The characteristics and environmental significance of BVOCs released by aquatic macrophytes.

Biogenic volatile organic compounds (BVOCs) emitted by plants serve crucial biological functions and potentially impact atmospheric environment and global carbon cycling. Despite their significance, BVOC emissions from aquatic macrophytes have been relatively understudied. In this study, for the first time we identified there were 68 major BVOCs released from 34 common aquatic macrophytes, and these compounds referred to alcohols, aldehydes, alkanes, alkenes, arenes, ethers, furans, ketones, phenol. For type of BVOC emissions from different life form and phylogenetic group of aquatic macrophytes, 34 of the 68 BVOCs from emergent and submerged macrophytes are classified into alkene and alcohol compounds, over 50% BVOCs from dicotyledon and monocotyledon belong to alcohol and arene compounds. Charophyte and pteridophyte emitted significantly fewer BVOCs than dicotyledon and monocotyledon, and each of them only released 12 BVOCs. These BVOCs may be of great importance for the growth and development of macrophytes, because many BVOCs, such as azulene, (E)-ß-farnesene, and dimethyl sulfide are proved to play vital roles in plant growth, defense, and information transmission. Our results confirmed that both life form and phylogenetic group of aquatic macrophytes had significantly affected the BVOC emissions form macrophytes, and suggested that the intricate interplay of internal and external factors that shape BVOC emissions from aquatic macrophytes. Thus, further studies are urgently needed to investigate the influence factors and ecological function of BVOCs released by macrophytes within aquatic ecosystem.

Influence of environmental filtering and spatial processes on macroinvertebrate community in urban lakes in the Taihu Lake Basin, China.

Studies identifying the relative importance of multiple ecological processes in macroinvertebrate communities in urban lakes at a basin scale are rare. In this study, 14 urban lakes in the Taihu Lake Basin were selected to explore the relative importance of environmental filtering and spatial processes in the assembly of macroinvertebrate communities. Our findings revealed significant spatiotemporal variations in macroinvertebrate communities, both between lakes and across seasons. We found that environmental filtering exerted a greater influence on taxonomic total beta diversity and its individual components (species turnover and nestedness) compared to spatial processes. Key environmental variables such as water depth, water temperature, total dissolved solids, chlorophyll a, and lake surface area were found to be crucial in shaping macroinvertebrate communities within these urban lakes. The observed high spatial heterogeneity in environmental conditions, along with intermediate basin areas, good connectivity and short distances between lakes, and the high dispersal ability of dominant taxa, likely contributed to the dominance of environmental filtering in macroinvertebrate community assembly. Our study contributes to a better understanding of the underlying mechanisms governing macroinvertebrate community assembly in urban lakes, thereby providing valuable insights for studies on community ecology and water environmental protection in urban lakes.

The origins of odor (ß-cyclocitral) under different water nutrient conditions: Algae or submerged plants?

Among the problems caused by water eutrophication, the issue of odor compounds has attracted notable attention. ß-Cyclocitral, a widely distributed and versatile odor compound, is commonly derived from both algae and aquatic plants. Planting aquatic plants is a common method of water purification. However, there is limited study on their impact on ß-cyclocitral levels in water. Here, we conducted a study on the ß-cyclocitral levels in water and the submerged plant leaves under three nutrient levels and six plant density treatments. Our findings revealed the following: (1) Chlorophyll-a (Chla), ß-cyclocitral in the water (Wcyc), ß-cyclocitral in Potamogeton lucens leaves (Pcyc) and the biomass of the submerged plants increase with rising nutrient concentration, which increased about 83 %, 95 %, 450 %, 320 % from eutrophic treatment to oligotrophic treatment, respectively. (2) In water, ß-cyclocitral is influenced not only by algae but also by submerged plants, with primary influencing factors varying across different nutrient levels and plant densities. The main source of ß-cyclocitral in water becomes from plants to algae as the water eutrophication and plant density decrease. (3) As submerged plants have the capability to emit ß-cyclocitral, the release of ß-cyclocitral increases with the density of submerged plants. Hence, when considering planting submerged plants for water purification purposes, it is crucial to carefully manage submerged plant density to mitigate the risk of odor pollution emanating from aquatic plants. This study offers fresh insights into selecting optimal water density for submerged plants and their role in mitigating the release of ß-cyclocitral.

