Effects of ecological protection and restoration on phytoplankton diversity in impounded lakes along the eastern route of China's South-to-North Water Diversion Project

Deciphering Planktonic Bacterial Community Assembly in the Storage Reservoir of the Long-Distance Water Diversion Project

Storage reservoirs are crucial components of long-distance water diversion projects, where water diversion may lead to changes in microbial diversity and community structure. Seasonal variations also drive alterations in microbial communities. However, the way that microbes assemble under the combined effects of water diversion and seasonal variations in the storage reservoir has not been extensively studied. Jihongtan Reservoir is the terminal storage reservoir of the Yellow River to Qingdao Water Diversion Project (YQWD), which had an average annual water diversion period exceeding 290 days in recent years. In this study, 16S rDNA amplicon sequencing was used to investigate the seasonal dynamics and assembly of planktonic bacterial communities during the water diversion period in Jihongtan Reservoir. The results indicate that planktonic bacteria were able to maintain stable diversity across all four seasons, while the community structure underwent significant seasonal succession. Water temperature (WT) was found to be the primary driving environmental factor influencing the seasonal dynamic of planktonic bacterial communities. Co-occurrence network patterns of planktonic bacterial communities varied across different seasons, particularly in spring and winter. The spring network displayed the most complexity, showcasing the highest connectivity and greater stability. In contrast, the winter network was simpler, exhibiting lower local connectivity but higher global connectivity and lower stability. The analysis of the neutral community model and null model revealed that the relative importance of deterministic and stochastic processes in governing planktonic bacterial community assembly varies seasonally. Stochastic processes (dispersal limitation) are more prominent in spring, summer, and autumn, while deterministic processes (heterogeneous selection) play a greater role in winter. This study is essential for gaining a comprehensive understanding of the effects of water diversion projects and offers valuable references for the assessment of other similar projects.

Evolution of CO2 flux over 60 years: Identifying source and sink changes caused by eutrophication of Hulun Lake

Understanding the carbon cycling process and assessing the carbon sequestration potential in freshwater lakes relies heavily on their source-sink relationship. However, human activity and climate change have obscured the clarity of this relationship and its driving mechanisms, particularly in northern grassland lakes. This study focused on Hulun Lake, the largest grassland lake in northern China, to quantitatively analyze the carbon dioxide exchange flux (FCO2) at the water-air interface from 1963 to 2023. The analysis revealed significant seasonal, interannual, and decadal variations in the FCO2. Over the past 60 years, FCO2 varying significant in seasons and years has notably decreased, averaging 0.324 ± 0.106 gC·m-2·d-1. Notably, there was a qualitative change in FCO2 from "sink" (0.161 ± 0.109 gC·m-2·d-1) to "source" (-0.130 ± 0.087 gC·m-2·d-1)between 2019 and 2020. From 1963 to 2019, the lake acted as a CO2 source, releasing an average flux of 0.438 ± 0.111 gC·m-2·d-1. During this period, FCO2 was the highest in spring, followed by summer, and the lowest in autumn and winter when the lake was covered by ice. In 2020, the lake transitioned into a CO2 sink with an average FCO2 of -0.248 ± 0.042 gCm-2·d-1 from 2020 to 2023. During this period, FCO2 peaked in autumn, followed by summer and spring, and was lowest in winter when the lake was ice covered. A structural model equation (SEM) was employed to analyze the effects of various factors, including physical, chemical, and biological aspects, on FCO2 and the source-sink pattern of Hulun Lake. This study suggested that lake eutrophication, compounded by global warming, may be the primary driving force behind these changes. Rising temperatures and eutrophication enhanced the primary productivity of the lake. The amount of CO2 fixed through photosynthesis surpassed that emitted by respiration. Consequently, the eutrophication may alter the CO2 exchange pattern in Hulun Lake, shifting it from a "source" to a "sink".

