Next Issue
Volume 13, August-1
Previous Issue
Volume 13, July-1

Water, Volume 13, Issue 14 (July-2 2021) – 116 articles

Cover Story (view full-size image): A riparian zone overgrazed by cattle on the Sprague River, Oregon, USA, is pictured. This is a common situation across the western United States. In the Western Mountains ecoregion, 30 + 6% of the stream length is in poor condition based on assessments of fish and macroinvertebrate assemblages. In the Xeric ecoregion, 44 + 5% and 27 + 5% of the stream length are in poor condition for macroinvertebrates and fish assemblages, respectively. These features are strongly associated with poor water quality and poor physical habitat structure. Studies have shown that livestock exclosures (fencing)—if extensive enough—can lead to a wooded riparian zone, stabilized riverbanks, and a narrower channel with cooler water. Such habitat changes improve conditions for fish, macroinvertebrate, mammal, and bird assemblages. View this paper
  • Issues are regarded as officially published after their release is announced to the table of contents alert mailing list.
  • You may sign up for e-mail alerts to receive table of contents of newly released issues.
  • PDF is the official format for papers published in both, html and pdf forms. To view the papers in pdf format, click on the "PDF Full-text" link, and use the free Adobe Readerexternal link to open them.
Order results
Result details
Section
Select all
Export citation of selected articles as:
Article
Hydrochemical Characteristics and Quality Assessment of Shallow Groundwater in the Xinzhou Basin, Shanxi, North China
Water 2021, 13(14), 1993; https://doi.org/10.3390/w13141993 - 20 Jul 2021
Cited by 3 | Viewed by 931
Abstract
The hydrochemistry and quality of local shallow groundwater was assessed within the Xinzhou basin in Shanxi, North China. Piper diagrams, correlation analysis, principal component analysis, chloro-alkaline indices, ion proportion diagrams, and Gibbs diagrams were used to reveal the hydrochemical characteristics and evolution mechanisms [...] Read more.
The hydrochemistry and quality of local shallow groundwater was assessed within the Xinzhou basin in Shanxi, North China. Piper diagrams, correlation analysis, principal component analysis, chloro-alkaline indices, ion proportion diagrams, and Gibbs diagrams were used to reveal the hydrochemical characteristics and evolution mechanisms of groundwater. Besides, two indicators of sodium adsorption ratio and soluble sodium percentage, USSL and Wilcox diagrams, and water quality index models were used to evaluate the groundwater quality for irrigation and drinking. In general, groundwater in most areas of the basin is fresh water with total dissolved solid lower than 1000 mg/L. But there are salt water in some parts of the southern basin, with total dissolved solid higher than 1000 mg/L, due to industrial and domestic pollution. The hydrochemical facies of groundwater in most areas are HCO3-Ca and mixed HCO3-Ca·Mg·Na types, while it is HCO3·SO4·Cl-Na type in a small part of the basin. Nitrate pollution widely occurred in the basin because of the use of nitrogenous fertilizers. The dominant mechanism controlling the evolution of groundwater chemistry compositions was the weathering of rock minerals. It mainly reflected in the dissolution of carbonate minerals. And the carbonate dissolution is the major origins of HCO3, Ca2+, and Mg2+ in groundwater. However, Na-Ca exchange is the important source of Na+. Shallow groundwater was suitable for irrigation and drinking except for some southern parts of the basin. These results will be helpful for the protection and efficient management of groundwater in the Xinzhou basin. Full article
(This article belongs to the Section Hydrology)
Show Figures

Figure 1

Article
A Continental Assessment of Reservoir Storage and Water Availability in South America
Water 2021, 13(14), 1992; https://doi.org/10.3390/w13141992 - 20 Jul 2021
Cited by 1 | Viewed by 1063
Abstract
This study presents the first continental assessment of water storage and its influence on the availability of water of the river systems of South America. Although hydraulic infrastructure has the potential to cause several impacts on river systems and the environment, their relevance [...] Read more.
This study presents the first continental assessment of water storage and its influence on the availability of water of the river systems of South America. Although hydraulic infrastructure has the potential to cause several impacts on river systems and the environment, their relevance in water resources systems is irrefutable. The human services that dams and reservoirs provide to society, e.g., hydroelectricity, water supply, irrigation, or flood control, are vital services that society requires to develop. Despite this fact, the interactions of dams and reservoirs in the river systems of South America have not been explored from a hydrological perspective. In this study, we present the first assessment of the potential effects of water storage at a basin scale in South America. For this purpose, first we present an analysis of the current conditions and the influence of water storage in the basins of the continent. Then, we estimate the potential water availability of each basin, to evaluate the role of water storage in the availability of water in the continent. Our findings indicate that the ‘Colorado’ and ‘Negro’ basins in Argentina are the most influenced by water storage in the continent. Moreover, our results suggest that reservoirs improve the potential water availability capacity, particularly in the southern basins of the continent. With this study, we expect to provide helpful insights about the current interactions of reservoirs with the river systems of the continent. Full article
(This article belongs to the Special Issue Water Resources Systems in a Changing World: Planning and Adaptation)
Show Figures

