Lake health-status evaluation in the middle reaches of the Yangtze River based on the phytoplankton biological integrity index

Assessment of eutrophication and water quality in the estuarine area of Lake Wuli, Lake Taihu, China

Factors influencing the spatio-temporal dynamics of plankton communities in small tropical lakes are not well-understood. This study assessed plankton communities in response to spatial (six sampling sites) and seasonal (wet vs. dry seasons) changes in environmental variables in Lake Kanyaboli, a small satellite lake on the northern shores of Lake Victoria, Kenya. Water quality variables, including pH, conductivity (EC), dissolved oxygen (DO), temperature, Secchi depth (SD), nitrates (NO3-), nitrites (NO2-), ammonium (NH4+), soluble reactive phosphorus (SRP), total nitrogen (TN), total phosphorus (TP), and chlorophyll-a(Chl-a), were monitored monthly at six sites spread throughout the lake for 1 year. Phytoplankton and zooplankton samples were collected and analyzed for taxon composition and abundance. Two-way ANOVA showed no significant interaction between site and season for all variables. Likewise, there were no significant spatial differences for all variables except Chl-a. At-test showed significant seasonal differences in SD, DO,NH4+,NO3-,NO2-, and TN. Thirty phytoplankton genera were identified belonging to Bacillariophyceae, Chlorophyceae, Cryptophyceae, Cyanophyceae, Euglenoidae, Trebouxiophyceae, and Zygnematophyceae, with Chlorophyceae being the most dominant (42.30%). Zooplankton comprised of 15 genera, belonging to Copepoda (55.4%), Rotifera (27.9%), and Cladocera (16.7%). Two-way ANOVA for plankton abundance showed no significant interaction between site and season, but there were significant differences in community composition between the wet and dry seasons. Canonical correspondence analysis identified water clarity (Secchi depth) and concentrations of dissolved fractions of nitrogen and phosphorus as the major water quality variables driving variation in the composition of plankton communities in the lake. This study showed that seasonality was a major driver of changes in plankton community composition between dry and wet seasons through changes in the concentrations of nutrients (NH4+,NO3-,NO2-, TN, and TP). Lake Kanyaboli's phytoplankton community indicated a non-equilibrial state, perhaps due to short residence times of water, especially during the wet season, and dense macrophytes fringing the lake that increase nutrient uptake and limit the dominance of select phytoplankton species. This study shows the importance of long-term studies covering dry and wet seasons to understand the dynamics of plankton communities and their drivers in small tropical waterbodies to inform management and conservation.

Lake phytoplankton communities are affected by environmental and spatial factors. We studied the relative importance of environmental and spatial factors on the phytoplankton community assembly in Lake Wuchang across three hydrological seasons, which were divided into dry (December to March), normal (April to June, October to November) and wet seasons (July to September) based on the water level and depth. Spatial and temporal patterns of environmental factors and phytoplankton community composition and diversity were studied using Kruskal–Wallis test, Wilcoxon test and NMDS. CCA, Mantel and partial Mantel tests, and PLS-PM were used to investigate the effects of environmental and spatial factors on phytoplankton community characteristics. Results showed that phytoplankton assemblages at the eight study sites were composed of totally 244 species belonging to 9 phyla, which changed from Bacillariophyta and Chlorophyta to Cyanophyta across the whole hydrological period. There was significantly higher abundance and biomass in the normal and wet seasons than that in the dry season. Phytoplankton alpha diversity exhibited uniform temporal distribution patterns with higher values in the dry season than in the normal and wet seasons. The Mantel and partial Mantel tests revealed that environmental (physicochemical conditions of lake water) and spatial factors (geographic distances among sites) jointly affected the phytoplankton community structure and beta diversity across the hydrological seasons, while spatial factors were more important in the wet season. Partial least squares path models showed that spatial factors exhibited a significant positive correlation with the phytoplankton diversity with the path coefficients of 0.53 and 0.71 in the normal and wet seasons, respectively. Phytoplankton composition had significant correlation with on phytoplankton diversity with the path coefficient of −0.75 and 0.61 in the normal and wet seasons, respectively. Our findings revealed that both environmental and spatial factors affected the phytoplankton community assembly in Lake Wuchang. Environmental factors played a more important role in the dry season, while spatial factors were more important in the wet season. With the exception of the abiotic factors (environmental and spatial), the impacts of biotic factors on phytoplankton community cannot be ignored. Therefore, it is also necessary to strengthen further research on the top-down control over phytoplankton communities in Lake Wuchang.

