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Zostera japonica, as one of the major seagrasses in the Yellow River Estuary, plays a critical ecological role, particularly in providing habitat for marine organisms, stabilizing sediment, and contributing significantly to carbon sequestration. In recent years, Zostera japonica seagrass beds have receded extensively due to multiple impacts of natural factors and human activities. This study investigates the complex effects of extreme climate events and human activities on the growth mechanisms of Zostera japonica in the Yellow River Estuary using a combination of field sampling, laboratory analysis, and quantitative calculations. The result shows that there are significant differences in sediment characteristics between the north and south shores, with the south shore having finer sediments and higher nutrient content, which support more robust seagrass growth. The Water and Sediment Regulation Scheme (WSRS) dramatically alters water quality by reducing salinity and increasing turbidity, thus inhibiting photosynthesis and disrupting the physiological functions of Zostera japonica. Additionally, WSRS introduces an increase in heavy metals, which could potentially impact plant health and stress levels. Extreme weather events, particularly Super Typhoon Lekima, further compound these impacts by causing soil erosion, uprooting seagrass beds, and reducing biomass and seed production. The interplay of WSRS, climate change, and anthropogenic activities necessitates integrated management strategies to mitigate adverse effects and enhance habitat resilience. This study underscores the need for specific management strategies, such as controlling heavy metal inflows, implementing sediment stabilization techniques, and regulating freshwater discharge during key growth periods, to mitigate adverse effects and enhance habitat resilience for Zostera japonica in the Yellow River Estuary.

Hydropower plants with a small installed capacity, which are widely distributed in mountainous areas with abundant rainfall and steep rivers, play an important role in resolving energy problems in remote rural areas. These plants are a crucial source of clean electricity generated from water power. Harnessing local water resources not only helps alleviate energy shortages, but also reduces reliance on fossil fuels, contributing significantly to China’s national goals of achieving peak carbon emissions and carbon neutrality. This study investigates the carbon footprint of the Huangshadong Reservoir Project in Chongqing, China. The entire life cycle of the hydropower plant is assessed, including the preparation, construction, operation and maintenance, and demolition phases. The uncertainty was evaluated using the error propagation method. Following analysis, suggestions for carbon footprint reduction measures were proposed. Results showed that the total carbon footprint and the carbon intensity of the Huangshadong Reservoir Project over its entire life cycle are 33,148.29 t CO2e and 417.75 g CO2e/kWh, respectively. Of the total carbon footprint, the preparation phase, construction phase, operation and maintenance phase, and demolition phase account for 0.04%, 67.06%, 26.2%, and 6.7%, respectively. It means that the requirement for cement during the construction phase represents an important contribution to the entire life cycle carbon footprint of a small hydropower plant. As an integrated water conservancy project, the carbon intensity of the Huangshadong Reservoir Project is higher than that of medium-sized and large hydropower plants. However, its carbon intensity is lower than the emission factor of fossil power plants. The research results provide reference for both planning and construction of small hydropower plants and low-carbon development of rural hydraulic engineering.

Intensive ecological interventions have been carried out in highly polluted shallow lakes to improve their environments and restore their ecosystems. However, certain treatments, such as dredging polluted sediment and stocking fish, can impact the aquatic communities, including benthos and fishes. These impacts can alter the composition and characteristics of aquatic communities, which makes community-based ecological assessments challenging. Here we develop a bacteria-based index of biotic integrity (IBI) that can clearly indicate the restoration of aquatic ecosystems with minimal artificial interventions. We applied this method to a restored shallow lake during 3-year intensive ecological interventions. The interventions reduced nutrients and heavy metals by 27.1% and 16.7% in the sediment, while the total organic carbon (TOC) increased by 8.0% due to the proliferation of macrophytes. Additionally, the abundance of sulfur-related metabolic pathways decreased by 10.5% as the responses to improved ecosystem. The score of bacteria-based IBI, which is calculated based on the diversity, composition, and function of benthic bacterial communities, increased from 0.62 in 2018 to 0.81 in 2021. Our study not only provides an applicable method for aquatic ecological assessment under intensive artificial interventions but also extends the application of IBI to complex application scenarios, such as ecosystems with significantly different aquatic communities and comparisons between different basins.

