Different facets of alpha and beta diversity of benthic diatoms along stream watercourse in a large near-natural catchment.

Understanding the processes and mechanisms that shape the distribution patterns and variations of biodiversity along spatial gradients continues to be a priority for ecological research. We focused on the biodiversity of benthic diatom communities within a large near-natural watershed. The objectives are: (1) to explore the overall spatial patterns of benthic diatom biodiversity; (2) to investigate the effects associated with watercourse position and environmental variables, as well as both common and rare species on two facets (i.e., taxonomic and functional) of alpha and beta diversity; and (3) to unveil the mechanisms underlying their spatial variations. Alpha diversity indices along the stream watercourse showed a clear increasing trend from upstream to downstream sites. Results of random forest regression identified conductivity as the primary factor influencing functional alpha diversity, while elevation emerged as the predominant factor for taxonomic alpha diversity. Beta diversity partitioning revealed that taxonomic beta diversity generally exceeded functional beta diversity. These diversity measures exhibited different patterns along the watercourse position: taxonomic beta diversity remained relatively consistent along the watercourse, whereas functional total beta diversity and its two components of middle stream sites were lower than those of upstream and downstream sites. Functional beta diversity was sustained by dominant and common species, while rare species made significant contributions to taxonomic beta diversity. Both taxonomic and functional beta diversity and its components displayed a stronger influence from spatial factors than from local environmental, geo-climatic, and nutrient variables. Collectively, taxonomic and functional alpha and beta diversity demonstrated distinct responses to the main environmental gradients and spatial factors within our catchment, highlighting their different insights into diatom diversity. Furthermore, research is required to assess the generalizability of our findings to similar ecosystems. In addition, this study presents opportunities for expansion to include other taxa (e.g., macroinvertebrates and fish) to gain a comprehensive understanding of the driving mechanisms behind stream biodiversity.

Predicting the governing factors for the release of colloidal phosphorus using machine learning.

Predicting the parameters that influence colloidal phosphorus (CP) release from soils under different land uses is critical for managing the impact on water quality. Traditional modeling approaches, such as linear regression, may fail to represent the intricate relationships that exist between soil qualities and environmental influences. Therefore, in this study, we investigated the major determinants of CP release from different land use/types such as farmland, desert, forest soils, and rivers. The study utilizes the structural equation model (SEM), multiple linear regression (MLR), and three machine learning (ML) models (Random Forest (RF), Support Vector Regression (SVR), and eXtreme Gradient Boosting (XGBoost)) to predict the release of CP from different soils by using soil iron (Fe), aluminum (Al), calcium (Ca), pH, total organic carbon (TOC) and precipitation as independent variables. Results show that colloidal-cations (Fe, Al, Ca) and colloidal-TOC strongly influence CP release, while bioclimatic variables (precipitation) and pH have weaker effects. XGBoost outperforms the other models with an R2 of 0.94 and RMSE of 0.09. SHapley Additive Explanations described the outcomes since XGBoost is accurate. The relative relevance ranking indicated that colloidal TOC had the highest ranking in predicting CP. This was supported by the analysis of partial dependence plots, which showed that an increase in colloidal TOC increased soil CP release. According to our research, the SHAP XGBoost model provides significant information that can help determine the variables that considerably influence CP contents as compared to RF, SVM, and MLR.

Near-natural streams: Spatial factors are key in shaping multiple facets of zooplankton α and ß 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 ß 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 ß diversity is more in the west, which may be affected by typical habitat, hydrological dynamics and underlying mechanisms. Taxonomic and phylogenetic ß diversity is dominated by turnover, and metacommunity heterogeneity is the result of substitution of species and phylogeny along environmental spatial gradients. Taxonomic and phylogenetic ß 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 ß 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.

Existing levels of biodiversity and river location may determine changes from small hydropower developments.

