Search Results (238)

Phosphorus (P) release from reservoir sediments critically influences water quality and ecosystem stability. This study analyzed surface sediments from four representative zones to investigate phosphorus fraction distribution, key influencing factors, and implications for water quality. Results showed that total phosphorus (TP) content in sediments from main and tributary inflow zones was significantly higher than in open-water and transition zones. Inorganic phosphorus (IP) was the dominant form, with iron-bound phosphorus (Fe-P) accounting for 33.2–42.0% of IP. A strong correlation existed between P release and the Fe/P molar ratio; notably, when the ratio approached 10, phosphorus desorption increased significantly, indicating a shift from sink to source. Sediments with grain sizes <0.01 mm had the highest P release rates, suggesting particle size, Fe content, and hydrodynamics jointly regulate P mobilization. Using the Diffusive Gradients in Thin Films (DGT) technique, phosphorus release in inflow zones exceeded 1 g/m² in all hydrological periods, contributing substantially to internal loading. Sediment-derived P primarily influenced bottom water, while surface water was more affected by external inputs. These findings highlight the spatial heterogeneity of P release and underscore the need for zone-specific management strategies in reservoir systems. Full article

Asynchrony between the movement of water and sediment in a reservoir will affect long-term maintenance of the reservoir’s capacity to a certain extent. Based on water and sediment data on the Three Gorges Reservoir (TGR) measured over the years and a river network model, optimization of the dispatching mode of the reservoir’s sand peak process was studied, and the corresponding water and sediment dispatching indicators were provided. The results show that (1) sand peak discharge dispatching of the TGR can be divided roughly into three stages, namely the flood detention period, the sediment transport period, and the sediment discharge period. (2) According to the process of the flood peak and the sand peak, a division method for each period is proposed. (3) A corresponding scheduling index is proposed according to the characteristics of the sand peak process and the needs of flood control scheduling. This research can provide operational indicators for the operation and management of the sediment load in the TGR and also provide technical support for sustainable reservoirs similar to TGR. Full article

Sediment fingerprinting was utilized to identify potential hotspots of soil erosion and sediment transport pathways in the Nile Nyabarongo Upper Catchment (NNYU) in Rwanda, where rivers and reservoirs are suffering from alarmingly high levels of sedimentation. Sediment fingerprinting is a practical approach used to identify erosional hotspots and sediment transport processes in highly mountainous regions undergoing swift land use transformation. This technique involves a statistical comparison of the elemental composition of suspended sediments in river water with the elemental composition of soils belonging to different geological formations present in the catchment, thereby determining the sources of the suspended sediment. Suspended sediments were sampled five times over dry and wet seasons in all major headwater tributaries, as well as the main river channel, and compared with soils from respective delineated watersheds. Elemental composition was obtained using laser ablation inductively coupled plasma mass spectrometry, and elements were chosen that could reliably distinguish between the various geological types. The final results indicate different levels of sediment contribution from different geological types. A three-level intervention priority system was devised, with Level 1 indicating the areas with the most serious erosion. Potential sources were located on an administrative map, with the highest likely erosion over the study period (Level 1) occurring in Kabuga cell in the Mwogo sub-catchment, Nganzo and Nyamirama cells in the Nyagako sub-catchment and Kanyana cell in the NNYU downstream sub-catchment. This map enables the pinpointing of site visits in an extensive and rugged terrain to verify the areas and causes of erosion and the pathways of sediment transport. Sediment concentrations (mg L⁻¹) were the highest in the Secoko and Satinsyi tributaries. The composition of suspended sediment was seen to be temporally and spatially dynamic at each sampling point, suggesting the need for an adequate number of sampling locations to identify erosion hotspots in a large mountainous watershed. Apart from prioritizing rehabilitation locations, the detailed understanding of critical zone soil–land cover–climate processes is an important input for developing region-specific watershed management and policy guidelines. Full article