Based on the focus on the role of reservoirs as carbon sources and sinks, this article explores their impact on the global carbon cycle. Reservoirs, which are “artificial lakes” created by human activities in rivers, are reviewed in terms of the key links in carbon cycling within reservoir areas, the influencing factors, and research methods related to carbon cycling and carbon emissions. By reviewing the literature on reservoir carbon cycling, we elucidate the mechanisms of carbon inputs, decomposition and transformation, carbon emissions, and carbon burial, summarizing the biogeochemical coupling processes of dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), particulate organic carbon (POC), and particulate inorganic carbon (PIC) with hydrological conditions and nutrients. The study concludes that the reservoir carbon cycling process is influenced by the characteristics of the reservoirs themselves, hydrological and hydrodynamic conditions, physicochemical and nutrient conditions, and human activities. Additionally, we further clarify the applications of field sampling and analysis, modeling, remote sensing technology, and isotope techniques in reservoir carbon cycling. In the future, it is recommended to continue monitoring and simulating the reservoir carbon cycle processes on a long-term and large-scale basis, and to deeply explore the multifactorial mechanisms of reservoir construction in the global carbon cycle.

Urban parks are a major component of urban green spaces and are reserved for recreation, aesthetics and cultural heritage. With increasing attention to carbon neutrality in China, urban parks play an important role in carbon sequestration. This new expectation requires us to examine the impacts of current design and management in urban parks on carbon density. This study took Beijing as an example and investigated a total of 9 parks within 4 functional categories, i.e., landscape parks with small, medium, and large sizes and natural forests. As parks worked for various functions, their plants species and tree sizes were distinct. Big trees were scattered in small parks; while big parks had natural-like landscape with ample medium- and small-sized trees. We analysed their aboveground and belowground carbon density, as well as associated variables, such as biodiversity, soil bulk density, nitrogen (N) content, etc. Soil types were the same for different parks, but managements leaded to different soil properties. Medium- and large-sized landscape parks had the highest aboveground carbon density (60.86 t·hm−2 and 79.18 t·hm−2, respectively), which was higher than that of natural forests (43.20 t·hm−2), while small-sized landscape parks had the highest belowground carbon density (185.22 t·hm−2), which was slightly less than that of natural forests (207.17 t·hm−2). The high aboveground carbon density in landscape parks with medium and large sizes was attributed to the well-planted trees and high biodiversity, especially for the high ratio of brush (62.12 %). High belowground carbon density in small landscape parks resulted from careful management, such as timely fertilization and frequent soil loosening, which led to high organic matter and low bulk density (1.1206 kg·cm−3), promoting soil carbon sequestration. We therefore provide specific advice in managing different parks in regard to their carbon density, expecting to increase carbon density in urban parks by an average of 224 %.

Zostera japonica (Z. japonica), the most widely distributed seagrass species in temperate estuaries, has experienced a dramatic decline of nearly 75% over the past decade. While previous research has investigated the adaptation of seagrass individuals and populations to single stress factors, the molecular mechanisms underlying the interaction of multiple stressors remain poorly understood. This study conducted laboratory experiments to examine the response of Z. japonica at different life stages to environmental pressures, specifically salinity and turbidity, as indicated by changes in free amino acids (FAAs). The results demonstrate that Z. japonica exhibits stronger adaptability to high salinity environments but displays weaker adaptability to freshwater conditions. Through single stress experiments, the salinity and turbidity thresholds for FAA homeostatic disturbance in Z. japonica were determined at seedling, juvenile, and mature stages. As Z. japonica matures, its metabolic pathways expand and diversify, allowing the regulation of key FAAs to enhance stress resistance. Turbidity stress exerts a more pronounced negative impact on the cellular homeostasis of Z. japonica compared to salinity stress, and when turbidity levels exceed 150 NTU, they significantly intensify the negative effects of salinity stress on the seagrass. Furthermore, under strong salinity-turbidity interactions, the concentration of key FAAs generally decreases by 20-30%, indicating inhibition of growth and development in Z. japonica. These findings have important implications for the conservation of intertidal seagrass beds and estuarine ecosystems in the face of multiple human activities and environmental stressors. The study provides valuable insights into the molecular mechanisms underlying Z. japonica’s adaptations to salinity and turbidity stress, contributing to the development of targeted strategies to mitigate the impacts of environmental pressures on seagrass populations and promote the resilience of these critical marine ecosystems.