Global ecosystems are facing anthropogenic threats that affect their ecological functions and biodiversity. However, we still lack an understanding of how biodiversity can mediate the responses of ecosystems or communities to human disturbance across spatial gradients. Here, we examined how existing, spatial patterns of biodiversity influence the ecological effects of small hydropower plants (SHPs) on macroinvertebrates in river ecosystems. This study found that levels of biodiversity (e.g., number of species) can influence the degrees of its alterations by SHPs occurring along elevational gradients. The results of the study reveal that the construction of SHPs has various effects on biodiversity. For example, low-altitude areas with low biodiversity (species richness less than 12) showed a small increase in biodiversity compared to high-altitude areas (species richness more than 12) under SHP disturbances. The increases in the effective habitat area of the river segment could be a driver of the enhanced biodiversity in response to SHP effects. Changes in the numerically dominant species contributed to the overall level of community variation from disturbances. Location-specific strategies may mitigate the effects of SHPs and perhaps other disturbances.

Phytoplankton species composition as bioindicator in the largest fragmented channel of the Pearl River, China.

To test the serial discontinuity concept (SDC) predictions in a regulated river ecosystem, environmental parameters and phytoplankton community structure were determined in a subtropical river (China) which was regulated by 11 cascade dams. Our results showed that total phosphorus (TP) and silicate during the wet period in several dams supported the SDC predictions. Variations of phytoplankton species composition in several cascade dams, such as Datengxia (DTX) and Changzhou (CZ), also supported the SDC predictions. Moreover, the stations near the dams showed the maximum or minimum values of total species numbers in each cascade segment. Predictive model indicated that the types of phytoplankton decreased in the middle reaches, conforming to SDC predictions. In the whole system of cascading dams, an increase in silicate concentration and phytoplankton communities in the downstream was also consistent with SDC predictions. Therefore, these findings aligned with the SDC predictions in the aspects of both single dam and whole cascade dam system to some extent. In future research, our aim is to further investigate the effects of cascade damming on additional phytoplankton-related indices in this aquatic ecosystem. We hope to gather more comprehensive data to fully validate the SDC predictions.

Spatiotemporal variation in macroplastic abundances along a subtropical Austral river system.

Plastic pollution is a ubiquitous problem that poses a threat to society and the environment. The issue is especially pervasive in the aquatic environment, where large amounts of plastic debris accumulate from numerous anthropogenic pathways. Relatively little is known about the extent of macroplastics in African subtropical Austral rivers, where management strategies are lacking. This study quantifies and compares the variation in macroplastic abundances along the Mvudi River, South Africa, over four sites and four seasons. We observed a non-significant difference in macroplastic abundance and variation across sites and seasons, with pollution therefore widespread across these contexts. However, the diversity of plastic debris (i.e. γ-diversity value) decreased generally along sites, with most macroplastic items being collected during winter, and fewer macroplastic during autumn. We observed high abundances of macroplastic debris on the shoreline compared to the mainstream, with high proportional abundances of plastic bags and film (> 57.8%) macroplastic physical type across all sites and seasons. We also observed a high proportional abundance of the polymer polypropylene (> 25.3%) across seasons. The information derived from this study serves as the baseline for understanding seasonal variations in plastic debris and their driving factors on this and other subtropical Austral rivers.

Comparison of different macroinvertebrates bioassessment indices in a large near-natural watershed under the context of metacommunity theory.