To investigate the spatiotemporal distribution characteristics of nitrogen and phosphorus in the water and sediment of the Danjiangkou Reservoir, the source of the Middle Route of China’s South-to-North Water Diversion Project, we designed a year-long monitoring program. The water and sediment samples were collected from 13 sampling points in the upstream and downstream areas over the year. The results revealed significant spatial heterogeneity in N and P concentrations, with higher levels of total nitrogen, nitrate nitrogen, and nitrite nitrogen in the upstream area compared to the downstream area (p < 0.01). Total phosphorus was also significantly higher in the upstream area (p < 0.05). Seasonal variations were observed, with TN and TP levels peaking in February and August, respectively. The TN:TP ratio indicated a severe P-limited state in most periods, transitioning to a co-limited state of N and P during summer. Sediment analysis showed that TN and TP concentrations were higher in the upstream area, with no significant differences between upstream and downstream on an annual basis, exhibiting strong stoichiometric internal stability. However, seasonal differences were noted, particularly in February and November. This study highlights the complex interactions between water and sediment, emphasizing the role of sediment resuspension, water flow, and seasonal changes in nutrient dynamics. These findings provide a scientific basis for the management and protection of water quality in the Danjiangkou Reservoir, ensuring its role as a critical water source for the South-to-North Water Diversion Project. Full article

Climate change and extreme events such as droughts, heavy rainfall and flooding can influence the water column stratification in reservoir dams, decrease storage capacity, increase sediment and pollutant loads and, as a result, affect water quality. The seasonal variation in the water column stratification of reservoirs is an important parameter for the study of dam life cycle as well as water management and use. In the present study a detailed bathymetric survey was carried out, and a digital elevation model (DEM) of the reservoir was constructed. Seasonal physicochemical monitoring data such as temperature, dissolved oxygen, pH and conductivity are presented. The seasonal thermal stratification was recorded, resulting in an isolated hypolimnion where anoxic layers formed below 17 m in summer and autumn. Manganese and iron concentrations exhibited values higher than 150 mg/L in the anoxic hypolimnion during summer and autumn, indicating solubilization from the sediment. The observed seasonal and depth-dependent variations in physicochemical parameters underline the reservoir’s susceptibility to eutrophication and metal mobilization, particularly during stratified periods. These findings are critical for designing management strategies to mitigate potential water quality issues. Full article

Freshwater bivalves play essential ecological roles in ecosystems, but they are among the most threatened fauna worldwide. Despite receiving industrial and domestic wastes, the Guandu River is the main source of drinking water for more than nine million people in the Rio de Janeiro metropolitan region. This study aimed to assess how infaunal bivalves respond to water and sediment quality in the Guandu River basin. Samples were collected at 10 sites across reservoirs, lotic, and lentic systems during cold–dry and warm–rainy seasons. Four bivalves were identified: Anodontites trapesialis, Diplodon ellipticus, Corbicula fluminea (non-native), and C. largillierti (non-native). Native species were restricted to two lentic sites at Guandu Lagoon, with the poorest environmental quality, significantly affected by high chlorophyll a and ammonia in the water. In contrast, C. fluminea was widely distributed and more abundant in the basin but restricted to less degraded sites, suggesting a lower tolerance to environmental pollution. Multivariate analyses indicated significant differences in environmental conditions and species–environment correlation. The non-native species spread and poor environmental quality threaten native bivalves in the Guandu River basin, leading them to a local extinction risk. Results highlight the need for effective management and conservation actions to protect biodiversity in tropical river basins. Full article

