South-North Water Diversion Research Articles

Rolling predictive control of tandem multi-canal pools based on water level elasticity intervals: A case study of the South-North water diversion middle route project

Study regionThe Middle Route of the South-North Water Transfer Project (SNWDMRP) is a major water transfer project to optimize the spatial allocation of water resources in China. Study focusIt is difficult for traditional flow adjustment to ensure the safe operation of open-channel water transfer projects. In this study, the Long Short Term Memory (LSTM) water level prediction model is combined with the elastic interval water level control method to achieve rolling prediction control of the water level in front of the gates of a single pool, and then the model is coupled with storage compensation algorithm for prediction control of the water level of the gate group of tandem multi-canal pools. The method is applied to the SNWDMRP, and the results show that the new method is stable within the restricted water level for both single and multiple canal pools. Moreover, the control algorithm proposed in this study can make full use of the storage capacity to satisfy the need of multiple scheduling scenarios

Response of blue-green water to climate and vegetation changes in the water source region of China's South-North water Diversion Project

The characteristics of water fluctuations within the basin have remained ambiguous in recent years due to climate and vegetation changes, posing a challenge to the planning and utilization of regional water resources. This study coupled the Priestley-Taylor Jet Propulsion Laboratory (PT-JPL) model, which can consider vegetation dynamics information and evapotranspiration physical mechanisms, into the Distributed Time Variant Gain Model (DTVGM) to improve the hydrological simulation accuracy under changing environments. Based on different simulation scenarios of the coupled model, the effects of climate and vegetation changes on hydrological processes were fully investigated using blue and green water (BW and GW) as assessment metrics. The upper Han River Basin (UHRB), as water source for the Central Line Project of China’s South-North Water Diversion (CSNWD), was selected as a typical basin for the study, results indicated that: (1) The DTVGM coupled with PT-JPL could better reflect the spatiotemporal patterns of major hydrological processes (runoff, evapotranspiration, and soil moisture) in UHRB from 2001 to 2019; (2) The BW in UHRB exhibited decreasing trend from 2001 to 2019, while the GW on the contrary. Surface runoff (Rs), vegetation transpiration (Et), and soil moisture (W) contributed most in the components of BW and GW; (3) Vegetation change dominated by greening in UHRB, which facilitated the transformation of BW to GW in the basin, and it increased the proportion of GW mainly by promoting Et. BW was mainly influenced by precipitation, but vegetation change altered the original correlation between climatic factors and hydrological processes. This study can support the management of water resources in the basin under changing environments.

Integrating SBAS-InSAR and Random Forest for Identifying and Controlling Land Subsidence and Uplift in a Multi-Layered Porous System of North China Plain

Controlling groundwater table decline could mitigate land subsidence and induced environmental hazards in over-explored areas. Nevertheless, this becomes a challenge in the multi-layered porous system as (in)elastic deformation simultaneously occurs due to vast spatiotemporal variability in the groundwater table. In this study, SBAS-InSAR was used to estimate annual land deformation during 2017–2022 in a specific region of North China Plain, in which aquifers are composed of many layers of fine-grained compressible sediments and the groundwater table has experienced a prolonged decline. The random forest (RF) was applied to establish the nonlinear relationship between accumulated deformation and its potential driving factors, including the depth to the groundwater table (GWD) and its change rate, and the compressible sediment thickness. Results show that the marked subsidence and uplift co-exist in the region even though the groundwater table has risen widely since the South–North Water Diversion Project. The land subsidence is attributed to inelastic compaction of the thick compressible deposits in depression cone centers, where the GWD is over 40 m and 90 m in the shallow and deep aquifers, respectively. In contrast, the marked uplift is primarily attributed to fast rising of the groundwater table (e.g., −2.44 m/a). The RF predictions suggest that, to control the subsidence, the GWD should be less than 20 and 70 m in the shallow and deep aquifers, respectively, and the rising rate of the GWD should increase to 2–5 times of current rates in the depression cones. To mitigate the marked uplift, the rising rate of the GWD should reduce to 1/2–1/5 of the current rates in the shallow aquifers. The uneven deformations of sediments in the depression cone centers and uplift in their boundaries may exacerbate geohazards. Therefore, it is vital to implement appropriate governance of groundwater recovery in the multi-layered porous system.