Figure 1

Article
Tomato and Watermelon Production with Mulches and Automatic Drip Irrigation in North Dakota
Water 2021, 13(14), 1991; https://doi.org/10.3390/w13141991 - 20 Jul 2021
Viewed by 872
Abstract
In North Dakota, agriculture contributes a large sector of the state’s economy, but vegetable production is limited due to the state’s climate condition. Inadequate soil moisture and low soil temperature are the two major factors prohibiting quality produce and high-yield vegetable production. In [...] Read more.
In North Dakota, agriculture contributes a large sector of the state’s economy, but vegetable production is limited due to the state’s climate condition. Inadequate soil moisture and low soil temperature are the two major factors prohibiting quality produce and high-yield vegetable production. In this study, a soil-water potential, sensor-based drip irrigation system was developed, designed, and installed to evaluate its application on tomato and watermelon productions in a two-year field experiment in 2019 and 2020. The experimental treatments were drip irrigation and no irrigation under three mulches: black plastic, clear plastic, and landscape fabric mulches. Irrigation was scheduled at 8:00 am for watermelon and 9:00 a.m. for tomato, with the ability for each irrigation event to be bypassed based on the soil moisture conditions. Due to rainfall differences in the two years, irrigation was barely needed in 2019, but in 2020, drip irrigation was applied frequently. On average, for the two-years’ field experiment, the highest yield for tomatoes was obtained from drip irrigation under black plastic drip irrigation treatment with 40.24 Mg ha−1 in 2020, whereas the highest yield for watermelon was from drip irrigation under clear plastic mulch with 165.55 Mg ha−1 in 2020. The effect of mulch, irrigation, and combined practices were analyzed based on the average fruit weight and diameter, electrical conductivity (EC), pH, and sugar content of the samples. The results showed that for watermelon, the average weight and diameter were significantly heavier and higher with irrigation treatments, but the EC and the pH values were significantly higher with mulch treatments. For tomatoes, the average weight, diameter, pH, and sugar content were all significantly higher with mulch treatment, but the EC was higher with irrigation treatment. Full article
(This article belongs to the Special Issue Application of Smart Technologies in Water Resources Management)
Show Figures

Figure 1

Article
When a Year Is Not Enough: Further Study of the Seasonality of Planktonic Protist Communities Structure in an Ice-Free High Arctic Fjord (Adventfjorden, West Spitsbergen)
Water 2021, 13(14), 1990; https://doi.org/10.3390/w13141990 - 20 Jul 2021
Cited by 1 | Viewed by 1065
Abstract
As a contribution to understanding the ecological framework of protistan seasonal succession patterns, we present the weekly-to-monthly (January–October) light microscopy-based study of nano- and microplanktonic protist communities of Adventfjorden waters in 2013. In general, protist dynamics corresponded to the classic paradigm for the [...] Read more.
As a contribution to understanding the ecological framework of protistan seasonal succession patterns, we present the weekly-to-monthly (January–October) light microscopy-based study of nano- and microplanktonic protist communities of Adventfjorden waters in 2013. In general, protist dynamics corresponded to the classic paradigm for the Arctic ice-free waters with extremely low abundance and diversity in winter, with the main abundance and chlorophyll-a peak in April-May, followed by a diverse but low abundant community during summer/autumn. However, the reference of the obtained data to the previously conducted year-round research in 2012 allows us to observe substantial variability in seasonal patterns between the two consecutive years. The most striking difference concerned the spring bloom composition and abundance, with clear domination of Phaeocystis pouchetii in Atlantified fjord waters in 2012 and Bacillariophyceae-dominated (mainly Fragilariopsis, Thalassiosira nordenskioeldii, and, in a lesser extent, also Pseudo-nitzschia seriata) bloom in 2013 when local water prevailed. On the other hand, a surprisingly high share of spring bloom taxa persisted throughout the summer/autumn of 2013 when they co-occurred with typical summer taxa (dinoflagellates and other small flagellates). Their extended growth could, at least in part, result from scarce Ciliophora throughout the season, which, in turn, can be attributed to the high grazing pressure of very numerous meroplankton and mesozooplankton. In light of this, our results may be relevant in discussions proposed for the West Spitsbergen waters link between the Atlantic water inflow and the spring bloom composition, as well as its further progression in the productive season. They also highlight the strong need for further high-resolution monitoring of annual plankton cycles and great caution when looking for phenological patterns within a single year or when interpreting short-term data. Full article
(This article belongs to the Special Issue Plankton Ecology in Shallow Coastal Waters)
Show Figures

Figure 1

Article
Silting in the Grand Canal in the Domain of Chantilly (Oise, France)—Catchment-Scale Hydrogeomorphological Reconnaissance and Local-Scale Hydro-Sedimentary Transport Modelling
Water 2021, 13(14), 1989; https://doi.org/10.3390/w13141989 - 20 Jul 2021
Viewed by 832
Abstract
The domain of Chantilly (Oise, France) includes a castle and a garden, both dating from the eighteenth century, which are seen as important legacies of France’s history. Nowadays, the 2.5 km canal that runs through the domain is subject to the phenomenon of [...] Read more.
The domain of Chantilly (Oise, France) includes a castle and a garden, both dating from the eighteenth century, which are seen as important legacies of France’s history. Nowadays, the 2.5 km canal that runs through the domain is subject to the phenomenon of silting, leading to the accumulation of sediments within the canal linked to the proliferation of algae, which has a dissuasive effect among visitors. HEC-RAS software (Hydrologic Engineering Centers River Analysis System, US army corps of Engineers, Washington, D.C., USA) was used to model and understand sediment accumulation within the canal. This model is widely used in the literature tackling sediment transport and accumulation, and allows the forecasting of which stretches of the canal are most susceptible to sediment accumulation. The simulation results highlight an accumulation of sediment near the entrance of the Nonette stream into the canal and a propagation through the canal. The total accumulated volume assessed by the model between 2001 and 2010 equals 3901 m3, when the reconnaissance of the catchment showed the sediment was not a limiting factor. However, the volumes determined are underestimated, as matter brought by vegetation or other systems different from the river (e.g., wind, rainfall) is not considered in the calculation. The quantity of sediment is also subject to uncertainties, as the bathymetry of the canal is not available. Full article
(This article belongs to the Special Issue Fluvial Hydraulics and Applications)
Show Figures

