Web Structure Research Articles

Algae–zooplankton relationships during the year-round cyanobacterial blooms in a shallow lake

Cyanobacterial blooms have a strong impact on the food web structure, interactions and ecosystem functioning. The aim of this study was to describe the seasonal changes in composition and abundance of heterotrophic nanoflagellates, ciliates, rotifers, and crustaceans in relation to algae and nutrients in a shallow eutrophic lake (north-eastern Poland) dominated by cyanobacteria and exposed to the strong impact of cormorants. Our results showed that algae accounted for a small part of the total phytoplankton abundance (9–40%) and biomass (10–21%) and were dominated by diatoms and cryptophytes. All of the studied groups of planktonic organisms were quite rich in species (95 algal, 79 ciliate, 44 rotifer and 25 crustacean species) and relatively abundant. Copepods formed a substantial part (45–83%) of the total zooplankton biomass during all seasons. Relatively low algal to zooplankton biomass ratio (0.8–1.1) suggests that during spring, summer, and winter algae were not sufficient food resources for metazooplankton, which supplemented its diet with protists (heterotrophic nanoflagellates and ciliates). In a shallow lake dominated by cyanobacteria, winter (ice-covered period) may be a more favourable period for the growth of some groups of algae, ciliates and rotifers than other seasons due to decreasing abundance of cyanobacteria.

Seasonal stratification leads to changes within the benthic food web of the Gulf of Lions (northwestern Mediterranean)

Due to its extensive continental shelf, the Gulf of Lions, situated in the northwestern Mediterranean Sea, plays a crucial role in providing ecological services amidst various natural and anthropogenic pressures. Exposed to the impacts of climate change and suitable for marine energy development projects, the conservation of marine biodiversity in this environment raises significant concerns. To detect any potential disturbances in the functioning of the terrigenous mud community on the continental shelf, we conducted stable carbon and nitrogen isotope analyses on suspended particulate organic matter, sediments, and benthic fauna. Since seasonality is a structuring factor for the functioning of such an oligotrophic ecosystem, we conducted two sampling campaigns in 2018 to capture contrasting scenarios of water column stratification — one in April during well-mixed conditions and high phytoplankton production, and another in September at the end of the summer thermal stratification period characterized by low primary productivity. Stable isotope analysis revealed changes in the structure of the benthic food web in response to seasonal stratification of the water column. While isotopic niches of taxa remained evenly distributed, the total niche space contracted between sampling dates, primarily affecting low trophic level consumers. The observed contraction aligns with that reported at the base of the pelagic food web. These results enhance our understanding of the functioning of the continental shelf of the Gulf of Lions. The intense trawling pressure on the study site affected sampling. In this context, this research contributes not only to the knowledge of seasonal trophic variations but also provides a reference state to understand the future of this Mediterranean continental shelf.

Seasonal and taxonomic variation in arthropod macronutrient content

Physiological regulation of internal body composition is critical for the fitness of many organisms. Arthropods are abundant around the world and exhibit incredible diversity, yet little is known about how these groups differ in body composition or the mechanisms behind internal changes in chemistry over time. The goal of this study was to examine the lipid and protein content of several common terrestrial arthropod orders, and to determine if this macronutrient composition changes across the season. Additionally, we describe relationships between arthropod body measurements and lipid, protein, and overall dry mass. Arthropod total length and width strongly correlated with macronutrient masses, while other body measurement relationships varied considerably. As expected, arthropod orders varied significantly in both lipid and protein content. Within-order lipid and protein content also varied significantly across the season. These results demonstrate that the nutritional content of invertebrates may fluctuate over time, likely due to shifts in size, ontogeny, and environmental conditions. Understanding the mechanisms behind these changes will be important for unraveling the evolutionary history of these groups as well as the roles they play in surrounding food web structure.

