Functional responses of aquatic invertebrates to anthropogenic stressors in riparian zones of Neotropical savanna streams

Taxonomic and functional responses of benthic macroinvertebrates to wastewater effluents in the receiving river of ecologically vulnerable karst areas in Southwest China

Discharges of wastewater effluents have a profound impact on the health of receiving river ecosystems, especially with regard to benthic macroinvertebrate communities. However, the effects of different wastewater types on the taxonomy and function of benthic macroinvertebrates in the receiving rivers in vulnerable karst regions of China are still rarely known. Here, we collected benthic macroinvertebrate samples from the Yanjin River, which could be divided into reaches mainly influenced by industrial, domestic and mixed wastewater, as well as from its adjacent Guanyinsi River, which was unaffected by wastewater. We found that both taxonomic and functional structures of benthic macroinvertebrates in the receiving river differed significantly under the influence of various wastewater types, which was linked to fluctuations in nutrient-related water quality, despite seasonal variation. Watershed-scale anthropogenic activities played important roles in determining the water quality, thereby indirectly driving the functional trait adaptation of benthic macroinvertebrate communities. Notably, we observed that the expansion of cropland dramatically decreased the functional diversities of benthic macroinvertebrates. Threshold responses of multi-faceted diversities in benthic macroinvertebrates to pollutants suggested that the critical concentrations of chemical oxygen demand (CODMn) and ammonia nitrogen (NH4-N) were 4.16 mg/L and 0.23 mg/L, respectively. Our study provided insights into the impacts of anthropogenic activities on benthic macroinvertebrates from both taxonomic and functional perspectives, highlighting the need to incorporate watershed-scale human activity management into water quality control strategies for urban river ecosystems, tailored to local conditions.

Cost-effective alternatives to facilitate biomonitoring and bioassessment of neotropical streams

A reliable response of bioindicators to environmental variation is a cornerstone for effective bioassessment and biomonitoring. Fish and aquatic macroinvertebrates are widely used as bioindicators of different human impacts in freshwater ecosystems, but the cost-effectiveness of their usage can be improved through the use of surrogates. We investigated congruence patterns between using different taxonomic and numeric resolutions for aquatic macroinvertebrates and fish to assess community-environment relationships. We also tested whether dataset characteristics (e.g., area sampled, species pool) could explain the variation in the effectiveness of using different taxonomic and numerical resolutions. We used a Brazilian nationwide database encompassing multiple datasets with a gradient of riparian deforestation each. Our findings suggest that families and genera can effectively represent macroinvertebrate genera and fish species, respectively, when using community matrices for assessing community-environment relationships, with an acceptable loss of information. EPT (Ephemeroptera, Plecoptera, and Trichoptera) and Characiformes or Siluriformes may be used as a surrogate, in some cases, for the entire assemblages of macroinvertebrates and fish, respectively, but their use may result in higher loss of information. Presence-absence data also presented a minimal loss of information compared to abundance data, for both macroinvertebrates and fish. The variation in congruence levels among macroinvertebrate datasets was less predicted by dataset characteristics than fish. Across distinct resolutions, on average, 10 % and 19 % of the variation in community composition of macroinvertebrates and fish, respectively, was explained by broad-scale environmental variables, and the effect size was negatively affected by the dataset's sample size and spatial extent for fish. Whereas identification at species (fish) and genus (macroinvertebrates) level and quantification of all individuals still provide the best scenario, we provide evidence that coarser taxonomical resolution and presence-absence data can be used as cost-effective alternatives to facilitate biomonitoring and bioassessment of freshwaters in the Neotropical region impacted by deforestation.

Biodiversity spatial distribution of benthic macroinvertebrate assemblages is influenced by anthropogenic disturbances at multiple spatial extents

Understanding the patterns and mechanisms of biodiversity and its organization in space is essential for developing effective conservation strategies. Zeta diversity is an index of how taxa are shared by several sites, providing information on how ecological filters, including anthropogenic disturbances, influence biodiversity distribution. This study documents how anthropogenic disturbances at multiple spatial extents affect the spatial variation of benthic macroinvertebrate assemblages in lotic ecosystems. To test the relation between zeta diversity and anthropogenic disturbances, we used three disturbance metrics. (a) For in-stream disturbances, we used the percentage of fine sediment in the substrate (PCT_FN). (b) For local/riparian disturbances, we used the Local Disturbance Index (LDI). (c) For catchment disturbances we used the Catchment Disturbance Index (CDI). Our results showed that differing anthropogenic disturbances were differently important for spatial biodiversity variation in benthic macroinvertebrate assemblages. Relatively rarer taxa were usually more susceptible to in-stream and local/riparian-scale disturbances or local environmental filters. On the other hand, relatively common taxa were usually more related to catchment-scale disturbances or landscape resistance to dispersal. These results indicate that conservation efforts to maintain headwater ecosystem biodiversity must incorporate multiple spatial extents because relatively rare and relatively common taxa appear to be affected to different degrees by different anthropogenic disturbances at different spatial extents.

