Factors associated with blooms of cyanobacteria in a large shallow lake, China

Eutrophication promotes resource use efficiency and toxin production of Microcystis in a future climate warming scenario

Addressing the risks of cyanobacterial blooms and toxin production under ongoing and accelerating eutrophication and climate warming is crucial for both water ecosystem services and human health. Therefore, we here explored the interactive effects of eutrophication and warming on freshwater ecosystems, focusing on Microcystis and its cyanotoxin production. We employed a large-scale mesocosm system simulating future climate warming scenarios in concert with varying degrees of nutrient enrichment. We explored the full range of identified cyanobacterial toxins and cyanotoxin-producing genes under different experimental conditions and assessed the effects of both eutrophication and warming on both phytoplankton community structure (algal densities, community stability) and function (resource use efficiency, RUE). We show here that eutrophication increases the RUE of Microcystis and promotes an increase in toxin-producing genes, leading to a substantial increase in the dominance of Microcystis. This increase correlates with enhanced cyanotoxin production, a trend exacerbated under the influence of future climate warming, suggesting interactions between eutrophication and climate warming on Microcystis ecology and cyanotoxin dynamics. Hence, heatwaves and eutrophication lead the phytoplankton community to be dominated by a minority of algal species with higher toxic capacity. In a broader context, our study underscores the urgent need for holistic management strategies, addressing both nutrient control and climate mitigation, to effectively manage the escalating ecological risks associated with cyanobacterial dominance and toxin production.

Relationships between Legionella and Aeromonas spp. and associated lake bacterial communities across seasonal changes in an anthropogenic eutrophication gradient

Anthropogenic eutrophication of lakes threatens their homeostasis and carries an increased risk of development of potentially pathogenic microorganisms. In this paper we show how eutrophication affects seasonal changes in the taxonomic structure of bacterioplankton and whether these changes are associated with the relative abundance of pathogenic bacteria of the genera Legionella and Aeromonas. The subject of the study was a unique system of interconnected lakes in northern Poland (Great Masurian Lakes system), characterized by the presence of eutrophic gradient. We found that the taxonomic structure of the bacterial community in eutrophic lakes was significantly season dependent. No such significant seasonal changes were observed in meso-eutrophic lakes. We found that there is a specific taxonomic composition of bacteria associated with the occurrence of Legionella spp. The highest positive significant correlations were found for families Pirellulaceae, Mycobacteriaceae and Gemmataceae. The highest negative correlations were found for the families Sporichthyaceae, Flavobacteriaceae, the uncultured families of class Verrucomicrobia and Chitinophagaceae. We used also an Automatic Neural Network model to estimate the relative abundance of Legionella spp. based on the relative abundance of dominant bacterial families. In the case of Aeromonas spp. we did not find a clear relationship with bacterial communities inhabiting lakes of different trophic state. Our research has shown that anthropogenic eutrophication causes significant changes in the taxonomic composition of lake bacteria and contributes to an increase in the proportion of potentially pathogenic Legionella spp.

Distribution, driving forces, and risk assessment of 2-MIB and its producer in a drinking water source-oriented shallow lake

Freshwater blooms of harmful cyanobacteria in drinking water source-oriented shallow lakes affect public health and ecosystem services worldwide. Therefore, identifying 2-methylisoborneol (2-MIB)-producing cyanobacteria and predicting the risks of 2-MIB are critical for managing 2-MIB-infected water sources. Previous studies on the potential producers and risks of 2-MIB have focused on reservoirs or have been limited by the ecosystems of phytoplankton-dominated areas. We investigated the producers, distribution, and occurrence of 2-MIB in East Taihu Lake-a drinking water source-oriented shallow lake with macrophyte- and phytoplankton-dominated areas-from August 2020 to November 2021. We observed that Pseudanabaena sp. produces 2-MIB in this lake, as determined by the maximum correlation coefficient (R = 0.71, p < 0.001), maximum detection rate, and minimum false positive/negative ratio exhibited by this genus. Extreme odor events occurred in this lake during late summer and early autumn in 2021, with the mean 2-MIB concentration increasing to 727 ± 426 ng/L and 369 ± 176 ng/L in August and September, respectively. Moreover, the macrophyte-dominated area, particularly the wetland area, exhibited a significant decrease (p < 0.01) in bloom intensity and 2-MIB production during these extreme odor events. Pseudanabaena sp. outbreak was likely owing to eutrophication, seasonal gradients, and macrophyte reduction, considering that temporal trends were consistent with high water temperature, high total phosphorus levels, and low-light conditions. Moreover, 2-MIB production was sensitive to short-term hydrometeorological processes, with high water levels and radiant intensity enhancing 2-MIB production. The risk assessment results showed that the probability of 2-MIB concentration exceeding the odor threshold (10 ng/L) is up to 90% when the cell density of Pseudanabaena sp. reaches 1.8 × 10⁷ cell/L; this risk is reduced to 50 and 25% at densities of < 3.8 × 10⁵ cell/L and 5.6 × 10⁴ cell/L, respectively. Our findings support calls for shallow lake management efforts to maintain a macrophyte-dominated state and control odorous cyanobacteria growth.

