Dependence of evolution of Cyanobacteria superiority on temperature and nutrient use efficiency in a meso-eutrophic plateau lake.

Algal blooms in lakes have been a challenging environmental issue globally under the dual influence of human activity and climate change. Considerable progress has been made in the study of phytoplankton dynamics in lakes; The long-term in situ evolution of dominant bloom-forming cyanobacteria in meso-eutrophic plateau lakes, however, lacks systematic research. Here, the monthly parameters from 12 sampling sites during the period of 1997-2022 were utilized to investigate the underlying mechanisms driving the superiority of bloom-forming cyanobacteria in Erhai, a representative meso-eutrophic plateau lake. The findings indicate that global warming will intensify the risk of cynaobacteria blooms, prolong Microcystis blooms in autumn to winter or even into the following year, and increase the superiority of filamentous Planktothrix and Cylindrospermum in summer and autumn. High RUETN (1.52 Biomass/TN, 0.95-3.04 times higher than other species) under N limitation (TN < 0.5 mg/L, TN/TP < 22.6) in the meso-eutrophic Lake Erhai facilitates the superiority of Dolichospermum. High RUETP (43.8 Biomass/TP, 2.1-10.2 times higher than others) in TP of 0.03-0.05 mg/L promotes the superiority of Planktothrix and Cylindrospermum. We provided a novel insight into the formation of Planktothrix and Cylindrospermum superiority in meso-eutrophic plateau lake with low TP (0.005-0.07 mg/L), which is mainly influenced by warming, high RUETP and their vertical migration characteristics. Therefore, we posit that although the obvious improvement of lake water quality is not directly proportional to the control efficacy of cyanobacterial blooms, the evolutionary shift in cyanobacteria population structure from Microcystis, which thrives under high nitrogen and phosphorus conditions, to filamentous cyanobacteria adapted to low nitrogen and phosphorus levels may serve as a significant indicator of water quality amelioration. Therefore, we suggest that the risk of filamentous cyanobacteria blooms in the meso-eutrophic plateau lake should be given attention, particularly in light of improving water quality and global warming, to ensure drinking water safety.

Spatiotemporal dynamics of phytoplankton biomass and community succession for driving factors in a meso-eutrophic lake.

Effects of climate change and nutrient load caused by human activities on lake phytoplankton blooms have attracted much attention globally. However, their roles and synergistic effects on phytoplankton biomass and community historical succession are not well understood, especially for meso-eutrophic plateau lakes. In this study, a multi-year (1997-2022) monthly dataset including hydro-chemical and meteorological indicators of the meso-eutrophic plateau lake Erhai in China, was used to explore the contributions of climate change and nutrients on phytoplankton biomass variation and community succession. Phytoplankton biomass increased from 1997 to 2006, slowly decreased from 2006 to 2015, then increased again from 2015 to 2022, according to a generalised additive model (GAM). Alongside warming, nitrogen, phosphorus and organic matter are key drivers of long-term interannual variation in phytoplankton biomass and historical succession of the phytoplankton community. The extensive blooms in recent years were strongly associated with both organic matter accumulation and global warming. Phytoplankton biomass in northern and southern districts was greater than in central areas, with Cyanophyta and Pyrrophyta dominating in the north and Chlorophyta prevalent in the south. Since 2015, phytoplankton diversity has increased significantly, and biomass has declined in the southern district but increased markedly in the northern district. Spatial heterogeneity was caused by the spatial distribution of nutrients and the buoyancy regulation capacity of cyanobacteria. The results demonstrate that bloom mitigation responds strongly to nitrogen and phosphorus control in meso-eutrophic lakes, therefore preventing and controlling blooms through nitrogen and phosphorus reduction is still an effective measure. Given the accumulation of organic matter in recent years, synergistic control of organic matter and total nitrogen and phosphorus could effectively reduce the risk of cyanobacterial and dinoflagellate blooms.

[Succession Pattern of Phytoplankton of Daning River in the Three Gorges Reservoir and Its Driving Factors].

