Revealing the dynamics of ultraphytoplankton diversity in cihu lake by integrated hplc and molecular sequencing analyses

SummaryTo quantify the major environmental drivers of stream bacterial population dynamics, we modelled temporal differences in stream bacterial communities to quantify community shifts, including those relating to cyclical seasonal variation and more sporadic bloom events. We applied Illumina MiSeq 16S rRNA bacterial gene sequencing of 892 stream biofilm samples, collected monthly for 36‐months from six streams. The streams were located a maximum of 118 km apart and drained three different catchment types (forest, urban and rural land uses). We identified repeatable seasonal patterns among bacterial taxa, allowing their separation into three ecological groupings, those following linear, bloom/trough and repeated, seasonal trends. Various physicochemical parameters (light, water and air temperature, pH, dissolved oxygen, nutrients) were linked to temporal community changes. Our models indicate that bloom events and seasonal episodes modify biofilm bacterial populations, suggesting that distinct microbial taxa thrive during these events including non‐cyanobacterial community members. These models could aid in determining how temporal environmental changes affect community assembly and guide the selection of appropriate statistical models to capture future community responses to environmental change.

Effects of nitrogen and phosphorus on phytoplankton composition and biomass in 15 subtropical, urban shallow lakes in Wuhan, China

Principal component analysis (PCA) was applied to evaluate some of the potential factors contributing to Secchi depth (SD) in the oligotrophic alpine Lake Oze-Numa, using seven water quality parameters obtained during 1990-1992. The data on SD, water temperature (WT), chemical oxygen demand (COD), total nitrogen (TN), suspended solids (SS), total phosphorus (TP), and chlorophyl-α (CHL) were examined. The first component had large loadings on SD, WT, SS, TP, and CHL attributable to phytoplankton population. COD and TN correlated with the second component, showing natural contributions. SD was revealed to be a reliable indicator of eutrophication in the lake, as it was predicted successfully by multiple linear regression analysis using SS, TP, and CHL as independent variables. A time-series analysis of the SD records was applied to a simple estimation of the eutrophication rate of the lake. SD has decreased for the past 25 years (1965-1990) at a rate of 0.065 m⋅yr-1 or 1.2%⋅yr-1. The SD trend was partly explained by the increase in TP concentration attributable to tourists.

Water quality plays an important role in river habitats. This study revealed the annual and seasonal variations and trend prediction of water quality in the middle Yangtze River after the third impoundment stage of the Three Gorges Reservoir. Multivariate statistical methods including principal component analysis/factor analysis (PCA/FA), Mann-Kendall (M-K) tests, discriminant analysis (DA), rescaled range (R/S) analysis, and the Canadian Council of Ministers of the Environment Water Quality Index (CCME-WQI) were used. Herein, eight water quality constituents including pH, electrical conductivity (EC), chloride (Cl), dissolved oxygen (DO), ammonia nitrogen (NH3N), total phosphorus (TP), water temperature (T), and permanganate index (CODmn) were monthly monitored in the Jiujiang hydrological transaction during 2010-2019. The information of eight water quality constituents, related to salinity, nutrient status, and oxidation reactions efficiency, was extracted. Water quality status remained as fair-good during 2010-2019 based on the results of CCME-WQI, with the seasonal significance ranked as T > DO > Cl > pH > EC > TP > NH3N > CODmn. In the future decade, annual average T was predicted to continue to increase although it might decrease in the wet season. EC was predicted to continue increasing annually especially in the wet season while Cl might decrease. NH3N and TP might maintain a significant decreasing trend in the future wet and dry seasons. DO maintained significantly increasing especially in the future dry seasons, whereas CODmn will continue to decrease annually and seasonally. The continued alkalization trend of waterbody was predicted, which is more significant in the wet season. The results provide helpful references for the ecological protection of the middle Yangtze River.

