Threats, challenges and sustainable conservation strategies for freshwater biodiversity

Distribution and bioaccumulation of trace elements in two Cyprinidae fish species in the Indus river, Pakistan, including the impact of hydraulic structure on macroinvertebrates' biodiversity

The concentration of trace elements (chromium, lead, zinc, copper, manganese, and iron) was determined in water, sediment and tissues of two Cyprinidae fish species - Labeo rohita and Tor putitora - collected from the eight sampling stations of Indus River in 2022 for four successive seasons (autumn, winter, spring, summer), and also study the present condition of macroinvertebrates after the construction of hydraulic structure. The obtained results of trace element concentrations in the Indus River were higher than the acceptable drinking water standards by WHO. The nitrate concentration ranges from 5.2 to 59.6 mg l-1, turbidity ranges from 3.00 to 63.9 NTU, total suspended solids and ammonium ions are below the detection limit (<0.05). In the liver, highest dry wt trace elements (μg/g) such as Cr (4.32), Pb (7.07), Zn (58.26), Cu (8.38), Mn (50.27), and Fe (83.9) for the Labeo rohita; and Tor Putitora has significantly greater accumulated concentration (Cr, Pb, Zn, Cu, Mn, Fe) in muscle and liver than did Labeo rohita species. Additionally, lower number of macroinvertebrates were recorded during the monsoonal season than pre-monsoon and post-monsoon. Local communities surrounded by polluted environments are more probably to consume more fish and expose them to higher concentrations of toxic trace elements (lead and copper). The findings also provide a basis for broader ecological management of the Indus River, which significantly influenced human beings and socioeconomic disasters, particularly in the local community.

Near-natural streams: Spatial factors are key in shaping multiple facets of zooplankton α and β diversity

In near-natural basins, zooplankton are key hubs for maintaining aquatic food webs and organic matter cycles. However, the spatial patterns and drivers of zooplankton in streams are poorly understood. This study registered 165 species of zooplankton from 147 sampling sites (Protozoa, Rotifers, Cladocera and Copepods), integrating multiple dimensions (i.e., taxonomic, functional, and phylogenetic) and components (i.e., total, turnover, and nestedness) of α and β diversity. This study aims to reveal spatial patterns, mechanisms, correlations, and relative contribution of abiotic factors (i.e., local environment, geo-climatic, land use, and spatial factors) through spatial interpolation (ordinary kriging), mantel test, and variance partitioning analysis (VPA). The study found that α diversity is concentrated in the north, while β diversity is more in the west, which may be affected by typical habitat, hydrological dynamics and underlying mechanisms. Taxonomic and phylogenetic β diversity is dominated by turnover, and metacommunity heterogeneity is the result of substitution of species and phylogeny along environmental spatial gradients. Taxonomic and phylogenetic β diversity were strongly correlated (r from 0.91 to 0.95), mainly explained by historical/spatial isolation processes, community composition, generation time, and reproductive characteristics, and this correlation provides surrogate information for freshwater conservation priorities. In addition, spatial factors affect functional and phylogenetic α diversity (26%, 28%), and environmental filtering and spatial processes combine to drive taxonomic α diversity (10%) and phylogenetic β diversity (11%). Studies suggest that spatial factors are key to controlling the community structure of zooplankton assemblages in near-natural streams, and that the relative role of local environments may depend on the dispersal capacity of species. In terms of diversity conservation, sites with high variation in uniqueness should be protected (i) with a focus on the western part of the thousand islands lake catchment and (ii) increasing effective dispersal between communities to facilitate genetic and food chain transmission.

Environmental DNA metabarcoding of freshwater fish in Malaysian tropical rivers using short-read nanopore sequencing as a potential biomonitoring tool

The approach of combining cost-effective nanopore sequencing and emerging environmental DNA (eDNA) metabarcoding could prove to be a promising tool for biodiversity documentation, especially in Malaysia. Given the substantial funding constraints in recent years, especially in relation to the country's biodiversity, many researchers have been limited to conduct restricted research without extended monitoring periods, potentially hindering comprehensive surveys and could compromise the conservation efforts. Therefore, the present study aimed to evaluate the application of eDNA metabarcoding on freshwater fish using short reads generated through nanopore sequencing. This assessment focused on species detection in three selected rivers within the Endau Rompin Landscape in Malaysia. Additionally, the study compared levels of species detection between eDNA metabarcoding and conventional sampling methods, examined the effectiveness of primer choice, and applied both metabarcoding and shotgun sequencing to the eDNA approach. We successfully identified a total of 22 and 71 species with an identification threshold of >97% and >90%, respectively, through the MinION platform. The eDNA metabarcoding approach detected over 13% more freshwater fish species than when the conventional method was used. Notably, the distinction in freshwater fish detection between eDNA primers for 12S rRNA and cytochrome oxidase I was insignificant. The cost for eDNA metabarcoding proved to be more effective compared to conventional sampling with cost reduction at 33.4%. With favourable cost-effectiveness and increased species detection, eDNA metabarcoding could complement existing methods, enhance holistic diversity documentation for targeted habitats and facilitate effective conservation planning.