As an important component of lake ecosystems, plankton are often used as indicators to evaluate the health of aquatic ecosystems, such as lakes and reservoirs. The plankton integrity index (P-IBI) is a highly utilized method for evaluating the ecological health of the lakes. This study took Dianchi Lake, located in the Yangtze River Basin, as the research object and analyzed the phytoplankton, zooplankton communities, and environmental factors at 11 sampling points in this lake during the wet season (July) in 2022 and the dry season (February) in 2023. The P-IBI was established to evaluate the health status of this lake ecosystem. The results showed that a total of 83 species of phytoplankton and 31 species of zooplankton were identified in Dianchi Lake, and the number of plankton species in the dry season was significantly higher than that in the wet season. The P-IBI evaluation results for the two hydrological periods were generally “good”. Linear regression analysis showed that there was a certain negative correlation between the P-IBI value and the comprehensive trophic level index (TLI), and the evaluation results were generally in line with the actual situation of the water body. Redundancy analysis (RDA) showed that there was a significant correlation between the P-IBI and its constituent parameters and individual water quality environmental factors, such as total nitrogen (TN) and electrical conductivity (EC). In summary, by reducing errors caused by spatial and temporal changes across various hydrological periods, P-IBI represents a more scientifically rigorous technique for lake water ecological health assessments within a certain time range.

Subtropical plateau lakes, which are distinguished by their elevated altitudes and subtropical climates, display distinct ecological dynamics. Nevertheless, the spatial and seasonal variations in the plankton community structure, as well as their interactions with environmental factors, remain inadequately understood. This study investigated the alterations in the phytoplankton and zooplankton community structure across different geographical regions (southern, central, and northern) and seasonal periods (rainy and dry) in Erhai lake, located in a subtropical plateau in China. The results indicated that the average values of total nitrogen (TN), total phosphorus (TP), chlorophyll-a (Chla), pH, and conductivity are significantly higher during the rainy season in comparison to the dry season. Furthermore, during the rainy season, there were significant differences in the concentrations of TN, TP, and Chla among the three designated water areas. Notable differences were also observed in the distribution of Microcystis, the density of Cladocera and copepods, and the biomass of copepods across the three regions during this season. Conversely, in the dry season, only the biomass of Cladocera exhibited significant variation among the three water areas. The redundancy analysis (RDA) and variance partitioning analysis demonstrated that the distribution of plankton groups (Cyanophyta, Cryptophyta, and Cladocera) is significantly associated with TN, Secchi depth (SD), and Chla during the rainy season, whereas it is significantly correlated with TP and SD during the dry season. These findings underscore the critical influence of environmental factors, shaped by rainfall patterns, in driving these ecological changes. In the context of the early stages of eutrophication in Lake Erhai, it is essential to ascertain the spatial distribution of water quality parameters, as well as phytoplankton and zooplankton density and biomass, during both the rainy and dry seasons.