借助综合营养状态指数法、箱须图法以及拐点探测分析法，分析了苏南地区11个主要湖泊的富营养化特征以及各湖之间的差异性，并探讨湖泊由轻度富营养化向中度富营养化状态转换的相关指标阈值。结果显示苏南地区各湖泊的营养物水平存在明显的阶梯状特征，不同湖泊所处的富营养化阶段有所不同。典型封闭型湖泊水源地尚湖与傀儡湖水质最好，总体为Ⅱ-Ⅲ类，评价为中营养状态。典型过水性湖泊淀山湖与澄湖水质最差，TN和TP均劣于Ⅴ类，评价为中度富营养状态，其他湖泊属于轻度富营养化状态。基于拐点分析，提出苏南地区湖泊群富营养化状态由轻度向中度转变的指标阈值：COD_Mn为4.7mg/L，NH₃-N为1.0mg/L，TN为2.3mg/L，TP为0.125mg/L，Chl-a为25μg/L，透明度为50cm；尚湖和傀儡湖处于富营养化最轻的下游区，元荡和阳澄湖目前处于敏感的拐点区域，而淀山湖、澄湖、长荡湖等其他湖泊处于富营养化程度较重的上游区。苏南湖泊群的富营养化状态差异性主要是由不同人为干扰强度和水资源管理模式引起的，实现管理目标由资源利用向资源保护合理转变是解决富营养化问题的关键。;Cultural eutrophication is the Earth's most widespread water quality problem, causing harmful algal blooms, fish deaths, underwater plant deaths, decreasing biodiversity, reduction of water clarity, and many other related problems. Southern Jiangsu Province (SJP), which is by far the most densely populated and most developed area of the east of the People's Republic of China, has in total 11 shallow lakes with a surface area ranging from 10km² to 2,428 km² and an average water depth of less than 2.5m. Unfortunately, accompanying the fast economic development in SJP is the serious deterioration and eutrophication of the water environment, with high levels of algal biomass, frequent algal blooms and low water clarity, which are threatening both the water supply to these regions and their economic development. In this article, in order to investigate the eutrophication features and differences in state of 11 lakes within the same geographic area, we obtained 1090 field monitoring data sets of potassium permanganate index (COD_Mn), ammonia nitrogen (NH₃-N), total phosphorus (TP), total nitrogen (TN), algal Chlorophyll-a (Chl-a) and Secchi depth (SD) of lakes from the environmental monitoring agencies attached to the EPA of Southern Jiangsu Province. All water samples were collected monthly or quarterly from 62 field sites across the 11 lakes and measured in the laboratory during the period from 1993 to 2012. We applied the method of trophic level indices (<em>TLI</em>_c) to assess the trophic level of all lakes, using Box-Whisker plots to compare the levels with current standards and provide spatial discrimination of eutrophication indicators (e.g., COD_Mn, NH₃-N, TP, TN, Chl-a, SD) among all lakes. Furthermore, change-point analysis was performed to determine the threshold values of indicators showing transition among different eutrophication levels in SJP. It was revealed that different eutrophication levels among all 11 lakes can be divided into mesotrophic, lightly-eutrophicated and moderately-eutrophicated states. Both Lake Shanghu and Lake Kuilei, which are under strict management as semi-enclosed drinking water resource areas, had the best water quality, achieving category Ⅱ to Ⅲ standards according to the state standards for surface water quality (GB 18918-2002) and belong to mesotrophic lakes category based on <em>TLI</em>_c. As the typical water-carrying lakes, Lake Dianshan and Lake Chenghu had the heaviest eutrophication level, with TN and TP concentrations recorded as an inferior Category V, classified as moderately-eutrophicated lakes. The other 7 lakes, including Lake Taihu were classified as lightly-eutrophicated. Based on change-point analysis, the threshold values for all indicators as transitional marks, from lightly-eutrophicated to moderately-eutrophicated states, were recommended as: 4.7mg/L of COD_Mn, 1.0mg/L of NH₃-N, 2.3mg/L of TN, 0.125mg/L of TP, 25μg/L of Chl-a, 0.5m of SD. It is notable that Lake Yangchenghu and Lake Yuandang were lingering near the turning point between the lightly-eutrophicated state and moderately-eutrophicated state; thereby, more efforts should be made to prevent these two lakes sliding into more heavily eutrophicated states. According to the main results, there is further discussion to be carried out on the advantages and disadvantages of lake-group analytical methods, as well as the reasons that caused differences in eutrophication level among all lakes within one geographic area (e.g. SJP), such as the natural characteristics of lakes, intensity of human disturbance and water resource management strategies. It can be suggested that setting the primary management goal as water-resource-protection rather than water-resource-utilization is the key to control lake eutrophication in SJP.