To elucidate succession pattern of phytoplankton in the Daning River and its driving factors, multivariate statistical analysis was conducted. By using the monitoring data in different seasons of Daning river during April 2012 to January 2013, this paper analyzed the succession pattern of phytoplankton in the Daning River and its driving factors in typical tributaries of river-style reservoirs. According to the characteristics of water level, the operational period of the TGR was classified into following four stages:stage Ⅰ (pre-November-April), stage Ⅱ (May-July), stage Ⅲ (July-September) and stage Ⅳ (September-November). ① The results indicated that the values of Chlorophyll-a concentrations and algal density showed similar seasonal variations, with the highest values occurring in stage Ⅲ, followed by stages Ⅳ, Ⅱ and Ⅰ. Succession of C-R-S growth strategies was the same generally:CR-R type dominated in stage Ⅰ, CS, CR/CS and R-CR dominated in stage Ⅱ, Ⅲ and Ⅳ, respectively. ② The mean values of Margalef index and Pielou index in stage Ⅳ and Ⅲ were significantly greater than those in stage Ⅱ and Ⅰ; the value of Shannon-waver index showed that the highest value in stage Ⅲ, followed in a descending order by stage Ⅰ,Ⅱ and Ⅳ; the successional rate had the highest value in stage Ⅳ, followed in descending order by stage Ⅲ, Ⅰ and Ⅱ. ③ The results of Correlation analysis suggested that no significant relationships were observed between the environmental parameters and phytoplankton abundance in stage Ⅰ. The results indicated that relative water column stability(RWCS), index of feasible energy for phytoplankton (Et) and index of feasible energy (Ef*) were key regulatory factors for phytoplankton community in stage Ⅰ. The results indicated that Et, Ef* and total phosphorus (TP) were key regulatory factors for phytoplankton abundance in stage Ⅱ. The results of the redundancy analysis (RDA) suggested that RWCS, TP and the ratio of euphotic depth[Deu(λPAR)] to mixing depth (Dmix)[Deu(λPAR)/Dmix] were key regulatory factors for phytoplankton community composition in stage Ⅱ. The results indicated that Ef* and TP were key regulatory factors for phytoplankton abundance in stage Ⅲ. The results of the RDA suggested that[Deu(λPAR)/Dmix],Et, Ef* and TP were key regulatory factors for phytoplankton community composition in stage Ⅲ. The results indicated that TP was key regulatory factor for phytoplankton abundance in stage Ⅳ. The results of the RDA suggested that[Deu(λPAR)/Dmix] was key regulatory factor for phytoplankton community composition in stage Ⅳ.

[Vertical migration of algal cells in the Daning River Bay of the Three Gorges Reservoir].

To support the basic data for forecast of algal blooms, circadian vertical migration experiment was carried out in the Daning River Bay of the Three Gorges Reservoir in July, 2011. The results were as follows: in this period, different algal species were found in the Daning River Bay, including cyanobacteria, green algae, dinoflagellates and diatoms etc; the distribution of algal cells was uneven, 72.5%-76.2% of algal cells aggregated at 0.5-4.0 m water depths from 10:00 AM to 10:00 AM next day, but 7.5%-16.3% of algal cells aggregated at 0-0.5 m. Morisita's indexes (MI) of algal cells were from 1.41 to 1.97 in day time, and from 1.17 to 1.55 at night. Morisita's indexes of chlorophyll a(Chla)were from 1.31 to 1.59 in day time, and from 1.17 to 1.39 at night. The vertical migration also occurred at 0.5-4.0 m water depths. The algal density was not significantly related with the concentrations of nutrient except that of dissolved total phosphorus (DTP) (r = 0.89). The algal density was also influenced by water temperature (WT), pH and specific conductance (SPC), and the correlation coefficients were 0.96, 0.97 and -0.99, respectively.

[Phosphorus forms and its distribution characteristics in sediments and soils of water-level-fluctuating zone of the backwater reach from input river of Three Gorges Reservoir].

