Water Diversion Research Articles

Effects of the Water Diversion Project from the Three Gorges Reservoir to the Hanjiang River on diatom blooms in Middle and Lower reaches of the Hanjiang River

ABSTRACT The algal blooms in the Middle and Lower reaches of the Hanjiang River (MLHR) have become a great aquatic eco-environmental problem over recent years. The planned implementation of the Water Diversion Project from the Three Gorges Reservoir to the Hanjiang River (WDP-TH) would influence the growth and propagation of diatoms and the development of algal blooms. In this paper, a dynamic model of diatom growth is developed that considers factors such as light exposure, water temperature, total phosphorus, and flow velocity. The effects of the WDP-TH on algal density and blooms in the MLHR were predicted for a typical median year, a typical dry year, and an extremely dry year. The results showed that following the water recharge in a typical median year, the propagation of diatoms in the MLHR was significantly promoted because of an increase in total phosphorus concentration. However, following the water recharge in typical dry and extremely dry years, increased flow rate and improved hydrodynamic conditions significantly inhibited diatom growth and accelerated the transport process. The results of the hypothetical simulation showed that after the initiation of the WDP-TH, inhibition effects of improved hydrodynamic force on algae were more apparent than promotion effects of increased total phosphorus concentration in the MLHR.

Optimal groundwater depth and irrigation amount can mitigate secondary salinization in water-saving irrigated areas in arid regions

Secondary salinization poses a significant threat to the sustainable development of water-saving irrigation districts. This study aims to explore the spatial and temporal variations in soil salinity and the factors influencing these changes in water-saving irrigation areas in the inland arid regions of Northwest China. The Manas River Irrigation District was selected as the study area. A grid measuring 10 km × 14 km grid was designed to determine the latitude and longitude coordinates of the grid centers, resulting in 66 sample points. Soil samples were collected from these points in 2013, 2014, 2020, and 2021 from the 0100 cm layer to obtain salinity data. Based on existing research and practical conditions in water-saving irrigation areas, 11 factors influencing soil salinity changes were identified, including irrigation area and irrigation amount. Classical statistical methods and interpretable machine learning techniques were employed to analyze the distribution characteristics of soil salinity and the influencing factors. This analysis proposes effective solutions to mitigate potential secondary salinization in irrigation areas. The results revealed that soil salinity in the irrigation area belonged to moderate variation (Cv = 46.74 %51.80 %). The horizontal direction of the irrigation area shows higher salt content in the upstream and downstream areas, and a gradual decrease in variability with increasing depth characterizes the vertical direction. From 2013–2021, soil salinization in the irrigation area gradually decreased. In 2013 and 2014, the area was predominantly covered by mild saline-alkali soil, accounting for 75.1 % and 76.6 % of the total area, respectively. However, in 2020 and 2021, non-saline soils became dominant, covering 60.9 % and 66.5 % of the total irrigation area, respectively. In order of importance, the factors affecting the spatial and temporal evolution of soil salinity are groundwater depth, annual water surface evaporation, water-saving irrigation area, underground water diversion amount, mineralization of groundwater, irrigation amount, surface water diversion amount, and annual rainfall. In the oasis irrigation area, maintaining a groundwater depth of 4.06.0 m and an irrigation amount of 55006000 m3 ha−1 can alleviate the problem of secondary salinization that may result from large-scale development of water-saving irrigation. The findings of this study provide a basis for the prevention and control of soil salinization in water-saving irrigation areas and the development and management of saline land in oasis areas.