In this study, water quality parameters of Hazar Lake have been investigated and evaluated according to water quality regulations. Some water quality parameters, such as dissolved oxygen, water temperature pH, electrical conductivity salinity, transparency, (Sechii disc depth), Chlorophyll a, total alkalinity, BOD, chloride, calcium, magnesium, total phosphorus, sulfate, ammonium nitrogen, nitrite nitrogene, nitrate nitrogene, total nitrogen were examined between September 2019-August 2020. The results were evaluated according to the quality criteria of the In-Continental Water Resources Classes of The Water Pollution and Control Regulation. According to the regulation, the water quality of Hazar Lake is classified as the 1st class in terms of dissolved oxygen, water temperature, ammonium nitrogen, total phosphorus, nitrate-nitrogen, nitrate nitrogen, biological oxygen demand; as the 3rd class in terms of chloride ion; as 4th class in terms of pH. The average chlorophyll a value of 1.09 µg/L in Lake Hazar indicates that the lake shows oligotrophic lake category feature. Secchi disc depth was 3.8 m), which shows that Hazar Lake is at the oligotrophic level in terms of light transmittance. It is noticed that for total phosphorus less than 10 µg/L, the lake is oligotrophic, for 10-20 µg/L is called mesotrophic, and for more than 20 µg/L is so-called eutrophic. This value was measured 0.02 µg/L in the lake; therefore, it can be concluded that the lake is oligotrophic. In addition, the change in alkalinity values of the lake between 402-450 mg CaCO3/L indicates that the lake has very hard water characteristics. Precautions should be taken to protect ecological balances and prevent water pollution in Hazar Lake.

Long-term (2000 to 2012) monthly data on communities of phytoplankton, and environmental variables were measured in water collected from Meiliang Bay and Wuli Lake of Tai Lake, China. Redundancy analysis (RDA) was conducted to explore relationships between the phytoplankton communities and environmental variables. Change points for concentrations of nutrients, which serve as early warnings of state shifts in lacustrine ecosystems, were identified using the Threshold Indicator Taxa Analysis (TITAN). The biomass of phytoplankton was positively correlated with the concentrations of total phosphorus (TP), suspended solids (SS), water temperature (WT), and pH but negatively correlated with the N/P ratio (by mass) and Secchi disk depth (SD). Furthermore, TP, rather than other factors, was a controlling factor limiting the primary production of phytoplankton in most of this region. The change points for concentrations of TP controlling the occurrences of sensitive and tolerant taxa were 56.1 and 103.5μgTP/L, respectively. These results imply that an abrupt change in this lacustrine ecosystem has occurred in most parts of the study area, and the turbid state of this lake can be altered by reducing TP loading. This study provides an alternative ecological method for exploring the production of algal blooms and could advance the understanding of HABs.

Is urban development an urban river killer? A case study of Yongding Diversion Channel in Beijing, China

The Changsha-Xiangtan-Zhuzhou City Group is a heavy industrial district and accepted as the serious pollution area in the Xiangjiang River basin. In this study, 7 metals (Pb, Hg, Cd, As, Zn, Cu and Se) and the river water quality parameters including pH, dissolved oxygen (DO), Escherichia coli (E. coli), potassium permanganate index (CODMn), dichromate oxidizability (CODCr), five-day biochemical oxygen demand (BOD5), ammonia nitrogen (NH4+-N), total nitrogen (TN), total phosphorus (TP) and fluoride (F−) in 18 sampling sites of the Changsha-Xiangtan-Zhuzhou section are monthly monitored in 2016, which is the year to step into the second stage of the “Xiangjiang River Heavy Metal Pollution Control Implementation Plan”. It is found that E. coli, TN and TP are the main pollutants in the Changsha-Zhuzhou-Xiangtan section, and the pollution of heavy metal is not serious but As with potential risk to local people especially children should be concerned. In addition, Xiangtan city is mainly featured with heavy metal pollution, while Zhuzhou and Changsha city are both featured with other pollutants from municipal domestic sewage.