Potential impacts of ocean warming on energy flow and fisheries production in an overexploited ecosystem: Implication for effective fisheries management

The influences of ocean warming on marine lives have accelerated over the 21st century, greatly altering the structure and function of marine food webs and causing distributional shifts, species invasions, and changes in productivity. It is imperative to clarify the overall ecosystem responses to ocean warming and develop fisheries management strategies adaptive to the ecosystem changes. In this study, the potential impacts of ocean warming on trophic structure, energy flows, and fisheries production of an overexploited ecosystem were examined, and the effectiveness of fisheries management in mitigating warming impacts were also evaluated. We constructed a mass-balance food web model in Haizhou Bay and simulated three climate scenarios (RCPs 2.6, 4.5, and 8.5) along with different levels of fishing pressure, in order to examine the ecosystem responses to the combined changes in fishing and climate changes. Results showed that the total biomass of commercial species and fisheries catches would decline with rising temperature, especially under the RCP8.5 scenario. Ocean warming could induce lower trophic transfer efficiency and decrease energy recycling capacity within the food web, leading to large losses in total biomass and total production. Reducing fishing intensity could help mitigate the negative effects of ocean warming on fisheries productivity, but was insufficient to maintain ecological properties. Moreover, the effectiveness of such alternative measures would be diminished with increased greenhouse gas emissions, especially under the climate scenario of RCP8.5. The findings of this study highlight the need to slow the rise of sea temperature and implement climate-adaptive fisheries management in the future.

Stream food webs in tropical mountains rely on allochthonous carbon regardless of land use

The relative importance of allochthonous and autochthonous carbon (C) as sources of energy for tropical stream food webs remains an open question. Allochthonous C might be the main energy source for small and shaded forest streams, while autochthonous C is more likely to fuel food webs draining land uses with less dense vegetation. We studied food webs in cloud forest streams draining watersheds with forests, coffee plantations, and pastures. Our goal was to assess the effects of those land uses on the C source and structure of stream food webs. The study took place in tropical montane streams in La Antigua Watershed, in eastern Mexico. We selected three streams per land use and sampled biofilm and leaf litter as the main food resources, and macroinvertebrates and aquatic vertebrates from different trophic guilds. Samples were analyzed for δ13C and δ15N isotopes. Using a Bayesian mixing model, we estimated the proportional assimilation of autochthonous and allochthonous carbon by each guild. We found that consumers were mostly using allochthonous C in all streams, regardless of watershed land use. Our findings indicate that montane cloud forest streams are dominated by allochthony even in watersheds dominated by pastures. Abundant precipitation in this life zone might facilitate the movement of allochthonous C into streams. While food webs of streams from coffee plantations and pastures also rely on allochthonous resources, other impacts do result in important changes in stream functioning.

Food web structure for high carbon retention in marine plankton communities

Total annual net primary productions in marine and terrestrial ecosystems are similar. However, a large portion of the newly produced marine phytoplankton biomass is converted to carbon dioxide because of predation. Which food web structure retains high carbon biomass in the plankton community in the global ocean? In 6954 individual samples or locations containing phytoplankton, unicellular protozooplankton, and multicellular metazooplankton in the global ocean, phytoplankton-dominated bottom-heavy pyramids held higher carbon biomass than protozooplankton-dominated middle-heavy diamonds or metazooplankton-dominated top-heavy inverted pyramids. Bottom-heavy pyramids predominated, but the high predation impact by protozooplankton on phytoplankton or the vertical migration of metazooplankton temporarily changed bottom-heavy pyramids to middle-heavy diamonds or top-heavy inverted pyramids but returned to bottom-heavy pyramids shortly. This finding has profound implications for carbon retention by plankton communities in the global ocean.