A multi‐site and hypothesis‐driven approach to identify controls on the bedload transport regime of an anthropised gravel‐bed river

AbstractUnderstanding the effects of human disturbance on the bedload transport regime of anthropised rivers is a topic of growing importance, as such information is of interest for adequate river diagnosis, correct implementation of restoration measures and appropriate design of post‐action monitoring programs. However, such assessments are complex, especially in sites where multiple factors simultaneously influence the bedload transport regime, so that it is difficult to establish simple causal relationships between human disturbances and changes in the sediment transport regime, notably on bedload. To overcome this, there is a need for rigorous hypothesis‐driven approaches to assess the isolated effects of each driver. With this in mind, we have characterised the dynamics of bedload transport in the Upper Garonne (Central Pyrenees, Spain‐France), a river impacted by sediment retention, flow diversion and mining that influence its morphological conditions and transport regime. We assessed the effects of (1) surface grain size distribution, (2) river morphology, (3) sediment supply and (4) flow diversion on the bedload transport regime. Four sites with different degrees of river anthropisation were selected. After defining hypotheses on the most likely bedload transport conditions for each site, we proposed a set of discriminating criteria to test these hypotheses, based on temporal within‐site and spatial between‐site comparisons of coarse particle tracking measurements over four years. The results of this research showed that the hydrosedimentary regime of the Garonne is controlled by a complex combination of drivers such as valley physiography, which exerts a first‐order control on differences in reach‐scale bedforms and bedload dynamics; and human disturbances which contribute to a reduction in sediment supply through changes in land cover and hydropower dams, or to changes in hydrology (i.e., flow competence) due to water diversion and abstraction.

Multi-scale closed-loop coupled real-time water quantity optimization scheduling of cascade pumping station in water supply canal systems

Closed-loop control is an effective control method to deal with uncertain disturbance in water supply canal system (WSCS). However, previous researches mainly focus on closed-loop control with a single time scale, and it is difficult to solve the uncertainty problem with a long time dimension. In this paper, a multi-scale closed-loop coupled real-time scheduling framework is established and solved by considering both large and small scale closed-loop scheduling models, so as to improve the performance of real-time scheduling in a longer time dimension under uncertain perturbations. The framework is applied to the virtual simulation test of the Xuhong River WSCS of the east route of the South-to-North Water Diversion project under different water distribution disturbances. The results show that the closed-loop control method can update the system status regularly through rolling optimization, and effectively reduce the prediction error of water level and energy consumption. In the two water distribution disturbance scenarios, the proposed method reduces the average relative deviation of water supply plan execution by 3.4 % and 5.9 %, and the unit energy consumption of cascade pumping station operation by 1.7 kWh/104m3 and 1.5 kWh/104m3, respectively, compared with the single-scale closed-loop scheduling method. In addition, the proposed method can effectively deal with the uncertainty of water distribution disturbance in limited computing time, and can meet the requirements of real-time scheduling in a long time dimension under uncertain disturbance.

Assessing the oxidative potential of dust from great salt Lake

Great Salt Lake (GSL) is one of the world's largest inland bodies of saltwater. Climate change, drought, and water diversions have led to the GSL reaching historically low levels, exposing over 1945 km2 of lakebed. Dust events can transport particulate matter (PM) from the GSL's exposed lakebed to the adjacent urban areas, presenting air quality and health concerns. In this study, we assessed the oxidative potential (OP) of dust from the exposed GSL bed compared to dust samples collected from other regional playas and to reference Arizona test dust. The oxidative potential of PM10 (particles ≤10 μm in aerodynamic diameter) derived from these dusts was assessed by two acellular assays: the ascorbic acid (OPAA) and dithiothreitol (OPDTT) and two extraction solvents: phosphate buffer saline and Gamble's simulated lung fluid. All samples were also analyzed for elemental composition. Our results show that the concentration of As and Li in most of the GSL dust samples exceeded the Environmental Protection Agency (EPA) soil residential regional screening levels, and the OPAA and OPDTT of dust samples from GSL playas were generally higher than the OP of other regional playas. Our findings also indicated that the OP of the GSL dust was associated with metals, including Cu, Mn, Fe, and Al. This is the first study evaluating the oxidative potential of dust from the GSL, which improves our understanding of how increasing aridity, particularly desiccation of saline lakes, affects air quality and public health.