3种不同营养水平的河流浮游植物群落结构及其与环境因子的相关性

BackgroundThe application of index of biotic integrity (IBI) to evaluate river health can be an essential method for river ecosystem management. However, these types of methods were developed in small, low-order streams, and are therefore, infrequently applied to large rivers. To that end, phytoplankton communities and environmental variables were monitored in 30 sampling segments of the middle and lower reaches of the Yangtze River, China during the wet (July–August) and dry (November–December) seasons in 2017–2018. We developed a phytoplankton-based index of biotic integrity (P-IBI) and used the index to assess the ecological health of the Yangtze River. Relationships among P-IBI, its component metrics, and environmental factors were analyzed across different seasons.ResultsResults obtained from the P-IBI indicated that the phytoplankton-based ecological health of the Yangtze River was rated as “good” during both seasons, with an overall better condition in the dry season. During the wet season, there were scattered river segments with P-IBI ratings of “fair” or below. Water quality and land use appeared to shape the patterns of P-IBI. In the wet season, P-IBI negatively correlated with total phosphorus, nitrate, total suspended solids, turbidity, conductivity, and dissolved oxygen. In the dry season, P-IBI positively correlated with total nitrogen, ammonium, and nitrite, and negatively correlated with water temperature.ConclusionsThe ecological health of the Yangtze River as reflected by the P-IBI exhibited spatial and temporal variability, with the effect of water quality being greater than that of local land use. This study indicated the importance of considering seasonal effects in detecting large river ecological health. These findings enhanced our understanding of the ecological health and characterized potential benchmarks for management of the Yangtze River. These findings also may be applicable to other large rivers elsewhere.

Lake Cajititlán is a small, shallow, subtropical lake located in an endorheic basin in western Mexico. It is characterized by a strong seasonality of climate with pronounced wet and dry seasons and has been classified as a hypereutrophic lake. This eutrophication was driven by improperly treated sewage discharges from four municipal wastewater treatment plants (WWTPs) and by excessive agricultural activities, including the overuse of fertilizers that reach the lake through surface runoff during the rainy season. This nutrient rich runoff has caused algal blooms, which have led to anoxic or hypoxic conditions, resulting in large-scale fish deaths that have occurred during or immediately after the rainy season. This study investigated the changes in the phytoplankton community in Lake Cajititlán during the rainy season and the association between these changes and the physicochemical water quality and environmental parameters measured in the lake’s basin. Planktothrix and Cylindrospermopsis were the dominant genera of the cyanobacterial community, while the Chlorophyceae, Chrysophyceae, and Trebouxiophyceae classes dominated the microalgae community. However, the results showed a significant temporal shift in the phytoplankton communities in Lake Cajititlán induced by the rainy season. The findings of this study suggest that significant climatic variations cause high seasonal surface runoff and rapid changes in the water quality (Chlorophyll-a, DO, NH4+, and NO3–) and in variations in the composition of the phytoplankton community. Finally, an alternation between phosphorus and nitrogen limitation was observed in Lake Cajititlán during the rainy season, clearly correlating to the presence of Planktothrix when the lake was limited by phosphorus and to the presence of Cylindrospermopsis when the lake was limited by nitrogen. The evidence presented in this study supports the idea that the death of fish in Lake Cajititlán could be mainly caused by anoxia, caused by rapid changes in water quality during the rainy season. Based on our review of the literature, this is the first study on the phytoplankton community in a subtropical lake during the rainy season using high throughput 16S rRNA and 18S rRNA amplicon sequencing.

Phytoplankton plays a key role in the stabilization of aquatic ecosystems. However, there is a lack of research on the structure of phytoplankton communities and their influencing factors in shallow lakes in Southeast Hubei. In this study, four typical lakes were selected in the summer of 2019, and the phytoplankton community structure and its drivers were investigated for each lake. The results showed that the number of phytoplankton species, dominant species, biomass, and abundance varied among lakes. A comprehensive trophic level index (TLI) assessment showed that Lake Xiandao was oligotrophic, Lake Baoan was light eutrophic, and Lake Wang and Lake Ci were moderate eutrophic. The Shannon–Wiener, Margalef, and Pielou indices showed that the phytoplankton communities of Lake Wang and Lake Ci are less stable, and the water bodies are more severely contaminated. In contrast, the communities of the Lake Baoan and Lake Xiandao are more stable and have superior water quality. A redundancy analysis (RDA) indicated that the primary variables influencing phytoplankton community structures were pH and water temperature (WT) (Lake Ci); permanganate index (CODMn) and pH (Lake Xiandao); WT and total nitrogen (TN) (Lake Wang); and WT and total phosphorus (TP) (Lake Baoan).