Co-occurrence patterns and environmental factors associated with rapid onset of Microcystis aeruginosa bloom in a tropical coastal lagoon

The environmental factors contributing to the Microcystis aeruginosa bloom (hereafter referred to as Microcystis bloom) are still debatable as they vary with season and geographic settings. We examined the environmental factors that triggered Microcystis bloom outbreak in India's largest brackish water coastal lagoon, Chilika. The warmer water temperature (25.31-32.48 °C), higher dissolved inorganic nitrogen (DIN) loading (10.15-13.53 μmol L^-1), strong P-limitation (N:P ratio 138.47-246.86), higher water transparency (46.62-73.38 cm), and low-salinity (5.45-9.15) exerted a strong positive influence on blooming process. During the bloom outbreak, M. aeruginosa proliferated, replaced diatoms, and constituted 70-88% of the total phytoplankton population. The abundances of M. aeruginosa increased from 0.89 × 10⁴ cells L^-1 in September to 1.85 × 10⁴ cells L^-1 in November and reduced drastically during bloom collapse (6.22 × 10³ cells L^-1) by the late November of year 2017. The decrease in M. aeruginosa during bloom collapse was associated with a decline in DIN loading (2.97 μmol L^-1) and N:P ratio (73.95). Sentinel-3 OLCI-based satellite monitoring corroborated the field observations showing Cyanophyta Index (CI) > 0.01 in September, indicative of intense bloom and CI < 0.0001 during late November, suggesting bloom collapse. The presence of M. aeruginosa altered the phytoplankton community composition. Furthermore, co-occurrence network indicated that bloom resulted in a less stable community with low diversity, inter-connectedness, and prominence of a negative association between phytoplankton taxa. Variance partitioning analysis revealed that TSM (16.63%), salinity (6.99%), DIN (5.21%), and transparency (5.15%) were the most influential environmental factors controlling the phytoplankton composition. This study provides new insight into the phytoplankton co-occurrences and combination of environmental factors triggering the rapid onset of Microcystis bloom and influencing the phytoplankton composition dynamics of a large coastal lagoon. These findings would be valuable for future bloom forecast modeling and aid in the management of the lagoon.

Metabolomic Analysis of Microcystis aeruginosa After Exposure to the Algicide L-Lysine

The widespread occurrence of cyanobacteria blooms damages the water ecosystem and threatens the safety of potable water and human health. Exogenous L-lysine significantly inhibits the growth of a dominant cyanobacteria Microcystis aeruginosa in freshwater. However, the molecular mechanism of how lysine inhibits the growth of M. aeruginosa is unclear. In this study, both non-target and target metabolomic analysis were performed to investigate the effects of algicide L-lysine. The results showed that 8 mg L^- 1 lysine most likely disrupts the metabolism of amino acids, especially the arginine and proline metabolism. According to targeted amino acid metabolomics analysis, only 3 amino acids (L-arginine, ornithine, and citrulline), which belong to the ornithine-ammonia cycle (OAC) in arginine metabolic pathway, showed elevated levels. The intracellular concentrations of ornithine, citrulline, and arginine increased by 115%, 124%, and 19.4%, respectively. These results indicate that L-lysine may affect arginine metabolism and OAC to inhibit the growth of M. aeruginosa.

