Identifying spatio-temporal dynamics of trace metals in shallow eutrophic lakes on the basis of a case study in Lake Taihu, China

Effect of pH, Temperature, and Salinity Levels on Heavy Metal Fraction in Lake Sediments

Heavy metals (HMs) in aquatic environments are characterized by high toxicity, a propensity for bioaccumulation, and non-degradability, and pose significant risks to biological communities. Previous studies of HMs in lakes have shown that the physical and chemical characteristics of the lake water may control both the migration of HMs in the sediments and the concentration of heavy metals in the lake water. In fact, the change in aquatic environments changes the heavy metal fraction in the sediment, which controls the release of HMs. In this paper, we investigated the effects of the pH, temperature, and salinity levels of overlying water on the chemical fraction of Cu and Zn in Wuliangsuhai Lake surface sediments. The results show that lower water pH and higher water salinity and temperature could increase Cu and Zn release from the sediment. An increase in pH led to changes in the speciation of solid fractions of Zn, namely increases in the residual fraction and decreases in the organic matter and sulfide, whereas acid-extractable and Fe-Mn oxide fractions remained largely the same. Increases in temperature and salinity led to opposite changes in the speciation of solid fractions, namely decreases in the residual fraction and increases in the organic matter and sulfide and Fe-Mn oxide fractions, whereas acid-extractable fractions remained largely the same. The effect of pH, temperature, and salinity on Cu fractions in the solids was much smaller. According to the ratio of the secondary phase to the primary phase (RSP), acidic, high-temperature, and high-salt conditions increase the release risks of Zn. Changes in water temperature have the greatest influence on the risk of Zn and Cu release from sediments, followed by the influence of salinity changes.

Exploring the primary magnetic parameters affecting chemical fractions of heavy metal(loid)s in lake sediment through an interpretable workflow

The magnetic properties of lake sediments account for close relationships with heavy metal(loid)s (HMs), but little is known about their relationships with chemical fractions (CFs) of HMs. Establishing an effective workflow to predict HMs risk among various machine learning (ML) methods in conjunction with magnetic measurement remains challenging. This study evaluated the simulation efficiency of nine ML methods in predicting the risk assessment code (RAC) and ratio of the secondary and primary phases (RSP) of HMs with magnetic parameters in sediment cores of a shallow lake. The sediment cores were collected and sliced, and the total amount and CFs of HMs, as well as magnetic parameters, were determined. Support vector machine (SVM) outperformed other models, as evidenced by coefficient of determination (R2) > 0.8. Interpretable machine learning (IML) methods were employed to identify key indicators of RAC and RSP among the magnetic parameters. Values of χARM, HIRM, χARM/χ, and χARM/SIRM of sediments ranging in 220-500 × 10-8 m3/kg, 30-40 × 10-5Am2/kg, 15-25, and 0.5-1, respectively, indicated the potential ecological risks of Cd, Hg, and Sb. This study offers new perspectives on the risk assessment of HMs in lake sediments by combining magnetic measurement with IML workflow.

Microcystis blooms caused the decreasing richness of and interactions between free-living microbial functional genes in Lake Taihu, China

Microcystis blooms have a marked effect on microbial taxonomical diversity in eutrophic lakes, but their influence on the composition of microbial functional genes is still unclear. In this study, the free-living microbial functional genes (FMFG) composition was investigated in the period before Microcystis blooms (March) and during Microcystis blooms (July) using a comprehensive functional gene array (GeoChip 5.0). The composition and richness of FMFG in the water column was significantly different between these two periods. The FMFG in March was enriched in the functional categories of nitrogen, sulfur, and phosphorus cycling, whereas the FMFG in July was enriched in carbon cycling, organic remediation, and metal homeostasis. Molecular ecological network analysis further demonstrated fewer functional gene interactions and reduced complexity in July than in March. Module hubs of the March network were mediated by functional genes associated with carbon, nitrogen, sulfur, and phosphorus, whereas those in July by a metal homeostasis functional gene. We also observed stronger deterministic processes in the FMFG assembly in July than in March. Collectively, this study demonstrated that Microcystis blooms induced significant changes in FMFG composition and metabolic potential, and abundance-information, which can support the understanding and management of biogeochemical cycling in eutrophic lake ecosystems.