The metacommunity theory proposes that community structure and biodiversity are influenced by both local processes (such as environmental filtering) and regional processes (such as dispersal). Despite the extensive use of traditional bioassessments based on species-environment relationships, the impact of dispersal processes on these assessments has been largely overlooked. This study aims to compare correlations between various bioassessment indices, including Shannon Weiner (H'), Biological Monitoring Working Party (BMWP), average score per taxon (ASPT), biotic index (BI), and EPT taxa index (EPT), based on macroinvertebrates collected from 147 sampling sites in a subtropical Chinese near-natural catchment. Modified indices were calculated by removing species strongly influenced by dispersal processes to address the influence of dispersal processes. Their relationship with environmental factors was then compared to the original indices. The study employed random forest regression (RFR) to compare the explanatory power of environmental factors using the two sets of indices. The spearman rank correlation analysis was conducted to examine the correlation between indices and environmental factors. The river health assessment was performed based on both modified and original indices. The results reveal significant differences between original and modified indices (especially H' and BI) providing a more accurate reflection of environmental conditions. Furthermore, the sensitivity of the different indices to various environmental factors varied, leading to differences in the bioassessment results between the modified and the original indices. Notably, original H', BMWP, and ASPT overestimated the bioassessment results, whereas the original BI underestimated them. These findings offer valuable insights into bioassessment and river health assessment evaluation within the catchment and other interconnected freshwater ecosystems, such as lakes, reservoirs, and wetlands. Our study underscores the importance of assessing and mitigating the impact of dispersal processes on bioassessment to obtain a more precise representation of the status of freshwater ecosystems.

Microplastic abundance, distribution, and diversity in water and sediments along a subtropical river system.

Microplastic pollution in aquatic environments has been a ubiquitous concern in recent years, owing to their rapid production combined with poor waste management practices. However, information on freshwater microplastics in the Global South is still scarce, despite growing research on freshwater microplastics in recent years, particularly within the Global North. To help address this knowledge gap, we studied water and sediment microplastic dynamics along a subtropical river system, i.e. Crocodile River around the Nelspruit City area (South Africa), across three different seasons (i.e. cool-dry, hot-dry, hot-wet) using a combination of diversity indices and multivariate analyses. Microplastics were more abundant during the cool-dry season in the surface water samples (mean 1058 particles m-3) and high during the hot-dry season (mean 568 particles kg-1 dwt) in the sediment samples. The hot-wet season had a low particle density in both surface water (mean 625 particles m-3) and sediments (mean 86 particles kg-1 dwt) samples. Microplastic shapes were dominated by fibres and fragments, with the colour scheme dominated by transparent, blue, and black. The abundance of microplastics was positively correlated with pH and resistivity, and negatively with river flow. Wastewater was attributed as a primary source of microplastics, particularly because of the observed dominant fibre microplastics, usually released during laundry. Our results suggest that Crocodile River and its tributaries are temporary sinks of microplastics during periods of low rainfall. Implications of this pollution are far-reaching, including effects on residents who are dependent on the Crocodile River as a source of drinking water and aquatic biota which may be exposed to these pollutants.

The Global Trend of Microplastic Research in Freshwater Ecosystems.

The study of microplastics and their impact on aquatic ecosystems has received increasing attention in recent years. Drawing from an analysis of 814 papers related to microplastics published between 2013 and 2022 in the Web of Science Core Repository, this paper explores trends, focal points, and national collaborations in freshwater microplastics research, providing valuable insights for future studies. The findings reveal three distinct stages of microplastics: nascent development (2013-2015), slow rise (2016-2018), and rapid development (2019-2022). Over time, the focus of research has shifted from "surface", "effect", "microplastic pollution", and "tributary" to "toxicity", "species", "organism", "threat", "risk", and "ingestion". While international cooperation has become more prevalent, the extent of collaboration remains limited, mostly concentrated among English-speaking countries or English and Spanish/Portuguese-speaking countries. Future research directions should encompass the bi-directional relationship between microplastics and watershed ecosystems, incorporating chemical and toxicological approaches. Long-term monitoring efforts are crucial to assessing the sustained impacts of microplastics.

Multiple anthropogenic stressors influence the taxonomic and functional homogenization of macroinvertebrate communities on the mainstream of an urban-agricultural river in China.