Multiple environmental gradients shape the functional structure of macrobenthic communities across the Pacific Arctic shelf

The Pacific Arctic shelf is undergoing significant environmental changes that are expected to impact the functioning of Arctic benthic ecosystem. By utilizing trait-based methods, we can better understand the effects of environmental changes on the functional structure of macrobenthic communities, offering a more detailed interpretation that complements traditional biodiversity assessments based on community structure. Using Biological Trait Analysis (BTA), we investigated shifts in the functional composition of macrobenthic communities across the subarctic to Arctic regions of the Pacific Arctic shelf, examining how these communities are responding to various environmental gradients. The study analyzed data from 14 environmental variables and 355 taxa, using 13 functional traits coded with 51 modalities collected from 78 boxcore stations. Multivariate statistics, including fuzzy correspondence analysis (FCA) and RLQ/fourth-corner combined analysis, were utilized. We find that the northern Bering Sea (NB) and southeastern Chukchi Sea (SEC) shelves exhibit shared functional similarities (e.g., small, chitinous skeletons, gregarious behavior, and low body flexibility) and significant regional differences from other subregions. The analysis revealed that sediment characteristics and sea ice cover influenced macrobenthic trait composition. The ongoing retreat of sea ice is expected to lead to rapid functional shifts in the Pacific Arctic shelves, potentially causing the migration of smaller, deposit-feeding, shorter-lived taxa to the Arctic seas. This could result in structural transformation in Arctic communities characterized by greater longevity, suspension-feeding, and larger size. These findings can inform future polar environmental management and help develop adaptive management strategies.

Contrasting diversity patterns and drivers of aquatic macroinvertebrates in floodplain and non-floodplain wetlands

Understanding diversity patterns and underlying drivers is one of the central topics in the fields of biogeography and community ecology. Aquatic macroinvertebrates are widely distributed in various wetlands and play vital ecological roles. Previous studies mainly have focused on macroinvertebrate diversity in a single type of wetland. Our understanding of the differences in diversity patterns and underlying drivers between different wetland types remains limited. Here, we compared diversity patterns and community assembly of floodplain wetlands (FWs) and non-floodplain wetlands (NWs) in the Sanjiang Plain, Northeast China. We found that the taxonomic richness and abundance were higher in NWs than those in FWs. Nineteen taxa were identified as habitat specialists in the NWs, whereas only four taxa were designated as habitat specialists in the FWs. In addition, the FW and NW assemblages exhibited contrasting compositions. Spatial and environmental variables explained the largest variations in the macroinvertebrate assemblages of NWs and FWs, respectively. Normalised stochasticity ratios and Sloan neutral models confirmed that the macroinvertebrate community assembly of both wetland types was driven largely by stochastic processes. Stochastic processes were more prominent in shaping macroinvertebrate communities of FWs, whereas a stronger dispersal limitation was detected in NWs. Our results revealed contrasting diversity patterns and assembly mechanisms of macroinvertebrate communities in FWs and NWs. We underscore the importance of flood disturbance in shaping wetland ecosystems in the Sanjiang Plain and highlight that conservation and restoration actions cover different types of wetland habitats.

Rehabilitation of tropical urban streams improves their structure and functioning