Temporal and spatial variation in the food web structure in artificial reef areas and adjacent habitats in Haizhou Bay

Artificial reef is regarded as an effective tool for restoring habitats and supporting the marine ecosystem. While the energy flow and material exchange in the food web of artificial reef ecosystem still remain vacant and should be further understood. In this study, stable isotopic characteristics (δ13C and δ15N) were used to identify the trophic niches and potential carbon sources of consumers (fish and invertebrates) in artificial reef areas and adjacent habitats in Haizhou Bay (the estuary area (EA), the aquaculture area (AA), the artificial reef area (AR), the natural area (NA) and the comprehensive effect area (CEA)) in spring and autumn. The results showed that the average δ13C for all consumers decreased from − 16.99 ± 2.07‰ to − 21.81 ± 1.66‰, and the average δ15N ranged from 11.37 ± 0.35‰ to 14.69 ± 0.64‰ in all seasons. A SIBER model revealed highly similar trophic niche among habitats in autumn, and lower overlap in spring. The SIMMR model showed that phytoplankton and sedimentary organic matter (SOM) were the major contributors to consumers, and particulate organic matter (POM) accounted for less contribution. In AA and NA phytoplankton and SOM generally contributed fairly equally to most fish, while single SOM sources were major contributors to nearly all the species in AR and CEA. Our findings reveal that ARs can serve as seascape mosaics to increase fish community diversity because of their high variation in the δ13C value and the trophic niches from EA to the NA. Preliminary multidisciplinary studies are needed for the mitigation of effects before any implementations deployed to the offshore waters that influence habitat connectivity, especially some habitat–specific migratory species.

Reconstructing Filaments around Galaxy Clusters from Spectroscopic Surveys using Machine Learning

Next-generation surveys such as the WEAVE Wide-Field Cluster Survey will soon give astronomers an unprecedented opportunity to study cosmic web structure and filamentary populations around clusters. Analysis of classical methods of extracting the cosmic web from simulated 2D projections has revealed significant incompleteness and contamination. In this note, we present the first results from a random forest trained and tested on the dark-matter simulation MDPL2. Our algorithm improves the precision of filament classification by 11% and decreases the structural reconstruction error by 43% compared to the previously published method.

Optimizing ecosystem function multifunctionality with cover crops for improved agronomic and environmental outcomes in dryland cropping systems

CONTEXTIntegrating cover crop mixtures into dryland crop-fallow rotations may foster ecological intensification by enhancing ecosystem function multifunctionality compared with conventional fallows and monoculture cover crops. However, the expression of functional traits in cover crop mixtures is influenced by arrays of agronomic and environmental filters that differently influence cover crop performance. OBJECTIVETo (1) determine the identity and diversity effects of different cover crop functional types on ecosystem functions and trade-offs, and (2) determine the optimal cover crop mixture that maximizes ecosystem function multifunctionality in a subtropical dryland environment. METHODSUsing three-site-year field experiments, we assessed if cover crop mixtures enhanced ecosystem function multifunctionality (MF) above that of monoculture cover crops and conventional fallow. We measured a range of ecosystem functions as indicators of three major ecosystem service categories: 1) provisioning services (biomass production, cash crop yield, and profitability); 2) supporting services (weed suppression, soil active carbon accrual, soil aggregate distribution, nitrogen (N) mineralization, N supply, and N retention); and 3) regulating services (parasitic nematode suppression, promotion of free-living nematodes, soil respiration, and soil water conservation). RESULTS AND CONCLUSIONSWe found greater suite of ecosystem functions following mixture cover crops compared to monocultures, likely due to synergistic trait combinations that increased ecosystem function multifunctionality. The legume and forage brassica monocultures had consistently low multifunctionality (MF < 0.5). The oat:legume mixture resulted in the highest multifunctionality (MF > 0.5), driven by moderate water use and aboveground biomass production, and high groundcover residency, thus favouring higher cash crop yields and system profitability. They also generated overall improvements in soil health by providing additional carbon inputs, increasing the proportion of larger soil aggregates, and improving soil food web structure. We predicted the optimum cover crop mixture to maximize ecosystem function multifunctionality was 64% oat, 36% legume and 0% forage brassica. SIGNIFICANCEThis study offers novel insight into the agronomic and environmental impacts of replacing fallow with cover crops in a subtropical dryland. It shows that integrating mixture of oat:legume cover crops can increase multifunctionality. Further research is required on the extent of ecosystem trade-offs between competing ecosystem functions. The predicted optimum cover crop mixture composition will likely vary when different ecosystem functions are considered or if long-term experiment data are used. Hence, the recommended optimum cover crop mixture must be interpreted with caution and cover crop selection should be based on practical recommendations according to target management goals.