Effects of sediment dredging on freshwater system: a comprehensive review

As a common geo-engineering method to control internal load of nutrients and pollutants, sediment dredging has been used in many freshwater basins and has achieved certain effects. However, dredging can disturb water bodies and substrates and cause secondary pollution. It negatively affects the water environment system mainly from the following aspects. Dredging suddenly changes the hydrological conditions and many physical indicators of the water body, which will cause variations in water physicochemical properties. For example, changes in pH, dissolved oxygen, redox potential, transparency, and temperature can lead to a series of aquatic biological responses. On the other hand, sediment resuspension and deep-layer sediment exposure can affect the cycling of nutrients (e.g., nitrogen, phosphorus), the release and valence conversion of heavy metals, and the desorption and degradation of organic pollutants in the overlying water. This can further affect the community structure of aquatic organisms. The aim of this paper is to analyze the relevant literature on freshwater sediment dredging, and to summarize the current knowledge of the potential environmental risks caused by the dredging and utilization of freshwater sediments. Based on this, the paper attempts to propose suggestions to mitigate these adverse environmental impacts. These are significant contributions to the development of environmentally friendly freshwater sediment dredging technologies.

Biophotoelectrochemical process co-driven by dead microalgae and live bacteria

Anaerobic reduction processes in natural waters can be promoted by dead microalgae that have been attributed to nutrient substances provided by the decomposition of dead microalgae for other microorganisms. However, previous reports have not considered that dead microalgae may also serve as photosensitizers to drive microbial reduction processes. Here we demonstrate a photoelectric synergistic linkage between dead microalgae and bacteria capable of extracellular electron transfer (EET). Illumination of dead Raphidocelis subcapitata resulted in two-fold increase in the rate of anaerobic bioreduction by pure Geobacter sulfurreducens, suggesting that photoelectrons generated from the illuminated dead microalgae were transferred to the EET-capable microorganisms. Similar phenomena were observed in NO3- reduction driven by irradiated dead Chlorella vulgaris and living Shewanella oneidensis, and Cr(VI) reduction driven by irradiated dead Raphidocelis subcapitata and living Bacillus subtilis. Enhancement of bioreduction was also seen when the killed microalgae were illuminated in mixed-culture lake water, suggesting that EET-capable bacteria were naturally present and this phenomenon is common in post-bloom systems. The intracellular ferredoxin-NADP+-reductase is inactivated in the dead microalgae, allowing the production and extracellular transfer of photoelectrons. The use of mutant strains confirmed that the electron transport pathway requires multiheme cytochromes. Taken together, these results suggest a heretofore overlooked biophotoelectrochemical process jointly mediated by illumination of dead microalgae and live EET-capable bacteria in natural ecosystems, which may add an important component in the energetics of bioreduction phenomena particularly in microalgae-enriched environments.

Investigation of cytotoxic cadmium in aquatic green algae by synchrotron radiation-based Fourier transform infrared spectroscopy: Role of dissolved organic matter