Biodiversity loss is caused by intensive human activities and threatens human well-being. However, less is known about how the combined effects of multiple stressors on the diversity of internal (alpha diversity) and multidimensional (beta diversity) communities. Here, we conducted a long-term experiment to quantify the contribution of environmental stressors (including water quality, land use, climate factors, and hydrological regimes) to macroinvertebrate communities alpha and beta diversity in the mainstream of the Songhua River, the third largest river in China, from 2012 to 2019. Our results demonstrated that the alpha and beta diversity indices showed a decline during the study period, with the dissimilarity in community composition between sites decreasing significantly, especially in the impacted river sections (upper and midstream). Despite overall improvement in water quality after management intervention, multiple human-caused stressors still have led to biotic homogenization of macroinvertebrate communities in terms of both taxonomic and functional diversities in the past decade. Our study revealed the increased human land use explained an important portion of the variation of diversities, further indirectly promoting biotic homogenization by changing the physical and chemical factors of water quality, ultimately altering assemblage ecological processes. Furthermore, the facets of diversity have distinct response mechanisms to stressors, providing complementary information from the perspective of taxonomy and function to better reflect the ecological changes of communities. Environmental filtering determined taxonomic beta diversity, and functional beta diversity was driven by the joint efforts of stressors and spatial processes. Finally, we proposed that traditional water quality monitoring alone cannot fully reveal the status of river ecological environment protection, and more importantly, we should explore the continuous changes in biodiversity over the long term. Meanwhile, our results also highlight timely control of nutrient input and unreasonable expansion of land use can better curb the ecological degradation of rivers and promote the healthy and sustainable development of floodplain ecosystems.

Macroinvertebrate diversity in relation to limnochemistry in an Austral semi-arid transboundary aquifer region pan system.

Pan-wetland systems are one of the world's essential and productive ecosystems and are considered important, unique and complex ecosystems. Anthropogenic activities around the temporary pans in the Khakhea Bray Transboundary Aquifer region are increasingly becoming a big issue of concern as this may affect pan biodiversity. The study specifically aimed to investigate spatial and temporal distributions of metal and nutrient concentrations within the pans in relation to land use, identify potential pollution sources in this water-scarce region, and assess macroinvertebrate diversity and distribution in relation to pan limnochemistry using a combination of multivariate analyses from 10 pans across three seasons. Environmental and anthropogenic variables influence water quality and the distribution of metals concentration in Khakhea-Bray pan systems. Anthropogenic activities such as animal grazing, infrastructure degradation, water withdrawal and littering have resulted in poor water quality within temporary pans, which may strongly influence macroinvertebrate diversity and distribution. Forty-one macroinvertebrate species from 5 insect orders (i.e., Coleoptera, Hemiptera, Odonata, Ephemeroptera, Diptera), Crustacea and Mollusca were identified. Significant differences were observed across the seasons for macroinvertebrate taxa, with high and low species richness being observed in autumn and winter, respectively. Water (i.e., temperature, dissolved oxygen, pH, salinity, conductivity), physical (i.e., stone composition) and sediment (i.e., sulphur, sodium) parameters were found to have a significant impact on the macroinvertebrate communities. Therefore, understanding the relationships between macroinvertebrates and their environment is crucial in understanding how the ecosystem taxa are structured and is vital for informing conservation managers on how to properly manage and protect these systems from further degradation.

Dissolved Oxygen and Water Temperature Drive Vertical Spatiotemporal Variation of Phytoplankton Community: Evidence from the Largest Diversion Water Source Area.