Urban streams are affected by a complex combination of stressors, which modify physical habitat structure, flow regime, water quality, biological community composition, and ecosystem processes and services, thereby altering ecosystem structure and functioning. Rehabilitation projects have been undertaken in several countries to rehabilitate urban streams. However, stream rehabilitation is still rarely reported for neotropical regions. In addition, most studies focus on structural aspects, such as water quality, sediment control, and flood events, without considering ecosystem function indicators. Here, we evaluated the structure and functioning of three 15-y old rehabilitated urban stream sites in comparison with three stream sites in the best available ecological condition (reference), three sites with moderate habitat alteration, and three severely degraded sites. Compared to degraded streams, rehabilitated streams had higher habitat diversity, sensitive macroinvertebrate taxa richness, and biotic index scores, and lower biochemical oxygen demand, primary production, sediment deposition, and siltation. However, rehabilitated streams had higher primary production than moderate and reference streams, and lower canopy cover, habitat diversity, sensitive macroinvertebrate taxa richness, and biotic index scores than reference streams. These results indicate that rehabilitated streams have better structural and functional condition than degraded streams, but do not strongly differ from moderately altered streams, nor have they reached reference stream condition. Nonetheless, we conclude that rehabilitation is effective in removing streams from a degraded state by improving ecosystem structure and functioning. Furthermore, the combined use of functional and structural indicators facilitated an integrative assessment of stream ecological condition and distinguished stream conditions beyond those based on water quality indicators.

Organophosphate pesticide residue impact on water quality and changes in macroinvertebrate community in an Afrotropical stream flowing through farmlands

River Chanchaga has experienced significant agricultural practices around its catchment, which involved the indiscriminate use of pesticides. However, residents of the study area are not well aware of the negative impact of pesticides on water quality and macroinvertebrates. In this study, the first report on the influence of organophosphate pesticide contamination on the abundance of the macroinvertebrate community was provided. Sampling for the determination of organophosphate pesticide residues was carried out during the peak of the two seasons, while macroinvertebrates and physicochemical variables were observed for 6 months. We examined 11 organophosphate pesticide residues using gas chromatography coupled with mass spectrometry, 12 water quality variables, and 625 macroinvertebrate individuals. The concentration of recorded organophosphate pesticide residues ranged from 0.01 to 0.52 μg/L. From the Canonical Correspondence Analysis plot, malathion, chlorine, and paraffin show a positive correlation with Unima sp., Hydrocanthus sp., Chironomus sp., and Potadoma sp. At station 3, depth shows a positive correlation with Biomphalaria sp. and Zyxomma sp., indicating poor water quality as most of these macroinvertebrates are indicators of water pollution. Diuron and carbofuran show a negative correlation with Lestes sp. and Pseudocloeon sp., and these are pollution-sensitive macroinvertebrates. The total mean concentration of organophosphate pesticide residues was above international drinking water standards set by the World Health Organization except for paraffin, chlorpyrifos, and diuron. In conclusion, the observations recorded from this research are useful in managing pesticide applications around the river catchment.

Trichoptera Life Stages Present Distinct Responses to Environmental Conditions in Amazonian Streams

Biological communities have their biodiversity patterns affected by environmental, spatial, and biogeographic factors that vary from taxa to taxa, and often between life stages. This is especially true when there are differences in the habitat the species use in each of them. Individuals of the insect order Trichoptera are mostly aquatic in their larval stage and terrestrial in their adult stage, which may result in different behaviors and environmental requirements. Our goal was to evaluate the congruence between the larval and adult stages of Trichoptera in Amazonian streams regarding their abundance, richness, and assemblage composition. Additionally, we tried to identify the main environmental factors related to each life stage. For this, larvae and adults of Trichoptera were sampled in the same sites at 12 streams in the Caxiuanã National Forest, Pará state, Brazil. Adult assemblages had greater richness of genera and abundance of individuals than the larval ones, and there was no congruence in the genera composition between these life stages. Our results also showed that different environmental variables structured Trichoptera larvae and adults. Since the sampling of larvae and adults proved to be complementary in the studied streams, we advise that Trichoptera diversity surveys consider both life stages of these organisms.

Freshwater invertebrate responses to fine sediment stress: A multi-continent perspective

Excessive fine sediment (particles <2 mm) deposition in freshwater systems is a pervasive stressor worldwide. However, understanding of ecological response to excess fine sediment in river systems at the global scale is limited. Here, we aim to address whether there is a consistent response to increasing levels of deposited fine sediment by freshwater invertebrates across multiple geographic regions (Australia, Brazil, New Zealand and the UK). Results indicate ecological responses are not globally consistent and are instead dependent on both the region and the facet of invertebrate diversity considered, that is, taxonomic or functional trait structure. Invertebrate communities of Australia were most sensitive to deposited fine sediment, with the greatest rate of change in communities occurring when fine sediment cover was low (below 25% of the reach). Communities in the UK displayed a greater tolerance with most compositional change occurring between 30% and 60% cover. In both New Zealand and Brazil, which included the most heavily sedimented sampled streams, the communities were more tolerant or demonstrated ambiguous responses, likely due to historic environmental filtering of invertebrate communities. We conclude that ecological responses to fine sediment are not generalisable globally and are dependent on landscape filters with regional context and historic land management playing important roles.