The fate of nitrogen in the Zarin-Gol River receiving trout farm effluent

This study investigated the Zarrin-Gol River ecosystem in Iran to trace organic matter in the food web and evaluate the impact of aquaculture farm effluent using stable isotopes of nitrogen (δ15N) and carbon (δ13C). Using a previously-developed model (Islam 2005), we estimated that a trout farm in the vicinity released 1.4 tons of nitrogen into the river. This was comparable to an estimated total nutrient load of 2.1 tons of nitrogen for the six-month fish-rearing period based on a web-based constituent load estimator (LOADEST). A model estimate of river nitrogen concentration at the time of minimum river discharge (100 L/s) was 2.74 mg/L. Despite relatively high nitrogen loading from the farm, isotope data showed typical food web structure. Several biological groups had elevated δ13C or δ15N values, but there was limited evidence for the entry of organic matter from the trout farm into the food web, with sites above and below trout farms having inconsistent patterns in 15N enrichment. By coupling nitrogen load modeling with stable isotope analysis we showed that stable isotopes might not be effective tracers of organic matter into food webs, depending on surrounding land use and other point sources of nutrients. The Zarrin-Gol River ecosystem, like other basins with high human population density, remains vulnerable to eutrophication in part due to trout farm effluent.

Outcrop to petrography scale and new age constraint of the Jatisamit Mélange in the Luk Ulo area, Central Java, Indonesia

To resolve the formation of the Luk Ulo Mélange in the Karangsambung area of Central Java, the matrix-dominated Jatisamit Mélange, which is a member of the Luk Ulo Mélange, was examined. Outcrop and petrographic observations of sandstone boudins and their shale matrix from the Jatisamit Mélange were used to assess deformational mechanisms and formation. We suggest the Jatisamit Mélange underwent three deformation phases: (1) formation of a web structure in the sandstone boudins through a cataclasis mechanism; (2) formation of boudins and cleavage through a ductile deformation; and (3) formation of open fractures and Riedel shears through pressure increasing. These deformations occurred at relatively low to medium temperatures during progressively increasing differential stress. Using illite crystallinity, the matrix of the Jatisamit Mélange has a maximum metamorphic temperature of 150–200 °C (diagenesis zone) at a 4–5 km depth. In addition, calcareous nannofossil assemblages of the Jatisamit Mélange and other related rock units in Karangsambung suggest a depositional matrix age of middle Eocene–early Oligocene. Therefore, the mixing of the Luk Ulo Mélange occurred not earlier than the middle Eocene–early Oligocene at a shallow structural level in the suture zone during the collision of the southeastern margin of Sundaland with the Gondwana micro-continent.

Effect of agricultural landscape pattern on the qualitative food web of epigaeic arthropods in low hilly areas of northern China

Under the macro background of global change and sustainable development, the sustainable and healthy development of agricultural landscapes is crucial for human well-being. Formulating targeted protection measures based on biodiversity conservation is currently a hot topic and challenge. Our study focused on Jianping County, a typical hilly area in northern China, to understand the impact of regional agricultural landscape patterns on qualitative food webs. We calculated food web parameters by constructing predator-pest qualitative food web matrices and compared the differences in food web structure characteristics under different agricultural landscape patterns. By using function regression method, we established landscape indices and food web parameter models. The results showed that the average number and community structure of predatory natural enemies and pests varied across different agricultural landscape patterns, but the common groups were similar. Maintaining a proportion of 30–40 % non-crop habitats is optimal for the stability of qualitative food webs. Different landscape elements have varying regulatory effects on the structure of qualitative food webs, and the food web parameter model can explain these effects more directly. Specifically, the Landscape Shape Index (LSI) is significantly positively correlated with Generality (G), while the Contagion Index (CONTAG) is significantly negatively correlated with vulnerability (V). We propose that in low hilly areas, where non-crop diversity is the primary source of heterogeneity, promoting measures for non-crop habitats through landscape planning will help maintain the richness of epigaeic arthropods and the stability of qualitative food webs. This research is of great significance in promoting ecological control and sustainable development of agroecosystems in low hilly areas.