Thermal stratification controls taste and odour compounds by regulating the phytoplankton community in a large subtropical water source reservoir (Xin'anjiang Reservoir).

2-Methylisoborneol (2-MIB) and geosmin are compounds released by algae that significantly degrade reservoir water quality, posing a threat to both the safety of drinking water and the quality of aquatic products sourced from these environments. However, few studies have explored how enhanced thermal stratification affects the occurrence and regulation of odorants in large drinking water reservoirs. Through systematic monitoring and investigation of Xin'anjiang Reservoir, we found that enhanced thermal stratification promotes filamentous cyanobacteria, particularly Leptolyngbya sp., as the primary contributor to 2-MIB production within the 1-10 m layer of the water column. The highest 2-MIB concentration, 92.5 ng/L, was recorded in the riverine region, which was 2.54 and 14.52 times higher than that in the transitional and central parts of the reservoir, respectively. Temperature indirectly impacted algal growth and odorant production by modulating TN/TP ratios. Geosmin concentration responded rapidly to relatively low TN/TP ratios (< 25). Our findings suggest that phosphorus control in estuaries should be enhanced during thermal stratification period. In summary, our study provides valuable insights to inform pragmatic water intake strategies and the distribution and release of odorants caused by thermal stratification. This is particularly relevant in the context of future global warming and extremely high temperatures during the warm season.

Eutrophication decreases ecological resilience by reducing species diversity and altering functional traits of submerged macrophytes.

Positive feedback is key to producing alternative stable states and largely determines ecological resilience in response to external perturbations. Understanding the positive feedback mechanisms in macrophyte-dominated lakes is crucial for resilience-based management and restoration. Based on the field investigation of submerged macrophyte communities in 35 lakes in China, we found that morphological complexity (MC) and morphological plasticity (MP) are correlated with the stoichiometric homeostasis of phosphorus (HP ) and are related to ecosystem structure, functioning, and stability. We also found that the positive feedback strength of lakes dominated by macrophytes is biomass- and diversity-dependent. Eutrophication can decrease the community biomass by decreasing community MC, MP, and HP and the species diversity through low-light availability, ultimately decreasing the positive feedback strength and resilience of clear water states. We argue that functional traits and species diversity should be considered to build more resilient ecosystems in future changing environment scenarios.

Linking the network topology of plant traits with community structure, functioning, and adaptive strategies of submerged macrophytes.

Plant trait network analysis can calculate the topology of trait correlations and clarify the complex relationships among traits, providing new insights into ecological topics, including trait dimensions and phenotypic integration. However, few studies have focused on the relationships between network topology and community structure, functioning, and adaptive strategies, especially in natural submerged macrophyte communities. In this study, we collected 15 macrophyte community-level traits from 12 shallow lakes in the Yangtze River Basin in the process of eutrophication and analyzed the changes in trait network structure (i.e., total phosphorus, TP) by using a moving window method. Our results showed that water TP significantly changed the topology of trait networks. Specifically, under low or high nutrient levels, the network structure was more dispersed, with lower connectance and higher modularity than that found at moderate nutrient levels. We also found that network connectance was positively correlated with community biomass and homeostasis, while network modularity was negatively correlated with community biomass and homeostasis. In addition, modules and hub traits also changed with the intensity of eutrophication, which can reflect the trait integration and adaptation strategies of plants in a stressful environment. At low or high nutrient levels, more modules were differentiated, and those modules with higher strength were related to community nutrition. Our results clarified the dynamics of community structure and functioning from a new perspective of plant trait networks, which is key to predicting the response of ecosystems to environmental changes.

Phosphorus accelerate the sulfur cycle by promoting the release of malodorous volatile organic sulfur compounds from Microcystis in freshwater lakes.

