River networks as biodiversity hotlines

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.

Determinants and Assembly Mechanism of Bacterial Community Structure in Ningxia Section of the Yellow River

The Yellow River is a valuable resource in the Ningxia Hui Autonomous Region and plays a vital role in local human activities and biodiversity. Bacteria are a crucial component of river ecosystems, but the driving factors and assembly mechanisms of bacterial community structure in this region remain unclear. Herein, we documented the bacterial community composition, determinants, co-occurrence pattern, and assembly mechanism for surface water and sediment. In comparison to sediment, the bacterioplankton community showed significant seasonal variation, as well as less diversity and abundance. The network topology parameters indicated that the sediment bacterial network was more stable than water, but the bacterioplankton network had higher connectivity. In this lotic ecosystem, COD_Mn, Chl a, and pH affected the structure of the bacterioplankton community, while TP was the primary factor influencing the structure of the sediment bacterial community. The combined results of the neutral community model and the phylogenetic null model indicate that Bacterial communities in both habitats were mainly affected by stochastic processes, with ecological processes dominated by ecological drift for bacterioplankton and dispersal limitation for sediment bacteria. These results provide essential insights into future research on microbial ecology, environmental monitoring, and classified management in the Ningxia section of the Yellow River.

Spatially structured freshwater fish population dynamics at the River Basin District scale: Implication for environmental management and fish conservation

European Union environmental policy has created a unique regulatory framework to favour aquatic ecosystem management and biodiversity conservation across European countries. Identifying the spatial structure of freshwater fish population dynamics is crucial to define region-specific management and conservation planning. To implement evidence-driven management and conservation decisions at a regional scale we assessed spatial heterogeneity in common freshwater fish population dynamics in France with a focus on trends in River Basin Districts (RBDs). The abundance and biomass growth rates of 18 common European freshwater fish species were estimated with state-space models on 546 sites distributed across the 5 main RBDs sampled in France between 1990 and 2011. Anguilla anguilla, Rutilus rutilus, Salmo trutta fario and Esox spp. exhibited large scale decline in abundance and/or biomass in several RBDs. The other species showed spatial heterogeneity in population growth rates. The main declines were observed in the Adour-Garonne and Loire-Bretagne RBDs, where management and conservation measures are urgently needed to halt the erosion of freshwater fish populations. In each of the 5 investigated RBDs, our results highlight areas where most of the common species we studied exhibited negative population growth rates. Freshwater fish surveys provide the fundamental information necessary to inform the European environmental policies and local environmental management needed to restore freshwater biodiversity. The next steps are to identify the main drivers of freshwater biodiversity erosion in the areas where we demonstrated major declines and to define the most cost-effective restoration measures.

Carbon cycling and exports over diel and flood-recovery timescales in a subtropical rainforest headwater stream

Catchment headwaters comprise the majority of all stream length globally, however, carbon (C) dynamics in these systems remains poorly understood. We combined continuous measurements of pCO2 and radon ((222)Rn, a natural groundwater tracer) with discrete sampling for particulate organic, dissolved organic and inorganic carbon (POC, DOC, and DIC) to assess the short-term carbon dynamics of a pristine subtropical headwater stream in Australia, over contrasting hydrologic regimes of drought, flash-flooding and recovery. Observations over 23days revealed a shift from carbon losses dominated by CO2 outgassing under conditions of low flow (66.4±0.4% of carbon export) to downstream exports of carbon during the flood (87.8±9.7% of carbon export). DOC was the dominant form of downstream exports throughout the study (DOC:DIC:POC=0.82:0.05:0.13). The broadest diel variability among variables occurred during the drought phase, with diel variability up to 662μatmd(-1) (or 27μM[CO2*]d(-1)), 17μMd(-1) and 268Bqm(-3)d(-1) for pCO2, dissolved oxygen and (222)Rn, respectively. Diel dynamics indicated multiple interrelated drivers of stream water chemistry including groundwater seepage and in-stream metabolism. The catchment exported terrestrial carbon throughout the field campaign, with a mean net stream flux of 4.7±7.8mmolCm(-2)(catchment area)d(-1) which is equivalent to 1.4±2.3% of the estimated local terrestrial net primary production. Our observations highlight the importance of accounting for hydrological extremes when assessing the carbon budgets and ecosystem metabolism of headwater streams, and provide a first estimate of aquatic carbon exports from a pristine Australian subtropical rainforest.