Land cover maps with high accuracy are essential for environmental protection and climate change research. The 30-meter-resolution maps, with their better resolution and longer historical records, are extensively utilized to assess changes in land cover and their effects on carbon storage, land–atmosphere energy balance, and water cycle processes. However, current data products use different classification methods, resulting in significant classification inconsistency and triggering serious disagreements among related studies. Here, we compared four mainstream land cover products in China, namely GLC_FCS30, CLCD, Globeland30, and CNLUCC. The result shows that only 50.34% of the classification results were consistent across the four datasets. The differences between pairs of datasets ranged from 21.10% to 37.53%. Importantly, most inconsistency occurs in transitional zones among land cover types sensitive to climate change and human activities. Based on the accuracy evaluation, CLCD is the most accurate land cover product, with an overall accuracy reaching 86.98 ± 0.76%, followed by CNLUCC (81.38 ± 0.87%) and GLC_FCS30 (77.83 ± 0.80%). Globeland30 had the lowest accuracy (75.24 ± 0.91%), primarily due to misclassification between croplands and forests. Misclassification diagnoses revealed that vegetation-related spectral confusion among land cover types contributed significantly to misclassifications, followed by slope, cloud cover, and landscape fragmentation, which affected satellite observation angles, data availability, and mixed pixels. Automated classification methods using the random forest algorithm can perform better than those that depend on traditional human–machine interactive interpretation or object-based approaches. However, their classification accuracy depends more on selecting training samples and feature variables.

Fungi play important roles in the process of material cycling and energy transfers in aquatic ecosystems. Yet, little is known about the fungal community in lake sediment. In this study, sediment samples from five habitat types in Baiyangdian Lake (BYD Lake) were collected across three seasons. High-throughput sequencing techniques were used to determine the compositions of fungal communities. Fungi are highly diverse in the sediment of BYD Lake, although some important fungi have not been accurately identified. The fungal diversity was highest in winter and lowest in summer, while there was no significant difference in species richness among sampling sites. The compositions of fungal community differed among seasons and habitats. Physicochemical properties of sediments were measured and the influence of the environmental factors on fungal communities were analyzed. Temperature, P, N, and heavy metals explained 48.98% of the variations of fungal communities across three seasons. Human activities have affected the species and biomass of fungi to some extent. Temperature is the most influential factor and negatively correlated to fungal diversity. Nutrients in different forms have different effects on shaping the fungal community. The effect of heavy metals is relatively low.