The heavy metal Cd can cause severe toxicity on aquatic algae, but there are few studies on the cytotoxicity of heavy metal on algae based on synchrotron radiation technology. In this study, synchrotron radiation-based Fourier transform infrared spectromicroscopy (SR-FTIR) was used to characterize in vivo the toxic effects of Cd on Cosmarium sp. cells, emphasizing the influence of dissolved organic matter (DOM) on Cd toxicity. Results showed that, in the absence of DOM, obvious growth inhibition, cell volume reduction, and photosynthesis disruption could be observed with increasing Cd concentrations (0-500 μg/L). Based on the SR-FTIR imaging and functional group quantification, it was shown that the biosynthesis of biomolecules such as proteins, lipids, and carbohydrates was inhibited in algal cells. However, the addition of DOM caused significant heterogeneities in biomacromolecule biosynthesis that an increased biosynthesis of carbohydrates and structural lipids but an inhibited biosynthesis of proteins and storage lipids were observed. Furthermore, the correlation analysis and principal component analysis showed a good correlation between v(C-OH)/Amide II and biochemical parameters, indicating that changes of carbohydrates could be used as the biomarker to indicate the cytotoxicity of heavy metals to algal cells. These findings provide insight into the mechanisms of heavy metal cytotoxicity to aquatic algae and systematic cytotoxicity assessment under various aquatic conditions.

Heavy metals (HMs) pollution in the aquatic environment: Role of probiotics and gut microbiota in HMs remediation

The presence of heavy metals (HMs) in aquatic ecosystems is a universal concern due to their tendency to accumulate in aquatic organisms. HMs accumulation has been found to cause toxic effects in aquatic organisms. The common HMs-induced toxicities are growth inhibition, reduced survival, oxidative stress, tissue damage, respiratory problems, and gut microbial dysbiosis. The application of dietary probiotics has been evolving as a potential approach to bind and remove HMs from the gut, which is called "Gut remediation". The toxic effects of HMs in fish, mice, and humans with the potential of probiotics in removing HMs have been discussed previously. However, the toxic effects of HMs and protective strategies of probiotics on the organisms of each trophic level have not been comprehensively reviewed yet. Thus, this review summarizes the toxic effects caused by HMs in the organisms (at each trophic level) of the aquatic food chain, with a special reference to gut microbiota. The potential of bacterial probiotics in toxicity alleviation and their protective strategies to prevent toxicities caused by HMs in them are also explained. The dietary probiotics are capable of removing HMs (50-90%) primarily from the gut of the organisms. Specifically, probiotics have been reported to reduce the absorption of HMs in the intestinal tract via the enhancement of intestinal HM sequestration, detoxification of HMs, changing the expression of metal transporter proteins, and maintaining the gut barrier function. The probiotic is recommended as a novel strategy to minimize aquaculture HMs toxicity and safe human health.

Mobilization of colloids during sediment resuspension and its effect on the release of heavy metals and dissolved organic matter

Natural colloids are important in mobilizing pollutants in aquatic environments. This study investigated the mobilization and aggregation of natural colloids during the sediment resuspension and re-sedimentation processes using nanoparticle tracking analysis. The metals and organic matter in overlying water were divided and examined in dissolved (<0.45 μm), colloidal (3 kDa - 0.45 μm), and truly dissolved (<3 kDa) forms. Excitation emission matrix-parallel factor analysis (EEM-PARAFAC) was used to characterize the dissolved organic matter (DOM). In overlying water, most natural colloids were < 200 nm before resuspension. An evident mobilization of colloids and an increase in colloid size were observed during resuspension. The formation of particles (>0.45 μm) and decreases of small colloids (<200 nm) indicated that resuspension promoted the aggregation of colloids. Mobilization of colloids was accompanied by increases in concentrations of Fe, Al, and organic carbon in colloidal fractions, which could be related to the formation of mineral-organic complexes under an oxic environment. The release of DOM from sediments mainly contributed to the truly dissolved humic-like fraction, and colloidal organic carbon accounted for, on average, 20 % of the total dissolved organic carbon (DOC). Fe and Al had the highest colloidal proportions as they are major compositions of inorganic colloids. Substantial removal of dissolved Al, Fe, Pb, and Zn occurred when colloids aggregated in the overlying water. Although the adsorption of suspended particles may also decrease the concentrations of dissolved metals, the increased proportions of colloidal metals indicated a possible role of colloids in this process. These findings provide insight into the behavior of colloids during the resuspension process and indicate that the aggregation of colloids could promote the removal of dissolved matter.

