Changhu Lake, a large, shallow, eutrophic lake in central China, experienced an extremely low water level event from November 2015 to January 2016 followed by an extremely high water level event in July 2016. In this study, we examined the effects of two extreme water levels on the nutrient dynamics of Changhu Lake over five years. The nutrient parameters in Changhu Lake showed significant interannual variations, and the nutrient concentrations at the sites in the western part of Changhu Lake were 2–41% higher than those at the outlet of the lake. In late 2015, the effects of low water levels led to a 17–74% increase in nutrient concentrations. After July 2016, however, a high water level event occurred, leading to a 34–48% decrease in nutrient concentrations. These changes in nutrient parameters were strongly related to water level fluctuations (p < 0.05). As extreme water levels are likely to become more frequent during the twenty-first century, this work may provide some insights into the conservation and management of lake ecosystems in the face of climate change and human activity.

为探讨在克氏原螯虾(Procambarus clarkii)稻田养殖水体中施用不同肥料对浮游植物群落结构的影响,以湖北省荆州市太湖农场稻虾模式试验基地为场所,于2019年4—5月进行试验,设置施化肥、施有机肥和施有机-无机复混肥3个处理.每块稻田中克氏原螯虾的放养密度为2.30ind/m2.结果发现,施化肥、施有机肥和施有机-无机复混肥稻田中分别鉴定出浮游植物74、81和81种;浮游植物丰度和生物量变化范围分别为(0.78—30.32)×106 ind./L、0.55—26.00 mg/L,且均以绿藻和隐藻占优势,群落动态主要表现为这两类植物的变动,浮游植物丰度和生物量总体表现为化肥>有机-无机复混肥>有机肥.施有机肥和施有机-无机复混肥的浮游植物均匀度指数和多样性指数均高于施化肥,且浮游植物群落能维持更加稳定的状态.浮游植物群落随时间表现出明显的动态变化,其中水温和营养盐对浮游植物的影响最大.在稻田养殖水体中施用有机-无机复混肥具有促进浮游植物生长、改善浮游植物群落结构的效果,施有机-无机复混肥优于单施化肥或有机肥.

The global decline of freshwater biodiversity caused by climate change and human activities are supposed to disrupt ecosystem services related to water quality and alter the structure and function of aquatic communities across space and time, yet the effects of the combination of these factors on plankton community ecosystem has received relatively little attention. This study aimed to explore the impacts of disturbances (e.g. human activity, temperature, precipitation, and water level) on phytoplankton community structure (i.e. community evenness and community composition) and function (i.e. resource use efficiency) in four subtropical reservoirs over 7 years from 2010 to 2016. Our results showed that community turnover (measured as community dissimilarity) was positively related to disturbance frequency, but no significant correlation was found between phytoplankton biodiversity (i.e. evenness) and disturbance frequency. Phytoplankton resource use efficiency (RUE = phytoplankton biomass/ total phosphorus) was increased with a higher frequency of disturbance with an exception of cyanobacteria. The RUE of Cyanobacteria and diatoms showed significantly negative correlations with their community evenness, while the RUE of Chlorophyta exhibited a positive correlation with their community turnover. We suggest that multiple environmental disturbances may play crucial roles in shaping the structure and functioning of plankton communities in subtropical reservoirs, and mechanism of this process can provide key information for freshwater uses, management and conservation.

湖泊富营养化是我国重要的水污染问题之一.为了研究富营养化湖泊生态恢复前后营养盐的动态变化,以湖北长湖为例,分析了2014-2018年期间长湖4个监测点的水质监测数据.结果表明:从时间变化看,长湖水体营养盐具有明显的年际和季节变化特征,2014-2018年,长湖水体各营养盐浓度总体呈逐渐下降趋势;营养盐含量在1、7月份较高,5月份较低.从空间变化看,沿庙湖、海子湖、马洪台和圆心湖区方向,营养盐含量呈下降趋势.尽管生态恢复工程实施后长湖水质逐渐改善,由恢复前的Ⅴ ～ 劣Ⅴ类转好为Ⅳ ～ Ⅴ类,但受湖泊周边畜禽养殖和农业种植等外源污染的影响,长湖水质依然不容乐观.为了恢复长湖水体的自净能力,需对流域内的农业面源污染进行有效控制.