TerraSAR-X and GNSS Data for Deformation Detection and Mechanism Analysis of a Deep Excavation Channel Section of the China South–North Water-Diversion Project

Due to expansive soils and high slopes, the deep excavated channel section of the China South–North Water-Diversion Middle-Route Project has a certain risk of landslide disaster. Therefore, examining the deformation law and mechanism of the channel slope in the middle-route section of the project is an extreme necessity for safe operation. However, the outdated monitoring method limits research on the surface deformation law and mechanism of the entire deep excavation channel section. For these reasons, we introduced a novel approach that combines SBAS-InSAR and GNSS, enabling the surface domain monitoring of the study area at a regional scale as well as real-time monitoring of specific target regions. By using SBAS-InSAR technology and leveraging 11-view high-resolution TerraSAR-X data, we revealed the spatiotemporal evolution law of surface deformations in the channel slopes within the study area. The results demonstrate that the predominant deformation in the study area was uplifted, with limited evidence of subsidence deformation. Moreover, there is a distinct region of significant uplift deformation, with the highest annual uplift rate reaching 19 mm/y. Incorporating GNSS and soil-moisture-monitoring timeseries data, we conducted a study on the correlation between soil moisture and the three-dimensional deformation of the ground surface, revealing a positive correlation between the soil moisture content and vertical displacement of the channel slope. Furthermore, combining field investigations on surface uplift deformation characteristics, we identified that the main cause of surface deformation in the study area was attributed to the expansion of the soil due to water absorption in expansive soils. The research results not only revealed the spatiotemporal evolution law and mechanism of the channel slope deformation in the studied section of the deep excavation channel but also provide successful guidance for the prevention and control of channel slope-deformation disasters in the study area. Furthermore, they offer effective technical means for the safe monitoring of the entire South–North Water-Diversion Middle-Route Project and similar long-distance water-conveyance canal projects.

Spatial-temporal characteristics of inorganic anions in the Middle Route of South-North Water Diversion project in Henan province (China)

Atmospheric deposition is a vital source of nutrient input into lakes and reservoirs. Therefore, it is of great significance to study the spatial-temporal variation of inorganic anions during the dry and wet atmospheric deposition to ensure the water ecological security of the South-North Water Diversion Middle Route Project (MRP). This study investigated the spatial-temporal variation of inorganic anions (F−, Cl−, NO3−, and SO42−) concentration and its sedimentation fluxes in dry and wet deposition, and their influence on water quality through 10 automatic dust rainfall collection devices installed in the Henan section of the MRP from October 2018 to October 2020. Results indicated that the anion concentration and deposition flux in dry and wet deposition varied in space and time, and SO42− was the highest anion in dry deposition (178.88 ± 175.60 mg/L) and NO3− was the highest anion in wet deposition (52.02 ± 24.63 mg/L). Furthermore, correlation analysis showed that there was a correlation between the wet deposition of anions (F−, Cl−, NO3−, and SO42−) and water quality in winter in the Henan section of the MRP (p < 0.05), and anions dry deposition fluxes have an effect on spring and winter water quality, while the wet deposition fluxes only have an impact on summer and autumn water quality due to the abundant precipitation in summer and autumn. This study could provide new data support for management measures such as strengthening the ecological environment and water quality protection in the MRP.

Simulation of groundwater dynamic conditions in the Baiquan spring region under optimal groundwater resource allocation

Abstract Xingtai, once been famous city for its spring groups in history, has become one of the regions in the country where water resources are in high demand due to long-term over-exploitation in groundwater resource. In the region where the springs in the area have dried up and been cutting-off over the years, including Baiquan and Dahuo. In order to allocate the amount of water diverted from the Middle Section of South-North Water Diversion Project reasonably, to effectively make the springs re-rushing and restore the groundwater level, this research established a numerical groundwater model based on the hydrogeological conditions of the study area. The calculate model is used to discuss the hydrodynamical patterns changes and predict the flowrate of spring groups under different allocation of supplement diversion schemes quantifiably. It was found that the scheme of using the amount of river diversion to rehabilitate the Xingtai urban funnel was most conducive to the recovery of groundwater levels in the spring groups, which is due to the reduction in groundwater extraction has reduced the influence range of the urban funnel and improved the hydrodynamic conditions in the northern preferential runoff zone. The results have demonstrated the feasibility of re-rushing the spring groups.