The combined impact of low temperatures and shifting phosphorus availability on the competitive ability of cyanobacteria

In freshwater systems, cyanobacteria are strong competitors under enhanced temperature and eutrophic conditions. Understanding their adaptive and evolutionary potential to multiple environmental states allows us to accurately predict their response to future conditions. To better understand if the combined impacts of temperature and nutrient limitation could suppress the cyanobacterial blooms, a single strain of Microcystis aeruginosa was inoculated into natural phytoplankton communities with different nutrient conditions: oligotrophic, eutrophic and eutrophic with the addition of bentophos. We found that the use of the bentophos treatment causes significant differences in prokaryotic and eukaryotic communities. This resulted in reduced biodiversity among the eukaryotes and a decline in cyanobacterial abundance suggesting phosphorus limitation had a strong impact on the community structure. The low temperature during the experiment lead to the disappearance of M. aeruginosa in all treatments and gave other phytoplankton groups a competitive advantage leading to the dominance of the eukaryotic families that have diverse morphologies and nutritional modes. These results show cyanobacteria have a reduced competitive advantage under certain temperature and nutrient limiting conditions and therefore, controlling phosphorus concentrations could be a possible mitigation strategy for managing harmful cyanobacterial blooms in a future warmer climate.

Assessment of a Multifunctional River Using Fuzzy Comprehensive Evaluation Model in Xiaoqing River, Eastern China

Rivers are beneficial to humans due to their multiple functions. However, human meddling substantially degrades the functions of rivers and constitutes a threat to river health. Therefore, it is vital to assess and maintain river function. This study used the Xiaoqing River in Shandong Province, China, as a case study and established a multilayered multifunctional river evaluation indicator system consisting of environmental function, ecological function, social function, and economic function. The weights of indicators were calculated using the analytic hierarchy process (AHP) and the entropy method. Furthermore, a fuzzy comprehensive evaluation model based on the Cauchy distribution function was developed to assess the operation status of each function in each river segment. The results of the indicator and criterion layers in different river sections varied. The multifunctionality of the river decreased from upstream to downstream. The Jinan section was the most multifunctional, followed by the Binzhou, Zibo, and Dongying sections, and finally the Weifang section. Through additional analysis, this study determined the constraint indicators and functions of each river section. Overall, the results reveal that the idea of a "multifunctional river" can advance the theoretical understanding of a river's function, and the fuzzy comprehensive evaluation model is demonstrated to provide fresh perspectives for evaluating river function.

Effects of lead pollution on bacterial communities in biofilm attached to submerged plants

Submerged plants and biofilms have significant advantages in hydro-ecology rehabilitation, but their tolerance and physiological responses to heavy metal stress have thus far been under-investigated. This study investigated the influence of lead on physiological and biochemical responses, as well as variation in bacterial communities and functional characteristics of submerged plant biofilms. The results showed that chlorophyll a content of two submerged plants decreased with increased lead concentration. The concentration of malondialdehyde of both submerged plants was higher under high lead concentrations than under low lead concentrations, and the concentrations of malondialdehyde and hydrogen peroxide in Vallisneria natans were more stable. The antioxidant enzyme systems of the two plants played protective roles against lead stress. High lead concentration can inhibit the bacterial community and lead to decreased diversity. The most abundant bacterial phyla were Proteobacteria (40.9%), Cyanobacteria (21.5%), and Bacteroidetes (14.3%). Proteobacteria abundance decreased with increased lead concentration, while Cyanobacteria abundance increased. The lead concentration in plants (19.7%, P < 0.01) and the lead concentration in aquatic environment (17.7%, P < 0.01) were significantly correlated with variation in bacterial communities. High lead concentration inhibits the activity of these bacteria related to the conversion of nitrogen and sulfur.