Structural characteristics of plankton community in Dongting Lake and its relationship with water environmental factors

The plankton community structure and environmental factors in Dongting Lake were investigated during four seasons from September 2020 to August 2021. The results revealed 147 species from 58 genera and 7 phyla of phytoplankton and 84 species from 56 genera and 4 phyla of zooplankton in Dongting Lake. The characteristics of plankton communities varied with time and space. The temporal variation of phytoplankton abundance ranged from 43.5201 × 104 to 120.7968 × 104 cells/L and the spatial variation ranged from 18.6707 × 104 to 247.5542 × 104 cells/L. The temporal variation of zooplankton abundance ranged from 18 to 42 ind/L and the spatial variation ranged from 19 to 62 ind/L. The temporal and spatial variations of the abundance range values were much larger for phytoplankton than for zooplankton, with phytoplankton dominating. However, environmental factors in Dongting Lake vary more temporally than spatially, and drive more temporal than spatial variations in planktonic organisms. Based on the redundancy analysis WT, DO, and CODMn were the main environmental factors affecting the distribution of phytoplankton, while WT, CODMn, NO2-N, and Chl-a were the main factors affecting the distribution of zooplankton. WT and CODMn were the common key influencing factors.

Biotic homogenization in multisystem cascade reservoirs: insights from sedimentary photopigment analysis

The existing literature provides limited insights into the dynamics of phytoplankton communities and the spatial heterogeneity of physicochemical parameters in multisystem cascade reservoirs (interconnected reservoirs derived from different rivers). The existing studies are concentrated on cascade reservoirs (interconnected reservoirs derived from the same river). To address this knowledge gap, the aims of the present study were as follows: (1) investigate the spatial heterogeneity, within and between reservoirs, of geochemical parameters associated with the eutrophication process, considering total phosphorus, chlorophyll-a, pheophytin, and metals (chromium, copper, nickel, lead, zinc, iron, and manganese); (2) evaluate sediment quality at the designated locations; (3) assess differences in the richness and concentration of sedimentary photopigments between the reservoirs. Application of principal component analysis revealed discernible gradients for the abiotic variables, although the differences were not statistically significant (one-way PERMANOVA test, p > 0.05). The observations suggested a tendency towards spatial homogeneity within and between the reservoirs. The metal concentrations were consistent with regional reference values, while phosphorus levels in the sediment approached the threshold for classification as pollution (~ 2000 mg/kg). Analysis of pigments indicated low dissimilarity among the reservoirs, which could be mainly attributed to the eutrophication process and high connectivity of the sampled areas. To counteract ongoing biotic homogenization, it is essential to reduce nutrient inputs and invest in ecological protection and restoration programs. The analysis of sedimentary photopigments provides an efficient and cost-effective alternative way to assess phytoplankton communities.

Seasonal Dynamics of Eukaryotic Microbial Communities in the Water-Receiving Reservoir of the Long-Distance Water Diversion Project, China

Inter-basin water transfer projects, such as the Yellow River to Qingdao Water Diversion Project (YQWD), are essential for addressing water scarcity, but impact local aquatic ecosystems. This study investigates the seasonal characteristics of eukaryotic microbial communities in the Jihongtan Reservoir, the main water-receiving body of YQWD, over a one-year period using 18S rDNA amplicon sequencing. The results showed that the eukaryotic microbial diversity did not exhibit significant seasonal variation (p > 0.05), but there was a notable variance in the community structure (p < 0.05). Arthropoda and Paracyclopina, representing the most dominant phylum and the most dominant genus, respectively, both exhibited the lowest abundance during the winter. The Chlorophyta, as the second-dominant phylum, demonstrates its higher abundance in the spring and winter. The Mantel test and PLS-PM (Partial Least Squares Path Modeling) revealed that water temperature (WT), dissolved oxygen (DO), and pH influenced the seasonal dynamic of eukaryotic microbial communities significantly, of which WT was the primary driving factor. In addition to environmental factors, water diversion is likely to be an important influencing factor. The results of the co-occurrence network and robustness suggested that the spring network is the most complex and exhibits the highest stability. Moreover, keystone taxa within networks have been identified, revealing that these key groups encompass both abundant and rare species, with specificity to different seasons. These insights are vital for understanding the seasonal variation of microbial communities in the Jihongtan Reservoir during ongoing water diversions.