Volatile organic sulfur compounds (VSCs) released by algae are of great significance in sulfur cycle, climate regulation and biological information transmission, and they also caused taste and odor in freshwaters. However, the categories, sources, and environmental regulatory factors of VSCs in freshwaters were less known. Here, we show that eight common freshwater cyanobacterium Microcystis, which bloom in freshwaters over the world, are found to be important producers of VSCs. Dimethyl sulfide (DMS), dimethyl disulfide (DMDS) and isopropyl methyl sulfide (IPMS) are the main VSCs with the highest concentrations 184.81 nmol/L, 162.01 nmol/L and 101.55 nmol/L, respectively. The amount of VSCs released from those Microcystis varied greatly, M. elabens, M. panniformis and M. flos-aquae released the largest amount of VSCs (1260.52 nmol S/L, 1154.75 nmol S/L and 670.58 nmol S/L), and M. wesenbergii had the smallest release amount. We also found for the first time that phosphorus (P) was one of the important factors for the regulation VSCs from most Microcystis. P can elevate the release of DMS by promoting the biomass and DMS yields of most Microcystis in the range 0.05 mg/L to 0.5 mg/L. Similar results were also found in 16 lakes at three different spatiotemporal scales. Overall, we revealed that the common freshwater Microcystis were able to release diverse thioethers, and the major VSCs were significantly influenced by water P concentrations. In the context of global freshwater eutrophication and Microcystis bloom, freshwater cyanobacteria driven sulfur cycle and water odor will probably be further strengthened.

Salinity and seasonality shaping free-living and particle-associated bacterioplankton community assembly in lakeshores of the northeastern Qinghai-Tibet Plateau.

Microorganisms in lakeshore zones are essential for pollution interception and biodiversity maintenance. However, the biogeographic patterns of bacterioplankton communities in lakeshore zones and the mechanisms that driving them are poorly understood. We analyzed the 16 S rRNA gene sequences of particle-associated (PA) and free-living (FL) bacterioplankton communities in the lakeshore zones of 14 alpine lakes in two seasons on Qinghai-Tibet Plateau to investigate the bacterial diversity, composition and assembly processes. Our results revealed that PA and FL bacterioplankton communities were driven by both seasonality and salinity in the lakeshores on Qinghai-Tibet Plateau. Compared to FL bacterioplankton, PA bacterioplankton communities were more susceptible to seasonality than spatial salinity. FL bacterioplankton communities were more salinity constrained than the PA counterpart. Besides, the Stegen null model analyses have validated a quantitative bias on stochastic processes at different spatial scales. At a regional scale, stochasticity was the predominant assembly process in both PA and FL bacterioplankton. While at a subregional scale, dispersal limitation was the main contributor of stochastic processes for PA bacterioplankton in summer and heterogeneous selection was the dominant deterministic processes in winter, whereas the community assembly of FL bacterioplankton was more stochastic processes (i.e., dispersal limitation) dominated in the freshwater type but deterministic process (i.e., heterogeneous selection) increased with increasing salinity. Our study provides new insights into both significant spatiotemporal patterns and distinct assembly processes of PA and FL bacterioplankton in alpine lakeshores on the northeastern Qinghai-Tibet Plateau.

Health Risks of Chronic Exposure to Small Doses of Microcystins: An Integrative Metabolomic and Biochemical Study of Human Serum.

Health risks of chronic exposure to microcystins (MCs), a family of aquatic contaminants produced mainly by cyanobacteria, are critical yet unsolved problems. Despite a few epidemiological studies, the metabolic profiles of humans exposed to MCs remain unknown, hindering the deep understanding of the molecular toxicity mechanisms. Here, sensitive nuclear magnetic resonance (NMR)- and liquid chromatography-mass spectrometry (LC-MS)-based metabolomics were applied to investigate the serum metabolic profiles of humans living near Lake Chao, where toxic cyanobacterial blooms occur annually. MCs were positively detected in 92 of 144 sera by ultra-high-pressure liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) with a median concentration of 0.016 µg/L. The estimated daily intake (0.15-0.27 µg MC-LReq/day) was less than the tolerable daily intake (TDI, 2.4 µg MC-LR for 60 kg adults) recommended by the World Health Organization (WHO). Obvious disruptions of the amino acid metabolism were confirmed and played important roles in renal impairments associated with serum MC burdens. Chronic oral exposure of mice to 30 µg MC-LR/kg body mass, which is less than the no observed adverse effect level, also led to obvious renal lesions and metabolic dysfunction. These observations provide the first evidence of metabolic disturbance of humans exposed to MCs and indicate that the WHO's TDI value determined traditionally should be lessened to protect human health effectively.