The contents of different phosphorus forms in surface sediments and the soils of water-level-fluctuating zone of the backwater reach from input river of Three Gorges Reservoirwere measured, using thestandard measurement and test (SMT) procedure of phosphorus forms in freshwater sediments. Correlation coefficients between phosphorus forms and sample geochemical characteristics, such as organic matter and major components were analyzed. The results indicated that the TP content in surface sediments varied from 483.4-848.4 mg/kg, and the average content was 569.0 mg/kg. The TP content in surface sediments placed in the mid-lower level, comparing with the TP content in surface sediment from the shallow lakes in the middle and lower reaches of Yangtze River. The TP content in soils of water-level-fluctuating zone varied from 488.9-1487.7 mg/kg, and the average content was 813.3 mg/kg. The average content of TP in soils of water-level-fluctuating zone whole exceeded the surface sediment, indicating of the influence of human's activity on phosphorus contents in soils of water-level-fluctuating zone. Distribution characteristics of phosphorus forms were different between the sediment and soils of water-level-fluctuating zone: (1) The ratio of IP/TP in the surface sediments (average value 55.7%) was higher than that in soils of water-level-fluctuating zone (average value 49.4%); (2) The domination phosphorus forms of IP in surface sediments was Ca-P (average ratio 83.5%), and the ratio of (Fe/Al-P)/IP was only 15%. The average ratio of Ca-P/IP in the soils of water-level-fluctuating zone was 73.9%, whereas the ratio of Fe/Al-P in IP raised to 22%; (3) The average content of active phosphorus (OP + Fe/Al-P) in surface sediment was 261.8 mg/kg, the average ratio of active phosphorus in TP was 49%, whereas the average content of active phosphorus (OP + Fe/Al-P) in soils of water-level-fluctuating zone was 405.7 mg/kg, the average ratio was 54%. The active phosphorus in soils of water-level-fluctuating zone would become potential pollution sources of water under correct environmental conditions,therefore, the potential impact of phosphorus on water eutrophication in soils of water-level-fluctuating zone couldn't be neglected.

[Analysis of algal blooms in Da-Ning River of Three Gorges Reservoir].

According to the survey conducted from Apr. to Jun. 2007 and from Apr. to May. 2008, the changes of water quality, forms and distributions of nutrient salts and characters of algal blooms in Da-ning River of Three Gorges Reservoir (TGR) were studied. The results indicated that the concentrations of nitrogen and phosphorus nutrient were abundant during sensitive period of algal blooms in Da-ning River. Total nitrogen (TN) and total phosphorus (TP) values are 0.84-3.21 mg/L and 0.011-0.531 mg/L respectively, and the nutrients concentrations become high gradually from upstream to downstream. Total dissolved nitrogen (TDN) is the major form of TN accounting for 84%, and total dissolved phosphorus (TDP) is dominant (TDP/TP = 60%). Algal blooms bring phosphorus nutrient bio-concentration. The rates of TN and TP are all in excess of 16, which show eutrophication is limited by phosphorus. Potassium permanganate index and dissolved oxygen (DO) are at low levels and change stably. But chlorophyll a (Chl-a) becomes frequently, the value is 1.41-219.04 mg x m(-3). Significant positive correlations are all observed by correlation analysis between Chl-a and the main parameters (r(Chla-TP) = 0.453, r(Chla-potassium permanganate index) = 0.641, r(Chla-DO) = 0.584, r(Chla-pH) = 0.409, p < 0.01), but significant negative correlations are observed between Chl-a and Secchi depth (SD) (r(Chla-SD) = - 0.392, p < 0.01). The pH is fluctuated by multiparameter esp. in algal blooms. Widespread algae are observed by microscope during sensitive period of algal blooms in Da-ning River accounting for 8 phylum 82 genus 124 species, which Bacillariophyta and Chlorophyta are dominant, and then Cyanophyta and Pyrrophyta. Three whole watershed algal blooms break out in Da-ning River during the period, and the highest values of algal density are 14-1 427 times as many as the normal values. The dominant species of algal blooms are mostly involved with O. borgei, C. microporum, Chlorococcum humicola, P. morum and C. vulgaris of Chlorophyta; P. pleuronectes and T. oblonga of Euglenophyta; Cyclotella, Stephanodiscus astraea and Navicula of Bacillariophyta; P. elpatiewskyi of Pyrrophyta. Multi-algal species blooms are observed in the same time and place, and there are few algae in the estuary of Da-ning River to Changjiang River.

[Analysis of phosphorus distribution characters and their sources of the major input rivers of Three Gorges Reservoir].

The seasonal characters of the water flux and suspended substance, phosphorus in the water of input rivers of Three Gorges Reservoir (TGR) were discussed, and the their distributions among three major input rivers (Changjiang river, Jialingjiang river and Wujiang river) were studied, according to the survey conducted from Jan. 2004 to Dec. 2005. The results indicate that those parameters' seasonal changes are obvious. The flux and suspended substance in abundant water period are more higher than them in low water period, which displays suspended substance origins from bedload and that the water and soil severely lose in drainage areas of three input rivers. In the three monitor sections of input rivers of TGR, the average contents per year of total phosphorus are about 0.12-0.29 mg/L, which exceeds the 1970s level of the three input rivers. Most of total phosphate is total solid phosphate (TPP) exceeding 75% of them. TP and TPP have both distinct positive correlation with the flux and suspended substance in water of input rivers of TGR, and TPP and TP have also the same correlation, which means that phosphate pollution in the input rivers of TGR comes from bedload. The nonpoint source pollution has had far-reaching influence upon phosphate pollution. Nitrogen and phosphate are not the major limiting factor of the nutritious salts in the input rivers of TGR. The rate of between nitrogen and phosphate (N/P) is in higher level (above 30), that is phosphate first will reach lower level and maybe become the limiting factor of the nutritious salts in the input rivers of TGR.