In order to study the vertical distribution characteristics of phytoplankton in the Danjiangkou Reservoir, the water source of the Middle Route Project of the South-North Water Diversion, seven sampling sites were set up in the Reservoir for quarterly sampling from 2017 to 2019, and water environment surveys were conducted simultaneously. The results showed that 157 species (including varieties) were identified, belonging to 9 phyla and 88 genera. In terms of species richness, Chlorophyta had the largest number of species, accounting for 39.49% of the total species. The Bacillariophyta and Cyanobacteria accounted for 28.03% and 13.38% of the total species, respectively. From the whole Danjiangkou Reservoir, the total phytoplankton abundance varied from 0.09 × 102 to 20.01 × 106 cells/L. In the vertical distribution, phytoplankton were mainly observed in the surface-thermospheric layer (I-II layer) and the bottom layer, while the Shannon-Wiener index showed a trend of gradually decreasing from the I-V layer. The Surfer model analysis showed that there was no significant stratification in the Q site's water temperature (WT) and dissolved oxygen (DO) levels in the water diversion area during the dynamic water diversion process. A canonical correspondence analysis (CCA) showed that DO, WT, pH, electrical conductivity (Cond), chemical oxygen demand (CODMn), total phosphorus (TP), ammonia nitrogen (NH4+-N), and total nitrogen (TN) had significant effects on the vertical distribution of phytoplankton (p < 0.05). A partial Mantel analysis showed that the vertical distribution of the phytoplankton community was related to WT, and the phytoplankton community structure at the other sites, except for Heijizui (H) and Langhekou (L), was affected by DO. This study has positive significance for exploring the vertical distribution characteristics of a phytoplankton community in a deep-water dynamic water diversion reservoir.

SER: An R package to characterize environmental regimes.

Environmental regimes (or environmental legacy or historical legacy) are the dynamics of environmental characteristics over a given (either long or short) time period, such as frequency of mean or extreme events and rate of change, which might be absent by using only contemporary variables. We present SER, an R package for estimating environmental regimes for different environmental variables. Using the data included in the package, several examples are shown. SER is suitable for any type of environmental or biotic variables, including nutrient concentration, light, and dissolved oxygen. In addition, by changing the argument "days_bf," it is possible to compute environmental regimes over any time period, such as days, months, or years. Our case study showed that the inclusion of environmental regimes increased the explained variation of temporal ß-diversity and its components. Environmental regimes are expected to advance the "environment-community" relationships in ecological studies. They can further be implemented in other subjects such as social science, socioeconomics, and epidemiology.

Lake morphological characteristics and climatic factors affect long-term trends of phytoplankton community in the Rotorua Te Arawa lakes, New Zealand during 23 years observation.

Monitoring the long-term dynamics of lake phytoplankton can help understand their natural temporal variability, as well as assess potential impacts of interventions aimed at improving lake ecological condition. However, investigating long-term changes in lake ecosystems has received scant attention. In the present study, we analyzed a long-term dataset of phytoplankton communities collected from 1990 to 2013 from eleven of the 12 Rotorua Te Arawa lakes in New Zealand, to explore their responses to changing abiotic conditions. We used a sequential algorithm to examine the likelihood of regime shifts in abiotic and biotic factors during the study period that could be attributable to lake interventions. Our analysis suggests that lake interventions have improved the abiotic factors, whereas the response of biotic factors was less clear. Total phosphorus levels were implicated in the decline in lake condition, including in two lakes subject to lake interventions, and in four control lakes. Both abiotic and biotic factors showed diverse trends (e.g., increase, decrease or no change), and abiotic factors had more regime shifts than biotic factors. Shifts in biotic indices also displayed time lags to shifts in abiotic factors. Long-term responses of abiotic and biotic factors were also influenced by lake morphological characteristics and climatic variables. This latter finding underscores the importance of considering lake morphological characteristics and climate changes when planning management practices. A sound understanding of resilience and threshold of phytoplankton shifts to environmental changes are needed to assess the effectiveness of previous management strategies and prioritize the future conservation efforts toward water quality goals.

How do multidimensional traits of dominant diatom Aulacoseira respond to abiotic and biotic factors in a river delta system?

