Stability Of Aquatic Ecosystems Research Articles

Mechanism of transport and toxicity response of Chlorella sorokiniana to polystyrene nanoplastics

The toxicity of nanoparticles to freshwater microalgae is of significant importance in maintaining the overall stability of aquatic ecosystems. However, the transport mechanism and toxicity response of microalgae towards nanoplastics (NPs) remain to be further investigated. In this study, we examined the toxicity and internalization mechanisms of polystyrene nanoplastics (PS-NPs) in the microalga Chlorella sorokiniana. The results revealed that the PS-NPs inhibited algal cells’ growth and disrupted cell integrity upon contact, leading to cell shrinkage or rupture. Moreover, amino-modified PS-NPs (Nano-PS-NH2) exhibited greater toxicity to C. sorokiniana than carboxyl-modified PS-NPs (Nano-PS-COOH). Furthermore, significant inhibition of PS-NPs internalization was observed when four different endocytosis-related inhibitors were used, indicating that internalized PS-NPs can enter algal cells through endocytic pathways. More importantly, C. sorokiniana exposed to Nano-PS-NH2 responded to the reduction in carbon sources and energy resulting from the suppression of photosynthesis by regulating the metabolism of carbohydrates. These findings elucidate the effects of PS-NPs on C. sorokiniana, including their impact on cell morphology and metabolism, while shedding light on the internalization mechanisms of NPs by C. sorokiniana which deepen our understanding of the toxicity of nanoplastics on algae and provide important theoretical support for solving such aquatic ecological environment problems.

High-frequency data significantly enhances the prediction ability of point and interval estimation

Accurate prediction of dissolved oxygen (DO) dynamics is crucial for understanding the influence of environmental factors on the stability of aquatic ecosystem. However, limited research has been conducted to determine the optimal frequency of water quality monitoring that ensures continuous assessment of water health while minimizing costs. To address these challenges, the present study developed a hybrid stochastic hydrological model (i.e., ARIMA-GARCH hybrid model) and machine learning (ML) models. The objective of this study is to identify the best-performing model and establish the optimal monitoring frequency. Results revealed that high-frequency DO monitoring data exhibit greater variability compared to low-frequency data. Moreover, the ARIMA-GARCH model demonstrates promising potential in predicting DO concentrations for low-frequency monitoring data, surpassing ML models in performance. Furthermore, increasing the monitoring frequency significantly improves the prediction accuracy of models, regardless of whether point (with lower R2 values of 0.64 and 0.51 for daily detection than these of every 15 min (0.96 and 0.99) at CHQ and LHT, respectively) or interval predictions (with RIW higher values of 2.00 and 1.55 for daily detection higher than these of 0.02 and 0.16 in every 15 min at CHQ and LHT, respectively) are considered. Additionally, a 4 hourly monitoring frequency was found to be optimal for water quality assessment using each model. These findings identify the superior performing of the ARIMA-GARCH model and highlight the crucial role of monitoring frequency in enhancing DO prediction and improving model performance.

Shifting enzyme activity and microbial composition in sediment coregulate the structure of an aquatic plant community under polyethylene microplastic exposure

It has been shown that microplastics (MPs) interfere with critical biological processes (including development, growth and fitness); however, there is no information about the impact of MPs on plant productivity and community structure in freshwater ecosystems. Here, we investigated the effects of two sizes (MIC: 20–300 μm, MAC: 2–3 mm) and three concentrations (0.03 %, 0.3 %, and 0.6 %) of low-density polyethylene MPs on submerged plant communities. The results showed that plant responses to MPs were species specific, which can affect plant community structure. For canopy-forming species (Hydrilla verticillata), total biomass increased by 4 %–46 % and relative abundance increased by 23 %–34 % under MP exposure, while rosette-forming species (Vallisneria natans) decreased by 44 %–67 % in total biomass and relative abundance decreased by 54 %–71 %. Myriophyllum spicatum growth was largely unaffected by MPs. Community diversity was negatively correlated with MAC treatments, and the community root to shoot ratio decreased by 40 %, while community productivity increased by 41 % at a 0.6 % MAC concentration. Although MPs did not change the microbial community composition, alpha diversity was reduced at the 0.6 % concentration. It is worth noting that 0.6 % is a higher concentration than most field sediment investigations. During the experiment, the activity of functional enzymes related to carbon and nitrogen increased under most MP treatments. Structural equation modelling showed that MIC changed the community structure mainly by driving sediment enzyme activity, while MAC changed the community structure mainly by driving plant growth. The results implied that MPs may affect sediment enzymatic activities, microbial alpha diversity and aquatic plant growth, potentially altering the diversity and stability of aquatic ecosystems.