Sediment accumulation in dam reservoirs significantly impacts hydropower efficiency and infrastructure sustainability. Bottom sediments often contain heavy metals such as Cr, Ni, Cu, Zn, Cd, and Pb, which can pose ecological risks and affect water quality. Moreover, excessive sedimentation reduces reservoir capacity, increases turbine wear, and raises operational costs, ultimately hindering energy production. This study examined the ecological risk of heavy metals in bottom sediments and explored predictive approaches to support sediment management. Using 27 sediment samples from Zemborzyce Lake, the concentrations of selected heavy metals were measured at two depths (5 cm and 30 cm). Ecological risk index (ERI) values for the deep layer were predicted based on surface data using artificial neural networks (ANNs) and multiple linear regression (MLR). Both models showed a high predictive accuracy, demonstrating the potential of data-driven methods in sediment quality assessment. The early identification of high-risk areas allows for targeted dredging and optimized maintenance planning, minimizing disruption to dam operations. Integrating predictive analytics into hydropower management enhances system resilience, environmental protection, and long-term energy efficiency. Full article

Understanding the impact of vegetation on organic matter content in sediments is essential for sustainable reservoir management and water quality protection. This study examined the relationship between land cover, erosion processes, and organic matter accumulation in the sediments of four small water reservoirs in the Republic of Serbia. Organic matter content was quantified and analyzed in relation to basin characteristics, including land-use composition, absolute and mean flow gradients, and sediment grain size distribution. Field sampling was conducted across the catchments of four small water reservoirs—Duboki potok, Resnik, Ljukovo, and Sot—with sediment samples collected from main tributaries and accumulation basins. A multi-method approach was employed, combining remote sensing for vegetation-cover assessment, granulometric analysis, organic matter evaluation via loss-on-ignition at 350 °C, and statistical correlation analysis to assess the influence of land use and hydrological gradients on sediment composition. The results revealed a strong correlation (R = 0.892) between forest cover and sedimentary organic matter content, confirming the significant role of vegetation in stabilizing sediments and promoting organic matter deposition. Reservoirs with higher forest and shrub cover (e.g., Sot and Duboki potok) exhibited greater organic matter accumulation (5.79–5.98%), while the agriculture-dominated Ljukovo catchment (76.85% agricultural land) recorded the lowest organic matter content (3.89%) due to increased sediment displacement and reduced erosion resistance. These findings underscore the critical role of vegetation in regulating sediment dynamics and enhancing organic matter retention in small water reservoirs. To mitigate excessive organic matter deposition and improve water quality, sustainable watershed management strategies—such as vegetation buffer strips, afforestation, and erosion control measures—are recommended. Full article

Beavers play a key role in creating temporary water reservoirs that significantly impact the natural environment and local river hydrology. The primary aim of this study was to assess the potential of increasing the number of beaver dams (Castor spp.), as an alternative method of water retention in the environment. Research conducted on three small lowland streams in central Poland revealed that beaver dams, even in modified riverbeds, enable the formation of shallow floodplains and ponds. Innovative analyses considered the structural materials of the dams and their impact on river hydromorphology and sediment transport. The findings emphasise the importance of beavers in water retention processes, the stabilisation of water levels during low flows and the protection of biodiversity. The study also demonstrated that beaver dams play a critical role in storing surface- and groundwater, mitigating drought impacts, reducing surface runoff, and stabilising river flows. These constructions influence local hydrology by increasing soil moisture, extending water retention times, and creating habitats for numerous species. The collected data highlight the potential of beaver dams as a tool in water resource management in the context of climate change. Further research could provide guidance for the sustainable utilisation of beavers in environmental conservation strategies and landscape planning. Full article

The conservation and monitoring of archaeological sites submerged in water reservoirs have become increasingly necessary in a climatic context where water management policies are possibly accelerating erosion and sedimentation processes. This study assesses the potential of using multitemporal LiDAR data and Machine Learning (ML)—specifically the XGBoost algorithm—to predict erosional and sedimentary processes affecting archaeological sites in the Valdecañas Reservoir (Spain). Using data from 2010 to 2023, topographic variations were calculated through a robust workflow that included the co-registration of LiDAR point clouds and the generation of high-resolution DEMs. Hydrological variables, topographic descriptors, and water dynamics-related factors were extracted and used to train models based on the detected measurement errors and the temporal ranges of the DEMs. The model trained with 2018–2023 data exhibited the highest predictive performance (R² = 0.685), suggesting that sedimentary and erosional patterns are partially predictable. Finally, a multicriteria approach was applied using a DEM generated from 1957 aerial photographs to estimate past variations based on historical terrain conditions. The results indicate that areas exposed to fluctuating water levels and different topographic orientations suffer greater damage. This study highlights the value of LiDAR and ML in assessing the vulnerability of archaeological sites in highly dynamic environments. Full article