Introducing Methods for Analyzing and Detecting Concrete Cracks at the No. 3 Huaiyin Pumping Station in the South-to-North Water Diversion Project in China

Concrete cracks pose significant threats to concrete structures, causing immediate strength loss and leading to gradual erosion that compromises structural integrity. Therefore, accurate and automatic detection and classification of concrete cracks, along with the evaluation of their effects on target structures, are critically important. This study focuses on the No. 3 Huaiyin pumping station, a large-scale hydraulic structure on the Eastern Route of the South-to-North Water Diversion Project in Jiangsu, China. First, relevant field test literature is reviewed, and the finite element method is applied to investigate the effects of an existing crack on the No. 2 supporting wall. Using thermomechanically coupled numerical simulations, the distribution of tensile stress in the supporting wall is reported in two cases: without a crack and with an existing crack. The findings indicate that the increase in tensile stress due to the existing crack is relatively small and can be considered negligible for the No. 2 supporting wall. Next, the pretrained YOLOX network for the detection and classification of three types of cracks is proposed and retrained using collected concrete crack datasets. The mean average precision of the retrained YOLOX network for all three types of cracks reaches 80%. Finally, the retrained YOLOX network is applied to detect and classify cracks at the No. 3 Huaiyin pumping station. This automatic detection and classification approach will enhance the high-quality management of the pumping station because it is labor-saving and easy to deploy.

Distribution and risk assessment of nutrients and heavy metals from sediments in the world-class water transfer projects

South-to-North Water Diversion Project, a globally renowned engineering feat, aims to address water supply issues. The sediments within reservoirs play a pivotal role in natural ecosystems, not only as habitats for diverse biota but also as repositories of heavy metals, organic matter, and other contaminants. These sediments serve as a critical interface between sediment and water bodies. This comprehensive analysis focused on the spatial patterns of nutrients, organic matter, and heavy metals in the surface layer and profiles of reservoirs, exploring their interconnectedness. Leveraging the integrated pollution index, organic pollution index, potential ecological risk index, and geo-accumulation index, an ecological risk assessment was performed. The key findings are as follows: (i) Along the Middle Route of the South-to-North Diversion Project, the nutrient and organic matter contents in sediments tends to rise with distance from the Danjiangkou Reservoir, with the TN and TC contents increasing by 2.35- and 3.05-fold, respectively. (ii) As the sediment depth increases, the carbon, nitrogen, phosphorus, and organic matter contents exhibit varying degrees of decline, with average decreases of 62.38%, 67.47%, 17.56%, and 41.83% for TN, TC, TP, and OM, respectively. (iii) Among the eight heavy metals, only manganese (Mn) and zinc (Zn) in the Yahekou Reservoir showed moderate pollution levels, according to the geo-accumulation index. The Mn content within the surface sediments of the six reservoirs ranges from 550 to 1837 mg/kg (average, 1019.5 ± 548.3 mg/kg), whereas the Zn content ranges from 89 to 360 mg/kg (average, 156.5 ± 101.6 mg/kg). (vi) Total phosphorus (TP) and total nitrogen (TN) emerged as the primary pollutants in surface sediments. Comprehensive nitrogen and phosphorus pollution assessment revealed that the surface sediment of Danjiangkou Reservoir is mildly polluted, while Baiguishan and Jiangang Reservoirs are moderately polluted, and the rest are heavily contaminated. For the Yahekou and Chaohe Reservoirs, the average pollutant content indicates moderate pollution, while the remaining reservoirs show mild pollution levels.Graphical

Study on the Structural Characteristics of Bulb Tubular Pumps Based on Fluid–Structure Interaction