Functional and taxonomic plant diversity for riverbank protection works: bioengineering techniques close to natural banks and beyond hard engineering

Erosion control is a major issue in the Prealps region since piedmont is subject to both intense flood hazards and anthropic pressure. Riverbank protections may have major impacts on local ecosystem functioning and ecological corridor continuity. This study aimed to estimate the effects of the types of riverbank protection technique (from pure riprap to pure bioengineering) on the taxonomic and ecological composition of plant communities in comparison with unmanaged riverbanks as the referential system. Thirty-eight embankments were sampled in the foothills of the French and Swiss Alps. Four distinct riverbank techniques were analyzed and natural young willow stands were chosen as the referential system. At each site, vegetation was sampled along three transects from the waterline to the top of the riverbank. Plant communities were characterized using biological group composition (growth forms and life history, life strategies and distribution in space and time) and functional diversity indices (MFAD, FDc and wFDc). We identified 177 distinct plant species on 38 sites. Higher species richness levels were observed on bioengineered banks (from an average of 12 species recorded on ripraps to 27 species recorded on bioengineered banks) strongly dominated by Salicaceae species, especially for fascine and cribwall banks. Functional analyses of plant communities highlighted significant differences among bank types (p-value: 0.001) for all selected biological groups. Competitive - ruderal strategy, rooting shoots, stems or leaves that lie down or break off, and unisexual - dioecious, as well as pioneer plants and low shrubs (<4 m tall) distinguished bioengineered bank types. Functional diversity indices confirmed these differences among bank types (MFAD: p-value: 0.002; FDc: p-value: 0.003; wFDc: p-value: 0.005). Riprap always showed the lowest levels on functional diversity indices, fascine and cribwall banks were at the medium level and finally mixed and natural banks the highest level. These results confirm the low ecological potential of purely hard engineering techniques and highlight the similarity of bioengineered techniques and unmanaged riverbanks.

Implementing cargo movement into climate based risk assessment of vector-borne diseases

During the last decades the disease vector Aedes albopictus (Asian tiger mosquito) has rapidly spread around the globe. Global shipment of goods contributes to its permanent introduction. Invaded regions are facing novel and serious public health concerns, especially regarding the transmission of formerly non-endemic arboviruses such as dengue and chikungunya. The further development and potential spread to other regions depends largely on their climatic suitability. Here, we have developed a tool for identifying and prioritizing European areas at risk for the establishment of Aedes albopictus by taking into account, for the first time, the freight imports from this mosquito's endemic countries and the climate suitability at harbors and their surrounding regions. In a second step we consider the further transport of containers by train and inland waterways because these types of transport can be well controlled. We identify European regions at risk, where a huge amount of transported goods meet climatically suitable conditions for the disease vector. The current and future suitability of the climate for Aedes albopictus was modeled by a correlative niche model approach and the Regional Climate Model COSMO-CLM. This risk assessment combines impacts of globalization and global warming to improve effective and proactive interventions in disease vector surveillance and control actions.

Distribution of endemic and alien plants along Mediterranean rivers: a useful tool to identify areas in need of protection?

The main aim was to obtain information about the more critical sectors of Mediterranean-type rivers, especially in the islands where the percentage of endemic species is high, even in riparian habitats. Our hypothesis was that endemic and alien species, considered important in defining conservation priorities along rivers, have different patterns of distribution and their coexistence indicates human impacts on fluvial systems, which can cause natural habitat loss. Generalized Additive Models were used to model the distribution patterns of endemic and alien species along the longitudinal gradient. They showed that endemic species were linked to the most natural areas in the middle and upper sections of the rivers, whereas the distribution of aliens in middle and lower sections can be regarded as a consequence of human impact. This finding underlined the presence in the middle sections of the rivers of areas with important floristic features that are also affected by alien species. What currently seems a situation of equilibrium turns out to call for careful control, first and foremost, by maintaining riparian vegetation. Our results highlighted the utility of our method for rapidly obtaining information about the criticalities of rivers in Mediterranean biodiversity hotspots.