Impacts of dyke systems on the distribution of benthic invertebrate communities and physicochemical characteristics of surface water in An Giang, Vietnam

The dyke system plays a vital role in cultivating rice intensively in the Vietnamese Mekong Delta, which protects rice paddy fields from annual floods. This study aimed to examine whether the full-dyke system (FD, which restricts water exchange for a long time) can cause degradation of surface water quality and reduction in benthic invertebrate biodiversity. The surface water quality and benthic invertebrate community were compared between the FD and semi-dyke systems (SD, which permits water exchange during flooding season) using a large number of samples collected seasonally in 2019. The results showed that the surface water quality within the FD system had significantly higher concentrations of TSS, COD, BOD5, N-NO3-, N-TKN, P-PO43-, and TP than compared to the SD system (p < 0.05), indicating greater pollution levels. The benthic invertebrate community was less diverse in the FD system than in the SD system. Only 17 species (belonging to 4 families) were detected in the FD system, and 30 species (belonging to 5 families) were detected in the SD system. The benthic invertebrate community structure changes and biodiversity loss were associated with degraded water quality. The P-PO43- and TP parameters were negatively correlated with the number of species, density, and biomass in the FD system and with the Shannon-Wiener (H') index in the SD system. In conclusion, the FD system has been degrading water quality and causing biodiversity loss.

Functional threshold responses of benthic macroinvertebrates to environmental stressors in reservoirs

Reservoirs are aquatic ecosystems created by humans to supply water needs. They can impair aquatic diversity due to the lack of connectivity, reduced water volume, and pressures exerted by surrounding human activities. These changes are expected to produce abrupt fluctuations in the reservoirs' environment, thus influencing the structure and functioning of aquatic communities. Therefore, this study aimed to understand the impact of a range of environmental stressors in reservoirs on benthic macroinvertebrates by analyzing their functional threshold response. Biological data were collected in six reservoirs from the semi-arid region of Northeast Brazil, as case study. A total of 37.874 benthic macroinvertebrates belonging to 35 taxa were collected. Nevertheless, almost 90% of this abundance belonged to three species alone, considered generalists, with multivoltine reproduction and from the gatherer-collectors feeding group. Increases in environmental stressors such as salinity, nitrate, ammonia, and dissolved solids led to the selection of macroinvertebrates with specific traits (e.g., protected body, gill respiration, and large body size). These functional traits showed differences in their threshold response depending on the stressors and are indicators of the effects of these stressors on the reservoirs. Some of the potential sensitive traits (with a negative threshold response to the stressor) could also associate with other stressors, demonstrating that tolerance of benthic macroinvertebrates is defined by a set of functional characteristics. Overall, the increase in stressor' gradients selected functionally tolerant organisms with high resistance capacity, but these were represented by dominant species. This resulted in low diversity in the reservoirs, which may compromise ecosystem functioning, and raises concerns about adequate management of the systems.

Taxonomic and Functional Diversity of Benthic Macroinvertebrate Assemblages in Reservoirs of South Korea

Numerous community indices have been developed to quantify the various aspects of communities. However, indices including functional aspects have been less focused on. Here, we examined how community composition varies in response to the environment and discovered the relationship between taxonomic diversity and functional diversity while considering the environment. Macroinvertebrate communities were collected from 20 reservoirs in South Korea. To characterize functional diversity, functional traits in four categories were considered: generation per year, adult lifespan, adult size, and functional feeding groups. Based on their community composition, we classified the reservoirs using hierarchical cluster analysis. Physicochemical and land use variables varied considerably between clusters. Non-metric multidimensional scaling indicated differences between reservoirs and clusters in terms of structure, functional diversity, and environmental variables. A self-organizing map was used to categorize functional traits, and network association analysis was used to unravel relationships between functional traits. Our results support the characteristics of species' survival strategies such as r- and K-selection. Functional richness exhibited a relationship with taxonomic diversity. Our findings suggest that different types of diversity could play complementary roles in identifying biodiversity. Our findings should prove useful in developing new criteria for assessing freshwater ecosystem health, as well as in evaluating and predicting future alteration of benthic macroinvertebrate communities facing anthropogenic disturbances.

