Climate change impacts on eutrophication in the Po River (Italy): Temperature-mediated reduction in nitrogen export but no effect on phosphorus.

Rivers worldwide are under stress from eutrophication and nitrate pollution, but the ecological consequences overlap with climate change, and the resulting interactions may be unexpected and still unexplored. The Po River basin (northern Italy) is one of the most agriculturally productive and densely populated areas in Europe. It remains unclear whether the climate change impacts on the thermal and hydrological regimes are already affecting nutrient dynamics and transport to coastal areas. The present work addresses the long-term trends (1992-2020) of nitrogen and phosphorus export by investigating both the annual magnitude and the seasonal patterns and their relationship with water temperature and discharge trajectories. Despite the constant diffuse and point sources in the basin, a marked decrease (-20%) in nitrogen export, mostly as nitrate, was recorded in the last decade compared to the 1990s, while no significant downward trend was observed for phosphorus. The water temperature of the Po River has warmed, with the most pronounced signals in summer (+0.13°C/year) and autumn (+0.16°C/year), together with the strongest increase in the number of warm days (+70%-80%). An extended seasonal window of warm temperatures and the persistence of low flow periods are likely to create favorable conditions for permanent nitrate removal via denitrification, resulting in a lower delivery of reactive nitrogen to the sea. The present results show that climate change-driven warming may enhance nitrogen processing by increasing respiratory river metabolism, thereby reducing export from spring to early autumn, when the risk of eutrophication in coastal zones is higher.

PAH (Polycyclic Aromatic Hydrocarbon) bioaccumulation and PAHs/shell weight index in Ruditapes philippinarum (Adams & Reeve, 1850) from the Vallona lagoon (northern Adriatic Sea, NE Italy).

The Vallona lagoon is a transitional area located in the Po River delta (NE, ITALY) traditionally exploited for Manila clam (Ruditapes philippinarum) farming. During 2007-2008, a pipeline was buried in the middle of the lagoon to connect an off-shore structure to facilities on land. PAH levels were monitored in Manila clams and sediments before, during and after the pipeline construction to assess the impact of the activities through the pattern of distribution of the PAH compounds. PAH bioaccumulation in clams displayed seasonal fluctuations with higher levels in autumnal and wintry surveys than in spring-summer. Principal component analysis applied to PAHs in clams highlighted a petrogenic input during ante operam period and a pyrolytic origin during the burying activities. On the contrary, sediment PAH concentrations resulted quite similar both among sites and periods. Biota-Sediment-Accumulation-Factor values also confirmed that sediments were not the major source of PAH pollution for clams in this study. The welfare of clams was examined through two physiological indices (condition index and survival in air) to check the effects of the activities on a commercial resource. Both physiological indices exhibited seasonal variations connected to natural endogenous and exogenous factors; however survival in air was the most sensitive index in highlighting the effects of the pipeline burying activities. Finally, to ensure that PAH bioavailability assessment was not affected by seasonal variation of soft tissues of molluscs, PAHs/shell weight index was applied. Higher levels of this index were observed before and during the burying activities, whilst, after that, values significantly lowered. Moreover, the normalization enabled us to highlight the PAH uptake from clams in some particular periods and to compare different populations in a long-term biomonitoring program with data obtained from different periods of the year.

Contrasting effects of climate change on denitrification and nitrogen load reduction in the Po River (Northern Italy).

An increase in water temperature is one of the main factors that can potentially modify biogeochemical dynamics in lowland rivers, such as the removal and recycling of nitrogen (N). This effect of climate change on N processing deserves attention, as it may have unexpected impacts on eutrophication in the coastal zones. Intact sediment cores were collected seasonally at the closing section of the Po River, the largest Italian river and one of the main N inputs to the Mediterranean Sea. Benthic oxygen fluxes, denitrification, and dissimilatory nitrate reduction to ammonium (DNRA) rates were measured using laboratory dark incubations. Different temperature treatments were set up for each season based on historical data and future predictions. Higher water temperatures enhanced sediment oxygen demand and the extent of hypoxic conditions in the benthic compartment, favoring anaerobic metabolism. Indeed, warming water temperature stimulated nitrate (NO3-) reduction processes, although NO3- and organic matter availability were found to be the main controlling factors shaping the rates between seasons. Denitrification was the main process responsible for NO3- removal, mainly supported by NO3- diffusion from the water column into the sediments, and much more important than N recycling via DNRA. The predicted increase in the water temperature of the Po River due to climate change may exert an unexpected negative feedback on eutrophication by strongly controlling denitrification and contributing to partial buffering of N export in the lagoons and coastal areas, especially in spring.