Trait-based approaches are being increasingly applied in ecology, and the influence of individual-level trait variation on communities and species has been demonstrated. However, the responses of individual trait variation to environmental changes remain to be explored. To examine the indicating functions of multidimensional traits, individual-level measurements of the dominant diatom genus Aulacoseira Thwaites in the Pearl River Delta were performed, and corresponding responses of three trait indices (trait richness, trait evenness, and trait dispersion) to abiotic and biotic factors were examined. Our results indicated that the three individual trait diversity indices were regulated by different factors. Trait richness was only significantly affected by abiotic factors (temperature), while trait evenness and trait dispersion were regulated by both abiotic and biotic factors. In addition, the direct influence of abiotic factors was more significant than that of biotic factors, implying that the multidimensional trait variation of Aulacoseira was more responsive to environmental changes than to interspecific interactions. Therefore, the multidimensional trait variation of Aulacoseira could be used as an effective indicator to track environmental changes. Our study elucidated the mechanisms relating individual-level trait variation to phytoplankton community dynamics; this could improve our ability to forecast changes in ecosystem properties across environmental gradients.

Understanding the relative roles of local environmental, geo-climatic and spatial factors for taxonomic, functional and phylogenetic ß-diversity of stream fishes in a large basin, Northeast China.

The primary objective of this study was to determine the relative roles of local environmental (Local), geo-climatic (Geo), and spatial (Spatial) factors to taxonomic, functional, and phylogenetic ß-diversity of stream fish in a large basin in Northeast China. We quantified the current biodiversity patterns of fish communities in the Hun-Tai River using ß-diversity. We assessed (i) corresponding contributions of turnover and nestedness within the taxonomic, functional, and phylogenetic ß-diversity of fishes; (ii) correlations among ß-diversity facets (i.e., taxonomic, functional, and phylogenetic facets); (iii) relative contributions of Local, Geo, and Spatial factors to ß-diversity. We collected fish communities from 171 sampling sites. Mantel tests were used to examine the correlation of three facets of ß-diversity and their components (i.e., total, nestedness, and turnover). Distance-based redundancy analysis and variation partitioning assess the relative contributions of Local, Geo, and Spatial factors to ß-diversity. We found that turnover is the main driving mechanism for ß-diversity in fish. Among the facets of ß-diversity, taxonomic and phylogenetic facets have strong ecological information association. Spatial factors have a general contribution to various facets of ß-diversity and its components. From aspects of fish ß-diversity conservation, connectivity and habitat heterogeneity need to be maintained in the entire aquatic environment. In addition, protecting taxonomic ß-diversity is helpful for maintaining phylogenetic ß-diversity.

Spatial Factors Outperform Local Environmental and Geo-Climatic Variables in Structuring Multiple Facets of Stream Macroinvertebrates' ß-Diversity.

One of the key targets of community ecology and biogeography concerns revealing the variability and underlying drivers of biodiversity. Most current studies understand biodiversity based on taxonomic information alone, but few studies have shown the relative contributions of multiple abiotic factors in shaping biodiversity based on taxonomic, functional, and phylogenetic information. We collected 179 samples of macroinvertebrates in the Hun-Tai River Basin. We validated the complementarity between the three facets and components of ß-diversity using the Mantel test. Distance-based redundancy analysis and variance partitioning were applied to explore the comparative importance of local environmental, geo-climatic, and spatial factors on each facet and component of ß-diversity. Our study found that taxonomic and phylogenetic total ß-diversity was mainly forced by turnover, while functional total ß-diversity was largely contributed by nestedness. There is a strong correlation between taxonomic and phylogenetic ß-diversity. However, the correlations of functional with both taxonomic and phylogenetic ß-diversity were relatively weak. The findings of variation partitioning suggested that distinct facets and components of macroinvertebrates' ß-diversity were impacted by abiotic factors to varying degrees. The contribution of spatial factors was greater than that of the local environment and geo-climatic factors for taxonomic, functional, and phylogenetic ß-diversity. Thus, studying different facets and components of ß-diversity allows a clearer comprehension of the influence of abiotic factors on diversity patterns. Therefore, future research should investigate patterns and mechanisms of ß-diversity from taxonomic, functional, and phylogenetic perspectives.

Distinct indicators of land use and hydrology characterize different aspects of riverine phytoplankton communities.