Numerical study on regime shifts in an urban subtropical shallow lake: Xinglong Lake, China

Aquatic ecosystem degradation is a considerable challenge of global interest. Although substantial efforts have been accomplished to restore phytoplankton-dominated shallow lakes to a clear state with high coverage of submerged macrophytes, the phenomenon, driving mechanism, and threshold range of such nonlinear regime shifts remain unclear. Here, we constructed an aquatic ecological model based on PCLake, simulated and predicted the aquatic ecological changes before and after treatments of Xinglong Lake, a subtropical artificial shallow lake that had been completed ecological restoration in Chengdu, China. The model included the future prediction of TN, TP, Chl-a, and aquatic vegetation biomass, as well as the threshold of regime shifts using bifurcation analysis. We also quantified the impact of some common management measures (point and non-point source pollution control, water level regulation) on the stability of the lake's aquatic ecosystem. The results showed that the thresholds of Xinglong Lake from a clear state to a turbid state were 1.405 mg/m2/day and vice versa 0.68 mg/m2/day, indicating its initial turbidity and transitional state after treatment. After treatment, phosphorus loads still exceeded the threshold for a clear-water state, while the non-point source pollution of Xinglong Lake accounted for more than 80%. To prevent the aquatic ecosystem from collapsing in the future, it is necessary to combine upstream water quality improvement, runoff and air pollution control to reduce total pollution by 60%. Reasonable water level regulation, such as adjusting the water level downwards by 0.5 m in spring, is beneficial in maintaining the health and stability of aquatic ecosystems. The present study can be used to evaluate the effectiveness of the management measures of Xinglong Lake as well as to provide scientific support for the management of shallow lakes.

Distribution Characteristics and Influencing Factors of Abundant and Rare Planktonic Microeukaryotes in Jinsha River

Planktonic microeukaryotes are usually composed of a few abundant species and a large number of rare species, which play an important role in maintaining the health and stability of aquatic ecosystems. At present, little is known about the biogeographical distribution patterns of these two groups of microeukaryotes in large damming rivers. This study analyzed the distribution patterns of abundant and rare planktonic microeukaryotes and the dominant factors affecting their spatial distributions in the Jinsha River, one of the largest rivers in southwestern China that is strongly regulated by cascade dams. The results showed that the alpha diversity of planktonic microeukaryotes in the Jinsha River was higher in the cascade dam reach than that in the upstream natural reach, and the increase in alpha diversity of rare species was larger than that of rich species. There were significant differences in microbial community composition among different river sections, and the relative abundances of the dominant genera such as Vermamoeba shared by them were also significantly different between the two river sections. The results of distance decay analysis revealed that the geographic distribution patterns of rare and abundant taxa were jointly influenced by environmental heterogeneity and dispersal limitation, and the results of variance decomposition analysis and partial Mantel further indicated that dispersal limitation was the dominant ecological process. The results provided data support for the distribution and ecological response of microorganisms in rivers in the areas lacking data in Southwest China.

Quantitative Analysis of Forest Water COD Value Based on UV–vis and FLU Spectral Information Fusion

As an important ecosystem on the earth, forests not only provide habitat and food for organisms but also play an important role in regulating environmental elements such as water, atmosphere, and soil. The quality of forest waters directly affects the health and stability of aquatic ecosystems. Chemical oxygen demand (COD) is commonly used to assess the concentration of organic matter and the pollution status of water bodies, which is helpful in assessing the impact of human activities on forest ecosystems. To effectively measure the COD value, water samples were prepared from Purple Mountain in Nanjing and nearby rivers and lakes. Using ultraviolet–visible (UV–vis) and fluorescence (FLU) spectroscopy combined with data fusion, the COD values of the forest water were accurately measured. Due to the large dimensionality of spectral data, the successive projections algorithm (SPA) and competitive adaptive reweighted sampling (CARS) were applied to the selection of characteristic wavelengths. By establishing a discriminant model for single-level data and using the voting mechanism to fuse the output results of different models, a relatively high determination coefficient (R2) of 0.9932 and a low root-mean-square error (RMSE) of 0.4582 were obtained based on the decision-level data fusion model. Compared with the single-spectrum and feature-level fusion models, the decision-level fusion scheme achieves an efficient, comprehensive, and accurate quantification of the water COD value. This study has important applications in forest protection, water resources management, sewage treatment, and the food processing field.