As a special type of through-flow device, bulb turbine pumps have been widely used in the Eastern Route of the South-to-North Water Diversion Project due to their compact structure, flexible installation process, easy maintenance, high efficiency, and strong adaptability. Therefore, structural improvements to enhance their safety and stability through fluid–structure interaction analysis have significant engineering value. This paper conducts static and transient fluid–structure interaction analyses of the bulb turbine pump structure. The results show that the rotor structure experiences the greatest deformation under low-flow conditions, with maximum deformation (2.13 mm) occurring at the leading edge of the impeller inlet and decreasing radially along a gradient distribution. The damping effect of water changes the mode shapes of the rotor structure, and although the vibration modes under wet conditions are similar to those in the air, the frequencies decrease to varying degrees. In transient analyses under different conditions, the total deformation of the rotor system is greater than in static analyses, showing significant regularity. Under low-flow conditions, the deformation of the pressure surface at the inlet and outlet of the blade tip is greater than that of the suction surface, with a maximum total deformation of 3.656 mm. The maximum total deformation under design flow is 3.337 mm; under high flow, it is 2.646 mm. The total deformation of the casing mainly occurs on both sides of the internal bulb body bottom support, with a maximum deformation of 2.0355 mm and an equivalent stress maximum of 44.848 MPa. The equivalent stress and total deformation distribution of the support structure are similar, located at the top support and trailing edge, with a maximum value of 22.94 MPa at the trailing edge. The research results provide technical references and theoretical foundations for the structural optimization of bulb turbine pumps.

Analysis on the Establishment of Standardized Management System for the Operation of Sluice Engineering

Baiyanghe Xiaocaohu Hub is an important water diversion hub project for industrial and agricultural water supply in Toksun County, Turpan City. After the project was reinforced in 2018, it plays an important role in local social stability and economic development. In recent years, in order to implement the new development concept, promote high-quality development, and improve the scientific level of water gate management, in accordance with the requirements of higher-level work deployment, the main responsibility of management has been implemented, and a comprehensive transformation has been carried out from five aspects of Xiaocaohu Water Conservancy Hub to improve the current situation of the project, standardize management behavior, and enhance management capabilities. This article summarizes the experience of standardization implementation, explores the formation of replicable and promotable management experience, and provides reference for promoting engineering standardization management work from point to area.

Stable isotopic characterization and sources of ammonium in wet deposition at the Danjiangkou Reservoir

Ammonium nitrogen (NHx) in atmospheric wet deposition is a primary external nitrogen source for reservoir-type water sources, and identifying its sources is crucial for controlling nitrogen pollution in water. This study aimed to examine the NHx characteristics and sources in wet deposition in the Xichuan reservoir area of the Danjiangkou Reservoir, the South-to-North Water Diversion Project (SNWDP) water source, from September 2019 to August 2020. Major inorganic nitrogen concentrations in precipitation and ammonia-nitrogen isotope (δ15N–NH4+) values were measured, and the sources were analyzed using the Bayesian mixing model. The results showed that NH4+ was the main inorganic nitrogen form in wet deposition, with a concentration ranged of 0.16–5.26 mg L−1. The δ15N–NH4+ values ranged from −14.7‰ to +6.3‰, with significant isotopic effects from agricultural sources and climatic conditions, showing higher values in summer and lower values in winter. The release of ammonia (NH3) from agricultural sources was the primary NHx source (58.0%–76.6%), with fertilizer application being the most significant contributor (32.1%–46.6%). Seasonally, the relative contribution of agricultural sources to NH4+ in wet deposition was higher in autumn and winter. Spatially, agricultural activities significantly impacted atmospheric nitrogen accumulation across the reservoir area. This study quantified NHx sources in wet deposition, providing isotopic evidence and scientific references for nitrogen control measures and atmospheric nitrogen cycling studies.