Sub-chronic exposure to waterborne extracellular microcystin-LR impairs calcium homeostasis in rainbow trout

Fish mortality is associated with harmful algal blooms, although whether toxicity is related directly to the presence of cyanotoxins or the prevailing water chemistry remains unclear. Similarly, while planktivorous fish may be exposed to toxin through the diet, the hazard posed by waterborne extracellular toxin to carnivorous fish is less well understood. In this study rainbow trout (Oncorhynchus mykiss) were exposed for up to 28 d to waterborne microcystin-LR at nominal concentrations of 1.5 and 50 µg L^-1 (measured values 2 and 49 µg L^-1, respectively). The former represents the Canadian drinking water guideline, and the latter an elevated environmental level. This study hypothesised that waterborne toxin exposure would specifically impact gill function, and given the importance of this tissue in freshwater fish ion regulation, effects on plasma ions and branchial ion transporter activity would be observed. Microcystin-LR exposure resulted in a significant and persistent hypocalcaemia at the higher exposure concentration, but plasma sodium and branchial activities of the sodium/potassium ATPase, proton ATPase and calcium ATPase enzymes remained unaffected. An in vitro assessment failed to show any effect of microcystin-LR on branchial calcium ATPase activity even at exposure concentrations as high as 1000 µg L^-1. A transient increase in hepatic alkaline phosphatase activity was also observed at 49 µg L^-1, but there were no effects of toxin exposure on branchial or hepatic lactate dehydrogenase activity. These results suggest that microcystin-LR exposure does not have a general effect on ion regulation, but instead produces a novel and specific impact on calcium metabolism in rainbow trout, although the mechanism underlying this effect remains unknown.

Response of Cajanus cajan to excess copper in the soil: tolerance and biomass production

Soil contamination by excess heavy metals or trace elements is a global concern, as these elements are highly bioaccumulated in living organisms, migrating throughout the food chain, and causing health problems. Sustainable technologies, using plants, have been increasingly studied and used to contain, reduce, or extract these elements from the soil. In this sense, it is essential to identify plant species that tolerate certain elements, present high biomass production and are resistant to adverse soil conditions. For this reason, we evaluated the biomass production and tolerance of Cajanus cajan in response to different concentrations of copper (30, 60, 120, and 240 mg/dm³, in addition to the control treatment) in the soil, as well as the effect of this metal on photosynthetic pigments and gas exchange. C. cajan was sown in soil previously contaminated with copper sulfate and cultivated in a greenhouse for 60 days after emergence. C. cajan is copper tolerant, approximately 88% copper is accumulated in the roots and therefore there is low copper translocation to the shoot, consequently, the chlorophyll content, the net photosynthesis rate, carbon assimilation, dry biomass, the root system development, and nodulation were not affected by copper. C. cajan can be explored in strategies to improve soil conditions and is a promising species in soil phytoremediation studies.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-022-01203-6.

In-situ biological effects, bioaccumulation, and multi-media distribution of organic contaminants in a shallow lake

Anthropogenic activity-impacted aquatic environment contains a complex mixture of contaminants, and ecological risk assessment solely based on chemical analysis is insufficient and biological assessment is required. However, traditional assessment heavily relies on laboratory bioassays, which may cause uncertainty due to inevitable laboratory-related artifact. A self-designed in-situ bioassay system was successfully applied to simultaneously evaluate water and sediment toxicity by co-exposure of two native species, Chinese rare minnows (Gobiocypris rarus) and Asian clams (Corbicula fluminea) in Tai Lake Basin, China. In-situ exposure caused pronouncedly lethal and sublethal effects (i.e., metabolic and oxidative stress, neurotoxicity, reproductive toxicity) on both fish and clams. Meanwhile, multi-media distribution of organic contaminants in water-sediment-biota system was analyzed. Besides hydrophobicity, metabolism was recognized as an influential factor on phase distribution of contaminants in water-fish and sediment-clam systems. Traditional hazard quotient (HQ) method based on environmental concentrations of 98 contaminants showed bias in risk assessment. Instead, a weight of evidence method by integrating three lines of evidence, including in-situ survival, enhanced integrated biomarker response values and environmental concentrations, successfully differentiate high- and moderate-risk sites in the shallow lakes. The present study incorporated in-situ bioassays into risk assessment using a weight of evidence approach, which reduced uncertainty in decision-making.