The impacts of reduced connectivity on multiple facets of aquatic insect diversity in floodplain wetlands, Northeast China

River-floodplain ecosystems are highly complex and dynamic systems that are subjected to human disturbance, such as the construction of levees. Aquatic insects are among the most widely used indicators to assess human impacts on floodplain wetlands. Most studies are still based on taxonomic biodiversity. However, trait-based approaches remain limited, which could impede the development of effective management strategies. Here, we investigated aquatic insect assemblages in eleven pairs of wetlands along the Wusuli River in two seasons (Spring and Autumn) and assessed their responses to the impact of levee construction, considering taxonomic and functional diversity. We found that pooled species richness (73 taxa) in river-connected wetlands was almost twice of that in levee-blocked wetlands (37 taxa). Six and one indicator taxa for river-connected wetlands were identified in May and October, respectively, while no indicator taxon for the levee-blocked wetlands was identified. Moreover, taxonomic and functional alpha diversity in river-connected wetlands was much higher than in levee-blocked wetlands, but beta diversity showed a contrasting pattern. Additionally, multivariate dispersion analysis indicated a more evident difference in beta diversity between river-connected and levee-blocked wetlands in May than in October, likely due to the temporary lateral connection in summer (i.e., water flowed over levees during flood events). Our results revealed that anthropogenic impacts (e.g., levee construction and agricultural activity) weakened the connectivity of floodplain wetland ecosystems, leading to decreased taxonomic and functional diversity of aquatic insects in isolated wetlands. Our study highlights the importance of combining taxonomic and trait-based approaches in biomonitoring programs of floodplain wetland ecosystems. It also underscores the necessity of restoring habitat connectivity of wetland ecosystems (e.g., river-floodplain connectivity and connections between different wetlands) to facilitate biodiversity recovery and enhance ecological functions and services supported by these valuable ecosystems.

Sustainable bioremediation technologies for algal toxins and their ecological significance

The emergence of algal toxins in water ecosystems poses a significant ecological and human health concern. These toxins, produced by various algal species, can lead to harmful algal blooms, and have far-reaching consequences on biodiversity, food chains, and water quality. This review explores the types and sources of algal toxins, their ecological impacts, and the associated human health risks. Additionally, the review delves into the potential of bioremediation strategies to mitigate the effects of algal toxins. It discusses the role of microorganisms, enzymes, and algal-bacterial interactions in toxin removal, along with engineering approaches such as advanced oxidation processes and adsorbent utilization. Microbes and enzymes have been studied for their environmentally friendly and biocompatible properties, which make them useful for controlling or removing harmful algae and their toxins. The challenges and limitations of bioremediation are examined, along with case studies highlighting successful toxin control efforts. Finally, the review outlines future prospects, emerging technologies, and the need for continued research to effectively address the complex issue of algal toxins and their ecological significance.

The response of stream ecosystem properties to two size classes of herbivorous minnow species

Losses in freshwater fish diversity might produce a loss in important ecological services provided by fishes in particular habitats. An important gap in our understanding of ecosystem services by fishes is the influence of individuals from different size classes, which is predicted based on known ontogenetic shifts in metabolic demand and diet. I used 20 experimental stream mesocosms located at Konza Prairie Biological Station (KPBS), KS, USA, to assess the influence of fish size on ecosystem properties. Mesocosms included two macrohabitats: one riffle upstream from one pool filled with consistent pebble and gravel substrate. There were four experimental and one control treatment, each replicated four times (N = 20). I used two size classes of central stonerollers (Campostoma anomalum) and southern redbelly dace (Chrosomus erythrogaster). Five ecosystem properties were assessed: algal filament length (cm), benthic chlorophyll a (μg/cm2), benthic organic matter (g/m2), macroinvertebrate biomass (g/m2), and stream metabolism (g O2/m2/day-1). Size structure of fish populations affected some, but not all, ecosystem properties, and these effects were dependent upon species identity. Size structure of both species had effects on algal filament lengths where stonerollers of both size classes reduced algal filaments, but only small redbelly dace kept filaments short. A better understanding of the relationship between these prairie stream minnows and their small stream habitats could be useful to both predict changes in stream properties if species are lost (redbelly dace are a Species In Need of Conservation) or size structure shifts.