This study aimed to evaluate the ecohydrological regime and ecological water demand of the Huangshui River Basin under changing environmental conditions, seeking to safeguard its ecosystem. Based on monthly data spanning from 1956 to 2016, the ecohydrological regimes of the Huangshui River and the Datong River were evaluated using methods such as the Pettitt mutation test, the Tennant method, and ecological deficit and surplus analyses. The data were mainly obtained from Xiangtang Station of the Datong River and Minhe Station of the Huangshui River. The results showed the following. (1) The most abrupt increase in measured runoff at Xiangtang Station occurred in 1993, while the point of abrupt change in measured runoff at Minhe Station occurred in 1990. (2) Following an increase in human activities, changes in the ecological surplus at Xiangtang Station were negative in January, April to May, July, and from September to November, while the changes in the ecological deficit were positive from January to April, July to August, and October to December. Changes in the ecological surplus at Minhe Station were negative from March to July and from September to December, while changes in the ecological deficit were positive from January to April and from July to December. (3) The annual average ecological flow of the Datong River, Xiangtang section, was 28.42 m3/s, and the annual average ecological water demand was 896 million m3. The annual average ecological flow of the Minhe section was 19.98 m3/s, and the annual average ecological water demand was 631 million m3. According to a calculation of the degree of ecological water demand and ecological flow satisfaction, prior to the implementation of the Water Diversion Project from the Datong River to Huangshui River, the water volumes in both rivers were generally sufficient to meet the ecological water demand. However, high water consumption during the irrigation period led to an ecological deficit. To address these issues, it is crucial to evaluate the potential impacts of human activities, such as water diversion projects, on river ecological flow. Recommendations include expediting the Water Diversion Project from the Yellow River to Xining to secure sufficient water flow in the Huangshui River and enhancing water conservation efforts in agricultural irrigation.

Estuarine ecosystems are influenced by the combination of freshwater runoff and ocean tides, and the natural environment is intricate and complex, with special natural environmental conditions and biological habitat characteristics. The Yellow River is characterized by high sediment-bearing water flow, and the estuary forms a unique clear and turbid confluence. The Water and Sand Regulation (WSRS) from the Xiaolangdi Reservoir to the estuary and nearshore has had significant impacts on the environmental conditions of water, sediment and nutrients, further affecting the growth and development of vegetation in the nearshore zone. In recent years, more studies have focused on the effects of climate change and ocean tides on vegetation in the Yellow River Estuary; however, few studies have been conducted on the effects of the WSRS on klysmoeionion. In this study, we investigated the influence of water flow, sediment and nutrients on klysmoeionion based on long-term field monitoring and indoor control experiments; constructed a three-dimensional hydrodynamic water quality model to simulate the hydrodynamic characteristics, sediment transport patterns and nutrient salt distribution in the Yellow River Estuary under the combined influence of tides and riverine water and sediment; and further combined the growth competition model of typical vegetation (including the native species Zostera japonica and invasive species Spartina alterniflora) to construct a suitable habitat simulation model for typical vegetation communities in the Yellow River Estuary. Habitat and biomass changes in Z. japonica and S. alterniflora in the Yellow River Estuary were simulated under the influence of the WSRS and climate change. The results showed that the distribution of suitable habitats for Z. japonica and S. alterniflora in the Yellow River Estuary and offshore was characterized by a zonal distribution along both sides of the estuary, with an increasing trend of suitable habitat area from the estuary to both sides of the estuary; due to environmental conditions and inter- and intra-species competition, the biomass of Z. japonica and S. alterniflora was mainly distributed in the estuary and near the northern and southern shores, with the southern shore have the most distribution. In contrast, S. alterniflora was mainly distributed in the northern shore away from the estuary and in Laizhou Bay. During the WSRS period, the suitable habitat area of Z. japonica decreased by 25%, and the biomass decreased by 50%, while the suitable habitat and biomass of S. alterniflora were not significantly affected. The growth of Z. japonica was severely affected by the dual effects of global warming and the WSRS, while the biomass of S. alterniflora showed an increasing trend. The WSRS can further consider the growth pattern of vegetation to protect the resources of Z. japonica and to curb the expansion of the invasive S. alterniflora.

Abstract The Yangtze River is the longest river in China, with abundant water resources, high water energy reserves, and rich biodiversity. Human activities have greatly changed the hydrology and ecology of the Yangtze River Basin since the 1950s. The aquatic biodiversity in the Yangtze River Basin has declined sharply, while the amount of fishery in the Yangtze River has been maintained due to higher intense of fishing, artificial proliferation intervention, and other factors. Human activities including overfishing, water polluting, damming, reclaiming wetlands, shipping and shoreline development, species introduction, and so forth have had great influence on aquatic ecosystems. This paper also reviewed the measures implemented to protect the aquatic ecosystems of the Yangtze River. By reviewing the evolutionary trend of aquatic organisms in the Yangtze River Basin and the related human activities, this paper helps to better understand the biodiversity of the Yangtze River, and requires more attention on the continuous impact of human activities, as well as the effectiveness of protection measures under the new situation of Yangtze River protection.