Spatiotemporal variability and controlling factors of groundwater depletion in endorheic basins of Northwest China

Recent global groundwater overpumping is threatening ecosystem stability and food security, particularly in arid basins. A solid investigation regarding the drivers of groundwater depletion is vital for groundwater restoration, hitherto, yet it remains largely unquantified. Here, a framework to quantify the contribution of natural forcing (NF) and anthropogenic perturbations (AP) to groundwater storage anomalies (GWSA) variability by separating the GWSA estimated by the Gravity Recovery and Climate Experiment (GRACE) satellite into natural- and human-induced GWSA was proposed in the northwest endorheic basin (NWEB) of China. Further, a multiple linear regression model was established for GWSA change prediction. Our results showed that, during the period 2003–2020, the GWSA depleted at a rate of 0.25 cm yr−1 in the entire NWEB. In addition, GWSA was found to decrease significantly (exceeding 1 cm yr−1) in the west of NWEB where there are heavily irrigated areas, and has become one of the regions with the most serious groundwater depletion in China. Whereas a significantly increasing trend (greater than 0.5 cm yr−1) was observed in the Qaidam basin and south part of the Tarim River basin, becoming a groundwater enrichment reservoir in NWEB. The negative contribution of AP to groundwater depletion has increased from 3% to 95% in the last decade, as determined by separating the effects of NF and AP on GWSA. The rapid expansion of the cropland area and the increase in water use due to population growth are investigated to be the main reasons for GWSA depletion, particularly in the North Tianshan Rivers, Turpan-Hami, and Tarim River basins. Therefore, we conclude that AP are dominating and accelerating groundwater depletion in the NWEB. The increase of GWSA in the Qaidam basin has been attributed to the increase in solid water melt and regional precipitation. The western route project of China’s south-north water diversion and water-saving irrigation are important ways to solve the problem of groundwater depletion in NWEB. Our results emphasize that a more feasible framework capable of reliably identifying the driving factors of groundwater storage change is a necessary tool for promoting the sustainable management of groundwater resources under both NF and AP in arid endorheic basins.

Investigating two-dimensional deformations of the head of the Central Route of the South–North Water Diversion Project in China with TerraSAR-X datasets

As a landmark in China’s hydraulic engineering history, the Central Route of the South–North Water Diversion Project (SNWD-CR) plays a major role in alleviating severe water shortages in Northern China. Existing InSAR monitoring of the SNWD-CR based on one-dimensional viewing geometry and Sentinel-1 imaging is insufficient for a comprehensive assessment of deformation causes. Moreover, the poor geocoding accuracy hampers the previous interpretation of the estimated deformations. Here we carry out comprehensive two-dimensional deformation analyses over the head of the SNWD-CR by integrating the multitemporal PS/DS InSAR and the stress–strain model, where the well-designed topography and geocoded error correction can help to identify the causes of deformation. We apply our strategy to ascending and descending TerraSAR-X meter-resolution datasets acquired from June 2020 to February 2021. Geocoding errors in both ascending and descending orbits are corrected, and the relationship between topography error and horizontal positioning error is discussed. The multi-data fusion results reveal insignificant deformations in the east–west direction except for a makeshift rigid-frame bridge, whereas the vertical deformation field shows two uplifts and a subsidence area in the narrow canal with a maximum rate of 23 mm/y, which are likely to be related to rainfall and water diversion pressure. Furthermore, the combination of the external DEM and topographic residual offers the chance to reconstruct the high-accuracy DEM.

Biomanipulation of Periphytic Algae in the Middle Route of South–North Water Diversion Project Canal: An In Situ Study in the Lushan Section