Experimental design and field deployment of an artificial bio-reef produced by mollusk shell recycling.

Shellfish farming is considered a highly sustainable form of aquaculture that has developed rapidly worldwide. Unfortunately, today biological and chemical pollution of the oceans and marine waters is widespread and has multiple negative impacts on marine ecosystems, which are exacerbated by global climate changes. In addition, such impacts on fisheries and aquaculture are significant in inducing socio-economic losses. Therefore, it is necessary to develop innovative solutions to improve productivity and environmental performance in line with the blue sustainable economy (European Green Deal). However, one upcoming problem associated with shellfish consumption is shell waste and its disposal. In addition, the percentage of wasted shells destined for reuse is much lower than the one accumulated in landfills or in more or less well-managed sites. This represents a weakness of the shellfish farming sector that can only be mitigated through a project of shellfish waste recycling moving towards the circular economy, with undoubted environmental and economic advantages. In the present study, we present a possible solution for recycling clam shells coming from the waste of the fishing industry (circular economy). Indeed, three eco-friendly bio-reefs for the stabilization and implementation of marine biodiversity (blue economy) were realized using additive manufacturing technology (3D printing) for large dimensions (technological innovation). Furthermore, before deploying the reefs on the sea bottom, they were colonized with oysters to promote repopulation.

Classification and distribution of freshwater microplastics along the Italian Po river by hyperspectral imaging.

In this work, freshwater microplastic samples collected from four different stations along the Italian Po river were characterized in terms of abundance, distribution, category, morphological and morphometrical features, and polymer type. The correlation between microplastic category and polymer type was also evaluated. Polymer identification was carried out developing and implementing a new and effective hierarchical classification logic applied to hyperspectral images acquired in the short-wave infrared range (SWIR: 1000-2500 nm). Results showed that concentration of microplastics ranged from 1.89 to 8.22 particles/m3, the most abundant category was fragment, followed by foam, granule, pellet, and filament and the most diffused polymers were expanded polystyrene followed by polyethylene, polypropylene, polystyrene, polyamide, polyethylene terephthalate and polyvinyl chloride, with some differences in polymer distribution among stations. The application of hyperspectral imaging (HSI) as a rapid and non-destructive method to classify freshwater microplastics for environmental monitoring represents a completely innovative approach in this field.

Trace metals accumulation on modern sediments from Po river prodelta, North Adriatic Sea.

Trace Metals (TMs: Pb, Zn, Cu, Cr, Cd, and Ni), major elements (Al and Fe) and radionuclides (210Pb/137Cs) investigations on EL-C01 sediment core provides new information on sedimentary regime and anthropogenic impacts during the last 175 years in the Po river prodelta area. The results allow to identify some TMs/Al peak in the upper part of the core, likely related to the major flood events of the Po river during the XXth century. Sediments deposited after the year 1900 exhibit a gradual increase of some TMs concentrations compared to pre-industrial era values. In particular, Pb, Zn, and Cu high contents are detected after the World War II and during the "Italian Economic Miracle" period. The decrease of heavy metal (Zn and Pb) contents from the second half of the 1980s is probably the effect of the Italian Law 319/76 and anti-pollution environmental policies concerning industrial and urban emitters.

Temporal variation of floatable plastic particles in the largest Italian river, the Po.

We investigated the temporal concentration of floatable plastic particles in the Po river, the largest contributor of freshwater to the Adriatic Sea. Surface waters were sampled in 2019 with a Manta trawl, with almost bimonthly frequency. In total, 5063 plastic particles were collected, 80.6% of which were microplastics (<5 mm). Characterization through FT-IR spectroscopy evidenced 7 polymers, of which polyethylene, polypropylene and polystyrene accounted for 40.5%, 25.7%, and 14.9%, respectively. The highest plastic concentration was recorded in December (3.47 particles m-3; 5.89 mg m-3), while the lowest in August (0.29 ± 0.01 particles m-3; 0.22 ± 0.08 mg m-3). We estimated the annual load of floatable plastic particles carried by the Po river to be 145 tons. Plastic particle load was correlated with the hydraulic regime, and was higher in autumn and spring months.

Linking contemporary river restoration to economics, technology, politics, and society: Perspectives from a historical case study of the Po River Basin, Italy.