Single toxicity of arsenic and combined trace metal exposure to a microalga of ecological and commercial interest: Diacronema lutheri

Eco-toxicological assays with species of economic interest such as Diacronema lutheri are essential for industries that produce aquaculture feed, natural food additives and also in drug developing industries. Our study involved the exposure of a single and combined toxicity of arsenic (As V) to D. lutheri for the entire algal growth phase and highlighted that a combined exposure of As V with other essential (Copper, Cu; Nickel, Ni) and non-essential (Cadmium, Cd; Lead, Pb) trace metals reduced significantly the cell number, chlorophyll a content, and also significantly increased the de-epoxidation ratio (DR) as a stress response when compared to the single toxicity of As V. Arsenic, as one of the ubiquitous trace metal and an active industrial effluent is reported to have an increased bio-concentration factor when in mixture with other trace metals in this study. In the combined exposure, the concentration of total As bio-accumulated by D. lutheri was higher than in the single exposure. Hence, polluted areas with the prevalence of multiple contaminants along with the highly toxic trace metals like As can impose a greater risk to the exposed organisms that may get further bio-magnified in the food chain. Our study highlights the consequences and the response of D. lutheri in terms of contamination from single and multiple trace metals in order to obtain a safer biomass production for the growing need of natural derivatives.

Do metals differentiate zooplankton communities in shallow and deep lakes affected by mining tailings? The case of the Fundão dam failure (Brazil)

The effects of exposure to mining tailings on water quality and biota of tropical lacustrine ecosystems remain poorly understood. We tested the hypothesis that after mining tailing spills, shallow lakes should retain higher metal concentrations in comparison with deep lakes, which might contribute to differentiating species sorting and community structure of zooplankton in both ecosystems. Surveys were performed in 6 Brazilian lakes affected by the Fundão dam failure from October 2018 to September 2019. The shallow lakes showed higher values of turbidity (19.4 ± 12.9 NTU), conductivity (846.5 ± 1727.1 μS.cm^-1), total organic carbon (11.6 ± 4.6 mg.L^-1), total nitrogen (2688.7 ± 2215.6 μg.L^-1), iron (2507.5 ± 726.9 μg.L^-1), aluminum (419.9 ± 166.5 μg.L^-1) and manganese (150.8 ± 146.2 μg.L^-1) and lower zooplankton richness (9.2 ± 3.2) compared to the deep lakes (13.4 ± 3.0), which showed higher cyanobacteria density (84.7 10³ ± 69.3 10³ cel.mL^-1). We recorded negative relationships between zooplankton richness and turbidity, conductivity, iron, zinc and vanadium, indicating that as well as morphometric characteristics of lakes (area and depth) have an important role in zooplankton richness, the coupling between metals and limnological variables represent decisive environmental filters for species sorting of zooplankton. The variation-partitioning analysis showed that limnological variables and metals explained zooplankton composition, highlighting that metals play major influence on zooplankton composition. We suggest that the shallowness of the lakes should had promoted often resuspension of mining tailings that caused increases in metal concentrations in water column. The results indicate that the shallow lakes presented higher vulnerability to mining tailings exposure than the deep lakes, which may have substantially contributed for differentiating zooplankton communities in both ecosystems. This study reveals the need for considering shallow lakes as priority target for conservation among freshwater ecosystems affected by mining tailings.