How reliable is chlorophyll-a as algae proxy in lake environments? New insights from the perspective of n-alkanes

Chlorophyll-a (Chl-a) has been employed as the "golden proxy" of algae biomass and algae cell densities in lake environments for many years. However, how reliable Chl-a is as algae proxy in lake environments needs further evaluation. Here, we take the eutrophic Lake Chaohu and 46 lakes and reservoirs across China as objects on temporal and spatial scales, respectively, to resolve this issue from the perspective of n-alkanes. Our results showed that Chl-a ranged from 10.5 to 735 μg∙L^-1 with a geometric mean of 92.4 μg∙L^-1 in Lake Chaohu. There were no statistically significant correlations between Chl-a and algae cell densities in all seasons (Pearson's correlation, p > 0.05), and also for macrophytes and terrestrial plants input (p > 0.05). It was related to the complex changes of environmental factors. By contrast, Chl-a ranged from 7.1 to 1608 μg∙L^-1 with a geometric mean of 125 μg∙L^-1 in nationwide lakes and reservoirs, and its occurrence was not only related to algae, but also associated with macrophytes and terrestrial plants (p < 0.05). In summary, Chl-a can be applied as an algae proxy, but its application is subject to certain restrictions. Besides, the multiple sources of Chl-a in lake environments may result in an overestimation of algae cell densities. Compared to Chl-a, biogenic n-heptadecane (bio C₁₇) could be regarded as a potential alternative. Hence, we compared the advantages and disadvantages of bio C₁₇ and Chl-a in the aspects of specificity, accuracy, sensitivity and applicability. We found that for most scenarios, their limitations could be surmounted by each other, but failed in some scenarios. Accordingly, an ensemble proxy system may be used for more reliable representation of algae in lake environments.

Changes in Phytoplankton Community Composition and Phytoplankton Cell Size in Response to Nitrogen Availability Depend on Temperature

The climate-driven changes in temperature, in combination with high inputs of nutrients through anthropogenic activities, significantly affect phytoplankton communities in shallow lakes. This study aimed to assess the effect of nutrients on the community composition, size distribution, and diversity of phytoplankton at three contrasting temperature regimes in phosphorus (P)–enriched mesocosms and with different nitrogen (N) availability imitating eutrophic environments. We applied imaging flow cytometry (IFC) to evaluate complex phytoplankton communities changes, particularly size of planktonic cells, biomass, and phytoplankton composition. We found that N enrichment led to the shift in the dominance from the bloom-forming cyanobacteria to the mixed-type blooming by cyanobacteria and green algae. Moreover, the N enrichment stimulated phytoplankton size increase in the high-temperature regime and led to phytoplankton size decrease in lower temperatures. A combination of high temperature and N enrichment resulted in the lowest phytoplankton diversity. Together these findings demonstrate that the net effect of N and P pollution on phytoplankton communities depends on the temperature conditions. These implications are important for forecasting future climate change impacts on the world’s shallow lake ecosystems.

Effect of Culture pH on Properties of Exopolymeric Substances from Synechococcus PCC7942: Implications for Carbonate Precipitation

The role of culture conditions on the production of exopolymeric substances (EPS) by Synechococcus strain PCC7942 was investigated. Carbonate mineral precipitation in these EPS was assessed in forced precipitation experiments. Cultures were grown in HEPES-buffered medium and non-buffered medium. The pH of buffered medium remained constant at 7.5, but in non-buffered medium it increased to 9.5 within a day and leveled off at 10.5. The cell yield at harvest was twice as high in non-buffered medium than in buffered medium. High molecular weight (>10 kDa) and low molecular weight (3–10 kDa) fractions of EPS were obtained from both cultures. The cell-specific EPS production in buffered medium was twice as high as in non-buffered medium. EPS from non-buffered cultures contained more negatively charged macromolecules and more proteins than EPS from buffered cultures. The higher protein content at elevated pH may be due to the induction of carbon-concentrating mechanisms, necessary to perform photosynthetic carbon fixation in these conditions. Forced precipitation showed smaller calcite carbonate crystals in EPS from non-buffered medium and larger minerals in polymers from buffered medium. Vaterite formed only at low EPS concentrations. Experimental results are used to conceptually model the impact of pH on the potential of cyanobacterial blooms to produce minerals. We hypothesize that in freshwater systems, small crystal production may benefit the picoplankton by minimizing the mineral ballast, and thus prolonging the residence time in the photic zone, which might result in slow sinking rates.