Extent of gross underestimation of precipitation in India

Abstract. The underestimation of precipitation (UoP) in the hilly and mountainous parts of South Asia is estimated by some studies to be as large as the observed precipitation (P). However, UoP has been analyzed to only a limited extent across India. To help bridge this gap, watershed-scale UoP was analyzed using various P datasets within a water imbalance analysis. Among these P datasets, the often-used Indian Meteorological Department (IMD) dataset is of primary interest. The gross UoP was identified by analyzing the extent of the imbalance in the annual water budget of watersheds corresponding to 242 river gauging stations for which quality-controlled data on catchment boundaries and streamflow are available. The water year (WY)-based volume of observed annual P was compared against the observed annual streamflow (R) and the satellite-based actual evapotranspiration (ET). Across many watersheds of both Northern and Peninsular India, spurious water imbalance scenarios (P≤R or P≪R+ET) were realized. It is shown that the management of water, such as groundwater extraction, reservoir storage and water diversion, is generally minimal compared to the annual P in such watersheds. It is also shown that annual changes in terrestrial water storage are minimal compared to the annual P in such watersheds. Assuming that data on R (and, to a lesser extent, ET) are reliable, it is concluded that UoP is very likely the cause of this imbalance. Inter-watershed groundwater flow (IGF) is assumed to be negligible. While the effect of IGF on R is unknown, examples are provided which show that IGF is unlikely to be the cause of the observed imbalance in certain watersheds. All 12 of the P datasets analyzed here suffer from UoP, but the extent of the UoP varies by dataset and region. The reanalysis-based datasets ERA5-Land and IMDAA are less affected by UoP than the IMD dataset. Based on the 30-year period of WY 1985–2014, P for the whole of India could be as much as 19 % (ERA5-Land) to 37 % (IMDAA) higher than that from the IMD, with substantial variability within years and river basins. The actual magnitude of UoP is speculated to be even greater. Moreover, trends seen in the IMD's P are not always present in ERA5-Land and IMDAA. Studies using IMD should exercise caution since UoP could lead to the misrepresentation of water budgets and long-term trends. Limitations of this study are discussed.

Experimental Investigation on a Water Diversion Shield Segment Using a Newly Developed Model Test Chamber

Jinan City in China is known for its abundant spring water, and the protection of underground spring water transport channels is a key issue that needs to be paid attention to in Jinan subway construction. In areas where underground spring water transport channels are easily disturbed, when the shield tunnel passes through a composite formation with a permeable layer in the middle and an impermeable layer in the upper and lower parts, the underground spring water transportation channel is blocked, the spring veins are damaged, and the underground spring water is blocked in the upstream, resulting in an increase in the water pressure difference on both sides of the tunnel. In this paper, based on the working principle of a new type of pipe segment with a diversion function, a diversion function pipe model test box is designed and fabricated. Using this model box, the working state of the diversion function pipe segments is simulated. An earth pressure box and pore water pressure gauges are embedded in the model box to measure the earth pressure and pore pressure around the pipe under seepage unsymmetrical pressure. Strain gauges are attached in a circular shape on the inner side of the pipe to measure and calculate the strain and stress of the pipe. Through model tests, the effective repair of the diversion pipe on blocking groundwater flow and the relief effect of the unsymmetrical pressure of the pipe are verified.

Anticipating responses to climate change and planning for resilience in California’s freshwater ecosystems

As human-caused climate changes accelerate, California will experience hydrologic and temperature conditions different than any encountered in recorded history. How will these changes affect the state’s freshwater ecosystems? Rivers, lakes, and wetlands are managed as a water resource, but they also support a complex web of life, ranging from bacteria, fungi, and algae to macrophytes, woody plants, invertebrates, fish, amphibians, reptiles, birds, and mammals. In much of the state, native freshwater organisms already struggle to survive massive water diversions and dams, deteriorating water quality, extensive land cover modification for agriculture and urban development, and invasions of exotic species. In the face of climate change, we need to expand efforts to recover degraded ecosystems and to protect the resilience, health, and viability of existing ecosystems. For this, more process-based understanding of river, lake, and wetlands ecosystems is needed to forecast how systems will respond to future climate change and to our interventions. This will require 1) expanding our ability to model mechanistically how freshwater biota and ecosystems respond to environmental change; 2) hypothesis-driven monitoring and field studies; 3) education and training to build research, practitioner, stewardship, and policy capabilities; and 4) developing tools and policies for building resilient ecosystems. A goals-driven, hypothesis-informed collaboration among tribes, state (and federal) agencies, nongovernmental organizations, academicians, and consultants is needed to accomplish these goals and to advance the skills and knowledge of the future workforce of practitioners, regulators, and researchers who must live with the climate changes that are already upon us and will intensify.