Behavioural responses of fishes to anthropogenic disturbances: Adaptive value and ecological consequences.

Aquatic ecosystems are changing at an accelerating rate because of human activities. The changes alter the abundance and distribution of fishes, with potential consequences for ecosystem structure and function. Behavioural responses often underlie these changes in population dynamics, such as altered habitat choice or foraging activity. Here, we present a framework for understanding how and why behaviour is affected by human activities and how the behavioural responses in turn influence higher ecological levels. We further review the literature to assess the present state of the field and identify gaps in our knowledge. We begin with discussing the factors that determine how an individual responds to a change in the environment and whether the response is adaptive or not. In particular, we explain the importance of the evolutionary history of the species. We then search the literature to assess our current knowledge of the impact of human disturbances on the behaviour of fishes and the consequences for ecosystems. The search reveals that much attention has been directed to the impact of human activities on the behaviour of fishes, but that worryingly little is known about the consequences of these responses for populations, communities and ecosystems. Yet, behavioural responses can have profound ecological consequences given that behaviour underly many, if not most, species interactions. Thus, more attention should be paid to the mechanisms and pathways through which behavioural responses influence higher ecological levels. Such information is needed if we are to determine the ultimate effects of human activities on biodiversity and the function and stability of aquatic ecosystems.

Spatiotemporal changes of bacterial communities during a cyanobacterial bloom in a subtropical water source reservoir ecosystem in China

Cyanobacterial blooms, which not only threaten the health and stability of aquatic ecosystems but also influence the microbial community within, emerges as one of the most concerning problems in China. However, how cyanobacterial blooms affect the spatiotemporal variation of aquatic microbial communities remains relatively unclear. In this study, we used high-throughput sequencing to investigate how the cyanobacterial and bacterial community spatiotemporally vary along with main cyanobacterial bloom phases in upstream rivers of a eutrophicated water source reservoir. Both cyanobacterial and bacterial diversities in each river were significantly lower (P < 0.05) during the bloom outbreak phase, showing the apparent influence of cyanobacterial bloom. Dominant cyanobacterial taxa included Cyanobacteriales and Synechococcales, and dominant bacterial taxa comprised Acinetobacter, CL500-29, hgcI clade, Limnohabitans, Flavobacterium, Rhodoluna, Porphyrobacter, Rhodobacter, Pseudomonas, and Rhizobiales, whose changes of relative abundance along with the bloom indicated distinct community composition. Non-metric multidimensional scaling analysis proved that community composition had significant difference amongst bloom phases. Linear discriminant analysis (LDA) with LDA effect size analysis (LEfSe) identified unique dominant cyanobacterial and bacterial OTUs at different phases in each river, indicating spatiotemporal variations of communities. Canonical correlation analysis or redundancy analysis revealed that at different bloom phases communities of each river had distinct correlation patterns with the environmental parameters (temperature, ammonium, nitrate, and total phosphorus etc.), implying the spatial variations of microbial communities. Overall, these results expand current understanding on the spatiotemporal variations of microbial communities due to cyanobacterial blooms. Microbial interactions during the bloom may shed light on controlling cyanobacterial blooms in the similar aquatic ecosystems.

Geographic range size, water temperature, and extrinsic threats predict the extinction risk in global cetaceans.