Associations between climate variables and water quality in low- and middle-income countries: A scoping review

Understanding how climate change will affect water quality and therefore, health, is critical for building resilient water services in low- and middle-income countries (LMICs) where the effect of climate change will be felt most acutely. Evidence of the effect of climate variables such as temperate and rainfall on water quality can generate insights into the likely impact of future climate change. While the seasonal effects on water quality are known, and there is strong qualitative evidence that climate change will impact water quality, there are no reviews that synthesise quantitative evidence from LMICs on links between climate variables and water quality. We mapped the available evidence on a range of climate exposures and water quality outcomes and identified 98 peer-reviewed studies. This included observational studies on the impact of temperature and rainfall events (which may cause short-term changes in contaminant concentrations), and modelling studies on the long-term impacts of sea level rise. Evidence on links between antecedent rainfall and microbiological contamination of water supplies is strong and relatively evenly distributed geographically, but largely focused on faecal indicator bacteria and on untreated shallow groundwater sources of drinking water. The literature on climate effects on geogenic contaminants was sparse. There is substantial research on the links between water temperature and cyanobacteria blooms in surface waters, although most studies were from two countries and did not examine potential effects on water treatment. Similarly, studies modelling the impact of sea level rise on groundwater salinity, mostly from south-Asia and the Middle East, did not discuss challenges for drinking water supplies. We identified key future research priorities based on this review. These include: more studies on specific pathogens (including opportunistic pathogens) in water supplies and their relationships with climate variables; more studies that assess likely relationships between climate variables and water treatment processes; studies into the relationships between climate variables and geogenic contaminants, including risks from heavy metals released as glacier retreat; and, research into the impacts of wildfires on water quality in LMICs given the current dearth of studies but recognised importance.

Responses of phytoplankton community structure and association to variability in environmental drivers in a tropical coastal lagoon

Spatial and seasonal heterogeneity in phytoplankton communities are governed by many biotic and abiotic drivers. However, the identification of long-term spatial and temporal trends in abiotic drivers, and their interdependencies with the phytoplankton communities' structure is understudied in tropical brackish coastal lagoons. We examined phytoplankton communities' spatiotemporal dynamics from a 5-year dataset (n = 780) collected from 13 sampling stations in Chilika Lagoon, India, where the salinity gradient defined the spatial patterns in environmental variables. Generalized additive models showed a declining trend in phytoplankton biomass, pH, and dissolved PO₄ in the lagoon. Hierarchical modelling of species communities revealed that salinity (44.48 ± 28.19%), water temperature (4.37 ± 5.65%), and season (4.27 ± 0.96%) accounted for maximum variation in the phytoplankton composition. Bacillariophyta (Indicator Value (IV): 0.74) and Dinophyta (IV: 0.72) emerged as top indicators for polyhaline regime whereas, Cyanophyta (IV: 0.81), Euglenophyta (IV: 0.79), and Chlorophyta (IV: 0.75) were strong indicators for oligohaline regime. The responses of Dinophyta and Chrysophyta to environmental drivers were much more complex as random effects accounted for ~70-75% variation in their abundances. Prorocentrum minimum (IV: 0.52), Gonyaulax sp. (IV: 0.52), and Alexandrium sp. (IV: 0.51) were potential indicators of P-limitation. Diploneis weissflogii (IV: 0.43), a marine diatom, emerged as a potential indicator of N-limitation. Hierarchical modelling revealed the positive association between Cyanophyta, Chlorophyta, and Euglenophyta whereas, Dinophyta and Chrysophyta showed a negative association with Cyanophyta, Chlorophyta, and Euglenophyta. Landsat 8-Operational Land Imager satellite models predicted the highest and lowest Cyanophyta abundances in northern and southern sectors, respectively, which were in accordance with the near-coincident field-based measurements from the lagoon. This study highlighted the dynamics of phytoplankton communities and their relationships with environmental drivers by separating the signals of habitat filtering and biotic interactions in a monsoon-regulated tropical coastal lagoon.