The biomanipulation technique has been developed and implemented for decades, yielding favorable results in various lakes both domestically and globally. This technology uses fish to reduce algae biomass, giving a natural and environmentally friendly solution to improve water quality. The effectiveness of biomanipulation technology in large-scale artificial water canals, on the other hand, has been unclear. To address this, from 15 December 2019 to 30 April 2020, an in situ experimental study on the biomanipulation of periphytic algae was conducted in the Lushan section of the main canal of the Middle Route of the South-to-North Water Diversion Project (MSNWDP). The study aimed to verify the control effect of fish on periphytic algae. Various combinations of Megalobrama terminalis and Xenocypris davidi were fixed on the canal with a triangular cylindrical cage, and their feeding effects on periphytic algae were observed. The results showed that the density of periphytic algae at the bottom of the cages was substantially lower than before the experiment, with a 68.75% average reduction. We graded the food-filling results based on the amount of digestive tract content, which was represented using Arabic numerals ranging from 0 to 5. The study discovered that M. terminalis had the best adaptability to the environment, with full intestines primarily composed of periphytic algae and a food-filling degree between grades 4 and 5. X. davidi, on the other hand, had a food-filling degree of 0. Furthermore, the weight of each M. terminalis increased significantly following the experiment, whereas the weight of each X. davidi decreased to varying degrees. Additionally, the study highlights the importance of selecting the appropriate fish species for biomanipulation, as different species may have varying levels of effectiveness in controlling periphytic algae. Overall, this study provides valuable insights into the potential of biomanipulation technology in large-scale artificial water canals and other water conservancy projects.

Time-Series InSAR Deformation Monitoring of High Fill Characteristic Canal of South–North Water Diversion Project in China

The Middle Route of the South–North Water Diversion Project has changed the water resources pattern in China. As advanced equipment for the country, it is responsible for the water supply “lifeline” of Beijing, Tianjin, Hebei, Henan, etc. Ensuring its safe operation is a top priority to promote social stability and coordinated economic development between the North and the South. Used persistent scatterer interferometric synthetic aperture radar (PS-InSAR) technology to monitor the deformation of the high fill characteristic canal in Wenzhuang Village, Ye County, during the period from October 2016 to June 2017 for the South–North Water Diversion Project showed that there was significant deformation on the 1 km-long slope of the east bank of the canal, with the maximum deformation volume reaching 36 mm. Through the comparison and verification with the second order leveling data, there are more than 87% of the root mean square error of both less than ±2 mm. The correlation coefficient is 0.96, and the two were highly consistent in deformation trends and values. Through the vertical and cross-sectional analysis of the canal’s east bank and four key monitoring sections, it was found that the east bank of the canal presents overall uneven subsidence, and the closer the canal is to the water, the greater the canal deformation, and vice versa. Further comparison of the PS-InSAR deformation results of the canal from October 2016 to February 2018 proves that this technology cannot only monitor the subsidence range and rate of the South–North Water Diversion canal but also accurately identify the subsidence sequence of the east and west banks. It can provide reliable technical support for the safety monitoring and disaster prevention of the South–North Water Diversion canal characterized by high fill and deep excavation.

Dissolved Oxygen and Water Temperature Drive Vertical Spatiotemporal Variation of Phytoplankton Community: Evidence from the Largest Diversion Water Source Area.

In order to study the vertical distribution characteristics of phytoplankton in the Danjiangkou Reservoir, the water source of the Middle Route Project of the South-North Water Diversion, seven sampling sites were set up in the Reservoir for quarterly sampling from 2017 to 2019, and water environment surveys were conducted simultaneously. The results showed that 157 species (including varieties) were identified, belonging to 9 phyla and 88 genera. In terms of species richness, Chlorophyta had the largest number of species, accounting for 39.49% of the total species. The Bacillariophyta and Cyanobacteria accounted for 28.03% and 13.38% of the total species, respectively. From the whole Danjiangkou Reservoir, the total phytoplankton abundance varied from 0.09 × 102 to 20.01 × 106 cells/L. In the vertical distribution, phytoplankton were mainly observed in the surface-thermospheric layer (I-II layer) and the bottom layer, while the Shannon-Wiener index showed a trend of gradually decreasing from the I-V layer. The Surfer model analysis showed that there was no significant stratification in the Q site's water temperature (WT) and dissolved oxygen (DO) levels in the water diversion area during the dynamic water diversion process. A canonical correspondence analysis (CCA) showed that DO, WT, pH, electrical conductivity (Cond), chemical oxygen demand (CODMn), total phosphorus (TP), ammonia nitrogen (NH4+-N), and total nitrogen (TN) had significant effects on the vertical distribution of phytoplankton (p < 0.05). A partial Mantel analysis showed that the vertical distribution of the phytoplankton community was related to WT, and the phytoplankton community structure at the other sites, except for Heijizui (H) and Langhekou (L), was affected by DO. This study has positive significance for exploring the vertical distribution characteristics of a phytoplankton community in a deep-water dynamic water diversion reservoir.