Traditionally, composition and biomass of phytoplankton communities are determined by microscopy, but this method is time-consuming and so does not allow for high-frequency data acquisition across space and time. Pigment-based chemotaxonomy (CHEMTAX) is now widely applied to study of phytoplankton community structure on broader spatial and temporal scales of oceans, but the ability of this approach to provide estimates of phytoplankton assemblage in freshwater ecosystems is yet underdeveloped. To investigate the efficiency of the high-performance liquid chromatography (HPLC)-CHEMTAX in quantifying the different phytoplankton groups in inland freshwater, we present a comparison between phytoplankton pigment analyses by HPLC with CHEMTAX and microscopic counting of phytoplankton samples from four subtropical reservoirs in January and July 2014, respectively. The correlation between pigment and phytoplankton abundance detected by microscopy was stronger than that between pigment and phytoplankton biomass. The published marker pigments and their revised ratios can be used to describe phytoplankton abundances in a mixed community of freshwater phytoplankton, and pigment-based CHEMTAX can successfully describe the overall pattern of phytoplankton community dynamics during different seasons. The use of pigment-based CHEMTAX for quick surveys of phytoplankton communities can be recommended as a useful supplement or alternative tool to microscopy for freshwater ecosystem management.

Although it is widely recognized that cyanobacterial blooms have substantial influence on the plankton community in general, their correlations with the whole community of eukaryotic plankton at longer time scales remain largely unknown. Here, we investigated the temporal dynamics of eukaryotic plankton communities in two subtropical reservoirs over a 6-year period (2010-2015) following one cyanobacterial biomass cycle-the cyanobacterial bloom (middle 2010), cyanobacteria decrease (late 2010-early 2011), non-bloom (2011-2014), cyanobacteria increase, and second bloom (late 2014-2015). The eukaryotic community succession that strongly correlated with this cyanobacterial biomass cycle was divided into four periods, and each period had distinct characteristics in cyanobacterial biomass and environments in both reservoirs. Integrated co-occurrence networks of eukaryotic plankton based on the whole study period revealed that the cyanobacterial biomass had remarkably high network centralities, and the eukaryotic OTUs that had stronger correlations with the cyanobacterial biomass exhibited higher centralities. The integrated networks were also modularly responded to different eukaryotic succession periods, and therefore correlated with the cyanobacterial biomass cycle. Moreover, sub-networks based on the different eukaryotic succession periods indicated that the eukaryotic co-occurrence patterns were not constant but varied largely associating with the cyanobacterial biomass. Based on these long-term observations, our results reveal that the cyanobacterial biomass cycle created distinct niches between persistent bloom, non-bloom, decrease and increase of cyanobacteria, and therefore associated with distinct eukaryotic plankton patterns. Our results have important implications for understanding how complex aquatic plankton communities respond to cyanobacterial blooms under the changing environments.

The composition of microbial communities can vary at the microspatial scale between free-living (FL) and particle-attached (PA) niches. However, it remains unclear how FL and PA bacterial communities respond to cyanobacterial blooms across water depths. Here, we examined the community dynamics of the FL (0.2-3 μm) and PA (>3 μm) bacterioplankton based on 16S rRNA gene high-throughput sequencing in a subtropical stratified reservoir under Microcystis aeruginosa bloom and non-bloom conditions. Both FL and PA bacterioplankton communities showed different responses in alpha- and beta-diversities to the bloom, suggesting the idea that the responses of bacterial community could depend on lifestyle. Specifically, abundant PA subcommunities showed a greater variation between bloom and non-bloom groups than abundant FL ones. In contrast, rare FL subcommunities exhibited a stronger response to water depth than rare PA ones. Furthermore, the rare taxa exhibited a preference for PA status, shaped and stimulated by the M. aeruginosa bloom. Our analyses also showed that PA bacterial communities were generally more diverse and appeared to be more responsive to routinely measured environmental variables than FL bacteria. Microcystis blooms had a facilitative influence on specific bacteria by mediating the transitions from free-living to particle-attached lifestyles. Altogether, these findings highlight the importance of bacterial lifestyle and abundance in understanding the dynamics of microbial community in cyanobacterial bloom aquatic ecosystem.