Phosphorus enrichment affects trait network topologies and the growth of submerged macrophytes.

Significant differences in the morphological and physiological characteristics of submerged macrophytes have been studied following nutrient addition, but little research has investigated the changes in plant trait network topology structures and trait interactions at the whole-plant perspective along nutrient gradients. Plant trait interactions and coordination strongly determine ecosystem structure and functioning. Thirty plant traits were collected from a three-month experiment to construct plant trait networks to clarify the variations in trait connections and network organization arising from five total phosphorus (TP) addition concentrations in water, including a control (CK), 0.1 (TP1), 0.2 (TP2), 0.4 (TP3), and 0.8 (TP4) mg L-1. Nonmetric multidimensional scaling analysis showed a clear difference in the distribution of plant trait space among the different TP treatments. Distinct network structures showed that water TP-deficiency and TP-repletion changed the plant trait network into loose assemblages of more modules, which was related to low plant carbohydrate levels. Most plant functions involving biomass accumulation and carbohydrate synthesis were reduced under high TP conditions compared to moderate TP enrichment. Moreover, the percentage of significant relationships between plant functions and corresponding network modules was lower in the CK and TP4 treatments. These results suggested that low plant carbohydrates in high TP environments induced by high water chlorophyll a and tissue phosphorus could not support rapid resource transport among organs and thus inefficiently performed plant functions. Plant carbohydrates were a vital variable that impacted the network edge density, trait interactions, and plant growth. In summary, we demonstrated that high water TP enrichment reduces plant trait network connectedness and plant functional potentials, which may be correlated with reducing tissue carbohydrates. This study explores the correlations between plant trait network topology and functions to improve our understanding of physiological and ecological rules regulating trait interactions among organs and plant growth under eutrophic conditions.

Eco-chemical mechanisms govern phytoplankton emissions of dimethylsulfide in global surface waters.

The anti-greenhouse gas dimethylsulfide (DMS) is mainly emitted by algae and accounts for more than half of the total natural flux of gaseous sulfur to the atmosphere, strongly reducing the solar radiation and thereby the temperature on Earth. However, the relationship between phytoplankton biomass and DMS emissions is debated and inconclusive. Our study presents field observations from 100 freshwater lakes, in concert with data of global ocean DMS emissions, showing that DMS and algal biomass show a hump-shaped relationship, i.e. DMS emissions to the atmosphere increase up to a pH of about 8.1 but, at higher pH, DMS concentrations decline, likely mainly due to decomposition. Our findings from lake and ocean ecosystems worldwide were corroborated in experimental studies. This novel finding allows assessments of more accurate global patterns of DMS emissions and advances our knowledge on the negative feedback regulation of phytoplankton-driven DMS emissions on climate.

Stoichiometric and physiological mechanisms that link hub traits of submerged macrophytes with ecosystem structure and functioning.

Eutrophication strongly influences plant stoichiometric characteristics and physiological status by altering nutrient and light availability in the water column. However, the mechanisms linking plant functional traits with ecosystem structure and functioning to clarify the decline of submerged macrophytes have not been fully elucidated to date. Therefore, based on a field investigation of 26 macrophytic shallow lakes on the Yangtze Plain, we first constructed a plant trait network at the whole-plant level to determine the hub traits of submerged macrophytes that play central regulatory roles in plant phenotype. Our results suggested that organ (leaf, stem, and root) phosphorus (P), starch, and total nonstructural carbohydrate (TNC) contents were hub traits. Organ starch and TNC were consistent with those in the experiment-based network obtained from a three-month manipulation experiment. Next, the mechanisms underlying the relationships between the hub traits and vital aspects of ecological performance were carefully investigated using field investigation data. Specifically, stoichiometric homeostasis of P (HP), starch, and TNC were positively associated with dominance and biomass at the species level, and community biomass at the community level. Additionally, structural equation modeling clarified not only a hypothesized pathway from eutrophication to water clarity and community TNC, but also combined effects of community TNC and HP on community biomass. That is, ecosystems dominated by more homeostatic communities tended to have more carbon (C)-rich compounds in relatively oligotrophic conditions, which promoted the primary production of macrophytes. Eutrophication was determined to affect community structure by inhibiting the predominance of more homeostatic species and the production of carbohydrates. Finally, reduced community biomass and increased nutrient contents and nutrient:C ratios in plants induced by eutrophication implied a decrease in the C sink in biomass and may potentially lead to an enhancement of litter decomposition rates and nutrient cycling rates. By adjusting plant responses to eutrophication, stoichiometric and physiological mechanisms linking plant traits with ecosystem structure have important implications for understanding ecosystem processes, and these results may contribute to practical management to achieve the restoration of submerged macrophytes and ecosystem services.