Integrated evaluation of the impact of water diversion on water quality index and phytoplankton assemblages of eutrophic lake: A case study of Yilong Lake

Water diversion has been widely utilized to enhance lake water quality and mitigate cyanobacterial blooms. However, previous studies have mainly focused on investigating the effects of water diversion on water quality or aquatic ecological health. Consequently, there is limited research investigating the combined impact of water diversion on the water quality and the ecological health of eutrophic lakes, and whether the WQI and phytoplankton assemblages demonstrate similar patterns following water diversion. In this study, the effects of water diversion on the ecosystem health of eutrophic lakes were comprehensively evaluated based on the WQI indices and phytoplankton assemblages during the NWDP-21 and WDP-22. The results showed that the annual mean of WQI increased from 52.02 to 54.36 after water diversion, which improved the water quality of the lake, especially NH3-N and TN decreased by 58.6% and 15.2%, respectively. The phytoplankton assemblages changed significantly before and after water diversion, and we observed that the total biomass of phytoplankton decreased by 12.3% and phytoplankton diversity indices (Shannon-Wiener diversity, Pielou evenness, and Simpson index) increased by 8.6%-8.9% after water diversion, with an improvement in the connectivity and stability of the phytoplankton. Notably, enhanced adaptations of rare sub-communities for resource use in water diversion environments, and water diversion inhibited the dispersal ability of dominant functional groups, and the effects of hydrological disturbances on the structure of phytoplankton assemblage favored the ecological health of eutrophic lakes. VPA analysis further reveals that water diversion alters the drivers of phytoplankton functional group biomass and phytoplankton diversity. The results of the PLS-PM analysis clarify that water diversion indirectly impacts the total phytoplankton biomass and phytoplankton diversity primarily by modifying light availability. Significant correlations are observed between the dominant functional groups biomass and diversity indices of WQI. The trends in changes observed in water quality indices and phytoplankton following water diversion align with the evaluation of water ecological health. This study provides valuable guidance for the ecological management of the diversion project in Yilong Lake and serves as a reference for similar projects in other lakes.

Hydro-meteorological factors and inflowing nutrients drive water quality in an impounded lake of China's South-to-North Water Diversion Project

Freshwater lakes play a vital role in global hydrological and biogeochemical cycles, serving various functions and maintaining ecological balance. However, freshwater resources are more vulnerable to deterioration due to multiple stressors. Gaoyou Lake is one of the impounded lakes of the Eastern route of South-to-North Water Diversion Project in China, and as an important source of drinking water, the lake has been routinely monitored. Long-term monitoring of water quality in Gaoyou Lake showed that concentrations of nutrients and chlorophyll a as well as trophic state in the water column increased while water transparency decreased, indicating that the water quality has declined during the last 12 years. Specifically, there was a notable and statistically significant increase in chlorophyll a concentrations, averaging an annual rate of 9.9%. Despite a slight decline in trophic level index until 2014, subsequent years saw an upward trend, ranging from 50.7 to 56.4 and indicating a light eutrophic state. Spatially, the western area displayed higher nutrient and chlorophyll a concentrations. Changes in hydro-meteorological variables and nutrients from inflowing rivers were the main factors correlated with water quality in Gaoyou Lake. Thus, pollution source apportionment and management within Huaihe River basin should be considered to reduce the external loadings of nutrients in order to improve and sustain long-term water quality.

The Spatio-Temporal Patterns of Regional Development in Shandong Province of China from 2012 to 2021 Based on Nighttime Light Remote Sensing

As a major coastal economic province in the east of China, it is of great significance to clarify the temporal and spatial patterns of regional development in Shandong Province in recent years to support regional high-quality development. Nightlight remote sensing data can reveal the spatio-temporal patterns of social and economic activities on a fine pixel scale. We based the nighttime light patterns at three spatial scales in three geographical regions on monthly nighttime light remote sensing data and social statistics. Different cities and different counties in Shandong Province in the last 10 years were studied by using the methods of trend analysis, stability analysis and correlation analysis. The results show that: (1) The nighttime light pattern was generally consistent with the spatial pattern of construction land. The nighttime light intensity of most urban, built-up areas showed an increasing trend, while the old urban areas of Qingdao and Yantai showed a weakening trend. (2) At the geographical unit scale, the total nighttime light in south-central Shandong was significantly higher than that in eastern and northwest Shandong, while the nighttime light growth rate in northwest Shandong was significantly highest. At the urban scale, Liaocheng had the highest nighttime light growth rate. At the county scale, the nighttime light growth rate of counties with a better economy was lower, while that of counties with a backward economy was higher. (3) The nighttime light growth was significantly correlated with Gross Domestic Product (GDP) and population growth, indicating that regional economic development and population growth were the main causes of nighttime light change.