Summary: Severe arable land loss and ecological problems raise attention to protect/develop land for food and ecology demand. Spatial conflict appears in front of multidemand for urbanization, food, and ecology. Our study took China as an example and explicitly outlined spatial preference of urbanization, food, and ecology. From the aspect of land amount, there are enough lands to support multidemand with a surplus of agriculture land of 45.5 × 106 ha. However, spatial conflict widely appears among the multidemands. We tested the impacts of different priorities on urban pattern, crop yield, and ecology and found the priority of food > ecology > urbanization gave the best outcome. Our results verified the importance of including priority of land multidemand to avoid confusion and increase efficiency in the implementation of land policies.

IntroductionSediment and nutrients flow into estuary with runoff, and then influence the estuary ecosystem. Much work has been done for investigating the response of water quality and species group (eg. phytoplankton or zooplankton) to the runoff from upstream, while few research has been taken to evaluate the response of the whole ecosystem.MethodsFood webs of different seasons and regions were established based on stable isotope analysis and Bayesian mixing model. The influences of upstream runoff and sediment transport on the estuarine food webs were analyzed.ResultsFood web in estuary had highly spatial-temporal variability. The stable isotope values of organisms were higher on the northern shore than that on the southern shore. The area with high-turbidity freshwater inflow nurtured more terrestrial- organic- matter (TOM) relying species. And the contribution of TOM to food web was higher in flood season than that in non-flood season. The trophic levels of major consumers in the non-flood season were generally higher than that in the flood season. Significant differences in the average TP of species between two shores appeared during the non-flood season (P < 0.05). Expect for the C value, all of the topological indexes of food webs on the northern shore were higher than those on the southern shore, and they were higher in the flood period.DiscussionThe input and diffusion of sediment and nutrients carried by runoff led to the changes in the dietary structure of estuarine organisms and the decrease in trophic levels of major consumers. At the same time, flow pulse with high sediment also aggravated the spatial differences of the structure of food webs. The higher contribution of TOM to consumers increased the link density of food web on the southern shore, making it a more robust system. However, the high diversity of food sources and aquatic species made the food web more complex on the northern shore.

IntroductionThe transport of suspended sediment plays an important role in regulating erosion-accretion in estuaries. The Yellow River, the second longest river in China, which has a large amount of sediment and contributes sediment to the Yellow River Estuary (YRE) every year. The water and sediment discharge patterns in the lower reaches of the Yellow River have experienced significant changes over recent decades. In particular, the water-sediment regulation scheme (WSRS) of the Xiaolangdi Reservoir transports large amounts of water and sediment to the YRE within a very short time, causing dramatic changes in the spatiotemporal estuarine sediment dynamics.MethodsIn this study, we presented a coupled numerical model based on FVCOM-SWAVE-SED that considered the highly dynamic sediment variations in the YRE. The sediment distribution and erosion-accretion patterns in the YRE during the WSRS in 2013 were analyzed by the high-resolution model.ResultsThe sediment entering the YRE spread with freshwater, forming a high sediment concentration zone near the river mouth, where most of the sediments were deposited. The sediment dispersal distance was limited by the tidal shear frontal (TSF), and the southeast outspread length of the sediment was slightly larger than the northwest spread. Outside of the YRE, the areas with high flow currents exhibited high erosion. We examined the effects of the main external driving forces (such as waves, tides, and runoff) on the sediment distribution and showed that runoff, tides, and waves were the key factors affecting the sediment distribution of the YRE.ResultsThis study shows that WSRS effectively changes the sediment distribution and erosion condition in the YRE and provides a data for researches on changes in estuarine ecosystems.