[Historical evolvement trends of nutrients in waters of Bohai Bay from 1985 to 2003].

The local condition and the historical evolvement trend of nutrient elements were studied by the collection and analysis of the local investigation and the historical data. The surface seawaters are under the bad nitrogen contaminative conditions. Beitang and Dagu estuary are the main contaminative sources of inorganic nitrogen and phosphorus. The historical evolvement trend of DIN and DIP has close correlation with the yearly runoff, especially in the coastal areas near Dagu estuary. The remarkable positive correlationship between DIN, DIP and the yearly runoff indicates that the main pollution emission source of nutrient elements is the exogenous discharge input. The nutrients structures have changed greatly from 1985 to 2003. Nitrogen limiting in 1985 has changed into phosphorus limiting in 2003, which will influence the structure of phytoplanktons in Bohai Bay.

[Trophic states and nutrient output of tributaries in Three Gorges Reservoir area].

TP, TN, chlorophyll a, potassium permanganate index and secchi depth (SD) and phytoplankton were determined in 15 tributaries of Three Gorges Reservoir. Trophic states were assessed and output fluxes of TN, TP and potassium permanganate index were calculated. The results showed that value of TN, TP, potassium permanganate index, SD and Chla were different in each tributary. SD, TN, TP, potassium permanganate index and Chla value are 0.45 - 1.5 m, 0.65 - 4.27 mg x L(-1), 0.011 - 0.432 mg x L(-1), 0.657 - 5.37 mg x L(-1) and 0.57 - 12.2 mg x m(-3) respectively. The water body of tributaries is polluted at various levels. The concentration of TN is abundant. The rate of TN and TP showed that a part of tributaries eutrophication are limited by TP. Utilizing the method of integrated nutrition state index, it assessed the trophic states degree of tributaries. All of the studied tributaries, 3 tributaries are eutropher, 10 tributaries are mesotropher and 2 tributaries are oligotropher respectively. 129 species of phytoplankton are identified, which belongs to 7 division and 67 genera. The dominant species are Bacillariophyceae, Chiorophyceae and Cyanophyta. The type of phytoplankton community is Bacillariophyceae-Chlorophyceaetype, Bacillariophyceae-Cyanophytatype and Cyanophyta-Chlorophyceaetype. The species and numbers of phytoplankton are various in different tributaries. The nutritive peculiarity belongs to responding type of phytoplankton. The nutrient fluxes load was calculated by discharge and concentration of each tributary. The nutrient fluxes load of TN, TP and potassium permanganate index are 3.14 x 10(5) t, 1.76 x 10(4) t and 2.74 x 10(5) t respectively in one year. After the Three Gorges Dam was completed in 2009, eutrophication trend of tributaries estuaries would be more serious with the decreasing of flow velocity.

[Analysis of nitrogen, phosphorus nutrients and COD in waters of Yangtze River Estuary].

The characters of the morphological, vertical and spatial distribution of nitrogen and phosphate in the water of Changjiang Estuary were discussed, according to the survey conducted in November 2003. Among the dissolved inorganic nitrogen species, nitrate accounted for 90% in the water of Changjiang Estuary. The concentration of nitrogen nutrients in the Changjiang Estuary show higher level, and 67% of sampling stations attained or exceeded the forth standard level of seawater, according to the national standard of seawater quality. Most of total phosphate in the water of Changjiang Estuary is total dissolved phosphate (TDP), which primary composition is dissolved organic phosphate (DOP). The dramatic changes of salinity in the water of Changjiang Estuary lead to the different distribution characteristics of nutrients. The concentrations of nitrate are higher inside the estuary and lower outside the estuary due to its conservatism. On the contrast, ammonium and phosphate are influenced by the change of particle concentrations and salinity, which are higher outside the estuary and lower inside the estuary. Besides, the contents of COD in the water of Changjiang estuary are very high, and the spatial distribution characteristics are higher inside the estuary and lower outside the estuary.