Pesticides drive differential leaf litter decomposition and mosquito colonisation dynamics in lentic conditions

Global contamination of freshwater ecosystems by chemical compounds, such as pesticides, may exert high pressure on biologically-driven organic matter decomposition. These pollutants may also impair the quality of organic substrates for colonising invertebrates and reduce primary productivity by decreasing the abundance of phytoplankton. In southern Africa, increasing pesticide usage associated with macadamia plantations, in particular, presents a growing risk to freshwater ecosystems. Here, we examined macadamia (Macadamia integrifolia) leaf litter decomposition following exposure to three pesticides (i.e., Karate Zeon 10 CS (lambda-cyhalothrin), Mulan 20 AS (acetamiprid), Pyrinex 250 CS (chlorpyrifos)) used commonly in macadamia plantations, via an ex-situ microcosm approach. We examined mosquito colonisation of these microcosms as semi-aquatic macroinvertebrates which form a significant component of aquatic communities within standing waters. Macadamia leaf litter tended to decompose faster when exposed to Karate and Pyrinex pesticide treatments. Additionally, chlorophyll-a, conductivity, total dissolved solids, and pH differed among pesticide treatments and controls, with pesticides (Karate Zeon and Mulan) tending to reduce chlorophyll-a concentrations. Overall, pesticide treatments promoted mosquito (i.e., Culex spp.) and pupal abundances. In terms of dominant aquatic mosquito group abundances (i.e., Anopheles spp., Culex spp.), the effect of pesticides differed significantly among pesticide types, with Pyrinex and Mulan treatments having higher mosquito abundances in comparison to Karate Zeon and pesticide-free treatments. These findings collectively demonstrate that common pesticides used in the macadamia plantation may exert pressure on adjacent freshwater communities by shaping leaf-litter decomposition, semi-aquatic macroinvertebrate colonisation dynamics, and chlorophyll-a.

The Impacts of Different Anthropogenic Disturbances on Macroinvertebrate Community Structure and Functional Traits of Glacier-Fed Streams in the Tianshan Mountains

Macroinvertebrates are sensitive to environmental disturbances, however, the effects of human activities on macroinvertebrate community structures and functional traits in glacier-fed streams are concerning. To elucidate the effects of horse, cattle and sheep grazing, hot spring scenic development, and historic iron ore mine development on macroinvertebrate communities, we conducted a study in three glacier-fed streams of the Tianshan Mountains in northwest China in April 2021. Our results showed that the species richness and density significantly decreased due to grazing (p < 0.05). There were more taxa with resilience traits such as “small size at maturity” in the grazing stream. The EPT richness and density affected by hot spring scenic development significantly decreased compared to the undisturbed point (p < 0.05). There was a significant increase in taxa with resistance traits such as “bi-or-multivoltine” in the hot spring stream. The stream affected by historic mine development is currently in the self-recovery stage following the closure of the mine ten years ago. Additionally, the species richness, EPT richness, and density at the mining site were significantly higher than the source site (p < 0.05), reflecting that the habitat fragmentation caused by previous mining activities prevented the upward dispersal of macroinvertebrates. The taxa in the mining stream were also characterized by higher resistance traits such as “abundant occurrence in drift”. These results were attributed to the impacts of human disturbance on habitat stability, habitat heterogeneity, water quality, and material cycling of stream ecosystems, indicating human disturbance on the efficiency of resource utilization and functional diversification. In addition, our results showed that functional indicators of macroinvertebrate communities are helpful for monitoring and evaluating habitat conditions.

The ecological niche and terrestrial environment jointly influence the altitudinal pattern of aquatic biodiversity

The altitudinal distribution of biodiversity in alpine ecosystems has captured academic attention, especially in streams because of their sensitivity to climate change. In the past years, research mainly focused on understanding the role played by alpine streams' internal factors such as aquatic environmental variables, as well as physical and hydrological conditions, on the shaping of benthic macroinvertebrate communities. More recently, external factors such as terrestrial environments were included in analyses worldwide. In particular, the inherent properties constituting the ecological niche of specific species were considered as factors regulating dispersal and influencing community construction. The objective of this study was to reveal the distribution pattern and the driving factors regulating aquatic biodiversity in alpine streams. We hypothesized that the altitudinal distribution of aquatic macroinvertebrates could be explained by the interaction of the aquatic environment with both species' ecological niche and the terrestrial environment surrounding their habitat, and that rare species display a more pronounced pattern than widespread dominant species. To test these hypotheses, samples were collected from two alpine streams situated on opposite slopes of Biluo Snow Mountain in Yunnan Province, China. Results of statistical analyses showed poor explanatory power from aquatic environmental factors, while the differences in vegetation type and the ecological niche of the species played an important role in determining the distribution pattern of aquatic biodiversity. Furthermore, we found that the altitudinal distribution pattern of aquatic biodiversity exhibits a bimodal type, with rare species fitting the bimodal peaks. These findings call for a better inclusion and further investigation on the effects of the terrestrial environment on aquatic ecosystems.