Although the influence of microbial community assembly processes on aquatic ecosystem function and biodiversity is well known, the processes that govern planktonic communities in human-impacted rivers remain largely unstudied. Here, we used multivariate statistics and a null model approach to test the hypothesis that environmental conditions and obstructed dispersal opportunities, dictate a deterministic community assembly for phytoplankton and bacterioplankton across contrasting hydrographic conditions in a subtropical mid-sized river (Jiulong River, southeast China). Variation partitioning analysis showed that the explanatory power of local environmental variables was larger than that of the spatial variables for both plankton communities during the dry season. During the wet season, phytoplankton community variation was mainly explained by local environmental variables, whereas the variance in bacterioplankton was explained by both environmental and spatial predictors. The null model based on Raup-Crick coefficients for both planktonic groups suggested little evidences of the stochastic processes involving dispersal and random distribution. Our results showed that hydrological change and landscape structure act together to cause divergence in communities along the river channel, thereby dictating a deterministic assembly and that selection exceeds dispersal limitation during the dry season. Therefore, to protect the ecological integrity of human-impacted rivers, watershed managers should not only consider local environmental conditions but also dispersal routes to account for the effect of regional species pool on local communities.

Plankton communities normally consist of few abundant and many rare species, yet little is known about the ecological role of rare planktonic eukaryotes. Here we used a 18S ribosomal DNA sequencing approach to investigate the dynamics of rare planktonic eukaryotes, and to explore the co-occurrence patterns of abundant and rare eukaryotic plankton in a subtropical reservoir following a cyanobacterial bloom event. Our results showed that the bloom event significantly altered the eukaryotic plankton community composition and rare plankton diversity without affecting the diversity of abundant plankton. The similarities of both abundant and rare eukaryotic plankton subcommunities significantly declined with the increase in time-lag, but stronger temporal turnover was observed in rare taxa. Further, species turnover of both subcommunities explained a higher percentage of the community variation than species richness. Both deterministic and stochastic processes significantly influenced eukaryotic plankton community assembly, and the stochastic pattern (e.g., ecological drift) was particularly pronounced for rare taxa. Co-occurrence network analysis revealed that keystone taxa mainly belonged to rare species, which may play fundamental roles in network persistence. Importantly, covariations between rare and non-rare taxa were predominantly positive, implying multispecies cooperation might contribute to the stability and resilience of the microbial community. Overall, these findings expand current understanding of the ecological mechanisms and microbial interactions underlying plankton dynamics in changing aquatic ecosystems.

Many countries in the world still suffer from high toxic cyanobacterial blooms in inland waters used for human consumption. Regional climate change and human activities within watersheds exert a complex and diverse influence on aquatic ecosystem structure and function across space and time. However, the degree to which these factors may contribute to the long-term dynamics of plankton communities is still not well understood. Here, we explore the impacts of multiple disturbance events (e.g. human-resettlement, temperature change, rainfall, water level fluctuations), including six combined disturbances, on phytoplankton and cyanobacteria in two subtropical reservoirs over six years. Our data showed that combined environmental disturbances triggered two apparent and abrupt switches between cyanobacteria-dominated state and non-cyanobacterial taxa-dominated state. In late 2010, the combined effect of human-resettlement (emigration) and natural disturbances (e.g. cooling, rainfall, water level fluctuations) lead to a 60–90% decrease in cyanobacteria biomass accompanied by the disappearance of cyanobacterial blooms, in tandem with an abrupt and persistent shift in phytoplankton community. After summer 2014, however, combined weather and hydrological disturbances (e.g. warming, rainfall, water level fluctuations) occurred leading to an abrupt and marked increase of cyanobacteria biomass, associated with a return to cyanobacteria dominance. These changes in phytoplankton community were strongly related to the nutrient concentrations and water level fluctuations, as well as water temperature and rainfall. As both extreme weather events and human disturbances are predicted to become more frequent and severe during the twenty-first century, prudent sustainable management will require consideration of the background limnologic conditions and the frequency of disturbance events when assessing the potential impacts on reservoir biodiversity and ecosystem functioning and services.