River restoration is a novel paradigm of 'mirescape' (land-and-water-scape) management that developed along with the emergence of aquatic ecology. River restoration can be seen as the application of an ecological perspective to return rivers to nature. However, the river restoration paradigm is also the contemporary iteration of historical phases of mirescape management. We review the long and varied recorded history of the Po River in northern Italy as a case study to illustrate the transformations and common themes of mirescape management. We find, first, that significant changes in mirescape management and river condition only occur in the context of larger social, political, technological and economic transformations. Second, we show how particular cultural understandings, economic interests, technological innovations and political powers have driven particular paradigms of mirescape management. These have tended towards increasing territorial separation of wet and dry. We find, third, that these separations lead not only to increasing economic precariousness for many, but also to increasingly severe disasters. We conclude that river restoration faces social and political challenges to becoming relevant at a mirescape scale, due to its lack of integration with land management, or with current social, political, technological and economic transformations. To act on this conclusion, we suggest philosophically aligned social movements that river restoration could work with to improve impact and uptake.

Embryo/larval toxicity and transcriptional effects in zebrafish (Danio rerio) exposed to endocrine active riverbed sediments.

Sediment toxicity plays a fundamental role in the health of inland fish communities; however, the assessment of the hazard potential of contaminated sediments is not a common objective in environmental diagnostics or remediation. This study examined the potential of transcriptional endpoints investigated in zebrafish (Danio rerio) exposed to riverbed sediments in ecotoxicity testing. Embryo-larval 10-day tests were conducted on sediment samples collected from five sites (one upstream and four downstream of the city of Milan) along a polluted tributary of the Po River, the Lambro River. Sediment chemistry showed a progressive downstream deterioration in river quality, so that the final sampling site showed up to eight times higher concentrations of, for example, triclosan, galaxolide, PAH, PCB, BPA, Ni, and Pb, compared with the uppermost site. The embryo/larval tests showed widespread toxicity although the middle river sections evidenced worse effects, as evidenced by delayed embryo development, hatching rate, larval survival, and growth. At the mRNA transcript level, the genes encoding biotransformation enzymes (cyp1a, gst, ugt) showed increasing upregulations after exposure to sediment from further downstream sites. The genes involved in antioxidant responses (sod, gpx) suggested that more critical conditions may be present at downstream sites, but even upstream of Milan there seemed to be some level of oxidative stress. Indirect evidences of potential apoptotic activity (bcl2/bax < 1) in turn suggested the possibility of genotoxic effects. The genes encoding for estrogen receptors (erα, erß1, erß2) showed exposure to (xeno)estrogens with a progressive increase after exposure to sediments from downstream sites, paralleled by a corresponding downregulation of the ar gene, likely related to antiandrogenic compounds. Multiple levels of thyroid disruption were also evident particularly in downstream zebrafish, as for thyroid growth (nkx2.1), hormone synthesis and transport (tg, ttr, d2), and signal transduction (trα, trß). The inhibition of the igf2 gene reasonably reflected larval growth inhibitions. Although none of the sediment chemicals could singly explain fish responses, principal component analysis suggested a good correlation between gene transcripts and the overall trend of contamination. Thus, the combined impacts from known and unknown covarying chemicals were proposed as the most probable explanation of fish responses. In summary, transcriptional endpoints applied to zebrafish embryo/larval test can provide sensitive, comprehensive, and timeliness information which may greatly enable the assessment of the hazard potential of sediments to fish, complementing morphological endpoints and being potentially predictive of longer studies.

An ounce of prevention is worth a pound of cure: Managing macrophytes for nitrate mitigation in irrigated agricultural watersheds.

Although ubiquitous elements of agricultural landscapes, the interest on ditches and canals as effective filters to buffer nitrate pollution has been raised only recently. The aim of the present study was to investigate the importance of in-ditch denitrification supported by emergent aquatic vegetation in the context of N budget in agricultural lands of a worldwide hotspot of nitrate contamination and eutrophication, i.e. the lowlands of the Po River basin (Northern Italy). The effectiveness of N abatement in the ditch network (>18,500 km) was evaluated by extrapolating up to the watershed reach-scale denitrification rates measured in a wide range of environmental conditions. Scenarios of variable extents of vegetation maintenance were simulated (25%, 50% and 90%), and compared to the current situation when the natural development occurs in only 5% of the ditch network length, subjected to mechanical mowing in summer. Along the typical range of nitrate availability in the Po River lowlands waterways (0.5-8 mg N L-1), the current N removal performed by the ditch network was estimated in 3300-4900 t N yr-1, accounting for at most 11% of the N excess from agriculture. The predicted nitrate mitigation potential would increase up to 4000-33,600 t N yr-1 in case of vegetation maintenance in 90% of the total ditch length. Moreover, a further significant enhancement (57% on average) of this key ecosystem function would be achieved by postponing the mowing of vegetation at the end of the growing season. The simulated outcomes suggest that vegetated ditches may offer new agricultural landscape management opportunities for effectively decreasing nitrate loads in surface waters, with potential improved water quality at the watershed level and in the coastal zones. In conclusion, ditches and canals may act as metabolic regulators and providers of ecosystem services if conservative management practices of in-stream vegetation are properly implemented and coupled to hydraulic needs.

