Preface Cyanobacterial blooms in China: ecology, toxicity, and treatment

Renhui LI , , Xiaoli SHI , Nanqin GAN , Junyi ZHANG , Xuechu CHEN

1 National and Local Joint Engineering Research Center of Ecological Treatment Technology for Urban Water Pollution, Wenzhou University, Wenzhou 325035, China

2 State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China

3 State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences,Wuhan 430072, China

4 Wuxi Environmental Monitoring Center, Wuxi 214121, China

5 School of Ecological and Environmental Sciences, East China Normal University, Shanghai 200241, China

Cyanobacterial blooms are one of the major threats to the health of aquatic ecosystems, and are increasing globally due to the synergistic eff ects of human activities and global climate change.The 7thNational Cyanobacteria Bloom Forum was successfully held in May 28-30, 2021 in Guiyang,Guizhou Province, China. The forum established a platform for exchanging views on the concerns of cyanobacterial blooms from Chinese researchers,lake managers, and treatment engineers. This special issue, “Cyanobacterial blooms in China: ecology,toxicity, and treatment” in Journal of Oceanography and Limnology, presents a collection of 14 papers on the physiological features and the inf luence on their concurrent aquatic biology of diff erent cyanobacterial groups.

Microcystisblooms are pervasive in temperate and tropical freshwater bodies throughout the world.We have six papers focused onMicrocystisrelated to the detection, the function of bound extracellular polymeric substances (bEPS), the eff ect on submerged macrophyte and the reed wetland, as well as the control strategy in the littoral area for emergency purposes. It is an essential task to conduct correct identif icaiton ofMicrocystisspecies in ecological studies and water bloom control. Zu et al. (2022) established an immunological method to identifyMicrocystis, and they usedMicrocystisaeruginosaPCC7806 lysates as coated antigens for screening specif icMicrocystisnanobodies based on the human domain antibody display library. The bEPS play an important role in the proliferation ofMicrocystis. Wang et al. (2022) found that at certain light intensities,M.aeruginosagrow quickly thanM.f los-aquaealong with the increase of negative charges, bEPS contents, growth, and tryptophan-like substance contents. Another study related to EPS inMicrocystisperformed by Duan et al. (2022), identif ied key physiological traits and chemical components of EPS for colony formation inMicrocystis. Their results further presented that the major physiological strategies forMicrocystisto produce excess EPS enhancing colony formation, as increasing number for both photosynthetic reaction center and light-harvesting antenna in the PSII and reducing the growth rate.

Microcystisbiomass can be largely accumulated to form heavy scums in large eutrophic lakes, posing a potential risk to public health. Gao et al. (2022)explored how decomposedMicrocystis-dominant cyanobacterial blooms aff ect submerged macrophytes by exposingMyriophyllumspicatumto the cell extracts from microcystin (MC)- and non-MC-producingMicrocystisstrains in a laboratory experiment. BothMicrocystiscell extracts exerted obvious damages to plant biomass, photosynthesis, primary and secondary metabolism measures, and resistance of plant antioxidant systems, as MC-producingMicrocystishas stronger eff ects due to the presence of MCs. Meanwhile, planktonic bacterial communities have the potential to use and degrade substances derived fromMicrocystiscell extracts, which may be benef icial forM.spicatumto alleviate damages fromMicrocystis. Ma et al. (2022a) investigated the concentration of chlorophyllaand nutrients in reedcovered littoral zones and unvegetated littoral zones of Chaohu Lake, and revealed that reed wetlands in the littoral zone of large eutrophic lake could trap and accumulate algal biomass. To alleviate ecological disasters in littoral zones, Liu et al. (2022)compared three f locculants for heavyMicrocystisbloom mitigation and subsequent environmental impacts. Polyaluminum chloride (PAC) was shown to be an effi cient f locculant through rapid reduce of cyanobacterial blooms at chlorophyll-aconcentrations over 1 500 μg/L within 15 min. Furthermore, the high accumulation of nutrients in sediments after the settling of cyanobacteria can cause high internal phosphorus and total organic carbon of the sediments,which can threaten lake restoration achieved by planting submerged macrophytes.