Figure 1

Article
The Effectiveness of “River Chief System” Policy: An Empirical Study Based on Environmental Monitoring Samples of China
Water 2021, 13(14), 1988; https://doi.org/10.3390/w13141988 - 20 Jul 2021
Cited by 1 | Viewed by 1098
Abstract
There has been controversy in theory and practice among studies about the governance of the “River Chief System” (RCS) policy and the watershed management issues behind it. This paper uses the regression discontinuity (RD) method and the water pollution monitoring data of 150 [...] Read more.
There has been controversy in theory and practice among studies about the governance of the “River Chief System” (RCS) policy and the watershed management issues behind it. This paper uses the regression discontinuity (RD) method and the water pollution monitoring data of 150 state-controlled monitoring points in China from 2007 to 2018 at the China National Environmental Monitoring Station to empirically study the effect of the “River Chief System” on water pollution treatment and the influencing factors behind the effect of the “River Chief System”. The results show that the “River Chief System” policy has a positive impact on river pollution treatment in the observation term. The implementation effectiveness of the “River Chief System” is limited by factors such as the boundaries of the river chief’s jurisdictions, the administrative conflict among river chiefs, local government environmental expenditure capacity, and environmental pressure. It is believed that the key to basin governance is to further improve the synergistic model of basin governance among regions. Full article
(This article belongs to the Section Water Resources Management, Policy and Governance)
Show Figures

Figure 1

Article
Analysis of Existing Equations for Calculating the Settling Velocity
Water 2021, 13(14), 1987; https://doi.org/10.3390/w13141987 - 20 Jul 2021
Cited by 1 | Viewed by 1009
Abstract
The settling velocity of sediment is one of the essential parameters in studying freshwater reservoirs and transporting sediment in flowing water, mainly when the suspension is the dominant process. Hence, their quantitative measurements are crucial. An error during the prediction of the settling [...] Read more.
The settling velocity of sediment is one of the essential parameters in studying freshwater reservoirs and transporting sediment in flowing water, mainly when the suspension is the dominant process. Hence, their quantitative measurements are crucial. An error during the prediction of the settling velocity may be increased by a factor of three or more in the estimation of the suspended load transport in the flowing water. Despite its significance, obtaining its real value in situ is practically impossible, and it is usually derived via laboratory tests or anticipated by empirical formulas. Numerous equations are available to calculate the settling velocity of the particle. However, it is exceedingly difficult to choose the best method when giving a specific solution for the same problem. Hence, a review of the existing equations is required. In this study, extensive data on settling velocity is collected from the literature, and previously proposed equations are analysed using graphical and statistical analysis. Full article
(This article belongs to the Special Issue Greenhouse Gas Emission from Freshwater Ecosystem)
Show Figures

Figure 1

Article
Simulations and Analysis of GNSS Multipath Observables for Frozen and Thawed Soil under Complex Surface Conditions
Water 2021, 13(14), 1986; https://doi.org/10.3390/w13141986 - 20 Jul 2021
Viewed by 748
Abstract
The transition of the freeze–thaw state of the land surface soil occurs every year with the season and is closely related to the human living environment. The freezing and thawing changes of the ground surface have important effects on hydrological activities, meteorological conditions, [...] Read more.
The transition of the freeze–thaw state of the land surface soil occurs every year with the season and is closely related to the human living environment. The freezing and thawing changes of the ground surface have important effects on hydrological activities, meteorological conditions, and ecological gas dynamics. Traditional monitoring methods have their limitations. In the past two decades, the emerging GNSS-R/IR (Global Navigation Satellite System-Reflectometry/Interference Reflectometry) technology has provided a new method for monitoring the surface f state; however, fewer works have paid attention to the scattering mechanism models in the current study. In this paper, a forward GNSS multipath model suitable for a complex cold surface is developed. The dielectric constant model with different surface parameters is added. The calculation of snow layer attenuation is employed to take the snow cover into consideration. Based on the first-order radiation transfer equation model, a polarization synthesis method is used to obtain the circularly and linearly polarized vegetation specular scattering characteristics. The surface characteristics and antenna model are coupled. A more detailed forward GNSS multipath model of frozen and thawed soil under complex surface conditions is established. The model is used to simulate and analyze the forward GNSS multipath (Signal to Noise Ratio (SNR), phase and pseudorange) responses of frozen and thawed soil under complex surface conditions (soil salinity, snow and vegetation coverage). Studies have shown that when the soil changes from freezing to thawing due to the change in the phase of the water in the soil, the dielectric constant and BRCS (bi-static radar cross-section) increase, causing the increase in the amplitude of the multipath observation. The higher the salinity content, the larger the amplitude of the multipath observation. The attenuation of the snow cover and the vegetation layer will lead to the reduction of the multipath observation amplitude. For the first time, the model developed by this paper reveals the GNSS multipath observation response of frozen and thawed soil under complex surface conditions in detail, which can provide some theoretical support for subsequent experimental design and data analysis. Full article
(This article belongs to the Special Issue Remote Sensing Application on Soil Moisture)
Show Figures