Study on habitat suitability and environmental variable thresholds of rare waterbirds

The conservation level of rare waterbirds reflects the quality of the regional ecological environment and wetlands, and suitable habitat patches and good environmental conditions are bases to support the activities of rare species in habitats. Establishing these conditions is also an important goal of habitat landscape and functional restoration. However, lack of these conditions limits population protection and habitat restoration of rare species. Based on the random forest (RF) algorithm and threshold indicator taxa analysis (TITAN), this paper performed habitat suitability assessment and environmental variable threshold analysis of rare waterbird species in Yancheng coastal wetlands. The results showed that the suitable area proportion of three waterbird species at different habitat sites was less than 20%. The unsuitable area proportions of red-crowned cranes and oriental storks at the CA habitat site were the highest, reaching 86.73% and 85.17%, respectively. In addition, analysis of the importance of environmental variables showed that the main influencing variables affecting the suitable habitat distribution of the three rare waterbirds were habitat type (T_hab), habitat area (A_hab), vegetation coverage (P_fvc), distance to farmland (D_far), distance to reeds (D_ree), ponds density (Ponds), distance to water surface (D_wat) and distance to main roads or seawalls (D_swa). These variables covered the type, area, coverage and distance indicators. With the exception of D_far, Ponds and D_swa, rare waterbirds had response thresholds to each environmental indicator, and these results supported the restoration of landscape structure and function of each habitat site. This study emphasized the importance of foods, water resources and hidden conditions for habitat selection in rare waterbirds. Finally, we proposed the maintenance and restoration patterns of the landscape structure and function of rare waterbird habitats, which are available for other coastal tidal wetlands.

Artificial Plantation Responses to Periodic Submergence in Massive Dam and Reservoir Riparian Zones: Changes in Soil Properties and Bacterial Community Characteristics

Simple Summary

This study focuses on plants in riparian zones that are very vulnerable due to water stress and anthropogenic disturbances, which are particularly important regarding their ecological and environmental role. Although plants and microbiome interactions are necessary for plant nutrient acquisition, relatively little is known about the responses of roots, bulk, and rhizosphere soil microbial communities of different artificial vegetation types in riparian areas of massive dams and reservoirs. Therefore, this study aims to assess the responses of woody and herbaceous plants in the riparian zones of the Three Gorges Dam Reservoir, China. Results revealed that the weight of dominant soil bacteria in different periods, including Proteobacteria, Acidobacteria, Actinobacteria, Chloroflexi, and Cyanobacteria, was higher, and their composition was different in the rhizosphere, bulk soil, and endophyte. In the soil co-occurrence networks, the weight of soil physical properties was higher than chemical properties in the early emergence stage. The current study provides knowledge about bacteria in bulk, rhizosphere soils, and within roots in different emergence phases. Additionally, these results provide valuable information to inoculate the soil with key microbiota members by applying fertilizers, potentially improving plant and soil production and health.

Abstract

Plant and microbiome interactions are necessary for plant nutrient acquisition. However, relatively little is known about the responses of roots, bulk, and rhizosphere soil microbial communities in different artificial vegetation types (woody and herbaceous) in riparian areas of massive dams and reservoirs. Therefore, this study aims to assess such responses at elevations of 165–170 m a.s.l. in the riparian zones of the Three Gorges Dam Reservoir, China. The samples were collected containing the rhizosphere soil, bulk soil, and roots of herbaceous and woody vegetation at different emergence stages in 2018. Then, all the samples were analyzed to quantify the soil properties, bacterial community characteristics, and their interaction in the early and late emergence phases. In different periods, the weight of dominant soil bacteria, including Proteobacteria, Acidobacteria, Actinobacteria, Chloroflexi, and Cyanobacteria, was higher, and their composition was different in the rhizosphere, bulk soil, and endophytes. Moreover, the soil co-occurrence networks indicated that the weight of soil physical properties was higher than chemical properties in the early emergence stage. In contrast, the weight of chemical properties was relatively higher in the late emergence stage. Furthermore, the richness and diversity of the bacterial community were mainly affected by soil organic matter. This study suggests that these herbaceous and woody vegetation are suitable for planting in reservoir areas affected by hydrology and human disturbance in light of soil nutrients and soil microbial communities, respectively. Additionally, these results provide valuable information to inoculate the soil with key microbiota members by applying fertilizers, potentially improving plant health and soil production.