Long-term continuous changes of vegetation cover in desert oasis of a hyper-arid endorheic basin with LandTrendr algorithm

Ecological water diversion projects (EWDP) is one of the most important initiatives for oases restoration in arid endorheic basins. Fine monitoring of the long-term and continuous changes in vegetation cover before and after the EWDP is important to evaluate the effects of EWDP on ecosystem restoration. In this study, a trajectory-based change detection approach was applied with the Landsat-based detection of trends in disturbance and recovery (LandTrendr) algorithm on Google Earth Engine to map vegetation cover change trajectories in Ejina Oasis in the lower Heihe River Basin of China during 1990–2020. In addition to monotonic changes (i.e., continuous greening and continuous browning), LandTrendr also can flexibly capture the breaks of greening or browning events, including the greening with negative break, browning with positive break, browning to greening, and greening to browning. These changes mainly happened in shrub land and the area with land use transition. Approximately 82 % of the oasis ecosystem has been restored by the implementation of EWDP since 2000. However, in the past decade, the EWDP also caused some negative effects on vegetation cover in some areas. Both the categories of browning with positive break and greening to browning became widespread after 2010, with the cumulative proportions accounting for 79.4 % and 70.1 % of each category. The mean magnitude and slope of change in NDVI in these two categories after 2010 were −0.03 and −0.008 yr−1, −0.12 and −0.035 yr−1, respectively. This research demonstrated that the proposed approach was effective and useful for continuously monitoring the timing and extent of vegetation recovery processes in the hyper-arid endorheic basin. The EWDP plays an important role in vegetation restoration, but we also need to continuously monitor negative impacts which are crucial for environmental assessment and policy making in the arid endorheic basin.

Beyond immediate relief: Investigating multi-faceted water management in inter-basin water transfer projects

Water scarcity is a compelling and complex global challenge that has far-reaching implications for both ecological systems and human societies. In response, inter-basin water transfer initiatives have been advocated as potential remedies. Though effective in providing immediate relief, the long-term viability of these initiatives is disputed. Notably, recurring scarcity can result from increased water demand in the recipient basin due to transferred water. Addressing this requires balancing water demand and supply. Beyond supply-focused measures such as water transfers, a crucial strategy involves adopting demand-focused approaches to reduce reliance on such transfers. This study centers on the Gavkhouni basin in Iran, where despite repeated water transfers, water scarcity remains persistent due to climate fluctuations, population growth, agricultural activities, and economic development. The research developed a comprehensive system dynamic model, integrating environmental, social, and economic variables impacting water balance in the region in order to assess the effectiveness of three distinct demand-focused water management strategies, namely, technology-based, cropping pattern-based, and land-based policies, both individually and in synergy. This analysis was conducted across a set of scenarios encompassing climate change, population growth, GDP dynamics, and water transfer patterns. The findings revealed a satisfactory accuracy of the water management system model, with a 6.2% mean absolute error. In addition, findings highlighted the advantages of a multifaceted strategy, with technology-driven interventions and optimized cropping patterns emerging as particularly effective. However, the economic dimensions of these policies warrant comprehensive exploration due to the significant impact they have on the feasibility and effectiveness of the policies. The study emphasizes the need to combine demand-side policies with supply strategies like water transfers. This comprehensive approach is vital for effective water management and long-term water security.

Competition in the Periphytic Algal Community during the Colonization Process: Evidence from the World's Largest Water Diversion Project.