Abundance and distribution of large microplastics (1-5 mm) within beach sediments at the Po River Delta, northeast Italy.

Coastal areas are especially prone to plastic debris, being subjected to various land- and sea-based sources. Nevertheless, knowledge about microplastic distribution on beaches is limited, as studies focused either on high tide lines, specific items, or relied on visual identification. Beaches exhibit several accumulation zones and microplastic deposition depends on particle properties. We thus studied microplastic distribution (1-5 mm), including various types and shapes, among three driftlines at three beaches within the Po River Delta. Particles were analyzed using ATR-FTIR spectroscopy. Abundances ranged from 2.92 (± 4.86 SD) to 23.30 (± 45.43 SD) microplastics per kilogram dry weight between the beaches. The accumulation of microplastics among driftlines showed no consistent pattern, besides expanded polystyrene tending to accumulate backshore. We observed that accumulation hotspots within a single driftline can disrupt a general observed accumulation pattern. Thus, microplastic monitoring guidelines should further include protocols for the handling of accumulation hotspots within datasets.

Gene expression and genotoxicity in Manila clam (Ruditapes philippinarum) modulated by sediment contamination and lagoon dynamics in the Po river delta.

The lagoons of the Po River delta are potentially exposed to complex mixtures of contaminants, nevertheless, there is a substantial lack of information about the biological effects of these contaminants in the Po delta lagoons. These environments are highly dynamic and the interactions between chemical and environmental stressors could prevent the proper identification of biological effects and their causes. In this study, we aimed to disentangle such interactions focusing on Manila clams, previously exposed to six lagoons of the Po delta, adopting three complementary tools: a) the detailed description via modelling techniques of lagoon dynamics for salinity and water temperature; b) the response sensitivity of a number of target genes (ahr, cyp4, ρ-gst, σ-gst, hsp22, hsp70, hsp90, ikb, dbh, ach, cat, Mn-sod, Cu/Zn-sod, cyp-a, flp, grx, TrxP) investigated in clam digestive glands by Real Time PCR; and c) the relevance of DNA adducts determined in clams as markers of exposure to genotoxic chemicals. The lagoons showed specific dynamics, and two of them (Marinetta and Canarin) could induce osmotic stress. A group of genes (ahr, cyp4, Mn-sod, σ-gst, hsp-22, cyp-a, TrxP) seemed to be associated with overall lagoon characteristics as may be described by salinity and its variations. Lagoon modelling and a second group of genes (hsp70, hsp90, cat, ikb, ach, grx, Cu/Zn-sod) also suggested that moderate increases of river discharge may imply worse exposure conditions. Oxidative stress seemed to be associated with such events but it was slightly evident also under normal exposure conditions. DNA adduct formation was mainly associated with overwhelmed antioxidant defences (e.g. low Cu/Zn-sod) or seemingly with their lack of response in due time. In Po delta lagoons, Manila clam can be affected by chemical and environmental factors which can contribute to induce oxidative stress, DNA adduct formation and, ultimately, to affect clam condition and health.

Distribution of endangered Italian gudgeon Romanogobio benacensis (Cypriniformes, Cyprinidae, Gobioninae) with remarks on distinguishing morphological characters.