With the development of the economy, the contradiction of water resources in the lower Yellow River area is becoming increasingly serious. Economic development not only increases the socio-economic water demand, but also causes damage to the environment. In order to ensure the safety of the vast plains along the lower Yellow River, protect the environment of the lower Yellow River and estuaries, and achieve environmental sustainability of the lower Yellow River, a model was established to optimize the allocation of water resources with the goal of ecological, safety, and social benefits, combining the uncertainty of water resources, the uncertainty of the water demand during the flood season under different water and sediment conditions, and the water requirements of different water users. An improved ecological footprint method considering soil water was applied during the allocation. Thirty different scenarios were set up, and appropriate scenarios for 2025 and 2030 in wet, normal, and dry years were calculated, providing a reference for decision makers. Results show that: 1) The water supply is affected by the amount of water resources and water demand for sediment transport in the lower Yellow River. The satisfaction of sediment transport and the water supply rate during wet years can reach a high level of satisfaction. 2) When the regional water resources ecological footprint is the smallest, the allocation of water resources tends to the section or unit with a smaller ecological footprint. Therefore, the river sections with the lowest water shortage rates are Lijin-Hekou and Sunkou-Aishan, and the unit with a low water shortage is ecological and industrial water.

Land use/cover change (LUCC), especially of urban expansion, drives terrestrial carbon stock change in urban agglomeration. Due to the spatial heterogeneity of urban agglomeration, zonation supplies a possible way for land management in metropolises to achieve land use sustainability. In this study, we took Beijing-Tianjin-Hebei (BTH) region, known as the Capital Economic Zone, as an example and proposed a zonation strategy, as well as land management of each zone, to better adjust LUCC planning. BTH region was divided as Ecological Barrier (EB) zone, Potential Carbon Sequestration (PCS) zone and Potential Carbon Loss (PCL) zone, by evaluating topography, carbon storage and historic carbon stock change from 1990 to 2020. The EB zone was characterized as area of high carbon density, storing around 50% of carbon stock of BTH region. It experienced 52 Mt carbon stock loss from 1990 to 2020. PCL zone was characterized as area of high carbon stock loss of 122 Mt from 1990 to 2020. PCS zone was characterized as area of carbon stock increase by 7.23 MtC from 1990 to 2020. We analysed LUCC for each zone and found distinct drivers of carbon stock change. Based on zonation analysis, ecological engineering projects should continue in the PCS zone, leading to a carbon increase of 0.18 Mt C per year. Revegetation and strict ecological conservation policies were suggested to the EB zone, giving a potential of 58.9–186 Mt C carbon gain. Internal conversion between urban and rural construction land was proposed to the PCL zone, which can possibly achieve zero carbon loss of urban sprawl.

Discharge containing large amount of sediment will cause a series of ecological effects on downstream river systems. To solve the siltation problem of Yellow River and Xiaolangdi reservoirs, water and sediment regulation has been carried out since 2000. To clarify the impact of the regulation on bacterial communities in the lower Yellow River, the composition of bacterial communities and functional groups in the riverbed and suspended sediment was analyzed by high-throughput sequencing and functional annotation of prokaryotic taxa method. The results showed that the overall diversity index of the Yellow River bacterial community was 3.014–7.045, and at a medium level compared to other large rivers in China. During the water and sediment regulation, the bacterial diversity index slightly decreased compared to the previous stage, while significantly increased at the post-stage of regulation, considering relatively small changes in chemical factors among three stages, it was thought that the The variation of bacterial community diversity was more influenced by the fluctuations of discharge, turbulent kinetic energy and sediment concentration. The relationship between suspended and riverbed samples to environmental factors also showed differences at three stages of regulation. During the regulation, increasing discharge and high velocity caused the ammoxidation related groups, such as nitrate and nitrite ammoxidation groups, to displace nitrification, nitrate reduction, and nitrate respiration groups, hence inhibit the water purification capabilities, while at the post-stage, the functional group of most sites recovered to similar level to the pre-stage. In summary, we reveal a characteristic pattern on how the microorganism in the high sediment river respond to the severe disturbance.

