATOX 3.1, providing a dynamic, quantitative representation of the main functional groups in the food web. To our knowledge, this is the first time that the functioning of the Po ecosystem is quantitatively described. The model was calibrated against observations of biomass density of riverine biota, as typically available for a large lowland river in Europe. The role of ecological interactions on the response of the modelled organisms to chemical exposure was tested on realistic and hypothetical exposure scenarios for two compounds contained in home and personal care products: the anionic surfactant linear alkylbenzene sulphonate and the antimicrobial triclosan. At realistic exposure concentrations the model showed no significant effect compared to control simulations. At hypothetical higher exposure, effects resulting from complex ecosystem-scale interactions emerge. Depending on the organism's position in the food web, indirect effects due to ecological interactions can either amplify or mitigate the effect of direct toxicity. Model results indicate that organisms’ responses to chemicals in real ecosystems is poorly correlated to their direct toxicity (i.e. measured by L/ECX values) for a range of simulated exposure, including concentrations equal to the reported PNEC values. AQUATOX is a useful tool to investigate the relative importance of direct toxicity and ecological interactions, but at this stage it is difficult to use it for prospective chemical risk assessment, given the underlying model uncertainties and the practical limitations of field scale evaluations. An improvement of the quantitative monitoring of feeding preferences and abundance over time of the most representative species within each functional group would be of great help to refine the model parameterisation and calibration. Nonetheless, the development of river ecosystem model scenarios is a stepping stone towards the incorporation of ecological modelling in risk assessment. When extensively tested on different scenarios AQUATOX provides a useful platform, which can be linked to mechanistic effect models as long as this component can be evaluated in controlled settings (i.e. laboratory or mesocosm scale).

Mouse Cardiac MitobkCa Associates with β1 Subunit Favoring Channel Expression and Activity

We previously showed that in rat cardiomyocytes two types of mitoBKCa are present with high and low Po (∼0.85 and ∼0.01, respectively, at −60 mV in 12 µM Ca2+). We hypothesized that this difference could be related to the association with regulatory subunits. As first step, we investigated the role of BKCa β1 subunit by characterizing cardiac mitoBKCa properties in wild type (wt) and β1 KO mice. In wt mice, mitoBKCa was frequently recorded (in 6 out of 7 patches and 3 different preparations), had a conductance of ∼313 ± 8 pS (n=4) resembling that of mitoBKCa channel from rat (∼305 ± 19 pS, n=7), and was Ca2+ (n=2) and paxilline sensitive (n=3). In contrast to rat, wt mice had predominantly one population of mitoBKCa with a high open probability (Po∼0.8) at all membrane potentials tested (−80 to +80 mV, in 12 µM Ca2+). Interestingly, while in wt mice mitoBKCa were frequently recorded, in β1 KO, mitoBKCa was recorded only in 5 out of 24 patches (n=5 preparations). This channel had a similar conductance as the wt channel but with a much lower Po (∼0.25 vs. ∼0.8 at +60 mV in 12 µM Ca2+). These results are consistent with the view that in cardiac mitochondria, mitoBKCa is forming a complex with its β1 subunit favoring mitoBKCa expression and a high channel activity. A contribution of alternative subunits to mitoBKCa targeting and function needs further investigation. Supported by NIH and AHA.

Oxidation controlled phase composition of FeCo(Zr) nanoparticles in CaF2 matrix

Results of the study of oxidised (FeCoZr)х(CaF2)100−х films in a wide composition range (30≤х≤74at.%) sintered at oxygen pressures PO=4.3 and 9.8mPa with X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray absorption spectroscopy (XAS), 57Fe Mössbauer spectroscopy (MS), and vibrating sample magnetometry (VSM) are reported.A “crystalline metallic core–amorphous oxide shell” structure of nanoparticles (NPs) in films oxidised at lower PO=4.3mPa is observed in TEM images. A combined use of XRD, MS and XAS techniques provides identification of NP phase composition evidencing α-FeCo(Zr) core of the variable content depending on x and a complex oxide shell including amorphous α-Fe3+2O3 together with Co2+1−yFe2+yO at low x (30–36at.%). Full oxidation of NPs at higher PO=9.8mPa is indicated by TEM, XRD, MS and XAS patterns evidencing the formation of “crystalline Co2+1−yFe2+yO core–amorphous α-Fe3+2O3 shell” structure. Progressive oxidation of NPs with decreasing x at PO=4.3mPa as well as with PO increase is followed by variation of average centre shifts <δ> obtained from deconvoluted 57Fe Mössbauer spectra. Magnetometry measurements of films sintered at PO=4.3mPa reveal an effect of exchange bias confirming “ferromagnetic metallic core–antiferromagnetic oxide shell” structure of NPs.The results show that phase composition of oxide shells is governed both by concentration of oxygen available during synthesis and on the x. Schemes of progressive NP oxidation with identified phase composition as a function of PO and x values are proposed.