The dynamics and release characteristics of microcystins in the plateau Lake Erhai, Southwest China.

Microcystins (MCs) have seriously polluted drinking water supplies and have caused great harm to aquatic organisms and humans. Understanding the dynamics of MC concentrations and its influencing factors is necessary for drinking water safety. Many previous studies on MC pollution focused on intracellular MCs rather than on extracellular MCs, which are more difficult to remove by water treatment. So far, the release characteristics of MCs and the relationships between intracellular and extracellular MCs are still unclear. To explore these questions, a survey was conducted at 18 sites across Lake Erhai from May 2014 to April 2015 as in Lake Erhai the frequency and coverage area of cyanobacterial blooms have been increasing. Variation of extracellular MCs lagged behind that of intracellular MCs. The highest value of intracellular MCs was 1.07 µg L-1 in October 2014 and the highest extracellular MC concentration was 0.035 µg L-1 in November 2014. Intracellular MCs were positively influenced by MC-producing cyanobacterial biomass, water temperature (WT), pH, and conductivity (Cond). The extracellular MCs showed little correlation with cyanobacterial abundances and intracellular MC concentrations, but showed significant negative correlations with WT, pH, and Cond. These results indicated that high biomass and high intracellular MC concentrations did not quickly lead to large releases of MCs, and that when cyanobacterial cells died and blooms disappeared, MCs were intensively released into the water, posing the greatest threat to drinking water supply.

Carbon, Nitrogen, and Phosphorus Allocation Strategy Among Organs in Submerged Macrophytes Is Altered by Eutrophication.

The allocation of limiting elements among plant organs is an important aspect of the adaptation of plants to their ambient environment. Although eutrophication can extremely alter light and nutrient availability, little is known about nutrient partitioning among organs of submerged macrophytes in response to eutrophication. Here, we analyzed the stoichiometric scaling of carbon (C), nitrogen (N), and phosphorus (P) concentrations among organs (leaf, stem, and root) of 327 individuals of seven common submerged macrophytes (three growth forms), sampled from 26 Yangtze plain lakes whose nutrient levels differed. Scaling exponents of stem nutrients to leaf (or root) nutrients varied among the growth forms. With increasing water total N (WTN) concentration, the scaling exponents of stem C to leaf (or root) C increased from <1 to >1, however, those of stem P to root P showed the opposite trend. These results indicated that, as plant nutrient content increased, plants growing in low WTN concentration accumulated leaf C (or stem P) at a faster rate, whereas those in high WTN concentration showed a faster increase in their stem C (or root P). Additionally, the scaling exponents of stem N to leaf (or root) N and stem P to leaf P were consistently large than 1, but decreased with a greater WTN concentration. This suggested that plants invested more N and P into stem than leaf tissues, with a higher investment of N in stem than root tissues, but eutrophication would decrease the allocation of N and P to stem. Such shifts in plant nutrient allocation strategies from low to high WTN concentration may be attributed to changed light and nutrient availability. In summary, eutrophication would alter nutrient allocation strategies of submerged macrophytes, which may influence their community structures by enhancing the competitive ability of some species in the process of eutrophication.

Rainfall is a significant environmental factor of microplastic pollution in inland waters.