Changing climate has raised attention toward weather-driven natural hazards, such as rain-induced flash floods. The flooding model is an efficient tool used in flash flood warning and hazard management. More and more evidence showed significant impacts of sediment on hydrodynamics and flooding hazard of flash flood. But little information is available regarding flooding hazard sensitivity to sediment characteristics, which hampers the inclusion of sediment characteristics into the flash flood warning system and hazard management. This study used a 1D model to simulate flood hazards. After calibrating and validating the hydrodynamic model, we carried out simulations to test the sensitivity of flood hazard to sediment characteristics like inflow point, size distribution, and concentration. Our results showed that sediment from highly erosive slopes affects the flooding hazard more than sediment from watershed. This is particularly true when sediment particles are fine particles with a medium size of 0.06 mm. When medium particle size of sediment increased above 1 mm, most of the sediment particles are deposited in the river and we see little effect on flooding hazard downstream. Sediment concentration significantly influenced the flooding hazard but was less important than sediment inflow point and medium particle size. Our study suggested considering more characteristics than concentration when including sediment particles into the flash flood warning system.

Mercury (Hg) is a global neurotoxic pollutant and has a long chain from economic activities to human health risks. Here the authors presented a map of Hg-related health risks in China and found significant impacts of interprovincial trade on health risks, such as the prevention of deaths from fatal heart attacks by the trade induced by final consumption.

Benthic bacteria are drivers of aquatic ecosystem material circulation and energy flow, and are sensitive to environmental changes. In this study, a total of 79 sediment samples were collected from four representative habitat types (duck farm, fish farm, lotus pond and residential area) and one reference site (conservation district) of Baiyangdian Lake, North China, in three seasons (winter, spring and summer). The physical and chemical properties and the levels of contaminants in sediment were determined. Bacterial communities were studied by 16S rRNA high-throughput sequencing techniques. The result showed that, Proteobacteria, Chloroflexi, Bacteroidetes, Firmicutes and Actinobacteria were the dominant species at the phylum level in Baiyangdian. Sulfuricurvum, Thiobacillus Dechloromonas, Sulfurovum, Nitrospira and Desulfatiglans were the dominant species at the genus level. The dominant genus was different among different habitats. Proteobacteria exhibited the highest relative abundance in all seasons, and the relative abundance of dominant bacteria was highest in winter. The main functional group from the sampling sites were contamination tolerance bacteria, such as sulfur-oxidizing, sulfate-reducing and nitrifying bacteria. Sulfur-oxidizing bacteria were found mainly in duck farms and residential areas, whereas sulfate-reducing bacteria and nitrifying bacteria occurred in lotus ponds. Habitat type was the most important factor influencing the bacterial community composition, evenness and diversity. Sediment pH and the amount of active phosphorus played the most important role in the composition of the bacterial community, and the heavy metals (Zn, Mn and Cr) and organic pollutants (polycyclic aromatic hydrocarbons, PAH) also had moderate influence. As Baiyangdian Lake is the central of Xiong’an New Area, the water quality management has become the hottest topic. Plenty of researches about environmental variables and aquatic species were taken, but lacking report of bacteria. This study provide basic information of bacterial community composition in this area, and help to understand the response of the bacterial community to habitat and seasonal change, which provide a scientific basis for the recovery and reconstruction of the degraded ecosystem.