Transmission of Microcystins in Natural Systems and Resource Processes: A Review of Potential Risks to Humans Health

The rapid rise of microcystins (MCs) poses a serious threat to global freshwater ecosystems and has become an important issue of global public health. MCs have considerable stability and are the most widely distributed hepatotoxins. It cannot only accumulate in aquatic organisms and transfer to higher nutrients and levels, but also be degraded or transferred during the resource utilization of cyanobacteria. No matter which enrichment method, it will lead to the risk of human exposure. This review summarizes the research status of MCs, and introduces the distribution of MCs in different components of aquatic ecosystems. The distribution of MCs in different aquatic organisms was summarized, and the potential risks of MCs in the environment to human safety were summarized. MCs have polluted all areas of aquatic ecosystems. In order to protect human life from the health threats caused by MCs, this paper also proposes some future research directions to promote MCs control and reduce human exposure to MCs.

Using environmental DNA metabarcoding to monitor fish communities in small rivers and large brooks: Insights on the spatial scale of information

Monitoring fish communities is central to the evaluation of ecological health of rivers. Both presence/absence of fish species and their relative quantity in local fish assemblages are crucial parameters to measure. Fish communities in lotic systems are traditionally monitored via electrofishing, characterized by a known limited efficiency and high survey costs. Analysis of environmental DNA could serve as a non-destructive alternative for detection and quantification of lotic fish communities, but this approach still requires further insights in practical sampling schemes incorporating transport and dilution of the eDNA particles; optimization of predictive power and quality assurance of the molecular detection method. Via a controlled cage experiment, we aim to extend the knowledge on streamreach of eDNA in small rivers and large brooks, as laid out in the European Water Framework Directive's water typology. Using a high and low source biomass in two river transects of a species-poor river characterized by contrasting river discharge rates, we found strong and significant correlations between the eDNA relative species abundances and the relative biomass per species in the cage community. Despite a decreasing correlation over distance, the underlying community composition remained stable from 25 to 300 m, or up to 1 km downstream of the eDNA source, depending on the river discharge rate. Such decrease in similarity between relative source biomass and the corresponding eDNA-based community profile with increasing distance downstream from the source, might be attributed to variation in species-specific eDNA persistence. Our findings offer crucial insights on eDNA behaviour and characterization of riverine fish communities. We conclude that water sampled from a relatively small river offers an adequate eDNA snapshot of the total fish community in the 300-1000 m upstream transect. The potential application for other river systems is further discussed.

Responses of macroinvertebrate functional trait structure to river damming: From within-river to basin-scale patterns

Revealing how aquatic organisms respond to dam impacts is essential for river biomonitoring and management. Traditional examinations of dam impacts on macroinvertebrate assemblages were frequently conducted within single rivers (i.e., between upstream vs. downstream locations) and based on taxonomic identities but have rarely been expanded to level of entire basins (i.e., between dammed vs. undammed rivers) and from a functional trait perspective. Here, we evaluated the effects of dams on macroinvertebrate assemblages at both the within-river and basin scales using functional traits in two comparable tropical tributaries of the Lancang-Mekong River. At different scales, maximum body size, functional feeding groups (FFG), voltinism and occurrence in drift respond significantly to dam impact. Armoring categories varied significantly between downstream sites and upstream sites, and oviposition behavior, habits and adult life span significantly differed between rivers. The key traits at the within-river scale resembled to those at the between-river scale, suggesting that within-river trait variation could further shape functional trait structure at the basin scale in dammed rivers. Furthermore, water nutrients and habitat quality induced by dams showed the most important role in shaping trait structure, although trait-environment relationships varied between the two different scales. In addition, the trait-environment relationships were stronger in the dry season than in the wet season, suggesting a more important role of environmental filtering processes in the dry season compared with the wet season. This study highlights the utility of the trait-based approach to diagnose the effects of damming and emphasizes the importance of spatial scale to examine dam impacts in riverine systems.

A Comprehensive Review on Wastewater Nitrogen Removal and Its Recovery Processes

Discharging large amounts of domestic and industrial wastewater drastically increases the reactive nitrogen content in aquatic ecosystems, which causes severe ecological stress and biodiversity loss. This paper reviews three common types of denitrification processes, including physical, chemical, and biological processes, and mainly focuses on the membrane technology for nitrogen recovery. The applicable conditions and effects of various treatment methods, as well as the advantages, disadvantages, and influencing factors of membrane technologies, are summarized. Finally, it is proposed that developing effective combinations of different treatment methods and researching new processes with high efficiency, economy, and energy savings, such as microbial fuel cells and anaerobic osmotic membrane bioreactors, are the research and development directions of wastewater treatment processes.