Pulses outweigh cumulative effects of water diversion from river to lake on lacustrine phytoplankton communities

Due to the allochthonous input of nutrients and species, the cumulative effects of water diversion on water-receiving lakes deserve attention. Taking the water diversion project from the Yangtze River to Lake Taihu (WDYT) as an example, we explored the temporal effects of WDYT on the phytoplankton community and physicochemical habitat of Lake Taihu in autumn and winter from 2013 to 2018. Although the short-term diversion significantly increased the risk of importing nutrients, the relatively high quality of the diversion water compared with other inflow rivers had improved the water quality of the water-receiving lake region. The seasonal water diversion significantly increased phytoplankton diversity and community network complexity and reshaped the lacustrine community to be diatom-dominated with their relative proportions of 24.1-64.9% during water diversion periods. The contributions of physicochemical habitat changes induced by water diversion to variations in phytoplankton communities were 24.0-28.0%. The differences in phytoplankton diversity, community composition and physicochemical habitat in the water-receiving lake region between the diversion and non-diversion years were more evident than those between the non-diversion years in the same season, when comparing the multivariate dispersion indices among them. However, the lacustrine phytoplankton community during non-diversion periods still has not been essentially altered after several years of diversion, so the pulse effects of short-term water diversion were more obvious than the long-term cumulative impacts. Better control of allochthonous nutrients, appropriate increase in inflow water, adhering to the long-term operation, should be effective to enhance ecological benefits of such water diversion projects.

Phytoplankton community variation and ecological health assessment for impounded lakes along the eastern route of China's South-to-North Water Diversion Project

Interbasin water diversion projects have been proven to effectively alleviate water resource shortages in areas along water diversion lines, but few studies have focused on ecological health in impounded lakes compared with research on water quality and pollutants. Herein, monitoring data were collected during the nonwater diversion period (NWDP) and the water diversion period (WDP) from 2018 to 2019, and the index of biological integrity (IBI) method based on phytoplankton communities was used to evaluate the ecological health of the impounded lakes (Nansi Lake and Dongping Lake) along the eastern route of the South-to-North Water Diversion Project. The results demonstrated that water diversion improved the water quality of the impounded lakes during the WDP, especially total nitrogen and ammonia nitrogen. Meanwhile, the water diversion affected the phytoplankton community structure and diversity, and network analysis further revealed water diversion could be beneficial to the ecological health of impounded lakes. Furthermore, the P-IBI showed that the overall ecological health assessment was "good" during the WDP. Water diversion substantially improved the ecological health status and stability of the impounded lakes during the dry season. Finally, the direct correlations between the water quality parameters and the P-IBI were weak, and water quality parameters could indirectly affect the P-IBI by changing the phytoplankton community structure. These findings will enhance our understanding of the ecological health of the impounded lakes of the South-to-North Water Diversion Project. Furthermore, this study will provide a reference to support the ecosystem security of impounded lakes in other large water diversion projects.

Metacoupling of Water Transfer: The Interaction of Ecological Environment in the Middle Route of China's South-North Project