Figure 1

Article
Propagation from Meteorological to Hydrological Drought and Its Influencing Factors in the Huaihe River Basin
Water 2021, 13(14), 1985; https://doi.org/10.3390/w13141985 - 20 Jul 2021
Cited by 3 | Viewed by 1155
Abstract
Understanding the propagation from meteorological to hydrological drought is crucial for hydrological drought monitoring and forecasting. In this study, daily precipitation and streamflow data of 16 sub-catchments in the Huaihe River Basin from 1980 to 2014 are used to establish a framework to [...] Read more.
Understanding the propagation from meteorological to hydrological drought is crucial for hydrological drought monitoring and forecasting. In this study, daily precipitation and streamflow data of 16 sub-catchments in the Huaihe River Basin from 1980 to 2014 are used to establish a framework to quantitatively reveal the propagation relationship between meteorological and hydrological drought and explore the impact of climate, catchment properties, and human activities on drought propagation. The propagation from meteorological to hydrological drought is divided into three types. Type-1 propagation indicates that one or several meteorological droughts trigger a hydrological drought. The occurrence probability of Type-1 calculated by the conditional probability on SPI and SRI series varies from 0.25 to 0.48 among all catchments. Features of Type-1 propagation can be concluded as lengthening of duration, amplification of severity, lag of onset time, and reduction of speed. Type-2 propagation indicates that a meteorological drought occurs but no hydrological drought occurs, which accounts for 63–77% of the total meteorological drought events in all catchments. Type-3 indicates that a hydrological drought occurs without a proceeding meteorological drought, which is caused mostly by human activities. The occurrence probability of Type-3 ranges from 0.31 to 0.58. Climate factors have significant effects on hydrological drought duration, while catchment properties represented by topographic index and base flow index significantly relate to hydrological drought severity, propagation time, and occurrence probability of Type-1 propagation. The ratio of crop land reflecting irrigation on hydrological drought is far less than that of topographic index, denoting that the impact of irrigation on hydrological drought is less than that of catchment properties. Reservoirs have significant effects on alleviating the duration and severity of extreme hydrological droughts, but little effects on the average duration and severity of hydrological droughts. Full article
(This article belongs to the Special Issue Human and Climate Impacts on Drought Dynamics and Vulnerability)
Show Figures

Figure 1

Article
Sustainable Model: Recommendations for Water Conservation Strategies in a Developing Country Through a Psychosocial Wellness Program
Water 2021, 13(14), 1984; https://doi.org/10.3390/w13141984 - 20 Jul 2021
Cited by 1 | Viewed by 1348
Abstract
Human industrial activities are bringing physiochemical changes to the land, air, and seas and leading towards more uncertain climate changes, like drought, thunderstorms, and heat waves. This has resulted in water scarcity because of overexploitation of water resources. It is therefore imperative to [...] Read more.
Human industrial activities are bringing physiochemical changes to the land, air, and seas and leading towards more uncertain climate changes, like drought, thunderstorms, and heat waves. This has resulted in water scarcity because of overexploitation of water resources. It is therefore imperative to develop effective conservation programs that consider the factors that affect the decisions of people with regard to water conservation and sustainable activities. This study considered the perspective of a developing country and explored the impact of three psychosocial factors, i.e., subjective happiness, perceived stress, and personal well-being, on individuals’ current and future intentions to conserve water. A sample of 304 respondents was collected via a self-administered questionnaire containing measures of demographic characteristics, psychological factors, and current and future water conservation behavior. The data were collected online as well as through hard copies. Correlational analysis showed that the three psychosocial factors had significant associations with both current and future intentions to conserve water. Furthermore, the effect size (f2) demonstrated that personal well-being was a significant predictor of current and future water conservation behavior. Stress, however, did not serve as a significant predictor of either current or future water conservation behavior. In contrast, subjective happiness was a significant predictor of only future water conservation behavior. Full article
(This article belongs to the Section Water Resources Management, Policy and Governance)
Show Figures