Effects of oxygen partial pressure on the structural and optical properties of undoped and Cu-doped ZnO thin films prepared by magnetron co-sputtering

Undoped and Cu-doped zinc oxide (ZnO:Cu) films were deposited on glass substrates by magnetron sputtering at different oxygen partial pressures po. Microstructure, surface morphology, resistivity, and optical properties were systematically investigated. The results show that lower po can degrade the crystallinity, and reduce the band gap. Undoped ZnO films are not obviously influenced by po, especially at high oxygen pressure. In contrast, ZnO:Cu thin films are remarkably affected by po. This work suggests that oxygen vacancies play an important role in modifying properties and allows us to accurately modulate the band gap of the ZnO-based films.

Gender differences in STEM undergraduates' vocational interests: People–thing orientation and goal affordances

This study addressed why women have greater representation in some STEM (science, technology, engineering, and mathematics) fields compared to others by linking two theoretical approaches, people–thing orientation (PO, TO) and role congruity theory, which emphasizes occupation goal affordances associated with traditionally feminine and masculine roles. Vocational interest and goal affordance ratings (having a positive social impact, family, and occupation status) for occupations characterized as working with people or things were assessed in 1848 students (42% female; 81% white non-Hispanic) majoring in biology (gender balanced), non-biology STEM (male-dominated), and female-dominated health fields. Participant PO and TO interests were also collected. Results indicated that non-biology STEM majors showed lower PO and higher TO interests than biology and health majors. Non-biology STEM majors also endorsed PO and TO interests at similar levels, but the other two major groups indicated higher PO than TO. People Jobs were perceived to more likely afford goals related to family and positive social impact; whereas Thing Jobs were perceived to more likely afford status goals. Interest in People Jobs was similar for women in both STEM major groups. Female non-biology STEM majors were equally interested in People and Thing Jobs; whereas biology majors preferred People Jobs. PO, TO, and goal affordance ratings independently predicted interest in People and Thing Jobs, and gender accounted for very little additional variance. Taken together, the findings point to the importance of using both person–thing orientation and role congruity theory when explaining varied gender representations in different STEM fields.

COMPSEC, a new tool to derive natural background levels by the component separation approach: application in two different hydrogeological contexts in northern Italy

The assessment of natural background levels (NBLs) is crucial in the management of groundwater resources and the definition of the status of groundwater bodies according to the Water Framework Directive 2000/60/EC. This work presents a new MATLAB code to assess NBLs by the component separation method, which concerns the identification and separation of a natural and an anthropogenic component within geochemical data. To increase the validity of the estimated NBL, the code calculates a set of possible solutions that should then be evaluated by the user. The following evaluation criteria are proposed: (i) stability of solution, (ii) hydrogeochemical reliability, (iii) agreement with the conceptual model and (iv) goodness of fit.The code is tested on groundwater Mn, Fe, As, Ni, Cr(VI) and NH4 concentrations observed in two study areas with different hydrogeological and geochemical features in northern Italy: the multi-layer aquifer of Cremona (lower Po Plain) and the alluvial aquifer of the Aosta Plain (western Alpine sector). The pre-selection method is also applied to estimate NBLs and threshold values are assessed.The NBLs calculated through the component separation method (4292, 27 and 1220μg/L for Fe, As and NH4 in Cremona and 56, 261, 9 and 2.3μg/L for Mn, Fe, Ni and Cr(VI) in Aosta, respectively) approach those estimated by the pre-selection (2798, 25 and 1820μg/L for Fe, As and NH4 in Cremona and 52, 264, 10 and 1.8μg/L for Mn, Fe, Ni and Cr(VI) in Aosta, respectively). This outcome increases the validity of the estimated NBLs. The code showed versatile applicability in different contexts and conditions (e.g., different numbers of samples and monitoring points, different sampling networks). This work highlights the strength of the component separation method although some criticisms are pointed out, mainly related to the superimposition of a log-normal function for modeling the natural component.

Cross-bridge Kinetics Impairment In Elite Octogenarian Masters Athletes

The association between adult normal aging and impairments of the neuromuscular system as well as the application of exercise training to attenuate these problems have already been reported by several studies. However, it is still not clear whether intrinsic cross-bridge kinetics, especially of the ‘slow’ resilient fibre type, are affected in aging muscle, and if this kinetics would be better preserved in high functioning elderly athletes. PURPOSE: to compare cross-bridge kinetics in healthy non-athlete octogenarians to age-matched world class masters athletes, and young controls. METHODS: Skinned muscle fibres obtained from vastus lateralis biopsies of young (∼23y), old non-athlete (NA) adults (∼80y), and age-matched world class masters athletes (MA; ∼80y) were first isometrically activated to assess force per cross-sectional (Po), then submitted to slack test, and shortening-re-stretch protocol, by which unloaded shortening velocity (Vo), and the rate constant of force redevelopment (ktr) were respectively obtained. A post-hoc analysis was performed, and only the mechanical properties of ‘slow type’ fibres based on unloaded shortening velocity measurements were used (the level of significance was set at P<0.05). RESULTS: MA and NA produced ∼55% and 45% lower Po than young. Vo for both MA and NA old groups were ∼62% and 42% slower, respectively, compared with young. Both MA and NA adults had ∼2 times slower values for ktr compared with young. CONCLUSION: The lower ktr in both old groups relative to young suggests that impaired cross-bridge kinetics was, at least in part, responsible for impaired single fibre contractile properties, i.e Vo, Po, with aging. Apparently, masters athletes’ higher performance cannot be attributed to their intrinsic cross-bridge kinetics.