Projected Effects of Climate Change on Species Range of Pantala flavescens, a Wandering Glider Dragonfly

Dragonflies are sensitive to climate change due to their special habitat in aquatic and terrestrial environments, especially Pantala flavescens, which have extraordinary migratory abilities in response to climate change on spatio-temporal scales. At present, there are major gaps in the documentation of insects and the effects of climatic changes on the habitat and species it supports. In this study, we model the global distribution of a wandering glider dragonfly, P. flavescens, and detected the important environmental factors shaping its range, as well as habitat shifts under historical and future warming scenarios. The results showed a global map of species ranges of P. flavescens currently, including southern North America, most of South America, south-central Africa, most of Europe, South, East and Southeast Asia, and northern Oceania, in total, ca. 6581.667 × 10⁴ km². BIO5 (the max temperature of warmest month) and BIO13 (the precipitation of wettest month) greatly explained its species ranges. The historic refugia were identified around the Great Lakes in the north-central United States. Future warming will increase the total area of suitable habitat and shift the type of suitable habitat compared to the current distribution. The habitat suitability of P. flavescens decreased with elevation, global warming forced it to expand to higher elevations, and the habitat suitability of P. flavescens around the equator increased with global warming. Overall, our study provides a global dynamic pattern of suitable habitats for P. flavescens from the perspective of climate change, and provides a useful reference for biodiversity research and biological conservation.

Nanotechnology- A ray of hope for heavy metals removal

Environmental effects of heavy metal pollution are considered as a widespread problem throughout the world, as it jeopardizes human health and also reduces the sustainability of a cleaner environment. Removal of such noxious pollutants from wastewater is pivotal because it provides a propitious solution for a cleaner environment and water scarcity. Adsorption treatment plays a significant role in water remediation due to its potent treatment and low cost of adsorbents. In the last two decades, researchers have been highly focused on the modification of adsorption treatment by functionalized and surface-modified nanomaterials which has spurred intense research. The characteristics of nano adsorbents attract global scientists as it is also economically viable. This review shines its light on the functionalized nanomaterials application for heavy metals removal from wastewater and also highlights the importance of regeneration of nanomaterials in the view of visualizing the economic aspects along with a cleaner environment. The review also focused on the proper disposal of nanomaterials with crucial issues that persist in the adsorption process and also emphasize future research modification at a large-scale application in industries.

Influence of hydrochemical factors on morphometric variability of Scardinius erythrophthalmus in a freshwater river system

Studying fish growth is a complex task because growth depends on many factors. The process of fish growth is influenced by ecological factors of the water environment. Each species of fish has growth characteristics and characteristic changes in this process as a result of the action of natural and anthropogenic factors. We investigated the morphometric features of Scardinius erythrophthalmus in the hydroecosystem conditions of the Horyn River. Fish were caught by amateur fishing methods during 2018–2021 in the section of the hydrographic system of the Horyn River within the Rivne Plateau, which is the northern part of the Volhynian Upland , namely the Horyn River and its tributaries – the Zamchysko River, the Ustia River, and the Stubelka River. The catches included fish aged from 0+ (one-year-olds) to 5+ (five-year-olds). Growth variability was studied for fish aged 1+ to 4+ because their numbers were sufficient for statistical evaluation. We noticed clear features of the morphometric variability of the fish. According to the coefficient of variation for the general populations of S. erythrophthalmus from different rivers, there was mostly significant variability of such growth characteristics as the largest and smallest fish body height, total length, Smith length and short body length of fish. We also noticed the similarity of the morphometric variability of fish of different ages for the Horyn River and Stubelka River and Zamchisko River and Ustia River. The analysis and evaluation of the surface water quality of these rivers was also similar. Thus, Horyn and Stubla districts had a transitional state from II to III quality class, and the Zamchysko River and Ustya River districts had a transitional state from III to IV quality class. We conducted a multivariate regression and it revealed statistical significance and a close correlation between the coefficients of variation of the growth characteristics of fish with the phosphate content in the water (with an average value of the weighting coefficients of 0.50 ± 0.06), nitrite nitrogen (0.39 ± 0.10) and nitrate nitrogen (0.84 ± 0.34). The calculation of the specific growth of fish by full length revealed that the intensity of growth is the highest between the first and second year of life of fish for small rivers (Zamchysko River, Ustya River, Stubelka River) and between the second and third year for the Horyn River. The results presented in the article are valuable and describe the local variation in the morphometric variability of S. erythrophthalmus. This expanded the understanding of the influence of ecological factors of the aquatic environment on the formation of growth characteristics of this species of fish. In the future, our research will continue and study the linear growth of natural fish populations against the background of changes in the ecological and hydrological conditions of the studied region