Despite the fact that cetaceans provide significant ecological contributions to the health and stability of aquatic ecosystems, many are highly endangered with nearly one-third of species assessed as threatened with extinction. Nevertheless, to date, few studies have explicitly examined the patterns and processes of extinction risk and threats for this taxon, and even less between the two subclades (Mysticeti and Odontoceti). To fill this gap, we compiled a dataset of six intrinsic traits (active region, geographic range size, body weight, diving depth, school size, and reproductive cycle), six environmental factors relating to sea surface temperature and chlorophyll concentration, and two human-related threat indices that are commonly recognized for cetaceans. We then employed phylogenetic generalized least squares models and model selection to identify the key predictors of extinction risk in all cetaceans, as well as in the two subclades. We found that geographic range size, sea surface temperature, and human threat index were the most important predictors of extinction risk in all cetaceans and in odontocetes. Interestingly, maximum body weight was positively associated with the extinction risk in mysticetes, but negatively related to that for odontocetes. By linking seven major threat types to extinction risk, we further revealed that fisheries bycatch was the most common threat, yet the impacts of certain threats could be overestimated when considering all species rather than just threatened ones. Overall, we suggest that conservation efforts should focus on small-ranged cetaceans and species living in warmer waters or under strong anthropogenic pressures. Moreover, further studies should consider the threatened statusof species when superimposing risk maps and quantifying risk severity. Finally, we emphasize that mysticetes and odontocetes should be conserved with different strategies, because their extinction risk patterns and major threat types are considerably different. For instance, large-bodied mysticetes and small-ranged odontocetes require special conservation priority.

Shifts in microbial communities in shallow lakes depending on trophic states: Feasibility as an evaluation index for eutrophication

Microbial communities are an important component of aquatic ecosystems. They play active roles in the biogeochemical cycles of organic matter and nutrients to maintain the health and stability of aquatic ecosystems. In the present study, the shifts in microbial communities in overlying water of 15 shallow lakes with different trophic states in Hubei Province (China) were assessed using Illumina MiSeq sequencing technology. The results revealed that the proteobacteria to be the most abundant phylum in lakes with different trophic states. Mesotrophic lakes were found to be similar to moderately eutrophic lakes in terms of the microbial community composition, the interrelation between microbial communities, and expression level of metabolic pathways. In mesotrophic and moderately eutrophic lakes, Bacillus and Pseudomonas were the dominant genera in overlying water. In lakes with less eutrophication, the microbial diversity tended to be higher. Lightly eutrophic lakes had the most microbial species; however, the interaction between microorganisms was the weakest in these lakes and the internal steady-state balance of the lakes was most susceptible to being broken. These results indicate that lightly eutrophication may be one of the most unstable transition states in the eutrophication process. Particulate organic matter, chlorophyll-a, and ammonium nitrogen were the main drivers affecting the distribution of microbial communities in the overlying water of lakes with different trophic states. In addition, the correlation between microbial communities and lake trophic states was analyzed based on the bacterial eutrophic index (BEI). An obvious positive correlation was noted between BEI and the trophic level index (TLI), indicating that microbial communities could play a role as biological factors in the evaluation of lake trophic states along with other known physicochemical indicators.

Microplastics can affect the trophic cascade strength and stability of plankton ecosystems via behavior-mediated indirect interactions

The negative effects of microplastics on the normal growth of aquatic organisms have been well studied, but relatively little is known about their potential adverse effects on the function and stability of aquatic ecosystems. We investigated here the effects of polyethylene (PE) microplastics on several aspects of plankton ecosystems, including Daphnia magna behavior, the grazing rate of D. magna on Chlorella vulgaris cells, trophic-cascade effects in the C. vulgaris-D. magna-larval damselfly food chain, the life-history of D. magna, and the stability and persistence of the D. magna-larval damselfly system. PE microplastics decreased the D. magna grazing rate as a result of reductions in their heart rate and hopping frequency. In the trophic-cascade experiment, PE microplastics increased the foraging success of larval damselflies on grazers due to hopping inhibition in grazers, which ultimately strengthened the trophic-cascade effect on algal growth. Long-term exposure to PE microplastics reduced the stability and persistence of the grazer population via increased predation risk and reduced reproductive capacity for grazer species. This study provides evidence that microplastics can affect the trophic cascade strength and stability of plankton ecosystems via behavior-mediated indirect interactions, suggesting that microplastics have more extensive impacts on aquatic ecosystems than presently recognized. Enviromental implicationThe massive production and environmental releasing of microplastics have become ubiquitous in the global environment. The negative effects of microplastics on the normal growth of aquatic organisms have been well studied, but little is known about potential adverse effects on the function and stability of aquatic ecosystems. Here, we found that microplastics increased the positive impacts of larval damselflies on algal growth, and reduced the stability and persistence of plankton ecosystems via a behavior-mediated indirect interaction. To our knowledge, this is the first systematic study assessing the effects of microplastics on the community-level characteristics of a freshwater ecosystem. SynopsisPE microplastics affect trophic cascade strength and reduce the stability and persistence of plankton ecosystems via behavior-mediated indirect interactions.