The degradation of freshwater quality induced by cyanobacterial blooms is a major global environmental concern. Microbially driven nitrogen removal could alleviate eutrophication to some degree in freshwater ecosystems. However, the response of anaerobic ammonium oxidizing (anammox) bacterial communities to cyanobacterial blooms remains poorly understood, especially in reservoir ecosystems. Here we compared the dynamics of anammox bacterial communities during and after a cyanobacterial bloom in a subtropical reservoir. Our data showed that a cyanobacterial bloom triggered a significant increase in bottom anammox bacterial abundance. During the bloom period, anammox bacterial abundance in bottom waters was 9-fold and 52-fold higher compared with non-bloom stratification and mixing periods, respectively. The community composition of anammox bacteria in surface waters changed substantially accompanied by the disappearance of the cyanobacterial bloom, and a shift of dominance from unidentified anammox genera to Ca. Brocadia was observed. Although Ca. Brocadia was always predominant in both middle and bottom waters, the non-bloom period had more unique taxa than the bloom period. Cyanobacterial bloom-related changes in environmental conditions (e.g. NH4-N and total organic carbon) and water stratification together influenced the distribution and dynamics of anammox bacteria. Altogether, our study lays the basis for a better understanding of the breakdown of cyanobacterial blooms in a stratified reservoir.

江汉水牛是湖北省优良地方水牛品种,通过引入国外优秀水牛品种(尼里瑞菲水牛)对其进行了改良.试验选用40头试验牛(尼里瑞菲水牛与江汉水牛的杂交后代母牛),测定其出生时、3月龄和6月龄体重以及体高、体长、胸围、腹围和管围等体尺指标及每日泌乳量、泌乳天数和泌乳期总产奶量等产奶性能,并进行乳成分和奶品质检测.结果表明杂交水牛不但乳脂率、乳蛋白率较高,其乳中体细胞数也远远低于优质乳40万/mL的要求,保持了江汉水牛抗逆性强的特点,健康状况良好,且杂交后代水牛体尺性状尤其是体高和管围性状尚有提升的空间.因此,对江汉水牛进行本品种选育和复壮,是进一步改良江汉水牛的基础.

Globally aquatic ecosystems are likely to become more vulnerable to extreme water fluctuation rates due to the combined effects of climate change and human activity. However, relatively little is known about the importance of water level fluctuations (WLF) as a predictor of phytoplankton community shifts in subtropical reservoirs. In this study, we used one year of data (2010–2011) from four subtropical reservoirs of southeast China to quantify the effects of WLF and other environmental variables on phytoplankton and cyanobacteria dynamics. The reservoirs showed an apparent switch between a turbid state dominated by cyanobacteria and a clear state dominated by other non-cyanobacterial taxa (e.g., diatoms, green algae). Cyanobacterial dominance decreased, or increased, following marked changes in water level. Multiple regression analysis demonstrated that pH, euphotic depth, WLF, and total phosphorus provided the best model and explained 30.8% of the variance in cyanobacteria biomass. Path analysis showed that positive WLF (i.e. an increase in water level) can reduce the cyanobacteria biomass either directly by a dilution effect or indirectly by modifying the limnological conditions of the reservoirs in complex pathways. To control the risk of cyanobacterial dominance or blooms, WLF should be targeted to be above +2m/month; that is an increase in water level of 2m or more. Given that WLF is likely to be of more frequent occurrence under future predicted conditions of climate variability and human activity, water level management can be widely used in small and medium-sized reservoirs to prevent the toxic cyanobacterial blooms and to protect the ecosystem integrity or functions.

The simultaneous analysis of multiple components of ecosystems is crucial for comprehensive studies of environmental changes in aquatic ecosystems, but such studies are rare. In this study, we analyzed simultaneously the bacterioplankton and phytoplankton communities in three Chinese subtropical reservoirs and compared the response of these two components to seasonal environmental changes. Time-lag analysis indicated that the temporal community dynamics of both bacterioplankton and phytoplankton showed significant directional changes, and variance partitioning suggested that the major reason was the gradual improvement of reservoir water quality from middle eutrophic to oligo-mesotrophic levels during the course of our study. In addition, we found a higher level of temporal stability or stochasticity in the bacterioplankton community than in the phytoplankton community. Potential explanations are that traits associated with bacteria, such as high abundance, widespread dispersal, potential for rapid growth rates, and rapid evolutionary adaptation, may underlie the different stability or stochasticity of bacterioplankton and phytoplankton communities to the environmental changes. In addition, the indirect response of bacterioplankton to nitrogen and phosphorus may result in the fact that environmental deterministic selection was stronger for the phytoplankton than for the bacterioplankton communities.