Reducing the Risk of Benthic Algae Outbreaks by Regulating the Flow Velocity in a Simulated South-North Water Diversion Open Channel.

The reduction in open-channel flow velocity due to China's South-to-North Water Diversion Project (SNP) increases the risk of benthic algal community blooms resulting in drinking water safety issues. Consequently, it has attracted attention from all walks of life. However, regulatory measures to mitigate the risk of algal blooms and the main risk-causing factors are unclear. This study simulated the river ecosystem of the SNP channel through water diversion. Simulated gradient-increasing river flow velocity affects environmental factors and benthic algal alterations, and can be used to explore the feasibility of regulating the flow velocity to reduce the risk of algal blooms. We found that the algal biomasses in the velocity environments of 0.211 and 0.418 m/s decreased by 30.19% and 39.88%, respectively. Community structure alterations from diatoms to filamentous green algae were 75.56% and 87.53%, respectively. We observed significant differences in biodiversity, especially in terms of richness and evenness. The α diversity index of a species is influenced by physical and chemical environmental factors (especially flow velocity). Our study revealed that flow velocity is the main factor affecting the growth and outbreak of benthic algae. The risk of algal blooms in open channels can be effectively mitigated by regulating the flow velocity. This provides a theoretical basis for ensuring the water safety of large-scale water conservancy projects.

Using GRACE to Detect Groundwater Variation in North China Plain after South-North Water Diversion.

The gravity recovery and climate experiment (GRACE) and its Follow-On mission provide a versatile tool for monitoring groundwater depletion in North China Plain (NCP). However, intermittent data gaps and inherent coarse spatial resolution have restricted the continuous detection of regional groundwater storage anomaly (GWSA) after 2014, the period of interest during the implementation of the south-to-north water diversion middle route project (SNWDP). Here, we investigated the spatiotemporal changes of GWSA in the NCP during 2004 to 2020 based on continuous downscaled GRACE data. First, we derived the continuous terrestrial water storage anomaly from six GRACE and Follow-On solutions (i.e., spherical harmonics (SH) and mass concentration [mascon] solutions). Second, we employed a long short-term memory (LSTM) model and water balance equation to downscale GWSA (i.e., 0.25° × 0.25°). Lastly, we investigated its spatiotemporal characteristics before (2004 to 2014) and after (2015 to 2020) the SNWDP operation. We show the applicability of the continuous downscaled GWSA to capture the characteristics of in situ measurements. The GWSA detects groundwater depletion at a significant (p < 0.05) rate of -17.09 ± 1.80 (SH) and -17.87 ± 1.65 (mascon) mm/a during 2004 to 2014, but a recovering trend of 7.18 ± 3.98 (SH) and 8.23 ± 4.99 (mascon) during 2015 to 2018. The subsequent groundwater extraction and precipitation reduction from 2019 to 2020, resulted in the decreasing trend of GWSA from 2015 to 2020, which is -19.11 ± 8.75 (SH) and -19.72 ± 9.08 mm/a (mascon), respectively. Spatially, the overall depletion trends become nonsignificant along the canals of SNWDP compared to the period 2004 to 2014, and groundwater recovering with trends <6 mm/a near Beijing and Tianjin are detected by the mascon solution during 2015 to 2020.

Characteristics and source analysis of water pollution in dry season (November to March) of Dongping Lake (China)

In this study, factor analysis, principal component analysis (PCA) and correlation analysis were used to analyze the water quality in dry season of Dongping Lake, which is the only natural lake in the lower Yellow River and an important hub of South-North Water Diversion Project (SNWDP) of China. The nutritional status of the lake was evaluated by trophic level index, and the spatial heterogeneity and aggregation status of the eutrophication level were studied by spatial autocorrelation analysis. Moreover, the pollution-discharge-coefficient method was carried out to clarify the potential pollutant sources. Results showed that the lake was in the light eutropher state with the water quality of V and poor V. Nitrogen pollutants were the primary driving factor of water quality, and water depth was the main environmental factor affecting the spatial distribution of nitrogen pollutants. The eutrophication level of the entire lake showed significant positive spatial autocorrelation. Due to the influence of regional eutrophication levels, the spatial heterogeneity of eutrophication level was low. Two hotspots (High-High concentration) of eutrophication were present in the southeast (P < 0.01) and the north (P < 0.05) of the lake. However, causes for the formation of these two hotspots were different, which mainly resulted from the non-point source discharge of surrounding towns along the southeastern lake and the weak hydrodynamic conditions in the northern lake, respectively. Therefore, it is necessary to pay more attention to control the non-point source discharge into Dongping Lake, especially for regions around the southeast of the lake, in the future management.