A case for seaweed aquaculture inclusion in U.S. nutrient pollution management

Seaweed aquaculture is capable of removing large quantities of nitrogen and phosphorus from coastal ecosystems, yet seaweed has gained little traction for its potential role in targeted nutrient assimilation. Marine nutrient pollution is increasing around the world, contributing to expanding eutrophic conditions and co-occurring with other stressors that impact the state and stability of aquatic ecosystems. In the United States, climate change, legacy nitrogen, and nonpoint source pollution make it increasingly difficult to curb growing eutrophication and the associated effects, such as hypoxia (dissolved oxygen < 2 mgL-1). Employing a synthetic semi-quantitative approach, we use the Gulf of Mexico as a case study – a U.S. priority area for aquaculture with substantial nutrient pollution and one of the largest hypoxic zones on the planet – to assess the potential for native seaweed aquaculture to augment upstream pollution control with downstream nutrient assimilation. Results from this analysis suggest that given growing market demand, new product pathways, and nutrient pollution markets, seaweed aquaculture may be a feasible tool for nutrient assimilation that could subsidize, if not pay for itself.

北方寒冷干旱地区内陆湖泊生态安全评价指标体系研究——以呼伦湖为例

呼伦湖作为我国北方寒冷干旱地区内陆湖泊的典型代表，在涵养水源、调节气候、防风固沙及维系呼伦贝尔草原生态系统平衡乃至我国北方生态安全屏障等方面发挥着不可替代的作用。准确识别呼伦湖流域主要生态安全问题、完善其生态安全评价指标体系对于科学研判呼伦湖生态环境状况、维持区域可持续发展及精准实施底线管控政策具有重要意义。在遥感影像、地面调查、实验模拟等多尺度数据分析基础上，结合历史资料收集、专家咨询、部门访谈等方式分析识别了呼伦湖区域生态安全问题及成因：（1）气候暖干化及超载放牧等因素使得草地退化显著，土地沙化、盐碱化面积扩大；（2）草原退化增加了干草入湖、大气干湿沉降及水土流失等水环境污染负荷；（3）气候暖干化造成湿地萎缩，加之长期的过度捕捞等人类活动使得渔业资源枯竭、鱼类小型化特征显著，水生生态系统稳定性下降，蓝藻水华频发。在全面诊断分析区域生态安全问题的基础上，以山水林田湖草系统方法论为理论指导，以改善呼伦湖流域生态环境质量为核心目标，依据评价指标的针对性、科学性、可操作性及系统性原则，采用压力-状态-响应（Pressure-State-Response，PSR）模型，以气象条件、人口、水资源、水环境压力及人类活动等5个一级指标构成的压力子系统，以水环境状况、水生态状况、陆域生态状况、生态系统服务功能和敏感性、景观格局及生态风险等6个指标构成的状态子系统，以生态治理措施及生态治理投入等2个指标构成的响应子系统，共同组成了一套包含13个一级指标38个二级指标的天空地一体、陆湖统筹的生态安全评价指标体系，以期为呼伦湖及北方寒冷干旱区类似湖泊的生态安全评价研究提供借鉴。;Hulun Lake, as a typical representative of inland lakes in the cold and arid areas of northern China, plays an irreplaceable role in water conservation, climate regulation, windbreak, and sand fixation. This lake maintains balance in the Hulun Buir grassland ecosystem and even the ecological-security barrier of northern China. Thus, identifying the main ecological-security problems in Hulun Lake Basin and improving its ecological-security evaluation index system are highly significant. The obtained data can be used for the scientific research and assessment of the ecological environment status of Hulun Lake, the maintenance of regional sustainable development, and the accurate implementation of bottom-line management and control policy.Based on remote-sensing imagery, ground survey, experimental simulation, and other multi-scale data analyses, this paper aims to analyze and identify the ecological-security problems of Hulun Lake area and their causes by combining historical data collection, expert consultation, and department interview. The results are as follows:(1) warm and dry climate, overgrazing, and other factors induce significant grassland degeneration, so land desertification and salinization area expand. (2) grassland degradation increases water-pollution load, such as hay into lake, atmospheric dry and wet settlement, and soil erosion. (3) climate warming and drying cause wetland shrinkage. Long-term overfishing and other human activities lead to the depletion of fishery resources and significant fish miniaturization. Consequently, the stability of aquatic ecosystem is reduced, and blue-green algal blooms occur frequently. Based on the comprehensive diagnosis and analysis of regional ecological-security problems, together with theoretical guidance by the methodology of mountains, rivers, forests, fields, lakes, and grass-system methodology, and improving the ecological environment quality of Hulun Lake basin as the core goal, the pressure-state-response (PSR) model is adopted in the present study according to the principles of focalization, scientific nature, operability, and systematicness of evaluation indices. The pressure subsystem comprises five first-class indicators, namely, meteorological conditions, population, water resources, water environment pressure, and human activities. The state subsystem comprises six indicators, namely, water environment, water ecology, land ecosystem, ecosystem service function and sensitivity, landscape pattern, and ecological risk. The response subsystem comprises two indicators, namely, ecological-management measures and ecological-management investment. Then, they jointly form an ecological-security evaluation index system with the integration of sky and land and the overall planning of land and lake, which includes 13 first-class indicators and 38 second-class indicators, to serve as a reference for studying the ecological-security evaluation of Hulun Lake and similar lakes in cold and arid areas.