Water Quality Analysis and Evaluation of Eutrophication in a Swamp Wetland in the Permafrost Region of the Lesser Khingan Mountains, China

Wuyiling Nature Reserve is located at the edge of a frozen soil area and has abundant vegetation resources. It is an important area for evaluating the impact of frozen soil degradation on the environment. Analyzing the water quality and eutrophication characteristics of different swamps and water bodies can provide a basis for protecting the water environment of frozen soil areas. The pollution characteristics of different swamps and water bodies were analyzed and the Levenberg-Marquardt back-propagation neural network was used to evaluate water quality and eutrophication. Finally, the eutrophication evaluation was compared with the nutritional status index. The results demonstrated that (1) the highest concentrations of the total phosphorus (TP), total nitrogen, ammonia nitrogen (AN), permanganate index (PI), chemical oxygen demand, and chlorophyll were all present in the Tangwang River, which could be caused by the effects of human and agricultural activities along the river. The maximum average concentrations of TP, AN, and PI in the four wetland swamps appeared in the shrub swamp; (2) The water quality category of shrub, grass, and forest swamps in Wuyiling Nature Reserve was Class II, and the water quality category of floating swamps and the Tangwang River was Class I. The nutrient levels of the four marsh swamp wetlands and the Tangwang River were in the mid-range for many nutrients; and (3) the LM-BP neural network model, which was used to evaluate water eutrophication, and the results of a comprehensive evaluation of a nutritional status index were similar, further demonstrating the credibility of the evaluation results.

Impact of paddy fields on water quality of Gala Lake (Turkey): An important migratory bird stopover habitat

Gala Lake is an internationally important lake due to its location on one of the world's most important bird migration routes. For this reason, water quality of the lake is of great concern. However, the lake surrounded by paddy fields may face eutrophication and toxic metal contamination due to excessive use of fertilizers and pesticides. In this study, impact of paddy fields on water quality of the Gala Lake was investigated. The concentrations of metal(loid)s and physico-chemical parameters in surface water samples taken from the lake were measured and compared with water quality guidelines. Also, human health risks and contamination status of metal(loid)s were assessed. The mean NO₂, SRP and BOD concentrations in the lake exceeded the permissible levels for both salmonid and cyprinid waters. The mean BOD value indicated contaminated water quality in the lake, while mean COD and SRP values indicated lightly contaminated water quality. The mean As, Cr and Pb values in the winter exceeded the drinking water limits set by WHO and EC, while the mean Cr and Zn values exceeded the limit values for the protection of freshwater aquatic organisms set by USEPA. Similarly, heavy metal pollution index and the degree of contamination values in the winter indicated that the lake water is moderately polluted. Health risk assessment results revealed that As and Cr in the lake water via ingestion exposure pathway may pose both non-carcinogenic and carcinogenic health risks to the residents. The results of this study indicated that paddy fields are a major source of nutrients, organic matter and toxic metal(loid)s to the Gala Lake. To improve the water quality of the lake, we suggest that excessive use of fertilizers and pesticides should be controlled to reduce metal(loid) and nutrient loads from the paddy fields.

Linking pollution to biodiversity and ecosystem multifunctionality across benthic-pelagic habitats of a large eutrophic lake: A whole-ecosystem perspective

Biodiversity loss is often an important driver of the deterioration of ecosystem functioning in freshwater ecosystems. However, it is far from clear how multiple ecosystem functions (i.e., ecosystem multifunctionality, EMF) relate to biodiversity across the benthic-pelagic habitats of entire ecosystems or how environmental stress such as eutrophication and heavy metals enrichment might regulate the biodiversity-EMF relationships. Here, we explored the biodiversity and EMF across benthic-pelagic habitats of the large eutrophic Lake Taihu in China, and further examined abiotic factors underlying the spatial variations in EMF and its relationships with biodiversity. In our results, EMF consistently showed positive relationships to the biodiversity of multiple taxonomic groups, such as benthic bacteria, bacterioplankton and phytoplankton. Both sediment heavy metals and total phosphorus significantly explained the spatial variations in the EMF, whereas the former were more important than the latter. Further, sediment heavy metals mediated EMF through the diversity of benthic bacteria and bacterioplankton, while nutrients such as phosphorus in both the sediments and overlaying water altered EMF via phytoplankton diversity. This indicates the importance of pollution in regulating the relationships between biodiversity and EMF in freshwater environments. Our findings provide evidence that freshwater biodiversity loss among phytoplankton and bacteria will likely weaken ecosystem functioning. Our results further suggest that abiotic factors such as heavy metals, beyond nutrient enrichment, may provide relatively earlier signals of impaired ecosystem functioning during eutrophication process.