Reviewing Interspecies Interactions as a Driving Force Affecting the Community Structure in Lakes via Cyanotoxins

The escalating occurrence of toxic cyanobacterial blooms worldwide is a matter of concern. Global warming and eutrophication play a major role in the regularity of cyanobacterial blooms, which has noticeably shifted towards the predomination of toxic populations. Therefore, understanding the effects of cyanobacterial toxins in aquatic ecosystems and their advantages to the producers are of growing interest. In this paper, the current literature is critically reviewed to provide further insights into the ecological contribution of cyanotoxins in the variation of the lake community diversity and structure through interspecies interplay. The most commonly detected and studied cyanobacterial toxins, namely the microcystins, anatoxins, saxitoxins, cylindrospermopsins and β-N-methylamino-L-alanine, and their ecotoxicity on various trophic levels are discussed. This work addresses the environmental characterization of pure toxins, toxin-containing crude extracts and filtrates of single and mixed cultures in interspecies interactions by inducing different physiological and metabolic responses. More data on these interactions under natural conditions and laboratory-based studies using direct co-cultivation approaches will provide more substantial information on the consequences of cyanotoxins in the natural ecosystem. This review is beneficial for understanding cyanotoxin-mediated interspecies interactions, developing bloom mitigation technologies and robustly assessing the hazards posed by toxin-producing cyanobacteria to humans and other organisms.

Seasonal dynamics of the bacterial communities associated with cyanobacterial blooms in the Han River

DNA-based analyses of bacterial communities were performed to identify the bacteria co-occurring with cyanobacterial blooms in samples collected at a single site over 2 years. Microcystis aeruginosa was the most predominant species (81% in 2018, and 94% in 2019) within the phylum Cyanobacteria, and microcystins were detected during all cyanobacterial blooms. The stereo microscope and scanning electron microscope observations showed bacterial associations on and around the aggregated M. aeruginosa cells. Culture-independent analyses of filtered bacterial communities showed that the Flavobacterium species in phylum Bacteroidetes (19%) was dominant in the cyanobacterial phycosphere, followed by the Limnohabitans species in Betaproteobacteria (11%). Using principal component analysis, major bacterial genus, including Microcystis and Flavobacterium species, were clustered during cyanobacterial blooms in both years. To identify key bacterial species that develop long-term symbiosis with M. aeruginosa, another culture-independent analysis was performed after the environmental sample had been serially subcultured for 1 year. Interestingly, Brevundimonas (14%) was the most dominant species, followed by Porphyrobacter (7%) and Rhodobacter (3.5%) within the Alphaproteobacteria. Screening of 100 colonies from cyanobacterial bloom samples revealed that the majority of culturable bacteria belonged to Gammaproteobacteria (28%) and Betaproteobacteria (57%), including Pseudomonas, Curvibacter, and Paucibacter species. Several isolates of Brevundimonas, Curvibacter, and Pseudomonas species could promote the growth of axenic M. aeruginosa PCC7806. The sensitivity of M. aeruginosa PCC7806 cells to different environmental conditions was monitored in bacteria-free pristine freshwater, indicating that nitrogen addition promotes the growth of M. aeruginosa.

Does an Emissions Trading Policy Improve Environmental Efficiency? Evidence from China

An emissions trading system is a market instrument for pollution control that has been used in China for many years. The Ministry of Environmental Protection of China has approved the implementation of emissions trading pilot projects in 11 provinces since 2007, yet the effectiveness of the policy has not been comprehensively estimated. With panel data from 29 provinces and cities in China between 2003 and 2012, this study uses the data envelopment model-slack based measurement (DEA-SBM) method to measure environmental efficiency indicators and a difference in difference (DID) model to examine the impact of the emissions trading system on environmental efficiency. The results indicate that the policy has significantly improved environmental efficiency in the pilot provinces. However, the effects are heterogeneous with different efficiency levels across the diverse regions. Higher impacts were found in the central and western regions. Some suggestions for the optimization of the emissions trading system are suggested in this study.