Livestock grazing modifies soil nematode body size structure in mosaic grassland habitats

Body size is closely related to the trophic level and abundance of soil fauna, particularly nematodes. Therefore, size-based analyses are increasingly prominent in unveiling soil food web structure and its responses to anthropogenic disturbances, such as livestock grazing. Yet, little is known about the effects of different livestock on the body size structure of soil nematodes, especially in grasslands characterized by local habitat heterogeneity. A four-year field grazing experiment from 2017 to 2020 was conducted in a meadow steppe characterized by typical mosaics of degraded hypersaline patches and undegraded hyposaline patches to assess the impacts of cattle and sheep grazing on the body size structure of soil nematodes within and across trophic groups. Without grazing, the hypersaline patches harbored higher abundance of large-bodied nematodes in the community compared to the hyposaline patches. Livestock grazing decreased large-bodied nematodes within and across trophic groups mainly by reducing soil microbial biomass in the hypersaline patches, with sheep grazing resulting in more substantial reductions compared to cattle grazing. The reduction in large-bodied nematode individuals correspondingly resulted in decreases in nematode community-weighted mean (CWM) body size, nematode biomass, and size spectra slopes. However, both cattle and sheep grazing had minimal impacts on the CWM body size and size spectra of total nematodes in the hyposaline patches. Our findings suggest that livestock grazing, especially sheep grazing, has the potential to simplify soil food webs by reducing large-bodied nematodes in degraded habitats, which may aggravate soil degradation by weakening the bioturbation activities of soil fauna. In light of the widespread land use of grasslands by herbivores of various species and the ongoing global grassland degradation of mosaic patches, the recognition of the trends revealed by our findings is critical for developing appropriate strategies for grassland grazing management.

Report on the 13th Workshop on Temporal Web Analytics (TempWeb 2023) at WWW 2023

TempWeb is an established Workshop (series) with a long-standing tradition as a co-located event at The Web Conference. Considering the constantly evolving Web as a primary object of research, TempWeb provides a platform to present longitudinal studies on the Web (structure), its contents, and its communities, etc. by aiming at the investigation of infrastructures, scalable methods, and innovative software for aggregating, querying, and analyzing heterogeneous data at Web scale. Since longitudinal aspects in Web analytics is becoming more and more inter- and transdiciplinary relevant for analysts from various domains, the studies, tools, and demonstrations are not only limited to computer science, but also open to sociology, marketing, environmental studies, politics, etc., to name just a few. As such, TempWeb has developed as a forum for a community from academia and industry covering temporal Web analytics at all levels of granularity and across various disciplines. Date : 1 May 2023. Website : http://temporalweb.net/.

Influence of fishery management on trophic interactions and biomass fluxes in Lake Taihu based on a trophic mass-balance model exercise on a long-term data series

With increasing anthropogenic activities, freshwater ecosystems around the world are becoming increasingly affected by various pressures, including eutrophication, overfishing, and irrational stocking, which may have a negative impact on the food web structure. Despite the extensive research and proposed management measures for eutrophic lakes, there are only few analysis on long-term monitoring data regarding fishery resources. Additionally, there is a lack of evaluation and prediction of the effectiveness of current fish management policies. To remedy this, we analyzed long-term monitoring data from Lake Taihu, China, a severely eutrophicated lake with a skewed fish size structure exhibiting dominance of small individuals. We first constructed 14 Ecopath models to investigate how trophic interactions and biomass fluxes changed from 2007 to 2020. Subsequently, the Ecosim model was used to predict how the biomass of fish and the ecosystem network respond to the initiated 10-years fishing ban. Our results demonstrate long-term changes in fish biomass and ecosystem stability. The analyses revealed that 1) the biomass development in different feeding types of fish is controlled by human activities (mainly catches and stocking) and trophic interactions and 2) the rate of decline in ecosystem network stability slows down during the fishing ban. The primary focus of this study was to fill the gap in long-term serial studies of fish monitoring data and ecosystem stability in the lake and, for the first time, to predict the outcome of the fishing ban from an ecosystem perspective using the Ecosim model. Overall, our results emphasize the importance of rational stocking and fishing policies and provide a better understanding of the changes in the ecological dynamics in Lake Taihu of relevance for the management and restoration of the lake.