Effects of heavy metals speciations in sediments on their bioaccumulation in wild fish in rivers in Liuzhou-A typical karst catchment in southwest China

Although fish are widely confirmed to be susceptible to heavy metals (HMs) contamination in sediments, this bioconversion haven't been detailed. This is especially the case in karst areas, where HMs are less stably retained in the sediments and are more bioavailable. Therefore, we surveyed representative karst rivers in Liuzhou, China, in order to study the relationship between the speciations of seven HMs in the sediments with their bioaccumulation in wild fish. The results showed that the HMs in sediments are all below their permissible exposure limit (PEL), but Cd and Zn are significantly higher than soil basline. Most HMs are in residual fraction, while their exchangeable fractions are present in extremely low proportions. The concentration of Zn, Cr and Cd in some fish are above their maximum recommended limit (MRL). The concentrations of most of the HMs in the fish are significantly correlated with the levels in the sediments and given the higher correlation coefficients for their carbonate-bound phase, this phase can be seen to play a critical role in HMs bioconversion. However, the presence of this phase in low proportions enables other phases, especially oxidizable form, to play a greater role in HMs bioaccumulation. Apart from Do, HMs in the fish samples are significantly correlated with multiple environmental factors, demonstrating environmental fluctuations can manipulate HMs bioconversion from sediments; however, their significance depend heavily on the proportion of particular species. HMs in reducible and oxidizable fraction are more important in regulating, rather than promoting, their bioconversion during environmental fluctuations. Fluctuations in EC, TDS and pH can increase the impacts of HMs in carbonate-bound fraction on their bioconversion. Given the higher background values of EC and TDS and lower pH values during the monsoon period, careful attention should be paid to the increased bioconversion of HMs in karst rivers during this season.

Simulating chlorophyll-a fluorescence changing rate and phycocyanin fluorescence by using a multi-sensor system in Lake Taihu, China

Algal pollution in water sources has posed a serious problem. Estimating algal concentration in advance saves time for drinking water plants to take measures and helps us to understand causal chains of algal dynamics. This paper explores the possibility of building a short-term algal early warning model with online monitoring systems. In this study, we collected high-frequency data for water quality and weather conditions in shallow and eutrophic Lake Taihu by an in situ multi-sensor system (BIOLIFT) combined with a weather station. Extracted chlorophyll-a from water samples and chlorophyll-a fluorescence differentiated according to different algal classeses verified that chlorophyll-a fluorescence continuously measured by BIOLIFT only represent chlorophyll-a of green algae and diatoms. Stepwise linear regression was used to simulate the chlorophyll-a fluorescence changing rate of green algae and diatoms together (ΔChl_a-f%) and phycocyanin fluorescence concentration (blue-green algae) on the water surface layer (CyanoS). The results show that nutrients (total N, NO₃-N, NH₄-N, total P) were not necessary parameters for short-term algal models. ΔChl_a-f % is greatly influenced by the seasons, so seasonal partition of data before modeling is highly recommended. CyanoS_max and ΔChl_a-f% were simulated by only using multi-sensor and meteorological data (R² = 0.73; 0.75). All the independent variables (wave, water temperature, relative humidity, depth, cloud cover) used in the model were measured online and predictable. Wave height is the most important independent variable in the shallow lake. This paper offers a new approach to simulate and predict the algal dynamics, which also can be applied in other surface water.