Model of interaction of pollution with aquatic technogenically loaded ecosystem

Scientific researches are devoted to the development of the theory of functional stability of ecosystems, as the stability of the functional of ecological safety. The conceptual (system of views of ensuring the ecosystem functional stability) and theoretical (the idea is comprehensively researched using scientifically-based approaches, methods, techniques, algorithms and mathematical models) of the theory of functional stability of ecosystems are offered. The theoretical bases of sustainable development of technogenically loaded ecosystems under conditions of synergism of components of ecological danger of different genesis are considered. On the example of the model of interaction of pollution of aquatic ecosystem its stability is investigated. The processes are described by Lot-Volterra type equations. This uses a modification of the first Lyapunov method, which is designed to study the stability of aquatic ecosystems of non-autonomous differential equations. For this purpose, a family of linear operators is constructed and the stability of systems of differential equations is determined by the signs of their logarithmic norms. Criteria for stability and asymptotic stability of fixed points by Lyapunov were obtained in the model of interaction of pollution with the aquatic ecosystem. The proposed method can be used to study a wide range of other ecosystems.

Biodegradation of Chiral Flufiprole in Chlorella pyrenoidosa: Kinetics, Transformation Products, and Toxicity Evaluation.

Pesticide pollution of surface water represents a considerable risk for algae and thus affects the structure and stability of aquatic ecosystems. To investigate the risk of flufiprole to phytoplankton, the digestion and uptake of flufiprole as well as the toxic effects of flufiprole enantiomers and the six metabolites to Chlorella pyrenoidosa were investigated. Flufiprole enantiomers were mainly metabolized to flufiprole amide and detrifluoromethylsulfinyl flufiprole in culture medium, while various metabolites were formed in algae, notably the amide derivative and fipronil. Chlorella pyrenoidosa showed a strong absorption capacity for the flufiprole series. The EC50 values (96 h) indicated that fipronil was the most toxic compound, approximately 5 times as toxic as rac-flufiprole. R-flufiprole was more toxic than S-flufiprole. The contents of chlorophylls, malondialdehyde (MDA), reactive oxygen species (ROS), and total antioxidant capacity (T-AOC) were significantly altered by the chemicals in most cases, especially fipronil. Our results supported the potential detrimental effect of the metabolites of flufiprole on algae.

Mechanisms of trophic niche compression: Evidence from landscape disturbance.