Distribution data on many freshwater fish species in Croatia are scarce and species identifications are difficult, requiring further detailed studies. This paper presents a report of the Italian gudgeon Romanogobio benacensis from the Mirna River in the Istra Peninsula in Croatia, in the south-east from its previously known distribution range. The identification of R. benacensis in Croatia was supported by a morphological comparison with R. benacensis from Italy and Slovenia, the common gudgeon Gobio gobio, and the Danubian gudgeon Gobio obtusirostris from geographically close locations. A combination of character states (number of scales between anus and anal-fin origin, branched pectoral-fin rays, lateral-line scales, total, abdominal, and caudal vertebrae, and the size and number of lateral blotches) distinguishes R. benacensis from both G. gobio and G. obtusirostris. The phylogenetic analyses using mitochondrial sequences of cytochrome b gene confirmed that specimens from the Mirna River belong to R. benacensis. Also, Reka River system (Adriatic Sea basin) in Slovenia is inhabited by a possibly introduced Danubian gudgeon, G. obtusirostris, and not by R. benacensis.

Occurrence of perfluorooctanesulfonate and perfluorooctanoic acid and histopathology in eels from north Italian waters.

A perfluorinated alkylated substances (PFAS) biomonitoring study was conducted in European eel (Anguilla anguilla) in Italy for the first time. Perfluorooctanesulfonate (PFOS) and perfluorooctanoic acid (PFOA) concentrations were assessed in the organs of 35 wild eels from two locations, the highly impacted Po River and the Comacchio Lagoon along the north-western Adriatic coast. PFAS were extracted by ion-pairing liquid extraction procedure and measured using high performance liquid chromatography with electrospray ionization tandem mass spectrometry. There were no significant differences in mean PFAS concentrations (p>0.05) between samples from the two sites. PFOS and PFOA were detectable (>0.4ngg(-1) wet weight, w.w) in 73% and 31% of the total samples, respectively. PFOS concentrations ranged from <0.4 to 6.28ngg(-1)w.w and PFOA from <0.4 to 92.77ngg(-1)w.w. The highest PFAS levels were observed in blood and the lowest in muscle. Histology showed macrophage aggregates and hepatocytic vacuolation in some liver samples. No tissue anomalies were seen in the gonads, suggesting no reproductive impairment. The PFAS contamination levels observed were comparable to, or lower than, those reported in fish in other European countries, seeming to indicate that PFAS pollution of the study area is not remarkable.

Hydrological simulation of Po River (North Italy) discharge under climate change scenarios using the RCM COSMO-CLM.

The impacts of climate change on Po River discharges are investigated through a set of climate, hydrological, water-balance simulations continuous in space and time. Precipitation and 2m mean temperature fields from climate projections under two different representative concentration pathways, RCP4.5 and RCP8.5, have been used to drive the hydrological model. Climate projections are obtained nesting the regional climate model COSMO-CLM into the global climate model CMCC-CM. The bias in climate projections is corrected applying the distribution derived quantile mapping. The persistence of climate signal in precipitation and temperature after the bias correction is assessed in terms of climate anomaly for 2041-2070 and 2071-2100 periods versus 1982-2011. To account for the overall uncertainty of emission scenarios, climate models and bias correction, the hydrological/water balance simulations are carried out using both raw and bias corrected climate datasets. Results show that under both RCPs, either considering raw and bias corrected climate datasets, temperature is expected to increase on the whole Po River basin and in all the seasons; the most significant changes in precipitation and discharges occur in summer, when the reduction of precipitation leads to an increase in low flow duration and occurrence likelihood, and in autumn and winter where precipitation shows a positive variation increasing the high flows frequency.

Changing hydrological conditions in the Po basin under global warming.

The Po River is a crucial resource for the Italian economy, since 40% of the gross domestic product comes from this area. It is thus crucial to quantify the impact of climate change on this water resource in order to plan for future water use. In this paper a mini ensemble of 8 hydrological simulations is completed from 1960 to 2050 under the A1B emission scenario, by using the output of two regional climate models as input (REMO and RegCM) at two different resolutions (25 km-10 km and 25 km-3 km). The river discharge at the outlet point of the basin shows a change in the spring peak of the annual cycle, with a one month shift from May to April. This shift is entirely due to the change in snowmelt timing which drives most of the discharge during this period. Two other important changes are an increase of discharge in the wintertime and a decrease in the fall from September to November. The uncertainty associated with the winter change is larger compared to that in the fall. The spring shift and the fall decrease of discharge imply an extension of the hydrological dry season and thus an increase in water stress over the basin. The spatial distributions of the discharge changes are in agreement with what is observed at the outlet point and the uncertainty associated with these changes is proportional to the amplitude of the signal. The analysis of the changes in the anomaly distribution of discharge shows that both the increases and decreases in seasonal discharge are tied to the changes in the tails of the distribution, i.e. to the increase or decrease of extreme events.