Figure 1

Article
Phosphorus Release from Sediments in a Raw Water Reservoir with Reduced Allochthonous Input
Water 2021, 13(14), 1983; https://doi.org/10.3390/w13141983 - 19 Jul 2021
Cited by 3 | Viewed by 1021
Abstract
Following successful abatement of external nutrient sources, one must shift the focus to the role of phosphorus (P) release from sediment. This enables us to better assess the causes for sustained eutrophication in freshwater ecosystem and how to deal with this challenge. In [...] Read more.
Following successful abatement of external nutrient sources, one must shift the focus to the role of phosphorus (P) release from sediment. This enables us to better assess the causes for sustained eutrophication in freshwater ecosystem and how to deal with this challenge. In this study, five sediment cores from the shallow YuQiao Reservoir in northern China were investigated. The reservoir serves as the main raw water source for tap water services of Tianjin megacity, with a population of 15.6 million. Sediment characteristics and P fractions were determined in order to assess the role of the sediments as the P source to the water body. The total P content (TP) in sediments was similar to what was found in catchment soils, although the P sorption capacity of sediments was 7–10 times greater than for the catchment soils. Isotherm adsorption experiments documented that when P concentration in overlying water drops below 0.032–0.070 mg L−1, depending on the site, the sediment contributes with a positive flux of P to the overlying water. Adsorbed P at different depths in the sediments is found to be released with a similarly rapid release rate during the first 20 h, though chronic release was observed mainly from the top 30 cm of the sediment core. Dredging the top 30 cm layer of the sediments will decrease the level of soluble reactive phosphate in the water being sustained by the sediment flux of P. Full article
Show Figures

Figure 1

Article
Application of SWAT Using Snow Data and Detecting Climate Change Impacts in the Mountainous Eastern Regions of Turkey
Water 2021, 13(14), 1982; https://doi.org/10.3390/w13141982 - 19 Jul 2021
Viewed by 1528
Abstract
In recent years, the potential impacts of climate change on water resources and the hydrologic cycle have gained importance especially for snow-dominated mountainous basins. Within this scope, the Euphrates-Tigris Basin, a snow-fed transboundary river with several large dams, was selected to investigate the [...] Read more.
In recent years, the potential impacts of climate change on water resources and the hydrologic cycle have gained importance especially for snow-dominated mountainous basins. Within this scope, the Euphrates-Tigris Basin, a snow-fed transboundary river with several large dams, was selected to investigate the effects of changing climate on seasonal snow and runoff. In this study, two headwater basins of the Euphrates River, ranging in elevation between 1500–3500 m, were assigned and SWAT was employed as a hydrological modeling tool. Model calibration and validation were conducted in a stepwise manner for snow and runoff consecutively. For the snow routine, model parameters were adjusted using MODIS daily snow-covered area, achieving hit rates of more than 95% between MODIS and SWAT. Other model parameters were calibrated successively and later validated according to daily runoff, reaching a Nash-Sutcliffe efficiency of 0.64–0.82 in both basins. After the modeling stage, the focus was drawn to the impacts of climate change under two different climate scenarios (RCP4.5 and RCP8.5) in two 30-year projection periods (2041–2070 and 2071–2099). From the results, it is estimated that on average snow water equivalent decreases in the order of 30–39% and snow-covered days shorten by 37–43 days for the two basins until 2099. In terms of runoff, a slight reduction of at most 5% on average volume is projected but more notably, runoff center-time is expected to shift 1–2 weeks earlier by the end of the century. Full article
Show Figures

Figure 1

Article
Retrieving Surface Soil Moisture over Wheat-Covered Areas Using Data from Sentinel-1 and Sentinel-2
Water 2021, 13(14), 1981; https://doi.org/10.3390/w13141981 - 19 Jul 2021
Cited by 5 | Viewed by 973
Abstract
Surface soil moisture (SSM) is a major factor that affects crop growth. Combined microwave and optical data have been widely used to improve the accuracy of SSM retrievals. However, the influence of vegetation indices derived from the red-edge spectral bands of multi-spectral optical [...] Read more.
Surface soil moisture (SSM) is a major factor that affects crop growth. Combined microwave and optical data have been widely used to improve the accuracy of SSM retrievals. However, the influence of vegetation indices derived from the red-edge spectral bands of multi-spectral optical data on retrieval accuracy has not been sufficiently analyzed. In this study, we retrieved soil moisture from wheat-covered surfaces using Sentinel-1/2 data. First, a modified water cloud model (WCM) was proposed to remove the influence of vegetation from the backscattering coefficient of the radar data. The vegetation fraction (FV) was then introduced in this WCM, and the vegetation water content (VWC) was calculated using a multiple linear regression model. Subsequently, the support vector regression technique was used to retrieve the SSM. This approach was validated using in situ measurements of wheat fields in Hebi, located in northern Henan Province, China. The key findings of this study are: (1) Based on vegetation indices obtained from Sentinel-2 data, the proposed VWC estimation model effectively eliminated the influence of vegetation; (2) Compared with vertical transmit and horizontal receive (VH) polarization, vertical transmit and vertical receive (VV) polarization was better for detecting changes in SSM key phenological phases of wheat; (3) The validated model indicates that the proposed approach successfully retrieved SSM in the study area using Sentinel-1 and Sentinel-2 data. Full article
(This article belongs to the Section Hydrology)
Show Figures