Effects of different types of land-use on taxonomic and functional diversity of benthic macroinvertebrates in a subtropical river network

Expansion of agricultural and urban areas and intensification of catchment land-use increasingly affect different facets of biodiversity in aquatic communities. However, understanding the responses of taxonomic and functional diversity to specific conversion from natural forest to agriculture and urban land-use remains limited, especially in subtropical streams where biomonitoring programs and using functional traits are still under development. Here, we conducted research in a subtropical stream network to examine the responses of macroinvertebrate taxonomic and functional diversity to different types of land-use in central China. Our results showed that medium body size, univoltine, gill respiration, and slow seasonal development were much higher in natural forest sites, while certain traits related to strong resilience and resistance (e.g., small body size, fast seasonal development, bi-or multivoltine, abundant occurrence in drift, sprawler) dominated in high-intensity agriculture and urbanization sites. We further found that land-use compromised water quality (e.g., increases in total phosphate, conductivity and water temperature) and habitat conditions (e.g., high proportion of sand and silt, gravel, and channel width) accounted for the changes in trait composition based on a combination of RLQ and fourth-corner analysis. Moreover, natural forest sites presented relatively high values of functional richness than other land-use, demonstrating the importance of natural forest maintenance to promote high levels of functional diversity. However, taxonomic diversity indexes showed higher sensitivity to distinguish different types of land-use compared to functional diversity measures. Even so, given that certain trait categories showed significant relationships with specific local environmental stressors, trait-based approaches can provide reliable evidence to diagnose the cause of impairment and complement the results of the taxonomic-based approaches. Our findings support the idea that taxonomic and functional approaches should be integrated in river restoration and land-use management.

Beta diversity of aquatic macroinvertebrate assemblages associated with leaf patches in neotropical montane streams

Over 70% of the total channel length in all river basins is formed by low order streams, many of which originate on mountaintops. Headwater streams play fundamental roles in processing and transporting terrestrial and aquatic organic matter, often harboring high biodiversity in bottom leaf patches deposited from riparian vegetation. The objective of this study was to assess the variation in taxonomic composition (measured by beta diversity of aquatic macroinvertebrates) among stream sites located in the Espinhaço Meridional Mountain Range, part of a UNESCO Biosphere Reserve in eastern Brazil. We tested two hypotheses. (a) Taxa turnover is the main reason for differences in aquatic insect assemblages within stream sites; we predicted that turnover would be higher than nestedness in all stream sites. (b) Stream site altitude and catchment elevation range are the main explanatory variables for the differences in beta diversity; we predicted that local stream site variables would account for only minor amounts of variation. In both dry and wet seasons, we sampled twice in two habitat types (five leaf patches in pools and five in riffles) in each of nine stream sites distributed in three different river basins. We computed average pairwise beta diversity among sampling stations and seasons in each stream site by using Jaccard and Bray-Curtis indices, and calculated the percentages of diversity resulting from turnover and nestedness. Finally, we tested the degree that local- or catchment-level predictor variables explained beta diversity. We found that turnover was the main component of beta diversity and that both dissolved oxygen and elevation range best explained Bray-Curtis beta diversity. These results reinforce the importance of leaf patches in montane (sky islands) Neotropical savanna streams as biodiversity hotbeds for macroinvertebrates, and that both local and landscape variables explained beta diversity.

Taxonomic and functional responses of macroinvertebrates to riparian forest conversion in tropical streams