Macrophyte-dominated shallow lakes are one of the commonest freshwater wetlands in plain area, and composed of lake, marsh, and terrestrial land. They are, however, facing great ecological risks of serious pollution and wetland degradation caused by the shortage of ecological water demand. Baiyangdian is the largest shallow lake in northern China. It is of great importance to ecosystem services in Xiongan New Area, China, providing food production, climate regulation and other functions. Water storage in Baiyangdian comprises components of lake, marsh and terrestrial land, each of which supplies a different ecosystem service value (ESV). As a result, the total ESV of a macrophyte-dominated shallow lake changes according to water storage fluctuation. In this study, we estimated the total and individual land ESVs (lake, marsh, and terrestrial land) of the Baiyangdian. We also quantified the relationship between ESV and water storage in the macrophyte-dominated shallow lake, taking water level as the indicator. The optimum water level varied, corresponding to the highest ESV of each type of land, and an optimum water level of 8.2 m was identified as achieving the highest total ESV of the Baiyangdian (6.697 billion yuan). We also divided ecosystem services into four functional categories: provisioning, regulating, supporting, and cultural and found these components also changed with water storage changes in the macrophyte-dominated shallow lake. Fluctuation in the total ESV was attributed mainly to the marshland because of its huge supply capacity for support and cultural services. An optimum water level range of 7.9–8.5 m existed where ESV was most balance among different functional categories. After considering the functional and land cover components of total ESV of the Baiyangdian, we recommend an optimum water level of 8.2 m, and emphasize the importance of including ESV in calculations of ecological water demand. Keywords: Ecosystem services, Ecological water level, Macrophyte-dominated shallow lake, Synergy and tradeoff

Abstract Microorganisms are important drivers of material and energy circulation in freshwater ecosystems. Altered aquatic sedimentary environments disturbed by human activities affect microbial community composition. Concentrations of heavy metals, and sediment physicochemical properties, are described for 25 sediment samples collected from five habitat types (residential, duck farm, lotus pond, fish farm, and a reference reserve shallow freshwater lake site) around Baiyangdian Lake, China. Bacterial and fungal communities in sediments were determined using 16S rRNA and 18S rRNA high‐throughput sequencing technology. Sediment physicochemical properties and heavy metal concentrations vary significantly among habitat types. Bacterial genera involved in S and N cycles are most abundant, followed by those that degrade organic pollutants, and are tolerant of heavy metals. Sediment bacterial Chao1 index is predominantly regulated by cobalt concentrations. The microbial communities within replicate samples within habitats are more similar to each other than they are between habitats. Redundancy analysis indicates Zn, pH, and TP are the main environment factors structuring bacterial communities, while fungal communities are most significantly influenced by Co and TP. The genus Cryptomonas is a food source for small zooplankton and fishes, and is mainly distributed in fish farm and lotus pond habitats. Species of Pseudallescheria that cause mycetoma, maduromycosis, and other infections in humans are highly abundant in duck farm and residential habitats. Species of Aleuria are saprobes; decompose organic matter, dead organisms, or biological excrement; and are highly accumulated in duck farm habitat.

To solve the water use conflicts between agriculture and ecosystems in arid and semiarid areas, a multi-objective trade-off analysis method was applied to determine the environmental flows (e-flows) for the Yellow River Estuary, by considering the temporal and spatial discrepancies in water allocation. The results showed that during average years, a loss of 3.7 × 108 yuan was caused with every 1 × 108 m3 of e-flows under the baseline scenario. The crop growth stages of April–July are sensitive periods for water requirements, and over 5000 yuan/ha production losses were caused by prioritizing e-flows during this time in dry years. The stages from July–October require more water by ecosystems than other stages, and the recommended e-flows during this time accounted for 57% of the e-flows during the total year. Under scenarios 1–3, which represent the short-term, medium-term and long-term scenarios, more water resources were supplied by underground water and water diversion projects; however, alleviating the water use contradiction remained difficult in dry years. During average years, e-flows between 148 and 168 × 108 m3 are recommended to meet the ecological objectives of survival, reproduction and biological integrity of species for the Yellow River Estuary. The recommended e-flows in wet years could meet higher ecological objectives but still barely achieve the targets of sediment transport and ecosystem dynamic balance. In dry years, the economic losses may be beyond the acceptance of irrigation stakeholders if more water is allocated to improve e-flows. In this case, 71 × 108 yuan would be paid to them to compensate for their losses. This study proposes an e-flow recommendation framework that is economically and ecologically optimal in areas with irreconcilable water-use contradictions.