Lakes play an important role in socioeconomic development and ecological balance in China, but their water quality has deteriorated considerably in recent decades. In this study, we investigated the spatial-temporal variations of eutrophication parameters (secchi depth, total nitrogen, total phosphorus, chemical oxygen demand, chlorophyll-a, trophic level index, and trophic state index) and their relationships with lake morphology, watershed land use, and socioeconomic factors in the Yunnan Plateau lakes. Results indicated that about 77.8% of lakes were eutrophic according to trophic state index. The plateau lakes showed spatial variations in water quality and could be classified into high-nutrient and low-nutrient groups. However, because watersheds were dominated by vegetation, all eutrophication parameters except chlorophyll-a showed no significant differences between the wet and dry seasons. Lake depth, water residence time, volume, and percentage of built-up land were significantly related to several eutrophication parameters. Agricultural land use and social-economic factors had no significant correlation with all eutrophication parameters. Stepwise regression analyses demonstrated that lake depth and water residence time accounted for 73.8% to 87.6% of the spatial variation of single water quality variables, respectively. Redundancy analyses indicated that lake morphology, watershed land use, and socioeconomic factors together explained 74.3% of the spatial variation in overall water quality. The results imply that water quality degradation in the plateau lakes may be mainly due to the domestic and industrial wastewaters. This study will improve our understanding of the determinants of lake water quality and help to design efficient strategies for controlling eutrophication in the plateau region.

Development and testing of the phytoplankton biological integrity index (P-IBI) in dry and wet seasons for Lake Gehu

No evidence for environmental and spatial processes in structuring phytoplankton communities

To investigate the differences in water quality response to landscape features at multiple spatial and temporal scales for different lake types， the Dianchi Lake （Tectonic Lake） in Kunming， Yunnan Province and Fushun West Lake （Hecheng Lake） in Zigong， Sichuan Province were used as the objects of the study. Land use types and landscape pattern indices were extracted at five spatial scales of 200， 400， 600， 800， and 1 000 m buffer zones of the Dianchi Lake basin in Kunming and 20， 40， 60， 80， and 100 m buffer zones of the Fushun West Lake Basin. Combined with lake water quality data from the wet season （July 2022） and dry season （April 2023）， the correlation analysis and the redundancy analysis （RDA） were used to quantitatively compare the differences in the multi-temporal and spatial scale responses of water quality to landscape characteristics between two types of lakes. The results showed that： ① All land use types of Fushun West Lake were urban land， and the land use types of Kunming Dianchi were richer， in which urban land was dominant. The landscape fragmentation of both lakes decreased with the increase of spatial scale. Due to the different landscape characteristics of the two lake basins， their water quality was better in the dry season than in the wet season， and the water quality of Fushun West Lake was better than that of Kunming Dianchi. ② Fushun West Lake had the highest explanation rate of the landscape characteristics to the water quality at the scale of 60 m lakeshore buffer zone in the dry season， whereas Kunming Dianchi had the strongest response to the landscape characteristics in the wet season and 800 m lakeshore buffer zone. The response of water quality to the landscape characteristics of Kunming Dianchi was higher than that of Fushun West Lake. ③ There were significant differences in the response of water quality of varying lake types to different landscape features at different spatial and temporal scales. In this study， the urban land was a "sink" landscape of water quality in the Dianchi Lake basin in both dry and wet seasons， while the Fushun West Lake basin was a typical "source" landscape. Forest land was a "source" of polluted water quality at multiple spatial and temporal scales in the Kunming Dianchi basin， with a negative correlation between buffer scale and most water quality indicators at more distant lakeshore zones during the dry season. Patch density was the most critical indicator affecting water quality in Dianchi and Fushun West Lake watersheds. Moreover， the landscape shape index had a greater impact on the water quality of Fushun West Lake than that of Kunming Dianchi. By studying the differences in the response of water quality of different lake types at multiple spatial and temporal scales， this study helps to better predict and respond to the potential impacts of environmental changes on water resources and ecosystems. It also provides a scientific basis for the development of more precise and effective water resource management and protection policies by optimizing the allocation of water resources and strengthening ecological protection and environmental governance.