Land use change threatens the ecological integrity of tropical rivers and streams; however, few studies have simultaneously analyzed the taxonomic and functional responses of tropical macroinvertebrates to riparian forest conversion. Here, we used community structure, functional diversity, and stable isotope analyses to assess the impacts of riparian deforestation on macroinvertebrate communities of streams in southern Mexico. Monthly sampling during the dry season was conducted in streams with riparian forest (forest streams), and in streams with pasture dominating the riparian vegetation (pasture streams). Samples were collected for water quality (physical-chemical variables, nutrient concentrations, and total suspended solids), organic matter (leaf litter abundance and algal biomass), and macroinvertebrate abundance and diversity. Higher temperature, conductivity, suspended solids, and chlorophyll a were detected in pasture streams, while nitrate concentrations and leaf litter biomass were greater in forest streams. Macroinvertebrate density was higher in pasture sites, while no differences in taxonomic diversity and richness were found between land uses. Functional evenness was greater in forest streams, while richness and divergence were similar between land uses, despite differences in taxonomic composition. Environmental variables were associated with taxa distribution but not with functional traits, suggesting current conditions still promote redundancy in ecological function. Isotopic analyses indicated consumers in pasture streams were enriched in ¹³C and ¹⁵N relative to forest streams, potentially reflecting the higher algal biomass documented in pasture systems. Isotopic niches were broader and more overlapped in pasture streams, indicating more generalist feeding habits. No significant losses of taxonomic or functional diversity were detected in pasture streams. However, changes in trophic ecology suggest landscape-level processes are altering macroinvertebrate feeding habits in streams. The changes we observed in habitat, water quality, and macroinvertebrate community were related to the removal of the riparian vegetation, suggesting the structure and function of the focal systems would benefit from riparian restoration.

The Biological Assessment and Rehabilitation of the World's Rivers: An Overview

The biological assessment of rivers i.e., their assessment through use of aquatic assemblages, integrates the effects of multiple-stressors on these systems over time and is essential to evaluate ecosystem condition and establish recovery measures. It has been undertaken in many countries since the 1990s, but not globally. And where national or multi-national monitoring networks have gathered large amounts of data, the poor water body classifications have not necessarily resulted in the rehabilitation of rivers. Thus, here we aimed to identify major gaps in the biological assessment and rehabilitation of rivers worldwide by focusing on the best examples in Asia, Europe, Oceania, and North, Central, and South America. Our study showed that it is not possible so far to draw a world map of the ecological quality of rivers. Biological assessment of rivers and streams is only implemented officially nation-wide and regularly in the European Union, Japan, Republic of Korea, South Africa, and the USA. In Australia, Canada, China, New Zealand, and Singapore it has been implemented officially at the state/province level (in some cases using common protocols) or in major catchments or even only once at the national level to define reference conditions (Australia). In other cases, biological monitoring is driven by a specific problem, impact assessments, water licenses, or the need to rehabilitate a river or a river section (as in Brazil, South Korea, China, Canada, Japan, Australia). In some countries monitoring programs have only been explored by research teams mostly at the catchment or local level (e.g., Brazil, Mexico, Chile, China, India, Malaysia, Thailand, Vietnam) or implemented by citizen science groups (e.g., Southern Africa, Gambia, East Africa, Australia, Brazil, Canada). The existing large-extent assessments show a striking loss of biodiversity in the last 2-3 decades in Japanese and New Zealand rivers (e.g., 42% and 70% of fish species threatened or endangered, respectively). A poor condition (below Good condition) exists in 25% of South Korean rivers, half of the European water bodies, and 44% of USA rivers, while in Australia 30% of the reaches sampled were significantly impaired in 2006. Regarding river rehabilitation, the greatest implementation has occurred in North America, Australia, Northern Europe, Japan, Singapore, and the Republic of Korea. Most rehabilitation measures have been related to improving water quality and river connectivity for fish or the improvement of riparian vegetation. The limited extent of most rehabilitation measures (i.e., not considering the entire catchment) often constrains the improvement of biological condition. Yet, many rehabilitation projects also lack pre-and/or post-monitoring of ecological condition, which prevents assessing the success and shortcomings of the recovery measures. Economic constraints are the most cited limitation for implementing monitoring programs and rehabilitation actions, followed by technical limitations, limited knowledge of the fauna and flora and their life-history traits (especially in Africa, South America and Mexico), and poor awareness by decision-makers. On the other hand, citizen involvement is recognized as key to the success and sustainability of rehabilitation projects. Thus, establishing rehabilitation needs, defining clear goals, tracking progress towards achieving them, and involving local populations and stakeholders are key recommendations for rehabilitation projects (Table 1). Large-extent and long-term monitoring programs are also essential to provide a realistic overview of the condition of rivers worldwide. Soon, the use of DNA biological samples and eDNA to investigate aquatic diversity could contribute to reducing costs and thus increase monitoring efforts and a more complete assessment of biodiversity. Finally, we propose developing transcontinental teams to elaborate and improve technical guidelines for implementing biological monitoring programs and river rehabilitation and establishing common financial and technical frameworks for managing international catchments. We also recommend providing such expert teams through the United Nations Environment Program to aid the extension of biomonitoring, bioassessment, and river rehabilitation knowledge globally.