Progress in Research on the Bioavailability and Toxicity of Nanoplastics to Freshwater Plankton

The present review critically examines the advancements in the past 5 years regarding research on the bioavailability and toxicity of the nanoplastics (NPLs) to freshwater plankton. We discuss the recent progress in the understanding of adsorption, absorption, trophic transfer, and biological effects in phyto- and zooplankton induced by NPLs exposure. The influence of plankton on NPLs’ bioavailability via the excretion of biomolecules and formation of eco-corona is also examined. Despite important research developments, there are still considerable knowledge gaps with respect to NPLs’ bioavailability and trophic transfer by plankton as well as a potential adverse effect in natural aquatic systems. As plankton play a critical role in primary production, nutrient cycling, and food web structure, understanding the interactions between NPLs and plankton is essential in assessing the potential implications of NPLs pollution for aquatic ecosystem biodiversity and services.

The influence of environmental parameters on spatial variation in zoobenthic density and stable isotopes (δ13C, δ15N, and δ34S) within a large lake

AbstractThe use of baselines in stable isotope studies to interpret food web structure is essential, but baseline isotope values are often assumed to be spatially homogeneous, even in large aquatic ecosystems. To test this assumption in large lakes, we quantified spatial variation in δ13C, δ15N (deposit‐feeding Oligochaeta and filter‐feeding Dreissena spp.), and δ34S (Dreissena spp. only) and density in Lake Erie between 2014 and 2016. Lake Erie's three distinct basins differ in size, bathymetry, and nutrient loading, making it an excellent system for exploring spatial variation in stable isotopes of baseline organisms. Dreissena spp. densities were highest in the western and lowest in the seasonally hypoxic central basin, while Oligochaeta densities were relatively consistent throughout Lake Erie. Values of δ13C, δ15N, and δ34S exhibited distinct spatial trends that were not related to population densities but followed the west to east direction of water flow within the lake. For both taxa, δ13C was lower in the deeper, oligotrophic east basin than the shallow, mesotrophic west basin, and δ15N and δ34S increased from west to east. Spatial patterns of low δ34S in Dreissena spp. in the western and central basins were likely related to hypoxia, whereas patterns of δ15N in both taxa were probably related to the greater influence of agricultural land uses in the western basin. Spatial trends of stable isotopes in large lake zoobenthos are driven by complex interactions of environmental gradients, which could introduce bias in evaluations of trophic structures within aquatic ecosystems that use stable isotopes.

Impacts of the accumulated extinction of endangered species on stream food webs

The world is facing a serious biodiversity-loss crisis and stream ecosystems are among the most vulnerable. Human-induced disturbances are accelerating the loss of stream biodiversity; however, their ecological impacts are poorly understood. Here, we comprehensively investigated the impact of biodiversity loss on stream food webs using massive food web data (> 1 300 webs). We analyzed the structural changes of food webs upon accumulation of biodiversity loss and specifically compared the severity of losses between fish or benthic macroinvertebrates. In particular, we focused on currently threatened and near-threatened species, to reflect realistic extinction. We simulated their sequential and accumulative extinctions and analyzed the changes in food web structural indices using a linear mixed effect model. Stream food webs tended to be robust against the loss of threatened species; however, the accumulated extinction, including both threatened and near-threatened species, caused substantial changes in food web structures. Notably, significant decreases in the number of links, link density, and generality were observed, indicating the vulnerability of the system. The loss of fish caused larger changes in the food web structure compared to that of benthic macroinvertebrates, indicating the relative importance of fish species in sustaining food web structures. Food web alteration may lead to substantial changes in ecosystem functioning. Our study suggests preemptive action to protect near-threatened species as well as threatened ones for conserving stream ecosystems and their services. Furthermore, we suggest that the food web framework is useful for diagnosing ecosystem-level impacts of species loss in biodiversity conservation.