Periphytic algal colonization is common in aquatic systems, but its interspecific competition remains poorly understood. In order to fill the gap, the process of periphytic algal colonization in the Middle Route of the South to North Water Diversion Project was studied. The results showed that the process was divided into three stages: the initial colonization stage (T1, 3-6 days), community formation stage (T2, 12-18 days) and primary succession stage (T3, 24-27 days). In T1, the dominant species were Diatoma vulgaris (Bory), Navicula phyllepta (Kützing) and Fragilaria amphicephaloides (Lange-Bertalot) belonging to Heterokontophyta; these species boasted wide niche widths (NWs), low niche overlap (NO) and low ecological response rates (ERRs). In T2, the dominant species were Diatoma vulgaris, Cymbella affinis (Kützing), Navicula phyllepta, Fragilaria amphicephaloides, Gogorevia exilis (Kützing), Melosira varians (C.Agardh), Phormidium willei (N.L.Gardner) and Cladophora rivularis (Kuntze). These species displayed wider NWs, lower NO, and lower ERRs than those in T1. In T3, the dominant species were Diatoma vulgaris, Cymbella affinis, Navicula phyllepta, Fragilaria amphicephaloides, Achnanthes exigu (Grunow), etc. Among them, Heterokontophyta such as Diatoma vulgaris and Cymbella affinis had a competitive advantage based on NWs and ERRs. Cyanobacteria like Phormidium willei lost their dominant status due to the narrower NW and the increased NO. It could be concluded the interspecific competition became fiercer and shaped the colonization process; this study will be helpful in understanding the colonization of periphytic algal communities.

Temporal variations in dissolved organic matter properties in a eutrophic lake under water dilution and aquatic plant litter decomposition: A simulated microcosm study revealing the environmental and microbial driving factors

Dilution by importing external clean water and restoration of aquatic vegetation are widely applied strategies for improving water quality of eutrophic lakes, while the influence of dilution or aquatic plant litter decomposition on dissolved organic matter (DOM) properties, which is closely associated with the health of aquatic ecosystems, is rarely known. In this study, the temporal variations of DOM properties in the overlying water of a eutrophic lake (Yilong lake in Yunnan, southwest China) under water dilution and aquatic plant litter decomposition were comparatively investigated via a simulated microcosm study using in situ samples. The results showed that water dilution reduced DOM concentration and bioavailability in the overlying water in a short term (about 45 d), and increased DOM humification, but such effect diminished over time. DOM concentration increased substantially during aquatic plant litter decomposition, and reed litter released much more amounts of DOM than that of cattail litter, which dominated by protein-like substances and characterized by high bioavailability and low humification degree. Nutrient (available phosphorus (AP), NH4+-N and TN) contents in the sediment indirectly affected DOM properties by remarkably influencing microbial community compositions and enzyme activities. The strong correlations between the relative abundances of dominant genera Bacillus and Clostridium and concentrations of DOM components implied the important roles of these taxa in DOM transformations. Our findings highlighted the effects and potential mechanisms of dilution and aquatic plant litter decomposition on DOM properties in eutrophic water bodies, and the necessity of proper water diversion and plant litter harvest to reduce endogenous organic pollution in lakes.

Effects of repeated drawdown flushing on riverbed fine sediment dynamics downstream from a dam

Sediment accumulation in reservoirs is frequently a problem, impelling dam managers to implement strategies such as drawdown flushing to limit siltation. Drawdown and other sediment removal methods may induce riverbed clogging downstream of dams, especially in river sections where water is diverted, thereby reducing transport capacity. In this study, we investigate the effects of drawdown flushing downstream of the Plan d’Arem run-of-the-river dam (Upper Garonne, Spain – France border) using an adaptive inter-site comparison strategy to consider a range of spatial and temporal conditions, which allow us to separate the effects of dam storage and flushing from other potential factors. Drawdown flushing has been undertaken three times during the study period over a short span of time (2 months). We couple bed material sampling, which provides direct information on bed composition, with airborne infrared thermal imaging to better interpret whether fine sediment interstitial storage within the bed is associated with clogging. We also measure bed surface grain size and bed mobility in order to investigate their potential role in controlling fine sediment dynamics. We identify surface grain size and water diversion as the main factors controlling fine sediment spatial distribution, with coarse-grained bed-surfaces and by-passing promoting fine sediment enrichment. As a result, sites located upstream and within the by-passed reached of the Plan d’Arem dam show higher fine sediment interstitial storage than sites downstream from the by-passed reach. Results from thermal imagery demonstrate such interstitial storage does not induce clogging effect. The reaches with the most important sediment storage host a high number of cool-water patches, indicating water exchanges with the hyporheic zone. Post-flushing bed composition indicates systematic export of fine sediments from the bed matrix at all sites after the first operation, afterwards fine levels remain low after the second and the third flushing. The low impact of dam flushing in term of clogging is interpreted by the fact that the interstitial material is very sandy.