Figure 1

Article
Simulating Diurnal Variations of Water Temperature and Dissolved Oxygen in Shallow Minnesota Lakes
Water 2021, 13(14), 1980; https://doi.org/10.3390/w13141980 - 19 Jul 2021
Cited by 4 | Viewed by 1312
Abstract
In shallow lakes, water quality is mostly affected by weather conditions and some ecological processes which vary throughout the day. To understand and model diurnal-nocturnal variations, a deterministic, one-dimensional hourly lake water quality model MINLAKE2018 was modified from daily MINLAKE2012, and applied to [...] Read more.
In shallow lakes, water quality is mostly affected by weather conditions and some ecological processes which vary throughout the day. To understand and model diurnal-nocturnal variations, a deterministic, one-dimensional hourly lake water quality model MINLAKE2018 was modified from daily MINLAKE2012, and applied to five shallow lakes in Minnesota to simulate water temperature and dissolved oxygen (DO) over multiple years. A maximum diurnal water temperature variation of 11.40 °C and DO variation of 5.63 mg/L were simulated. The root-mean-square errors (RMSEs) of simulated hourly surface temperatures in five lakes range from 1.19 to 1.95 °C when compared with hourly data over 4–8 years. The RMSEs of temperature and DO simulations from MINLAKE2018 decreased by 17.3% and 18.2%, respectively, and Nash-Sutcliffe efficiency increased by 10.3% and 66.7%, respectively; indicating the hourly model performs better in comparison to daily MINLAKE2012. The hourly model uses variable hourly wind speeds to determine the turbulent diffusion coefficient in the epilimnion and produces more hours of temperature and DO stratification including stratification that lasted several hours on some of the days. The hourly model includes direct solar radiation heating to the bottom sediment that decreases magnitude of heat flux from or to the sediment. Full article
(This article belongs to the Special Issue Physical Processes in Lakes)
Show Figures

Figure 1

Editorial
Chemical and Biochemical Processes of Watershed Ecosystems and Their Impacts on Water Quality
Water 2021, 13(14), 1979; https://doi.org/10.3390/w13141979 - 19 Jul 2021
Viewed by 689
Abstract
This Special Issue of Water focuses on the natural and anthropogenic impacts on water quality in watershed ecosystems [...] Full article
Article
Low Frequency Oscillations in a Hydroelectric Generating System to the Variability of Wind and Solar Power
Water 2021, 13(14), 1978; https://doi.org/10.3390/w13141978 - 19 Jul 2021
Viewed by 830
Abstract
The penetration of multiple integrated renewable energies to the power grid are relevant for decision making in energy policy, environment and business. Such an electricity penetration is affected by the intermittent and volatile characteristics of integrated energies, mostly significantly related to the safe [...] Read more.
The penetration of multiple integrated renewable energies to the power grid are relevant for decision making in energy policy, environment and business. Such an electricity penetration is affected by the intermittent and volatile characteristics of integrated energies, mostly significantly related to the safe and stable electricity production and supply in real world. Here, this paper focuses on the low frequency oscillation analysis of the hydropower generation response to the wind and solar variability. To enable this analysis, a hybrid model of hydropower system integrating with the wind and solar power system is presented. The Nyquist and root-locus stability methods are used to investigate the sensitivity performance of the hydropower governor to the fluctuation of the integrated renewable energies. Additionally, to quantify the risk of the hybrid system, the low frequency oscillation response of hydropower system to wind/solar/hydropower quota and transmission line distance ratio is extensively investigated in this study. The results show that under the case of the wind, solar and hydropower ratio is 40:1:150, the optimal values for maximally reducing hydropower low frequency oscillation are finally determined as kp = 0.8, ki = 0.25 and kd = 0.5. Regarding a certain wind/solar/hydropower quota, it is a promising strategy to increase the solar-load transmission line in order to achieve the safe and stable operation of the hybrid system and a relatively excellent dynamic regulation capacity of the hydropower governor. The model, methods and results implemented in this study are exploited to markedly improve new knowledge applications, policy management, low carbon emissions and investment competitiveness of future energy systems. Full article
Show Figures

Figure 1

Article
Reanalysis of Soil Moisture Used for Rainfall Thresholds for Rainfall-Induced Landslides: The Italian Case Study
Water 2021, 13(14), 1977; https://doi.org/10.3390/w13141977 - 19 Jul 2021
Viewed by 900
Abstract
Landslides are one of the most frequent natural disasters that can endanger human lives and property. Therefore, prediction of landslides is essential to reduce economic damage and save human lives. Numerous methods have been developed for the prediction of landslides triggering, ranging from [...] Read more.
Landslides are one of the most frequent natural disasters that can endanger human lives and property. Therefore, prediction of landslides is essential to reduce economic damage and save human lives. Numerous methods have been developed for the prediction of landslides triggering, ranging from simple methods that include empirical rainfall thresholds, to more complex ones that use sophisticated physically- or conceptually-based models. Reanalysis of soil moisture data could be one option to improve landslide forecasting accuracy. This study used the publicly available FraneItalia database hat contains almost 9000 landslide events that occurred in the 2010–2017 period in Italy. The Copernicus Uncertainties in Ensembles of Regional Reanalyses (UERRA) dataset was used to obtain precipitation and volumetric soil moisture data. The results of this study indicated that precipitation information is still a much better predictor of landslides triggering compared to the reanalyzed (i.e., not very detailed) soil moisture data. This conclusion is valid both for local (i.e., grid) and regional (i.e., catchment-based) scales. Additionally, at the regional scale, soil moisture data can only predict a few landslide events (i.e., on average around one) that are not otherwise predicted by the simple empirical rainfall threshold approach; however, this approach on average, predicted around 18 events (i.e., 55% of all events). Despite this, additional investigation is needed using other (more complete) landslide databases and other (more detailed) soil moisture products. Full article
(This article belongs to the Section Hydrology)
Show Figures