Natural and anthropogenic disturbances commonly alter patterns of biodiversity and ecosystem functioning. However, how networks of interacting species respond to these changes remains poorly understood. We described aquatic food webs using invertebrate and fish community composition, functional traits and stable isotopes from twelve agricultural streams along a landscape disturbance gradient. We predicted that excessive deposition of fine inorganic sediment (sedimentation) associated with agricultural activities would negatively influence aquatic trophic diversity (e.g. reduced vertical and horizontal trophic niche breadths). We hypothesized that multiple mechanisms might cause trophic niche 'compression', as indicated by changes in realized trophic roles. Food-web properties based on consumer stable isotope data (δ13 C and δ15 N) showed that increasing sediment disturbance was associated with reduced trophic diversity. In particular, the aquatic invertebrate community occupied a smaller area in isotopic niche space along the sedimentation gradient that was best explained by a narrowing of the invertebrate community δ13 C range. Decreased niche partitioning, driven by increasing habitat homogeneity, environmental filtering and resource scarcity all seemingly lead to greater trophic equivalency caused by the collapse of the autochthonous food-web channel. Bayesian mixing-model analyses supported this contention with invertebrate consumers increasingly reliant on detritus along the sedimentation gradient, and predatory invertebrates relying more on the prey using these basal resources. The narrowing of the fish community δ13 C range along the sedimentation gradient contributed to an apparent 'trophic shift' towards terrestrial carbon, further indicating the loss of the autochthonous food-web channel. On the vertical trophic niche axis, fish became increasingly separated from aquatic invertebrates with an increase in their estimated trophic position. In combination, these responses were most likely mediated through reduced fish densities and a diminished reliance on aquatic prey. Although species losses remain a major threat to ecosystem integrity, the functional roles of biota that persist dictate how food webs and ecosystem functioning respond to environmental change. Sedimentation was associated with nonlinear reductions in trophic diversity which could affect the functioning and stability of aquatic ecosystems. Our study helps explain how multiple mechanisms may radically reshape food-web properties in response to this type of disturbance.

Predicting cyanobacteria bloom occurrence in lakes and reservoirs before blooms occur

With increased global warming, cyanobacteria are blooming more frequently in lakes and reservoirs, severely damaging the health and stability of aquatic ecosystems and threatening drinking water safety and human health. There is an urgent demand for the effective prediction and prevention of cyanobacterial blooms. However, it is difficult to effectively reduce the risks and loss caused by cyanobacterial blooms because most methods are unable to successfully predict cyanobacteria blooms. Therefore, in this study, we proposed a new cyanobacterial bloom occurrence prediction method to analyze the probability and driving factors of the blooms for effective prevention and control. Dominant cyanobacterial species with bloom capabilities were initially determined using a dominant species identification model, and the principal driving factors of the dominant species were then analyzed using canonical correspondence analysis (CCA). Cyanobacterial bloom probability was calculated using a newly-developed model, after which, the probable mutation points were identified and thresholds for the principal driving factors of cyanobacterial blooms were predicted. A total of 141 phytoplankton data sets from 90 stations were collected from six large-scale hydrology, water-quality ecology, integrated field surveys in Jinan City, China in 2014–2015 and used for model application and verification. The results showed that there were six dominant cyanobacterial species in the study area, and that the principal driving factors were water temperature, pH, total phosphorus, ammonia nitrogen, chemical oxygen demand, and dissolved oxygen. The cyanobacterial blooms corresponded to a threshold water temperature range, pH, total phosphorus (TP), ammonium nitrogen level, chemical oxygen demand, and dissolved oxygen levels of 19.5–32.5 °C, 7.0–9.38, 0.13–0.22 mg L−1, 0.38–0.63 mg L−1, 10.5–17.5 mg L−1, and 4.97–8.28 mg L−1, respectively. Comparison with research results from other global regions further supported the use of these thresholds, indicating that this method could be used in habitats beyond China. We found that the probability of cyanobacterial bloom was 0.75, a critical point for prevention and control. When this critical point was exceeded, cyanobacteria could proliferate rapidly, increasing the risk of cyanobacterial blooms. Changes in driving factors need to be rapidly controlled, based on these thresholds, to prevent cyanobacterial blooms. Temporal and spatial scales were critical factors potentially affecting the selection of driving factors. This method is versatile and can help determine the risk of cyanobacterial blooms and the thresholds of the principal driving factors. It can effectively predict and help prevent cyanobacterial blooms to reduce the global probability of occurrence, protect the health and stability of water ecosystems, ensure drinking water safety, and protect human health.