Assessment and source analysis of heavy metal contamination in water and surface sediment in Dongping Lake, China

Dongping Lake is the only natural lake in the lower Yellow River and an important hub of South-North Water Diversion Project, its water quality is of vital importance to the environmental protection and the security of water supply. To assess the heavy metal (HM) contamination in Dongping Lake, samples in water and surface sediment were taken from 59 sampling sites over the entire lake. The statistical characteristics, pollution conditions, and source identifications were analyzed using coupling methods of entropy water quality index (EWQI), modified pollution index (mCd), enrichment coefficient (EF), geo-accumulation index (Igeo), potential ecological risk index (PERI), and positive matrix factorization (PMF). In present study, the averaged concentrations of all studied HMs in water body of Dongping Lake were below the limit of drinking water quality standard recommended by WHO, and the EWQI and mCd of HM concentrations were identified to be in good and excellent conditions. The concentrations of almost all studied HMs in surface sediment of Dongping Lake exceeded the background values in the soil of Shandong Province, and Cd (cadmium) was the dominant pollutant. With EF > 2, Igeo > 1, and Er > 80, Cd in sediment was under moderate pollution. The outcomes of source analysis revealed that the HMs in surface sediment were mainly derived from the primary and secondary industries. Specifically, manufacturing industries contributed the most to the HM contaminations in sediment of Dongping Lake.

Extreme historical droughts and floods in the Hanjiang River Basin, China, since 1426

Abstract. The major droughts and floods in the Hanjiang River Basin, central China, have a significant impact on flood prevention and control in the middle reaches of the Yangtze River and water resources management in the areas of the South–North Water Diversion Middle Line Project. However, there is a lack of understanding of the multi-decadal to centennial-scale patterns of extreme droughts and floods in the area. Applying the yearly drought and flood records from historical documents and precipitation data in the period of instrumental measurements, this study constructs a time series of extreme droughts and floods in the Hanjiang River Basin from 1426–2017 and analyzes the temporal and spatial characteristics of the extreme drought and flood event variations. The results show that there were a total of 45 extreme droughts and 52 extreme floods in the basin over the past 592 years. Extreme droughts and floods were highly variable on a multi-decadal to centennial scale, and the frequencies were higher in the first and last 100 years or so of the study period and lower in between. Spatially, the frequencies of extreme droughts and floods were generally higher in the middle and lower reaches than in the upper reaches. It was also found that there is a good correlation of drought and flood frequencies between the upper Hanjiang River Basin and North China. These results are informative for the study of mechanisms and predictability of multi-decadal to centennial-scale variability of extreme hydroclimatic events in the river basin.

Community Structure of Phytoplankton and Environmental Impact Factors in Lake Hongze from 2015 to 2020

Lake Hongze is an essential storage lake for the "Eastern Route of the South-North Water Diversion Project" and plays an important role in climate adjustment and flood prevention and control. To study the structural evolution of phytoplankton communities in Lake Hongze and their relationship with environmental factors and to understand the status of the ecosystem of Lake Hongze before the "ten-year fishing ban," monthly monitoring was carried out from 2015 to 2020. During the study period, total nitrogen showed a significant downward trend starting in 2017, the total phosphorus and chemical oxygen demand declined slightly, the water temperature had no obvious change trend, and the water depth and transparency increased from 2015 to 2018 and then declined significantly. A total of 102 genera of phytoplankton in eight phyla were identified, with a total of 310 species. The dominant phytoplankton phyla mainly included Chlorophyta and Bacillariophyta, followed by Cyanophyta and Pyrrophyta. The dominant genera were Scenedesmus, Aulacoseira, Cryptomonas, Cyclotella, Tetraedron, Microcystis, and Dolichospermum. The results of non-metric multidimensional scaling (NMDS) showed that the structural composition of the phytoplankton community differed significantly among years, seasons, and sampling areas, mainly due to the redistribution among dominant genera. NMDS analysis also indicated that variation in the phytoplankton community in Lake Hongze was mainly related to water temperature, total nitrogen, total phosphorus, water depth, and transparency. Total nitrogen, water depth, and phytoplankton community structure were significantly correlated with interannual succession, whereas water temperature, total nitrogen, and phytoplankton seasonal succession were also significantly correlated. Combined with the measures taken by the management department in recent years, the changes in the structure of the phytoplankton community may be related to the removal of the fence and other management and restoration measures in Lake Hongze.