Figure 1

Article
Modeling Water-Induced Base Particle Migration in Loaded Granular Filters Using Discrete Element Method
Water 2021, 13(14), 1976; https://doi.org/10.3390/w13141976 - 19 Jul 2021
Cited by 1 | Viewed by 793
Abstract
Results are reported from a series of filtration tests simulated using coupled computational fluid dynamics and the discrete element method (CCFD-DEM) to investigate the factors controlling the mechanism of base particle erosion and their subsequent capture in loaded granular filters. Apart from geometrical [...] Read more.
Results are reported from a series of filtration tests simulated using coupled computational fluid dynamics and the discrete element method (CCFD-DEM) to investigate the factors controlling the mechanism of base particle erosion and their subsequent capture in loaded granular filters. Apart from geometrical factors such as particle and void sizes, the filter effectiveness was found to be controlled by the magnitudes of the hydraulic gradients and the effective stresses. The results of numerical simulations revealed that the base soils exhibit significant stress reduction that reduces further due to seepage, and the base particles migrate into the filter, bearing very low effective stresses (i.e., localized piping in base soil). Based on the limit equilibrium of hydraulic and mechanical constraints, a linear hydromechanical model has been proposed that governs the migration and capture of base particles in the filter (i.e., filter effectiveness avoiding piping) for cases simulated in this study. Nevertheless, the proposed model agrees closely with the simulation results of this study and those adopted from other published works, thereby showing a reasonable possibility of using the proposed model as a measure of retention capacity of loaded protective filters. Full article
(This article belongs to the Section Hydraulics and Hydrodynamics)
Show Figures

Figure 1

Article
Simulations of the Soil Evaporation and Crop Transpiration Beneath a Maize Crop Canopy in a Humid Area
Water 2021, 13(14), 1975; https://doi.org/10.3390/w13141975 - 19 Jul 2021
Cited by 1 | Viewed by 727
Abstract
Soil evaporation (Es) and crop transpiration (Tc) are important components of water balance in cropping systems. Comparing the accurate calculation by crop models of Es and Tc to the measured evaporation and transpiration has significant advances to the optimal [...] Read more.
Soil evaporation (Es) and crop transpiration (Tc) are important components of water balance in cropping systems. Comparing the accurate calculation by crop models of Es and Tc to the measured evaporation and transpiration has significant advances to the optimal configuration of water resource and evaluation of the accuracy of crop models in estimating water consumption. To evaluate the adaptation of APSIM (Agricultural Production Systems simulator) in calculating the Es and Tc in Nanjing, APSIM model parameters, including the meteorological and soil parameters, were measured from a two-year field experiment. The results showed that: (1) The simulated evaporation was basically consistent with the measured Es, and the regulated model can effectively present the field evaporation in the whole maize growth period (R2 = 0.85, D = 0.96, p < 0.001); and (2) The trend of the simulated Tc can present the actual Tc variation, but the accuracy was not as high as the evaporation (R2 = 0.74, D = 0.87, p < 0.001), therefore, the simulation of water balance process by APSIM will be helpful in calculating Es and Tc in a humid area of Nanjing, and its application also could predict the production of maize fields in Nanjing. Full article
(This article belongs to the Special Issue Soil Moisture Content and Crop Production Research)
Show Figures

Figure 1

Article
Reactivation of Frozen Stored Microalgal-Bacterial Granular Sludge under Aeration and Non-Aeration Conditions
Water 2021, 13(14), 1974; https://doi.org/10.3390/w13141974 - 19 Jul 2021
Cited by 4 | Viewed by 1044
Abstract
In this paper, reactivation of microalgal-bacterial granular sludge (MBGS) stored at −20 °C for 6 months was investigated under respective aeration (R1) and non-aeration (R2) conditions. Results showed that the granular activity could be fully recovered within 21 days. The average removal efficiency [...] Read more.
In this paper, reactivation of microalgal-bacterial granular sludge (MBGS) stored at −20 °C for 6 months was investigated under respective aeration (R1) and non-aeration (R2) conditions. Results showed that the granular activity could be fully recovered within 21 days. The average removal efficiency of ammonia was higher in R1 (92.78%), while R2 showed higher average removal efficiencies of organics (84.97%) and phosphorus (85.28%). It was also found that eukaryotic microalgae growth was stimulated under aeration conditions, whereas prokaryotic microalgae growth and extracellular protein secretion were favored under non-aeration conditions. Sequencing results showed that the microbial community underwent subversive evolution, with Chlorophyta and Proteobacteria being dominant species under both conditions. Consequently, it was reasonable to conclude that the activity and structure of frozen stored MBGS could be recovered under both aeration and non-aeration conditions, of which aeration-free activation was more feasible on account of its energy-saving property. This study provides important information for the storage and transportation of MBGS in wastewater treatment. Full article
(This article belongs to the Special Issue Innovative Technologies for Wastewater and Water Treatment)
Show Figures