Research on heavy-haul adaptive technology and strengthening measures for existing railway steel bridge

PurposeThis research addresses the diverse characteristics of existing railway steel bridges in China, including variations in construction age, design standards, structural types, manufacturing processes, materials and service conditions. It also focuses on prominent defects and challenges related to heavy transportation conditions, particularly low live haul reserves and severe fatigue problems.Design/methodology/approachThe study encompasses three key aspects: (1) Adaptability assessment: It begins with assessing the suitability of existing railway steel bridges for heavy-haul operations through comprehensive analyses, experiments and engineering applications. (2) Strengthening: To combat frequent crack defects in the vertical stiffener end structure of girder webs, fatigue performance tests and reinforcement scheme experiments were conducted. These experiments included the development of a hot-spot stress S-N curve for this structure, validating the effectiveness of methods like crack stop holes, ultrasonic hammering and flange angle steel. (3) Service life extension: Research on the cruciform welded joint structure (non-fusion transfer type) focused on fatigue performance over the long life cycle. This led to the establishment of a fatigue S-N curve, enhancing Chinese design codes.FindingsThe research achieved several significant outcomes: (1) Successful implementation of strengthening and retrofitting measures on a 64-m single-span double-track railway steel truss girder on an existing heavy-duty line. (2) Post-reinforcement, a substantial 26% to 32% reduction in live haul stress on bridge members was achieved. (3) The strengthening and retrofitting efforts met design expectations, enabling the bridge to accommodate vehicles with a 30-ton axle haul on the railway line.Originality/valueThis research systematically tackles challenges and defects associated with Chinese existing railway steel bridges, providing valuable insights into adaptability assessment, strengthening techniques and service life extension methods. Furthermore, the development of fatigue S-N curves and the successful implementation of bridge enhancements have practical implications for improving the resilience and operational capacity of railway steel bridges in China.

Hurricane disturbance drives trophic changes in neotropical mountain stream food webs.

Food webs are complex ecological networks that reveal species interactions and energy flow in ecosystems. Prevailing ecological knowledge on forested streams suggests that their food webs are based on allochthonous carbon, driven by a constant supply of organic matter from adjacent vegetation and limited primary production due to low light conditions. Extreme climatic disturbances can disrupt these natural ecosystem dynamics by altering resource availability, which leads to changes in food web structure and functioning. Here, we quantify the response of stream food webs to two major hurricanes (Irma and María, Category 5 and 4, respectively) that struck Puerto Rico in September 2017. Within two tropical forested streams (first and second order), we collected ecosystem and food web data 6 months prior to the hurricanes and 2, 9, and 18 months afterward. We assessed the structural (e.g., canopy) and hydrological (e.g., discharge) characteristics of the ecosystem and monitored changes in basal resources (i.e., algae, biofilm, and leaf litter), consumers (e.g., aquatic invertebrates, riparian consumers), and applied Layman's community-wide metrics using the isotopic composition of 13 C and 15 N. Continuous stream discharge measurements indicated that the hurricanes did not cause an extreme hydrological event. However, the sixfold increase in canopy openness and associated changes in litter input appeared to trigger an increase in primary production. These food webs were primarily based on terrestrially derived carbon before the hurricanes, but most taxa (including Atya and Xiphocaris shrimp, the consumers with highest biomass) shifted their food source to autochthonous carbon within 2 months of the hurricanes. We also found evidence that the hurricanes dramatically altered the structure of the food web, resulting in shorter (i.e., smaller food-chain length), narrower (i.e., lower diversity of carbon sources) food webs, as well as increased trophic species packing. This study demonstrates how hurricane disturbance can alter stream food webs, changing the trophic base from allochthonous to autochthonous resources via changes in the physical environment (i.e., canopy defoliation). As hurricanes become more frequent and severe due to climate change, our findings greatly contribute to our understanding of the mechanisms that maintain forested stream trophic interactions amidst global change.