Inland navigation and land use interact to impact European freshwater biodiversity.

Inland navigation in Europe is proposed to increase in the coming years, being promoted as a low-carbon form of transport. However, we currently lack knowledge on how this would impact biodiversity at large scales and interact with existing stressors. Here we addressed this knowledge gap by analysing fish and macroinvertebrate community time series across large European rivers comprising 19,592 observations from 4,049 sampling sites spanning the past 32 years. We found ship traffic to be associated with biodiversity declines, that is, loss of fish and macroinvertebrate taxonomic richness, diversity and trait richness. Ship traffic was also associated with increases in taxonomic evenness, which, in concert with richness decreases, was attributed to losses in rare taxa. Ship traffic was especially harmful for benthic taxa and those preferring slow flows. These effects often depended on local land use and riparian degradation. In fish, negative impacts of shipping were highest in urban and agricultural landscapes. Regarding navigation infrastructure, the negative impact of channelization on macroinvertebrates was evident only when riparian degradation was also high. Our results demonstrate the risk of increasing inland navigation on freshwater biodiversity. Integrative waterway management accounting for riparian habitats and landscape characteristics could help to mitigate these impacts.

Microplastics distribution in river side bars: The combined effects of water level and wind intensity.

Rivers are the main pathway for microplastics (MP) transport toward the ocean. However, the understanding of the processes involved in the deposition and mobilization of MP in rivers, specifically in sediment side bars (SB), remains very limited. The objectives of this study were: (i) to examine the effect of hydrometric fluctuations and wind intensity on the distribution of microplastics (MP < 5 mm) in the SB of large river (the Paraná River), (ii) to determine the characteristics of MP to infer their origin and fate, and (iii) to discuss potential similarities or differences between MP suspended in the water column and MP found in sediment. The SB and water column were sampled during the autumn, winter, and spring of 2018, and the summer of 2019 at different river discharges and wind intensities. >90 % of the MP items found were fiber of polyethylene terephthalate (PET; FT-IR analysis), the most common MP color was blue, and most were in the 0.5-2 mm size range. The concentration/composition of MP varied according to the river discharge and wind intensity. During the falling limb of the hydrograph when discharge is decreasing and sediments are exposed for short periods (13-30 days), MP particles transported by the flow were deposited on temporarily exposed SB, accumulating there in high densities (309-373 items/kg). However, during the drought, when sediments remained exposed for a long time (259 days), MP were mobilized and transported by the wind. During this period (no influence of the flow), MP densities significantly decreased on SB (39-47 items/kg). In conclusion, both hydrological fluctuations and wind intensity played a significant role in MP distribution in SB.

The challenge of reducing macroplastic pollution: Testing the effectiveness of a river boom under real environmental conditions.

Improving collection technologies is crucial to develop effective and economically feasible solutions for catching plastic from riverine environments. However, floating booms are being constructed and deployed in river around the world without rigorously testing its effectiveness. In this study, we tested the effectiveness of a boom under realistic conditions for several configurations and treatments (including "C-shape" and "Slash-shape" configurations). For this, we used the same macroplastics that leak out of waste management channels in order to be as realistic as possible. In total we used 52 plastic articles of 13 different polymers. The global effectiveness of the tested C-shape boom was lower than expected under such conditions (around 37 % of retention). The effectiveness of the Slash-shape boom was considerably worst (<10 %). However, the effectiveness varies greatly according to the particular characteristics of the plastic articles (i.e., shape and polymer composition), ranged from 0 to 100 %. For example, the boom could be 100 % effective retaining plastics such as Stylofoam trays and cups, 40-20 % for food-wrappers but 0 % for disposable plates and spoons, straws, monofilament fishing lines, packaging straps, hoses, pipes, elastic bands, etc. It seems that to have a reasonable catch-effectiveness and be cost-efficient, boom designs need to be improved and tested under different environmental conditions before to reach the market. In addition, it is unrealistic to select only high buoyancy plastics for testing them.

The role of hydrodynamic fluctuations and wind intensity on the distribution of plastic debris on the sandy beaches of Paraná River, Argentina.

Plastic in the environment is considered an emerging pollutant of global concern. In spite of intensive research, many questions remain open, such as the processes that drive the deposition and remobilization of plastic debris on river beaches. The objectives of this study were: i) to analyze the influence of the natural hydrological fluctuations and wind intensity on the distribution of mesoplastic (0.5-2.5 cm) and macroplastic (>2.5 cm) debris in beach sediments of a large river, ii) to describe the type of plastic debris found and iii) to explore potential relations between the number of items and weight of macro- and mesoplastics. Our results suggest that, during lowering water levels, flow removes the plastic debris and transports it further downstream. Conversely, when the beach sediments remain exposed during long periods, the plastic debris accumulates considerably. Nevertheless, the influence of wind intensity on plastic debris transport was comparatively negligible. In other words, in our study the water flow had a greater capacity to remobilize and transport plastic debris than the wind. The most abundant mesoplastic items were foam, hard plastic, film and small fragments of fishing line. The dominant macroplastic items recorded were pieces of fishing line (nylon) and cigarette filters (cellulose acetate), typically discarded by beach users. Other items found in large quantities were soft packaging elements (expanded polystyrene), hard plastic containers (polystyrene, polyethylene terephthalate) and beverage bottles (polyethylene terephthalate), typical items of domestic use in the Paraná River region. Finally, we found that the density of macroplastic items is highly correlated to the density of mesoplastic items, serving as surrogate for further estimations. Our results could help to develop better mitigation strategies in seasonal riverscapes, based on the influence of the hydrological cycle and the characteristics of the most abundant meso- and macroplastics.