Excess nutrient loads to Lake Taihu: Opportunities for nutrient reduction

Intensive agriculture and rapid urbanization have increased nutrient inputs to Lake Taihu in recent decades. This resulted in eutrophication. We aim to better understand the sources of river export of total dissolved nitrogen (TDN) and phosphorus (TDP) to Lake Taihu in relation to critical nutrient loads. We implemented the MARINA-Lake (Model to Assess River Inputs of Nutrients to seAs) model for Lake Taihu. The MARINA-Lake model quantifies river export of dissolved inorganic and organic N and P to the lake by source from sub-basins. Results from the PCLake model are used to identify to what extent river export of nutrients exceeds critical loads. We calculate that rivers exported 61 kton of TDN and 2 kton of TDP to Lake Taihu in 2012. More than half of these nutrients were from human activities (e.g., agriculture, urbanization) in Sub-basins I (north) and IV (south). Most of the nutrients were in dissolved inorganic forms. Diffuse sources contributed 90% to river export of TDN with a relatively large share of synthetic fertilizers. Point sources contributed 52% to river export of TDP with a relatively large share of sewage systems. The relative shares of diffuse and point sources varied greatly among nutrient forms and sub-basins. To meet critical loads, river export of TDN and TDP needs to be reduced by 46-92%, depending on the desired level of chlorophyll-a. There are different opportunities to meet the critical loads. Reducing N inputs from synthetic fertilizers and P from sewage systems may be sufficient to meet the least strict critical loads. A combination of reductions in diffuse and point sources is needed to meet the most strict critical loads. Combining improved nutrient use efficiencies and best available technologies in wastewater treatment may be an effective opportunity. Our study can support the formulation of effective solutions for lake restoration.

Highly time-resolved analysis of seasonal water dynamics and algal kinetics based on in-situ multi-sensor-system monitoring data in Lake Taihu, China

Predicting algal blooms is challenging due to rapid growth rates under suitable conditions and the complex physical, chemical, and biological processes involved. Physico-chemical parameters, monitored in this study by a high-resolution in-situ multi-sensor system and derived from lab-based water sample analyses, show the seasonal variation and have different degrees of vertical gradients across the water column. Through analyzing the changes and relations between multi-factors, we reveal pictures of water quality dynamics and algal kinetics. Nitrate has regular seasonal changes different to the seasonal patterns of total dissolved Phosphorus. Positive correlations are found between Chlorophyll a fluorescence and temperature, wind-induced resuspension and mixing promote the augment of Cyanobacteria fluorescence (Phycocyanin) signal. While the resuspension can also result in the increase of turbidity and affect the light environment for hydrophytes, the algal scums are the main reason for the high turbidity on the surface, which lower the illumination radiation in the water body. Those parameters are the primary dominants responsible for the change of algae from our monitoring data, which could be used as indicators for the dynamic changes of algae in the future.

Multiple biomarker responses in caged benthic gastropods Bellamya aeruginosa after in situ exposure to Taihu Lake in China

BACKGROUND

Freshwater sediments have been recognized as a long-term sink and potential source for environmental pollutants released into the aquatic ecosystems. In this study, the sediment quality of Taihu Lake, which is susceptible to anthropogenic contamination, was assessed by a combination of chemical analytical and biological end points. Specifically, the snail Bellamya aeruginosa was caged in situ at two locations representing different pollution levels for different exposure times (7, 14 and 21 days). At each of these time points, biochemical parameters, i.e., phase I biotransformation enzymes ethoxyresorufin-O-deethylase (EROD), the antioxidant enzymes superoxide dismutase and catalase, reactive oxygen species, protein carbonyl content and lipid peroxidation, were evaluated in the hepatopancreas of snails. In addition, surface sediments were collected for analysis of contaminants of concern, including inorganic pollutants, organochlorine pesticides, polychlorinated biphenyls and polybrominated diphenyl ethers.

RESULTS

Chemical analyses revealed that sediments from Taihu Lake were contaminated with trace elements and organic pollutants. Concentrations of trace elements (Cu, Ni and As) and organochlorinated pesticides (4,4'-DDE) exceeded their corresponding threshold effect level according to the sediment quality assessment values for freshwater ecosystems in Canada, indicating that adverse biological effects may occur. All biomarkers, except EROD activity, were induced in snails during all exposure times. The integrated biomarker response index (IBR) indicated that during the initial exposure phase (7 days), B. aeruginosa were subjected to significant environmental stress, which diminished during later sampling time points.

CONCLUSIONS

Results showed that IBR correlated well with the levels of environmental contaminants, demonstrating the applicability of this biomonitoring approach to complex environmental exposure scenarios.