Spatial and temporal characteristics, influencing factors and prediction models of water quality and algae in early stage of Middle Route of South-North Water Diversion Project

The Middle Route (MR) of the South-to-North Water Diversion Project (SNWDP) of China is one of the world's largest inter-basin water diversion projects. As an important source of drinking water in North China, its water quality safety determines the success or failure of a sizable water supply. At present, there is a lack of in-depth and systematic understanding of the interaction between hydrodynamics and the water environment as well as water ecological processes in the main canal at the early stages of operation. It is not currently possible to accurately predict water quality and algae status at the early stage of canal ecosystem succession. Change trends and distribution characteristics of the main water ecological environment elements in the main canal at the early MR stage are analyzed in this study. The main factors influencing algae are investigated by principal component analysis (PCA) to characterize the water quality and algae transport distribution in the main MR canal under the complex multi-sluice joint dispatching conditions. The relationship between environmental factors, hydrodynamic, water quality, and algae in the coupled canal-sluice system in the SNWDP MR is determined. Algae distributions under different water transmission conditions in a typical canal section are predicted accordingly. CODMn and algal density in the main canal are shown to increase from south to north along the canal. DO decreases from south to north; other water quality indexes do not significantly differ from north to south. Algal density along the canal differs to the greatest extent in summer, followed by spring and autumn, and is the weakest in winter. The predicted algae densities in the main canal under different water conveying conditions show that single sluice control and strong water flow from Taocha Head Section increase the flow velocity after passing through the sluice with a fixed opening. Algal density decreases flow rate increases under single sluice regulation conditions. The maximum rate of algal density change reaches 22.13% and 29.55% under double sluice and four sluice scheduling. Algae control effects grow significantly as the number of control sluices increases. The results of this work may provide technical support for water quality forecasting and algae risk warning in the SNWDP MR as well as a workable reference for similar projects.

The Migration and Transformation of Nitrogen in the Danjiangkou Reservoir and Upper Stream: A Review

The Danjiangkou Reservoir in China is characterized by significantly high concentrations of total nitrogen (TN), and the sources are not clear. Recently, research on this reservoir has focused on the N cycle, the spatial and temporal distribution characteristics of N, and the factors influencing N concentration. Significant temporal and spatial differences in TN concentrations exist, both in the reservoir area and the tributaries. N concentration in the area is affected by numerous factors, including N transported by tributaries, nonpoint source pollution around the reservoir, internal N release, and atmospheric N deposition. Moreover, a dam heightening project led to a larger water-fluctuation zone and more bays in the reservoir, directly affecting its N cycle. However, further research is required to explore the N cycle on a large watershed scale in the Danjiangkou Reservoir and upper stream areas, determine N pollution sources using satellite remote sensing, and conduct simulations of a water body N cycle model based on data fusion. Although the issue of excessive TN has been alleviated to some extent by the South-North Water Diversion Project, the excessively high TN concentrations require more research to aid the implementation of N-reducing strategies.

Assessment of the value of ecosystem services in water sources of the South-North Water Diversion Central Project: the case of Dengzhou City, Henan Province

Dengzhou City is the first ecological water recharge city after the commissioning of the South-North Water Diversion Project. A study on the ecological service value of Dengzhou City and its evolutionary characteristics can provide a theoretical basis for the water supply security of the Central Line Project and regional ecological environmental protection. Based on the ecosystem service value equivalent factor method, GIS, ENVI and GeoSOS-FLUS software were used to monetize the ecosystem service values of Dengzhou City in 2007, 2011, 2014, 2015 and 2020; analyze the spatial and temporal change characteristics under its land use change conditions and predict the regional ecosystem service values of Dengzhou City in 2025. The results show that since the completion and commissioning of the South-North Water Transfer Central Project in 2014, the value of ecosystem services in Dengzhou City has rapidly increased from US$3.792 billion to US$4.612 billion, and in 2025, the value of ecosystem services in Dengzhou City is expected to reach US$4.8 billion.