Biochar is generally available to absorb nitrogen, phosphorus and other pollutants to improve water quality. However, the feasibility of biochar in improving water quality deterioration after straw returning is still unclear. In this study, pot experiments were conducted to evaluate the effects of straw decomposition on total phosphorus (TP), ammonium nitrogen (NH4+-N), nitrate nitrogen (NO3−-N) and potassium permanganate index (CODMn) under CK (no straw returning), ST (straw of 7 t/hm2 returning) and SC (straw of 7 t/hm2 and biochar of 20 t/hm2 returning) conditions. Results showed that straw returning could significantly increase the nitrogen and phosphorus contents in field water. After adding biochar, there were significant differences in TP, NH4+-N, NO3−-N and CODMn both in surface water and 0–10 cm soil water in SC treatment compared to ST treatment. The concentration of TP, NH4+-N, NO3−-N and CODMn in surface water under SC treatment were always lower than that under ST treatment, and the maximum concentration could decrease by 52.29%, 39.67%, 35.23% and 44.50%, respectively. In 0–10 cm soil water, the concentration of TP, NO3−-N and CODMn under SC treatment was always significantly higher than that under ST treatment, and the NH4+-N concentration in SC treatment was gradually higher than that under ST treatment at the middle-late observation period. Results indicate that straw returning combined with biochar can effectively decrease the nitrogen concentration, phosphorus concentration and organic pollutants in surface water, inhibit the diffusion of non-point source pollutant, and reduce the risk of water pollution caused by straw returning.

The connection between nutrient input and algal blooms for inland water productivity is well known but not the spatial pattern of water nutrient loading and algae concentration. Remote sensing provides an effective tool to monitor nutrient abundances via the association with algae concentration. Twenty-one field campaigns have been conducted with samples collected under a diverse range of algal bloom conditions for three central Indiana drinking water bodies, e.g., Eagle Creek Reservoir (ECR), Geist Reservoir (GR), and Morse Reservoir (MR) in 2005, 2006, and 2008, which are strongly influenced anthropogenic activities. Total phosphorus (TP) was estimated through hyperspectral remote sensing due to its close association with chlorophyll a (Chl-a), total suspended matter, Secchi disk transparency (SDT), and turbidity. Correlation analysis was performed to determine sensitive spectral variables for TP, Chl-a, and SDT. A hybrid model combining genetic algorithms and partial least square (GA-PLS) was established for remote estimation of TP, Chl-a, and SDT with selected sensitive spectral variables. The result indicates that TP has close association with diagnostic spectral variables with R 2 ranging from 0.55 to 0.72. However, GA-PLS has better performance with an average R 2 of 0.87 for aggregated dataset. GA-PLS was applied to the airborne imaging data (AISA) to map spatial distribution of TP, Chl-a, and SDT for MR and GR. The eutrophic status was evaluated with Carlson trophic state index using TP, Chl-a, and SDT maps derived from AISA images. Mapping results indicated that most MR belongs to mesotrophic (48.6%) and eutrophic (32.7%), while the situation was more severe for GR with 57.8% belongs to eutrophic class, and more than 40% to hypereutrophic class due to the high turbidity resulting from dredging practices.

Algal blooms have become a critical environmental issue worldwide, with chlorophyll-a (Chl-a) serving as a key biological indicator for assessing bloom intensity and providing essential insights into bloom dynamics. Based on four field investigations conducted in the Danjiangkou Reservoir between 2023 and 2024, this study utilized data on Chl-a, nutrients (total nitrogen, total phosphorus, ammonia nitrogen, etc.), water temperature, and light intensity to develop a Chl-a concentration prediction model using the XGBoost algorithm. The Shapley Additive Explanations method was further employed to quantitatively evaluate the relative contributions of environmental variables to Chl-a in the Danjiangkou Reservoir area and the Hanjiang Reservoir area. The results showed that the XGBoost model achieved high accuracy in modeling Chl-a concentrations (R2 > 0.8). In the Hanjiang Reservoir, water temperature and light intensity were identified as the dominant factors influencing Chl-a, together accounting for over 58% of its variation, highlighting the leading role of physical conditions in algal growth. In contrast, in the Danjiang Reservoir, water temperature, total phosphorus, and ammonia nitrogen were the primary drivers, jointly contributing approximately 62.2%, indicating a stronger influence of nutrient availability. This study elucidates the major environmental drivers affecting Chl-a levels in the Danjiangkou Reservoir and provides important implications for safeguarding water quality in the water source area of the South-to-North Water Diversion Project.