Flood frequencies, along with the associated loss of life and property, have risen significantly due to climate change and increasing human activities. While prior research has primarily focused on high-intensity rainfall events and reservoir management in flood management, the influence of sediment-starved water—termed “hungry water”—released from dams in controlling flood dynamics has not gained much attention. The present study is aimed at exploring the potential role of sediment-starved water, or the “hungry water effect” on the valley degradation, bed material changes and flood inundation in the Pamba River during the Kerala Flood, 2018, through a detailed characterization of bed materials and their deposition in the channel bed. The release of sediment-starved water from the Kakki reservoir during the episodic precipitation event (15 to 17 August 2018) resulted in significant bed degradation and scouring of the valley slopes, leading to the deposition of large boulders and rock masses and the inundating of approximately 196 km² of floodplains. This study highlights the need for integrated sediment management strategies in reservoir operations by providing essential insights into sediment transport dynamics during extreme weather events. Understanding these processes is crucial for formulating effective flood mitigation strategies and improving the resilience of riverine ecosystems, particularly as the interaction between intense rainfall and sediment-depleted releases significantly exacerbated the flood’s severity. Full article

Marine sediments are recognized as crucial reservoirs of antibiotic resistance genes (ARGs). However, the antibiotic resistome in sediments of the East China Sea, an area heavily impacted by human activities, has not been thoroughly studied. Here, we conducted a systematic investigation into the antibiotic resistome in these sediments using metagenomic analysis. Overall, we detected eighty ARG subtypes and nineteen ARG types. Beta-lactams were the dominant ARG type, and Gammaproteobacteria was the main ARG host in this study. Mobile genetic elements (MGEs) were not major drivers of ARG profiles. Although the ARG host communities significantly differed between the spring and autumn (p < 0.05), the antibiotic resistome remained stable across the two seasons. The assembly of ARGs and their hosts was governed by stochastic processes, and a high ratio of stochastic processes implied its crucial role in the assembly and stabilization of the antibiotic resistome. Co-occurrence network analysis revealed an important role of Deltaproteobacteria in the stabilization of ARG profiles across seasons. Environmental parameters (e.g., temperature and density) played certain roles in the stabilization of the antibiotic resistome between spring and autumn. Moreover, nine human pathogen bacteria (HPB) were detected in this study. We also found that the health risks caused by ARGs were relatively higher in the spring. Our results will provide a strong foundation for the development of targeted management strategies to mitigate the further dissemination and spread of ARGs in marine sediments. Full article

The natural process of lake and reservoir eutrophication through nutrient accumulation within sediments has been accelerated through anthropogenic sources of nitrogen and, especially, phosphorus (P). Stored nutrients can result in significant internal loading (during periods of low sediment redox potential or elevated pH), which may drive poor water quality despite best practices in catchment management. Internal P loading can promote proliferation of cyanobacterial and algal taxa responsible for harmful algal blooms (HABs), as well as taste and odour (T&O) and cyanotoxin events. Here, we investigate the sediment and water column P content of eight reservoirs by analysing iron-bound (Fe-P), calcium-bound (Ca-P), and labile P fractions. We find that all but one reservoir demonstrated high iron (Fe) content (27–52 g Fe/kg sediment), suggesting a high Fe-P binding capacity and hence a potentially high susceptibility to redox-mediated internal loading. However, we found no correlation between Fe-P and Fe content in sediments, suggesting the Fe pool was not saturated with P and thus has capacity for further storage. All sites had low levels of labile P (up to 0.14 mg P-PO₄/g dry sediment), with the highest pool of P being Ca-bound, which would be expected based on catchment geology and the presence of Ca-minerals which bind P. Currently, within industry, emphasis falls on controlling the external loading of nutrients from the surrounding catchment, often ignoring the critical role of internal loading. However, here, we demonstrate the need to continually monitor sediment P content and potential internal loading as part of the standard monitoring regime used by water companies to inform reservoir management strategies. Full article