Worldwide, increasing attention is being paid to the issue of microplastic pollution in marine ecosystems, yet there is a relative lack of knowledge concerning the pollution of microplastic in inland water systems, although these microplastics are major sources of ocean pollution. In aquatic environments, previous efforts have mainly been devoted to exploring the impact of human-related activities on microplastic pollution, but little is known about non-anthropogenic effects on microplastic distribution. In this paper, the relationship between rainfall and the microplastic concentration of surface water was studied for the first time. The investigation was conducted in Lake Donghu (the largest urban lake in China) from July 23 to September 1, 2019. The abundance of microplastics in the lake water ranged from 7.4 to 29.6 items/L. The dominant size of the collected microplastics was less than 2 mm, with a dominant fiber shape and a dominant transparent color. Our results demonstrated that microplastic concentration was significantly related to rainfall. Therefore, high frequency sampling and rainfall data are needed to accurately evaluate microplastic pollution as well as its consequences.

Attribution of Lake Warming in Four Shallow Lakes in the Middle and Lower Yangtze River Basin.

Many physical, chemical, and biological processes in lakes depend on lake water temperature. However, attribution of the warming rate in a shallow lake is not well understood yet. Here, we evaluated a one-dimensional lake model FLake by observed daily lake surface water temperature (LSWT) at four typical lakes in the Middle and Lower Yangtze River basin and then attributed LSWT warming to climate variables during the period 1979-2017. We found that FLake could capture well the seasonal/interannual variation of observed LSWT. During the 39-year study period, LSWT significantly warms at a rate of 0.26-0.28 °C per decade, 24-35% slower than the air temperature. Increased solar radiation and air temperature contributed to most (>80%) of the LSWT warming. The warming trend of LSWT in the spring is the largest among the four seasons, 2-4 times the warming rate of the other seasons. Brightening in the spring contributes 50-64% of the largest spring warming. The future air warming plus the brightening trend with the Clean Air Act in China would amplify LSWT warming and, thus, advance and/or deteriorate algae blooms, especially in spring.

Spatial and interspecies differences in concentrations of eight trace elements in wild freshwater fishes at different trophic levels from middle and eastern China.

There have been numerous studies on concentrations of trace elements in aquatic ecosystems, but few have been conducted at a large spatial scale. This study collected 410 samples of five wild freshwater fishes at different trophic levels from middle and eastern China. Concentrations of eight trace elements, chromium (Cr), iron (Fe), nickel (Ni), copper (Cu), zinc (Zn), arsenic (As), lead (Pb) and cadmium (Cd) and stable isotope ratios (δ13C and δ15N) were determined in dorsal muscle of fishes. Spatially, concentrations of trace elements were least in fishes from the Hai River Basin, while those in fishes from the Taihu Lake Basin were greatest. The carnivorous topmouth culter and omnivorous common carp and crucian carp accumulated greater amounts of trace elements than did the planktivorous silver carp and bighead carp. Trophic biomagnification was for Cu, Fe and Zn, but not for Cr, Ni, As, Pb and Cd. Concentrations of As in 15 muscle samples (3.7%) from Taihu Lake Basin exceeded the guidelines (1.0 mg/kg, wet mass) provided by FAO/WHO (2014), while the total target hazard quotient (TTHQ) values were <1.0, indicating no obvious non-carcinogenic risks to humans that consume those fishes. However, people who consume larger amounts of fish products, or people who are vulnerable, such as pregnant women, children and people with poor health, might be at greater risk. Also, exposure to trace metals through other routes cannot be ignored. Accumulations of trace elements in Chinese freshwater fishes were affected by both geographical conditions and human activities.

Effects of high ammonium enrichment in water column on the clonal growth of submerged macrophyte Vallisneria natans.