At present, nearly half of the population of China live in water-deficient areas where water needs to be transferred from surrounding or remote water sources to meet local water demands. Although the water transfer project has alleviated the demands for water in the water-deficient areas, and brought water-supply income to water source regions, it has also posed some cross-regional negative impacts, including the changes in the original ecology within the water source, the impacts on the downstream water demands, and the risk of biological invasion in the distant water receiving areas. Therefore, it can be seen that the impact of water transfer is complicated and will be manifested in various aspects. The Middle Route of China's South-North Water Transfer Project (SNWTP-MR), as the world's largest cross-watershed water transfer project, exerts particularly important effects on regional sustainable development; however, it also produces complex interactions within the ecological environment itself, downstream and in the distant water receiving cities. Thus, this work attempts to apply a metacoupling analysis framework of water transfer to explore the ecological interaction of water transfer in SNWTP-MR on each system. The metacoupling framework can be divided into intracoupling, pericoupling and telecoupling. This study focuses on the analysis of the causes and effects of the intracoupling, pericoupling and telecoupling of SNWTP-MR from the perspective of ecological values and ecological risks. We found that the coupling of water transfer brings about 23 billion yuan of ecological service value to the water source annually, but also increases the internal ecological risk index by 9.31%, through the calculation of changes in land use; secondly, the power generation benefit significantly increases, and the flood control standards have shifted from once-in-20 years to once-in-a-century. However, the ecological risks are also significant, such as poor water quality, eutrophication of water resources, competition for water between industry and agriculture, deterioration of waterway shipping, and threats to biodiversity, etc. Considering only water supply, the population carrying capacity of the water resource in distant water receiving cities is increased by 16.42 million people, which enhances the value of water resources and creates a cross-regional green ecological landscape belt. Nevertheless, the biological invasion and water pollution have greatly affected the safety of water supply. It can be seen that the cross-regional water transfer does not always damage the interests of the sending system and the spillover system while benefiting the receiving system; its impacts are complex and variable. Through this paper, it is hoped to provide a reference for the analysis of the ecological compensation, resource development and allocation in SNWTP-MR by revealing the metacoupling relationship of SNWTP-MR. This paper will provide new ideas for researching the metacoupling relationship, thereby offering valuable reference for the study of the interaction generated by large-scale water transfer.

Effects of shining pondweed (Potamogeton lucens) on bacterial communities in water and rhizosphere sediments in Nansi Lake, China

Submerged macrophytes and microbial communities are important parts of lake ecosystems. In this study, the bacterial community composition in rhizosphere sediments and water from areas cultivated with (PL) and without (CK) shining pondweed (Potamogeton lucens Linn.) was investigated to determine the effects of P. lucens Linn. on the structure of the bacterial communities in Nansi Lake, China. Molecular techniques, including Illumina MiSeq and qPCR targeting of the 16S rRNA gene, were used to analyze the composition and abundance of the bacterial community. We found that bacterial alpha diversity was higher in PL water than in CK water, and the opposite trend was observed in sediment. In addition, 16S rRNA gene copy number in sediment was lower in PL than in CK. We found 30 (e.g., Desulfatiglans) and 29 (e.g., Limnohabitans) significantly different genera in sediment and water, respectively. P. lucens Linn. can change chemical properties in sediment and water and thereby affect the bacterial community. At the genus level, members of bacterial community clustered according to source (water/sediment) and area (PL/CK). Our study demonstrated that submerged macrophytes can affect the bacterial community composition in both sediment and water, suggesting that submerged macrophytes affect the transportation and cycling of nutrients in lake ecosystems.

Decision-Making Model Based on Discriminant Analysis Fuzzy Method for Low-Carbon and Eco-Friendly Residence Design: Case Study of Conghua District, Guangzhou, China

Many countries aim to promote low-carbon and eco-friendly development and find a route to sustainable development. For such development, a model that helps design and build appropriate constructions is necessary. Thus, this study is carried out to establish such a model by combining the Delphi method, analytical hierarchy process (AHP), and fuzzy logic theory (FLT) (DAFuzzy model). In the Delphi method, the expert’s opinions are reflected in three dimensions (green facilities, ecological facilities, and community participation) and nine factors (green building materials, photovoltaic power generation, energy-saving equipment (green facilities), green roof, planting/vegetation, rainwater collection/water recycling (ecological facilities), subsidies, resident participation, appropriate norms (community participation)). Then, AHP is used to calculate the relative weight of each factor. Finally, by using FLT, the output value of each factor is calculated to find out the best scenarios and influencing factors for the scenario. The result shows that green facilities are the most important dimension, followed by community participation and ecological facilities. Among 45 different scenarios for the model, the best is to consider green facilities and ecological facilities with community participation. The important factors in the best scenario include photovoltaic power generation, planting/vegetation, energy-saving equipment, green building materials, appropriate norms, rainwater collection/water recycling, subsidies, and green roof. The proposed model is validated with residential houses in Conghua District, Guangzhou city, China. Considering the dimensions and factors of the best scenario, the proposed DAFuzzy model proves that a low-carbon and eco-friendly development requires support with appropriate policies and a large investment. The research result suggests that building a low-carbon and eco-friendly house needs the support of the government and people’s understanding and participation in eco-friendly development.