It is imperative to assess and comprehend the hydrological processes of the river basin in light of the potential effects of land use/land cover and climate changes. The study’s main objective was to evaluate hydrologic response of water balance components to the projected land use/land cover (LULC) and climate changes in the Omo–Gibe River Basin, Ethiopia. The study employed historical precipitation, maximum and minimum temperature data from meteorological stations, projected LULC change from module for land use simulation and evaluation (MOLUSCE) output, and climate change scenarios from coupled model intercomparison project phase 6 (CMIP6) global climate models (GCMs). Landsat thematic mapper (TM) (2007) enhanced thematic mapper plus (ETM+) (2016), and operational land imager (OLI) (2023) image data were utilized for LULC change analysis and used as input in MOLUSCE simulation to predict future LULC changes for 2047, 2073, and 2100. The predictive capacity of the model was evaluated using performance evaluation metrics such as Nash–Sutcliffe Efficiency (NSE), the coefficient of determination (R2), and percent bias (PBIAS). The bias correction and downscaling of CMIP6 GCMs was performed via CMhyd. According to the present study’s findings, rainfall will drop by up to 24% in the 2020s, 2050s, and 2080s while evapotranspiration will increase by 21%. The findings of this study indicate that in the 2020s, 2050s, and 2080s time periods, the average annual Tmax will increase by 5.1, 7.3, and 8.7%, respectively under the SSP126 scenario, by 5.2, 10.5, and 14.9%, respectively under the SSP245 scenario, by 4.7, 11.3, and 20.7%, respectively, under the SSP585 scenario while Tmin will increase by 8.7, 13.1, and 14.6%, respectively, under the SSP126 scenario, by 1.5, 18.2, and 27%, respectively, under the SSP245 scenario, and by 4.7, 30.7, and 48.2%, respectively, under the SSP585 scenario. Future changes in the annual average Tmax, Tmin, and precipitation could have a significant effect on surface and subsurface hydrology, reservoir sedimentation, hydroelectric power generation, and agricultural production in the OGRB. Considering the significant and long-term effects of climate and LULC changes on surface runoff, evapotranspiration, and groundwater recharge in the Omo–Gibe River Basin, the following recommendations are essential for efficient water resource management and ecological preservation. National, regional, and local governments, as well as non-governmental organizations, should develop and implement a robust water resources management plan, promote afforestation and reforestation programs, install high-quality hydrological and meteorological data collection mechanisms, and strengthen monitoring and early warning systems in the Omo–Gibe River Basin. Full article

This study presents a numerical investigation of the hydrodynamic and thermal interactions at the confluence of the Ebro and Segre Rivers in the Riba-roja Reservoir, using the Finite Element Method (FEM) within the Kratos Multiphysics framework. The coupled Navier–Stokes and energy equations were solved, employing the variational multi-scale (VMS) method for stabilization. Field data from thermal imaging and in situ measurements in March and October 2011 were used for model validation. The results revealed complex mixing and stratification dynamics influenced by regulated and unregulated flows, seasonal temperature variations, and reservoir geometry. Despite some discrepancies in temperature predictions due to the decoupled energy equation, the model effectively captured the system’s thermal behavior. This work represents a first step toward incorporating a fully coupled energy equation and exploring the effects of thermal mixing and stratification on suspended sediment transport. This study enhances understanding of fluid–thermal interactions in reservoir systems, with implications for water quality management and ecological conservation. Full article