Given the many threats to freshwater biodiversity, we need to be able to resolve which of the multiple stressors present in rivers are most important in driving change. Phytoplankton are a key component of the aquatic ecosystem, their abundance, species richness and functional richness are important indicators of ecosystem health. In this study, spatial variables, physiochemical conditions, water flow alterations and land use patterns were considered as the joint stressors from a lowland rural catchment. A modeling approach combining an ecohydrological model with machine learning was applied. The results implied that land use and flow regime, rather than nutrients, were most important in explaining differences in the phytoplankton community. In particular, the percentage of water body area and medium level residential urban area were key to driving the rising phytoplankton abundance in this rural catchment. The proportion of forest and pasture area were the leading factors controlling the variations of species richness. In this case deciduous forest cover affected the species richness in a positive way, while, pasture share had a negative effect. Indicators of hydrological alteration were found to be the best predictors for the differences in functional richness. This integrated model framework was found to be suitable for analysis of complex environmental conditions in river basin management. A key message would be the significance of forest area preservation and ecohydrological restoration in maintaining both phytoplankton richness and their functional role in river ecosystems.

Succession and Driving Factors of Periphytic Community in the Middle Route Project of South-to-North Water Division (Henan, China).

The Middle Route Project of the South-to-North Water Diversion is an artificially independent system that does not connect to other surface waters. Excessive periphyton proliferation causes a series of environmental problems in the canal. In this study, the periphyton community and environmental factors on the left and right banks of the canal in the algal growing area were investigated and sampled six times (June, September, and November of 2019 and 2020). The succession pattern of the attached organism community in the artificial canal was analyzed, and the key factors affecting the algal community were analyzed using RDA and GAM. The results showed that the seasonal variability of the environmental factors was more significant than the spatial variability. A total of 114 taxa of periphytic algae were found, belonging to seven phyla and 69 genera, and mainly composed of Bacillariophyta. Species richness was ranked as Bacillariophyta (60 taxa), Chlorophyta (31 taxa) and Cyanobacteria (15 taxa), and higher in autumn than in summer. The dominant taxa were Cymbella sp., Fragilaria sp., Navicula sp. and Diatoma sp. The abundance of periphytic algal varied from 0.07 × 105 to 8.99 × 105 ind./cm2, with trends similar to that of species richness. The redundancy analysis and generalized additive model showed that water temperature and nutrient concentration were the key factors influencing the structure of the algal community, followed by discharge rate and velocity, which were the determinants of the spatial and temporal patterns of the algal community. In view of the influence of discharge and velocity on the structure of algal communities, it is suggested that ecological scheduling could be used to regulate the structure of the algal community on the canal wall in the operation of later water division projects to ensure the safety of water division.

Evolving framework of studies on global gulf ecosystems with Sustainable Development Goals.

Gulf ecosystems provide many beneficial services to humanity and play a key role in achieving the Sustainable Development Goals (SDGs). However, the sustainability of gulf ecosystems has been severely threatened by climatic and anthropogenic stresses. Using network analysis of article records downloaded from Web of Science, we summarize the current research framework of gulf ecosystems via the perspectives of research themes, interdisciplinarity, and international collaborations. Research themes involve nutrient and eutrophication, biodiversity, mangrove and sediment pollution, and ecosystem service and climate change. Nevertheless, these themes usually focus on gulf ecosystems themselves with little consideration of their connectivity with other ecosystems. Interdisciplinarity has remained mostly within natural sciences while international collaborations exist mainly between developed and developing countries and among developed countries. Combined with the SDGs, we propose the future research framework where research themes should consider the impacts of terrestrial and freshwater ecosystems on gulf ecosystems at the watershed scale. Interdisciplinarity between natural and social and management sciences needs to be promoted by utilizing the advantages of data sciences. Collaborations with developing countries led by China, Mexico, Brazil, and India need to be strengthened. The evolved research framework could offer decision support for stakeholders to manage gulf ecosystems and achieve the SDGs.