Impacts of the Middle Route of the South-to-North Water Diversion Project on Land Surface Temperature and Fractional Vegetation Coverage in the Danjiang River Basin

The Middle Route of the South-to-North Water Diversion Project is a critical infrastructure that ensures optimal water resource distribution across river basins and safeguards the livelihood of people in China. This study investigated its effects on the land surface temperature (LST) and fractional vegetation coverage (FVC) in the Danjiang River Basin. Moreover, it examined the spatial and temporal patterns of this project, providing a scientific basis for the safe supply of water and ecological preservation. We used the improved interpolation of mean anomaly (IMA) method based on the digital elevation model (DEM) to reconstruct LST while FVC was estimated using the image element dichotomous model. Our findings indicated a general increase in the average LST in the Danjiang River Basin post-project implementation. During both wet and dry seasons, the cooling effect was primarily observed in the south-central region during the daytime, with extreme values of 6.1 °C and 5.9 °C. Conversely, during the nighttime, the cooling effect was more prevalent in the northern region, with extreme values of 3.0 °C and 2.3 °C. In contrast, the warming effect during both seasons was predominantly located in the northern region during the daytime, with extreme values of 5.3 °C and 5.5 °C. At night, the warming effect was chiefly observed in the south-central region, with extreme values of 5.8 °C and 5.9 °C. FVC displayed a seasonal trend, with higher values in the wet season and overall improvement over time. Statistical analysis revealed a negative correlation between vegetation change and daytime temperature variations in both periods (r = −0.184, r = −0.195). Furthermore, a significant positive correlation existed between vegetation change and nighttime temperature changes (r = 0.315, r = 0.328). Overall, the project contributed to regulating LST, fostering FVC development, and enhancing ecological stability in the Danjiang River Basin.

Trade-off between the future water resource utilization and grain production in a water-deficient region from the perspective of the Water−Land−Grain nexus

The utilization and future evolution of water resources in water-deficient regions will have a significant impact on sustainable agricultural development. The trade-off between water resource utilization and grain production in the Daqing River Basin (DRB) was explored, and the characteristics of the future evolution of the water − land − grain system was analyzed. The main planting patterns of farmland in the DRB are winter wheat, spring maize, summer maize, or a winter wheat − summer maize rotation. The total water consumption and supply are 61.6 × 108 and 54.4 × 108 m3, respectively. The water supply gap is approximately 7.2 × 108 m3, which is mainly supplemented by the overexploitation of groundwater. Under the current land use structure, grain production in the DRB has achieved self-sufficiency, but excessive water consumption in agricultural production has led to severe groundwater overexploitation. Despite the exploration and implementation of a fallow land policy in the DRB, the quantity of water resources conserved currently falls significantly short in comparison to the extent of groundwater overexploitation. From the trade-off between water resource utilization and grain production, if winter wheat areas were left completely fallow, or winter wheat planting regions establish three crops in two years or a single crop in a year, the total amount of irrigation water that could be saved was 18.4 × 108, 7.5 × 108, and 15.2 × 108 m3, although the grain production capacity would be reduced by 31 %, 12 %, and 24 %, respectively. This study proposes prioritizing fallow areas in the winter wheat planting regions with high water demand located in the Diandong Plain, and changing the current system of two crops a year to three crops in two years or a single crop a year. The implementation of this approach is anticipated to alleviate the strain on water resources. To achieve the control of groundwater overexploitation and balance the supply and demand of water resources, it is necessary to continue to expand the fallow area of winter wheat in the eastern and southern plains of Baiyangdian by approximately 25.3 × 104 hm2, or increase the amount of water diverted from outside the basin by approximately 7.20 × 108 m3. By 2030, the DRB will face the dual pressures of both water and grain security, with a water resource gap of 13.8 × 108 m3. It is therefore necessary to increase inter-basin water transfer or continue to expand the fallow area of winter wheat in the future.