ObjectiveIn this study, the dry-wet seasonal variation characteristics of sap flow of the two afforestation poplar species in semi-arid Lhasa river valley, and the environmental impact factors were investigated in order to provide a theoretical base for species selection for vegetation reconstruction in the river valley. MethodThe Granier's thermal dissipation probe was employed to continuously measure the stem sap flow of Populus beijingensis and Populus szechuanica during the wet and dry seasons. At the same time, environmental factors, such as solar radiation (Q), air temperature (Ta), soil water content (SWC), and vapor pressure deficit (VPD), were recorded. ResultsThe main meteorological factors in the Lhasa river valley were quite different in wet and dry seasons. The Q, Ta, SWC, and VPD values during the wet season were higher than that in the dry season, and the average of them in the dry season wrer around 60% of those in wet season. In both seasons, the sap flow velocity in P. beijingensis was lower than that in P. szechuanica.The sap flux density of P. beijingensis was 71% and 58% lower than those of P. szechuanica during the dry and wet seasons, respectively. During the dry season, the sap flux density of two poplars declined by 65% and 76% compared with that in wet season. The main environmental factors of Q and VPD had less influence on the stem sap flow of P. beijingensisthan on that of P. szechuanica. ConclusionIn the Lhasa river valley area between dry and rainy season, the sap flux density of two poplar species all had obvious circadian rhythm. However, there were significant differences in peak value, daily average value, start-up time and the impact environmental factors between the two species, especially in the dry season.P. szechuanica, as native tree species, showed a stronger adaptability.

The Eastern Lake Region is the most eutrophic in China and is most affected by human activities. In recent years, phytoplankton have proliferated in most lakes in the lake region, with the frequent occurrence of water blooms, and the driving mechanisms and spatial differences for long-term changes in the phytoplankton community of lakes at the regional scale remain unclear. Among them, Lake Taihu, Lake Hongze, and Lake Luoma are located in the Yangtze River Economic Zone and have important ecological functions such as storage, drinking water, and irrigation. They are greatly affected by human activities and are typical lakes in the Eastern Lake Region. We used hydro-meteorological data, physical and chemical index data, and phytoplankton biomass data from 2016 to 2021 to study the phytoplankton community changes in typical lakes in the Eastern Lake Region based on redundancy analysis and combined hierarchical partitioning and variance decomposition to identify the main drivers of phytoplankton community changes. The results showed that the long-term trends of climate background were generally consistent among typical lakes in the Eastern Lake Region, but their nutrients, phytoplankton community, and environmental driving factors were different. The dominant phytoplankton phyla and genera in Lake Taihu, Lake Hongze, and Lake Luoma were significantly different. The lake characteristic, mainly characterized by water depth, was the main driving factor that led to spatial differences in phytoplankton communities among typical lakes in different seasons. The explanatory rates of water depth in spring, summer, autumn, and winter were 46.32%, 30.79%, 26.92%, and 35.80%, respectively. However, the secondary driving factors had seasonal differences. Among them, in spring, the secondary driving factors were conductivity （13.48%） and total nitrogen （12.74%）. In summer, the secondary driving factors were total phosphorus （19.02%） and conductivity （14.71%）. In autumn, the secondary driving factors were total phosphorus （19.43%） and dissolved total nitrogen （15.86%）. In winter, the secondary driving factors were total phosphorus （23.53%） and the daily minimum temperature （14.91%）. Quantifying the contribution of different drivers was important for future lake eutrophication management and policy formulation.