Predictive nutrient criteria method, combined with expert elicitation and structural equation model (SEM), was proposed in this study for establishing lake nutrient standard in Chinese lakes (Yungui Plateau ecoregion and Eastern Plain ecoregion). Expert elicitation was involved to quantify the probability of attainment of the designated-use (drinking water source) based on monitoring data. The experts scoring results were introduced to SEM to assess predictive relationships between candidate standard variables and the designated-use attainment. In Yungui ecoregion, the standardized effects of chlorophyll-a (Chl-a), chemical oxygen demand and total phosphorus (TP) on designated-use attainment were −0.41, −0.14, and −0.43, respectively. These result demonstrated that the two most predictive indicators for designated-use attainment were TP and Chl-a. In Eastern ecoregion, the standardized effects of TP, total nitrogen (TN), dissolved oxygen and water temperature (T) on designated-use attainment were 0.77, −0.12, 0.13 and −0.02, respectively. The most predictive indicator was TP. The model was further used for estimating the designated-use attainment associated with various levels of candidate standards. TP, TN, Chl-a and Secchi depth (SD) were selected as standard indicators in Yungui ecoregion. TP, TN, and Chl-a were selected in Eastern ecoregion. In order to achieve the 85 % designated-use attainment, standard values of TP, TN, Chl-a and SD in Yungui ecoregion would be 0.02 mg/L, 0.2 mg/L, 1.4 μg/L, and 0.581 m; and standards of TP, TN, and Chl-a in Eastern ecoregion would be 0.039 mg/L, 0.95 mg/L, and 1.75 μg/L, respectively. Finally, the differences between standards in these two ecoregions were also analyzed.

Bacterial communities are an important part of biological diversity and biogeochemical cycling in aquatic ecosystems. In this study, the relationship amongst the phytoplankton species composition and abiotic environmental factors on seasonal changes in the community composition of free-living and attached bacteria in Lake Erhai were studied. Using Illumina high-throughput sequencing, we found that the impact of environmental factors on both the free-living and attached bacterial community composition was greater than that of the phytoplankton community, amongst which total phosphorus, Secchi disk, water temperature, dissolved oxygen and conductivity strongly influenced bacterial community composition. Microcystis blooms associated with subdominant Psephonema occurred during the summer and autumn, and Fragilaria, Melosira and Mougeotia were found at high densities in the other seasons. Only small numbers of algal species-specific bacteria, including Xanthomonadaceae (Proteobacteria) and Alcaligenaceae (Betaproteobacteria), were tightly coupled to Microcystis and Psephonema during Microcystis blooms. Redundancy analysis showed that although the composition of the bacterial communities was controlled by species composition mediated by changes in phytoplankton communities and abiotic environmental factors, the impact of the abiotic environment on both free-living and attached bacterial community compositions were greater than the impact of the phytoplankton community. These results suggest that the species composition of both free-living and attached bacterial communities are affected by abiotic environmental factors, even when under strong control by biotic factors, particularly dominant genera of Microcystis and Psephonema during algal blooms.

Natural lake systems represent important reservoirs for residential water supply, fish production, recreational activities and enjoyment of their natural beauty. Nevertheless, human impacts may affect their health status resulting in degradation and loss of biodiversity. The aim of the present study was to obtain data on the health status of a natural lake located in an indigenous reservation in the Brazilian Amazon, using the phytoplankton community changes along the rainy (June) and dry (November) seasons of 2006. We collected water (temperature, pH, Secchi depth and conductivity) and phytoplankton samples from the subsurface, middle of the water column, and approximately 30 cm above the bottom, over 24-hour sampling periods, from a central station in the lake. Samples taken from biotic and abiotic variables were correlated using canonical correspondence analysis (CCA). Results showed that the lake exhibited high temperatures in both seasons, and showed thermal stratification only during the rainy season. Dissolved oxygen exhibited a clinograde pattern in the rainy season and high oxygen in the hypolimnion in the dry season. In the rainy season, the water near the bottom was acidic, turbid and had a greater concentration of phosphorus. Dissolved oxygen, conductivity, pH, nitrite, total phosphorus and total dissolved phosphorus exhibited diel variations in the rainy season, whereas water temperature, dissolved oxygen, total nitrogen and total dissolved phosphorus exhibited significant differences between hours of the day in the dry season. The phytoplankton was represented by 39 taxa, and Chlorophyta showed the greatest species richness, totaling 25 taxa. Among Chlorophyta, desmids were the most diverse, accounting 52%. Bacillariophyta (nine species) was the second most diverse group. Cyanophyta was represented by three species, including Merismopedia tenuissima, the most abundant taxon. Despite the occurrence of taxa that indicate organic pollution, their biomass and frequency indicate that the system is not currently threatened. Lake Caracaranã is an oligotrophic system, with low algal density and isolated blooming episodes due to its shallow depth.