Raphidiopsisraciborskiiis becoming a cosmopolitan species in freshwater systems around the world and attract interest due to its invasion,expansion, and toxicity. We have three papers dealing withR.raciborskii. Wu et al. (2022) presented an overview ofR.raciborskii’s global distribution and adaptation strategy and demonstrated that the expansion of its geographical distribution could be linked to its genome, toxicity, and ecophysiology.Shi et al. (2022a) reportedR.raciborskiito cope with P def iciency at coordinated and complex cellular and physiological responses, ref lecting the multifaceted machinery ofR.raciborskidealing with environmental P f luctuations. Ma et al. (2022b)performed bialgal cultures at diff erent initial ratios of biomasses ofR.raciborskiiand microcystins (MCs)-producing or non-MCs-producingM.aeruginosastrains, and revealed thatR.raciborskiiin the co-cultures stimulated the growth of both MCsproducing and non-MCs-producingM.aeruginosastrains, comparing toM.aeruginosamonoculture.Such a result indicatedM.aeruginosato outcompeteR.raciborskiiand gradually become into dominant species even at a lower initial concentration.

Aphanizomenonis a common f ilamentous and bloom-forming cyanobacterial group. Wen et al.(2022) used the co-culture experiment at diff erent ratios of initial biomass, to conf irm that temperature as the dominating factor in the succession ofA.f losaquaeandM.aeruginosa.A.f los-aquaewas shown at a specif ic higher growth rate even the coexistence of the both species at 15 °C, however the growth ofA.f los-aquaeat 25 °C was inhibited by the biomass ofM.aeruginosa.

Eutrophication and climate warming have intensif ied the global expansion ofCylindrospermopsisspp. andChrysosporumspp., two potential producers of Cylindrospermopsin (CYN). Yin et al. (2022)explored the eff ect of CYN on the structure and function of the bacterioplankton community based on high-throughput sequencing. High concentrations of CYN (40 μg/L) caused a signif icant decrease in microbial abundance and functional groups.Actinobacteria had the strongest tolerance to CYN.High CYN concentrations were shown to reduce the correlation among diff erent bacterioplankton groups, and inhibit the abundances of some bacterial taxa functioning in the process of denitrif ication and carbon transfer in the microbial food web. Dissolved organic phosphorus could be used by cyanobacteria via alkaline phosphatase. Wan et al. (2022) review the current knowledge of extracellular phosphatase excreted by cyanobacteria, highlighting the development of detection method and its ecological roles in regulating phosphorus cycling in freshwater systems, which is based on reports for around 100 species of cyanobacteria.

Shi et al. (2022b) investigated the dynamics of the abundance and diversity of aerobic anoxygenic phototrophic bacteria (AAPB) based onpufMgene in Taihu Lake. The ratios of AAPB to total bacteria varied from 3.4% to 11.5% and peaked in winter in both sites. AAPB abundance was positively correlated with dissolved organic carbon (DOC) concentration.AAPB community compositions showed a diff erence between warm seasons and cold seasons.

Zheng et al. (2022) investigated the phytoplankton communities both in a semi-closed lake and a closed lake in the Oujiang River mouth in Zhejiang Province, to explore the eff ect of tides-induced water exchange on aquatic ecosystem. In the closed lake,cyanobacteria were the dominant species. However,in the semi-closed lake, the diversif ication of the dominant species was greater, and some species of diatoms and green algae became dominant. Water exchange driven by local tidal movement was shown to increase salinity and decrease transparency of water, consequently shaping the phytoplankton community structures and reducing the occurrence of cyanobacterial blooms in the semi-closed lake.

We thank editors of Journal of Oceanology and Limnology for giving us the opportunity to edit this special issue and supervise the whole editorial process, and we also thank all reviewers that have thoroughly reviewed these manuscripts. We hope that this collection of papers will be of interest for a broad scientif ic audience and will bring about new ideas and new research programs from a wide range of water bodies.