As we know, the survival of young ramets and stolons is essential for the clonal growth of many aquatic plants. However, few NH4+ enrichment experiments on clonal growth of submerged macrophytes have been conducted to provide possible evidences for their declines in eutrophic lakes. Here, the growth and physiological responses of V. natans to the enrichment of NH4+-N were examined under six inorganic nitrogen (IN, i.e., the sum of nitrate nitrogen (NO3--N) and ammonium nitrogen (NH4+-N)) concentrations (control, 2.5, 4.5, 6.5, 8.5, and 10.5 mg L-1). When NH4+-N concentration increased over 0.5 mg L-1, free amino acid (FAA) contents in leaves and stolons increased while soluble carbohydrate (SC) and starch contents decreased, and major growth indices (total biomass of plants, number of ramets, and stolon dry weight (DW)) also showed a degressive tendency. Remarkably, the stolon DW significantly declined with increasing FAA, but significantly positively related to SC and starch. These results indicated that clonal growth of V. natans was inhibited by high NH4+-N concentration, and imbalance of C-N metabolism of stolons partly explained the decline of submerged clonal macrophytes. In this study, the leaves of new and small (NS) ramets contained significantly more FAA and less SC than that of mature and mother (MM) plants, indicating that the C-N metabolism of young ramets was easier to be disrupted, consequently inhibiting the clonal growth of aquatic plants. Furthermore, under the condition of high NH4+-N concentration, FAA may be a useful indicator of both macrophyte growth and physiological stress of plants.

Use the predictive models to explore the key factors affecting phytoplankton succession in Lake Erhai, China.

Increasing algae in Lake Erhai has resulted in frequent blooms that have not only led to water ecosystem degeneration but also seriously influenced the quality of the water supply and caused extensive damage to the local people, as the lake is a water resource for Dali City. Exploring the key factors affecting phytoplankton succession and developing predictive models with easily detectable parameters for phytoplankton have been proven to be practical ways to improve water quality. To this end, a systematic survey focused on phytoplankton succession was conducted over 2 years in Lake Erhai. The data from the first study year were used to develop predictive models, and the data from the second year were used for model verification. The seasonal succession of phytoplankton in Lake Erhai was obvious. The dominant groups were Cyanobacteria in the summer, Chlorophyta in the autumn and Bacillariophyta in the winter. The developments and verification of predictive models indicated that compared to phytoplankton biomass, phytoplankton density is more effective for estimating phytoplankton variation in Lake Erhai. CCA (canonical correlation analysis) indicated that TN (total nitrogen), TP (total phosphorus), DO (dissolved oxygen), SD (Secchi depth), Cond (conductivity), T (water temperature), and ORP (oxidation reduction potential) had significant influences (p < 0.05) on the phytoplankton community. The CCA of the dominant species found that Microcystis was significantly influenced by T. The dominant Chlorophyta, Psephonema aenigmaticum and Mougeotia, were significantly influenced by TN. All results indicated that TN and T were the two key factors driving phytoplankton succession in Lake Erhai.

Microcystis aeruginosa/Pseudomonas pseudoalcaligenes interaction effects on off-flavors in algae/bacteria co-culture system under different temperatures.

We conducted an experiment to study the interaction effects of Microcystis aeruginosa and Pseudomonas pseudoalcaligenes on off-flavors in an algae/bacteria co-culture system at three temperatures (24, 28 and 32°C). Gas chromatography-mass spectrometry was applied to measure off-flavor compounds dimethyl sulfide (DMS), dimethyl trisulfide (DMTS), 2-methylisoborneol, geosmin (GEO) and ß-cyclocitral. During the lag phase of co-cultured M. aeruginosa (first 15days), P. pseudoalcaligenes significantly increased the production of DMS, DMTS and ß-cyclocitral at all three temperatures. In the exponential phase of co-cultured M. aeruginosa (after 15days), M. aeruginosa became the main factor on off-flavors in the co-culture system, and ß-cyclocitral turned to the highest off-flavor compound. These results also indicated that DMS, DMTS and ß-cyclocitral were the main off-flavor compounds in our M. aeruginosa/P. pseudoalcaligenes co-culture system. Univariate analysis was applied to investigate the effects of M. aeruginosa and P. pseudoalcaligenes on the production of off-flavors. The results demonstrated that both M. aeruginosa and P. pseudoalcaligenes could increase the production of DMS and DMTS, while ß-cyclocitral was mainly determined by M. aeruginosa. Our results also provide some insights into understanding the relationship between cyanobacteria and heterotrophic bacteria.