Phytoremediation of Cd, Ni, Pb and Zn by Salvinia minima

Most metals disperse easily in environments and can be bioconcentrated in tissues of many organisms causing risks to the health and stability of aquatic ecosystems even at low concentrations. The use of plants to phytoremediation has been evaluated to mitigate the environmental contamination by metals since they have large capacity to adsorb or accumulate these elements. In this study we evaluate Salvinia minima growth and its ability to accumulate metals. The plants were cultivated for about 60 days in different concentrations of Cd, Ni, Pb and Zn (tested alone) in controlled environmental conditions and availability of nutrients. The results indicated that S. minima was able to grow in low concentrations of selected metals (0.03 mg L−1 Cd, 0.40 mg L−1 Ni, 1.00 mg L−1 Pb and 1.00 mg L−1 Zn) and still able to adsorb or accumulate metals in their tissues when cultivated in higher concentrations of selected metals without necessarily grow. The maximum values of removal metal rates (mg m2 day−1) for each metal (Cd = 0.0045, Ni = 0.0595, Pb = 0.1423 e Zn = 0.4046) are listed. We concluded that S. minima may be used as an additional tool for metals removal from effluent.

Metabolic power of aquatic ecosystems as a measure of their stability to external effects

117 The problem of stability of aquatic ecosystems has become urgent due to intensification of human eco� nomic activity. The limits of stability of aquatic eco� systems determine the highest possible anthropogenic loads, an excess of which can lead to irreversible deg� radation of ecosystems. Thereupon stability is consid� ered as one of the main characteristics of aquatic eco� systems. The notion of stability in scientific literature is diverse and vague to a certain degree. In one review [1] 163 notions of ecological stability based on 70 differ� ent concepts of stability were analyzed. In our work we do not consider the problem of stability in detail but touch upon the assessment of stability in different regimes of functioning of aquatic ecosystems. As was published earlier [2, 3], the ratio of destruc� tion to primary production can be considered as a measure of thermodynamic order of the ecosystem and the rate of changes of the ratio of destruction to primary production can be considered as a thermody� namic criterion of evolution of the ecosystem state. Numerous experiments which have been conducted over 20 years in field models (mesocosms) have dem� onstrated that the known principles of functioning of dissipative systems can be applied for description of the evolution of the state of aquatic ecosystems sub� jected to the impact of hazardous pollutants [4–9]. Analysis of the dynamics of production and destruc� tion processes in the phase space { R/P; Δ(R/Р) ⋅ Δt –1 }, where R is destruction and P is the gross primary pro� duction, made it possible to determine the following main patterns of the ecosystem functioning on the basis of these criteria: undisturbed ecosystems have the minimum density of the phase space; the density of the phase space increases in response to the external effect; the transition of the ecosystem from one state to another occurs after bifurcation not gradually but spasmodically; the presence of attractors has been revealed in the phase space; and a shift of the impact stationary region in the phase space along the R/P axis is observed [10, 11].

Oscillations of algal biomass, nutrients and dissolved oxygen as a measure of ecosystem stability

Graphic presentation of weekly rates of change of algal biomass (expressed as chlorophyll a) and nutrient and dissolved oxygen concentrations can be regarded as harmonic oscillation motion. Maximum amplitudes of these oscillations provide a useful tool to assess the degree of stability of aquatic ecosystems in relation to their trophic state. Data sets from seven different lakes ranging from hypereutrophic to oligo-mesotrophic were processed using a computerized method. The high values of oscillation amplitudes of approximately 150 μg l−1 wk−1 chlorophyll a, 500 μg l−1 wk−1 ammonia nitrogen, 50 μg l−1 wk−1 soluble reactive phosphorus and 10 mg l−1 wk−1 dissolved oxygen, indicated strong ecosystem instability, while low values of less than 10 μg l−1 wk−1 of chlorophyll a, 20 μg l−1 wk−1 ammonia nitrogen, 2 μg l−1 wk−1 soluble reactive phosphorus, and 3 mg l−1 wk−1 dissolved oxygen represented a stable system. Oscillation amplitudes of the chlorophyll a values were found to be the most representative indicator of ecosystem stability.