The ecological restoration zones were constructed in Baiyangdian Lake by planting Trapa bispinosa and Nelumbo nucifera, and their purifying effects were estimated. The results showed that there were significant increases in transparency and biodiversity indexes. Transparency in Trapa bispinosa restoration zone increased by 0.55 m(65%) more than that of the control zone, and 0.21 m(52%) in Nelumbo nucifera restoration zone. Phytoplankton density significantly decreased by 1.15 × 107individual/L in Trapa bispinosa zone and 8.24×107individual/L in Nelumbo nucifera zone. Biodiversity indexes kept higher levels than control zones. The peaks of biomass, total nitrogen and total phosphorus contents, nitrogen and phosphorus accumulation of Trapa bispinosa, and transparency of waterbody presented in July. But after then, the water quality began to become worse, and till September 30, 2010, the water quality in the restoration zones was worse than that in the control zone. The biomass, nitrogen and phosphorus accumulation in Nelumbo nucifera were higher than those of Trapa bispinosa. Meanwhile, nitrogen and phosphorus accumulated in Nelumbo nucifera were still maintain 7.85 g/m2and 2.17 g/m2on September 30, 2010, respectively. Due to the differences of the purifying effects between the 2 species, different plant combinations and harvest methods should be adopted.

In order to investigate the phytoplankton community structure and assess the water quality, the 7 sampling sites in Baoding city watercourse of Daqinghe basin was sampled 4 times in 2012 May, July, September and November, respectively. The results showed that 140 species of 7 phylum of phytoplankton were identified, including 69 species of Chlorophyceae, 15 species of Cyanophyta, 3 species of Bacillariophyta, 4 species of Euglenophyta, 21 species of Cryptophyta, 24 species of Chrysophyta and 4 species of Dinophyta. The regularity of number changing of phytoplankton species was MayJulySeptemberNovember. The diversity of phytoplankton, which was located in the upstream of Qingshui Bridge, was greater than other sampling sites. The density of phytoplankton in all sampling sites was not less than 1 000 ind/mL, and the water body reached the level of eutrophication. By using the phytoplankton index to assess the water quality, the water body was in mesotropher before Daqinghe basin flowed into Baoding city, and it was in hypereutropher when Daqinghe basin flowed out of Baoding city. The assessment result of water quality due to density index of phytoplankton was in accordance with that due to physicochemical index, but the result due to Shannon-Wiener biodiversity index and Pielou evenness index was obviously different from that due to physicochemical index. The applicability of biotic index for assessing water quality of city watercourse was discussed.

In order to explore growth characteristics and accumulation regulation of nitrogen and phosphorus of Myriophyllum spicatum,some growth indices and contents of nitrogen and phosphorus of M.spicatum and physic chemical factors of water body were determined in Xiaoxidian belonging to Baiyang Lake from April to September 2011.The results showed:plant height and biomass of M.spicatum increased over time;population growth began in late March and early April,prevailed between June and August,and ended in September;total nitrogen and total phosphorus contents of M.spicatum presented a high level from June to August,corresponding to the main growing periods;accumulation of nitrogen and phosphorus was the highest in leaf,and then stem and root;the highest accumulation of nitrogen and phosphorus in M.spicatum happened in July,and their contents were 9.10g/m2 and 1.08g/m2,respectively;nitrogen and phosphorus accumulation of M.spicatum had a negative correlation with the nitrogen and phosphorus concentration in water,a positive correlation with water transparency,which proved that M.spicatum could purify water;in late August,large areas of M.spicatum decayed,water nitrogen and phosphorus concentrations began to increase,resulting in the decline of water transparency.In conclusion,there was a suggestion that M.spicatum should be harvested in the growth period for avoiding the secondary pollution of water.