How to manage potential groundwater contaminations by As, Fe and Mn in lower Po Plain: a proposal from the case study of Cremona

The Legislative Decree 152/06 on environmental regulations also governs polluted site remediation (Part IV). A potentially contaminated site is defined when concentrations exceed the limits reported in the Attachment 5 (Title V). Nevertheless, the Legislative Decree 152/06 considers the possibility of higher limits than Attachment 5 for trace elements in the case of natural high contents by the definition of natural background levels. The lower Po Plain is characterized by high natural concentrations of As, Fe and Mn in groundwater and, at the same time, is one of the most important areas for the Italian productive system, and thus, possible direct sources of As, Fe and Mn or indirect anthropogenic influences could also exist. Therefore, an operative tool is required to determine the natural background levels and to understand if measured high concentrations are attributable to natural backgrounds or to anthropogenic sources/influences, and consequently, to decide on the beginning of the administrative procedure requested by the Legislative Decree 152/09 through the site characterization phase. This work presents a proposal of procedure to manage potentially contaminated site by As, Fe and Mn in the lower Po Plain, that was developed in the framework of a scientific collaboration between the Province of Cremona and the University of Milano-Bicocca. The procedure involves the following four steps, preceded by the derivation of natural background levels as step zero: (1) comparing new measurements to natural background levels; (2) testing the presence of direct anthropogenic sources of As, Fe and Mn; (3) excluding false positives and (4) testing the presence of indirect anthropogenic influences on As, Fe and Mn concentrations. The operative application of the proposed procedure is actually under consideration by the Province of Cremona.

Polysomnographic Differences Associated with Pulmonary Hypertension in Patients with Advanced Lung Disease Due to Cystic Fibrosis

Pulmonary hypertension (PH) commonly occurs in patients with cystic fibrosis (CF), but there is no current data regarding alterations of sleep in patients with PH. A single-center, retrospective review was performed in patients with advanced lung disease due to CF who completed both nocturnal polysomnography and right heart catheterization (RHC) from January 2010 to June 2013. For statistical analysis, two-tailed unpaired t tests and Pearson correlation coefficient analysis were performed after normal distribution was confirmed. A total of 18 consecutive CF patients were enrolled with RHC identifying PH in 56 % (10/18) of patients. The PH group had significantly lower mean sleep efficiency (72 ± 4 vs. 87 ± 3 %, p = 0.01), significantly higher ETCO(2) levels (54.5 ± 2.2 vs. 43.8 ± 3.0 mmHg, p = 0.01) on capnography, and significantly lower PO(2) (53.8 ± 3.1 vs. 65.5 ± 3.9 mmHg, p = 0.03) on capillary blood gas. Correlations with poor sleep efficiency included mean PAP (r = - 0.55, p = 0.01), systolic PAP (r = -0.5, p = 0.03), ETCO(2) (r = - 0.53, p = 0.02), and PO(2)) (r = 0.62, p = 0.01); ETCO(2) with systolic PAP (r = 0.47, p = 0.04) and PCO(2) (r = - 0.57, p = 0.01); and PO(2) to 6-min walk distance (r = 0.55, p = 0.02). We found significant differences in sleep efficiency and gas exchange associated with PH in CF patients with advanced lung disease.

Introduction of exotic fish species and decline of native species in the lower Po basin, north‐eastern Italy

ABSTRACTFreshwater ecosystems worldwide are experiencing native fish losses with severe threats to the conservation of freshwater biodiversity and ecosystem functioning, and the debate on whether the cause is biotic or abiotic disturbance is still open.Temporal variation in fish assemblages was analysed over an 18 year period in 14 waterways of the lowland backwaters of the Po River in north‐eastern Italy, which are important feeding, spawning and nursery sites for native fish.In 1991, 14 native and eight exotic species were collected. In less than 20 years 10 native species underwent local extinction, three of which –Rutilus pigus,Rutilus aula, andChondrostoma soetta– were endemic to the Padano‐Veneto District in northern Italy.Ordination of the data (MDS, CLUSTER, ANOSIM, SIMPER) showed a clear temporal gradient in fish community structure. After the establishment of the exotic predatorSilurus glanis, some native species significantly declined in abundance and biomass (i.e.Alburnus arborellaandScardinius erythrophthalmus) or disappeared (i.e.Rutilus aulaandTinca tinca). Moreover, exotic speciesCyprinus carpio,Ameiurus melas, andCarassius auratusfrom previous introductions, underwent significant changes in their abundance and biomass. No correlation was found between fish community structure and water quality parameters (BIOENV).The success of exotic species, particularlyS. glaniswhich thrived in this degraded habitat, seems to have led to the decline of native fish fauna in the canals of the lower portion of the Po River basin. Conservation strategies focusing on the containment of exotic species and habitat restoration are recommended.Copyright © 2013 John Wiley &amp; Sons, Ltd.