More than one million barriers fragment Europe's rivers.

Rivers support some of Earth's richest biodiversity1 and provide essential ecosystem services to society2, but they are often fragmented by barriers to free flow3. In Europe, attempts to quantify river connectivity have been hampered by the absence of a harmonized barrier database. Here we show that there are at least 1.2 million instream barriers in 36 European countries (with a mean density of 0.74 barriers per kilometre), 68 per cent of which are structures less than two metres in height that are often overlooked. Standardized walkover surveys along 2,715 kilometres of stream length for 147 rivers indicate that existing records underestimate barrier numbers by about 61 per cent. The highest barrier densities occur in the heavily modified rivers of central Europe and the lowest barrier densities occur in the most remote, sparsely populated alpine areas. Across Europe, the main predictors of barrier density are agricultural pressure, density of river-road crossings, extent of surface water and elevation. Relatively unfragmented rivers are still found in the Balkans, the Baltic states and parts of Scandinavia and southern Europe, but these require urgent protection from proposed dam developments. Our findings could inform the implementation of the EU Biodiversity Strategy, which aims to reconnect 25,000 kilometres of Europe's rivers by 2030, but achieving this will require a paradigm shift in river restoration that recognizes the widespread impacts caused by small barriers.

The use of anthropogenic debris as nesting material by the greater thornbird, an inland-wetland-associated bird of South America.

Plastic pollution has become a globally pressing environmental issue. In birds, plastic may cause harm by entangling or ingestion when used for nesting. The use of anthropogenic nesting material has so far been mostly studied in birds of terrestrial or marine habitats, but there are yet very few reports for inland water-associated birds. The aim of this study is to better understand the extension and magnitude of the use of anthropogenic debris as nesting material by the greater thornbird (Phacellodomus ruber), a bird species preferably nesting in river floodplain wetlands in South America. We found that P. ruber uses disproportionally large quantities of plastic debris as nesting material (more than 90% of some nest chambers is plastic). This occurred even if ample vegetation (commonly used as soft material) was available. Most of the artificial nesting material was derived from wrapping material released into the environment. We suggest that this species has the potential to indicate vulnerable areas to plastic pollution associated with urban waste mismanagement.

Massive plastic pollution in a mega-river of a developing country: Sediment deposition and ingestion by fish (Prochilodus lineatus).

The aim of this study was to determine the amount, composition and origin of plastic debris in one of the world largest river, the Paraná River in Argentina (South America), focusing on the impact of urban rivers, relationships among macro, meso and microplastic, socio-political issues and microplastic ingestion by fish. We recorded a huge concentration of macroplastic debris of domestic origin (up to 5.05 macroplastic items per m2) dominated largely by bags (mainly high- and low-density polyethylene), foodwrapper (polypropylene and polystyrene), foam plastics (expanded polystyrene) and beverage bottles (polyethylene terephthalate), particularly downstream from the confluence with an urban stream. This suggests inadequate waste collection, processing and final disposal in the region, which is regrettably recurrent in many cities of the Global South and Argentina in particular. We found an average of 4654 microplastic fragments m-2 in shoreline sediments of the river, ranging from 131 to 12687 microplastics m-2. In contrast to other studies from industrialized countries from Europe and North America, secondary microplastics (resulting from comminution of larger particles) were more abundant than primary ones (microbeads to cosmetics or pellets to the industry). This could be explained by differences in consumer habits and industrialization level between societies and economies. Microplastic particles (mostly fibres) were recorded in the digestive tract of 100% of the studied Prochilodus lineatus (commercial species). Contrary to recently published statements by other researchers, our results suggest neither macroplastic nor mesoplastics would serve as surrogate for microplastic items in pollution surveys, suggesting the need to consider all three size categories. The massive plastic pollution found in the Paraná River is caused by an inadequate waste management. New actions are required to properly manage waste from its inception to its final disposal.

Global warming may lower thermal barriers against invasive species in freshwater ecosystems - A study from Lake Constance.

European freshwater ecosystems are increasingly invaded by exotic animal and plant species. Apart from increased connectivity between previously separated watersheds, the increasing temperature of the hydrosystems favors the spread of exotic species. The freshwater fauna of Central Europe is still shaped by the cold-adapted animal assemblages resulting from the last glaciation. It is less diverse, and the species are putatively less performant competitors, compared to the warm-adapted, species-rich fauna of the Ponto-Caspian realm, from which many current aquatic invaders are coming. Our study analyses potential mechanisms explaining the coexistence between one of the most impacting aquatic invaders of the past decades, the 'killer shrimp' Dikerogammarus villosus and the previously dominating amphipod Gammarus roeselii in Lake Constance, using laboratory predation experiments and field surveys. Our results indicate two key drivers for coexistence: low winter temperatures and the substrate structure of the alga Chara sp. At temperatures below 6 °C, the predation pressure on G. roeselii was strongly reduced; G. roeselii can therefore disperse throughout the littoral in winter, avoiding predation by D. villosus. Artificial heating of a section of the lake shore, however, resulted in local extinction of G. roeselii by D. villosus. The macroalga Chara sp. completely inhibited predation by D. villosus on G. roeselii. Climate change scenarios indicate that global warming might destroy this thermal refuge during winter until 2085. For the survival of G. roeselii it will then be crucial, which part of the Chara population will maintain epigeic plant parts during winter. The complex interplay between thermal and physical refuges for native species in the context of climate change and changing trophic status of freshwater systems, as disentangled by our study, shows that ecosystem management and restoration strategies need to better consider multiple stressors (and their rather complex mitigation strategies).