Figure 1

Article
Temperature Changes and Their Impact on Drought Conditions in Winter and Spring in the Vistula Basin
Water 2021, 13(14), 1973; https://doi.org/10.3390/w13141973 - 19 Jul 2021
Cited by 2 | Viewed by 721
Abstract
Inter-annual variability of hydro-meteorological variables indirectly influence soil moisture conditions in winter and early spring seasons. The interactions between temperature changes and drought conditions are studied by an application of statistical analyses of minimum temperature (Tmin), consecutive days with temperature exceeding the 0 [...] Read more.
Inter-annual variability of hydro-meteorological variables indirectly influence soil moisture conditions in winter and early spring seasons. The interactions between temperature changes and drought conditions are studied by an application of statistical analyses of minimum temperature (Tmin), consecutive days with temperature exceeding the 0 °C threshold value, the number of melting pulses in the winter season and Standardized Evaporation Precipitation Index (SPEI). Additionally, shifts in the onset of days with spring temperature and snow cover occurrence are analysed. A Mann–Kendall test is applied for the trend analysis. Studies have shown significant changes in thermal characteristics in the winter season over the past 70 years, which affect the moisture conditions in the Vistula River Basin. As a result of those changes, the Vistula Basin is more prone to droughts. Full article
(This article belongs to the Special Issue Human and Climate Impacts on Drought Dynamics and Vulnerability)
Show Figures

Figure 1

Article
Numerical Analysis of Ultrasonic Nebulizer for Onset Amplitude of Vibration with Atomization Experimental Results
Water 2021, 13(14), 1972; https://doi.org/10.3390/w13141972 - 19 Jul 2021
Cited by 3 | Viewed by 904
Abstract
In this study, the onset amplitude of the initial capillary surface wave for ultrasonic atomization of fluids has been implemented. The design and characterization of 485 kHz microfabricated silicon-based ultrasonic nozzles are presented for the concept of economic energy development. Each nozzle is [...] Read more.
In this study, the onset amplitude of the initial capillary surface wave for ultrasonic atomization of fluids has been implemented. The design and characterization of 485 kHz microfabricated silicon-based ultrasonic nozzles are presented for the concept of economic energy development. Each nozzle is composed of a silicon resonator and a piezoelectric drive section consisting of three Fourier horns. The required minimum energy to atomize liquid droplets is verified by COMSOL Multiphysics simulation software to clarify experimental data. The simulation study reports a minimum vibrational amplitude (onset) of 0.365 μm at the device bottom under the designated frequency of 485 kHz. The experimental study agrees well with the suggested frequency and the amplitude concerning the corresponding surface vibrational velocity in simulation. While operating, the deionized water was initially atomized into microdroplets at the given electrode voltage of 5.96 V. Microdroplets are steadily and continuously formed after the liquid feeding rate is optimized. This newly designed ultrasonic atomizer facilitates the development of capillary surface wave resonance at a designated frequency. A required vibrational amplitude and finite electric driving voltage promote not only the modern development in the green energy industry, but also the exploration of noninvasive, microencapsulated drug delivery and local spray needs. Full article
(This article belongs to the Special Issue Gas-Liquid Two-Phase Flow in the Pipe or Channel)
Show Figures

Figure 1

Article
Quantitative Response of Maize Vcmax25 to Persistent Drought Stress at Different Growth Stages
Water 2021, 13(14), 1971; https://doi.org/10.3390/w13141971 - 19 Jul 2021
Cited by 1 | Viewed by 740
Abstract
Drought stress has adverse effects on crop growth and yield, and its identification and monitoring play vital roles in precision crop water management. Accurately evaluating the effect of drought stress on crop photosynthetic capacity can provide a basis for decisions related to crop [...] Read more.
Drought stress has adverse effects on crop growth and yield, and its identification and monitoring play vital roles in precision crop water management. Accurately evaluating the effect of drought stress on crop photosynthetic capacity can provide a basis for decisions related to crop drought stress identification and monitoring as well as drought stress resistance and avoidance. In this study, the effects of different degrees of persistent drought in different growth stages (3rd leaf stage, 7th leaf stage and jointing stage) on the maximum carboxylation rate at a reference temperature of 25 °C (Vcmax25) of the first fully expanded leaf and its relationship to the leaf water content (LWC) were studied in a field experiment from 2013 to 2015. The results indicated that the LWC decreased continuously as drought stress continued and that the LWC decreased faster in the treatment with more irrigation. Vcmax25 showed a decreasing trend as the drought progressed but had no clear relationship to the growth stage in which the persistent drought occurred. Vcmax25 showed a significantly parabolic relationship (R2 = 0.701, p < 0.001) with the LWC, but the different degrees of persistent drought stress occurring in different growth stages had no distinct effect on the LWC values when Vcmax25 reached its maximum value or zero. The findings of this study also suggested that the LWC was 82.5 ± 0.5% when Vcmax25 reached its maximum value (42.6 ± 3.6 μmol m−2 s−1) and 67.6 ± 1.2% (extreme drought) when Vcmax25 reached zero. These findings will help to improve crop drought management and will be an important reference for crop drought identification, classification and monitoring as well as for the development of drought monitoring and early warning systems for other crops or maize varieties. Full article
(This article belongs to the Section Water, Agriculture and Aquaculture)
Show Figures

Figure 1

Article
Weather Risk Assessment for Collective Water Supply and Sewerage Systems
Water 2021, 13(14), 1970; https://doi.org/10.3390/w13141970 - 18 Jul 2021
Cited by 2 | Viewed by 941
Abstract
The weather derivatives market as an instrument of effective weather risk management is still not flexible enough for many industries. The water supply and sewerage industry is sensitive primarily to heavy rainfalls and periods of high and low temperatures: days with heavy rainfall [...] Read more.
The weather derivatives market as an instrument of effective weather risk management is still not flexible enough for many industries. The water supply and sewerage industry is sensitive primarily to heavy rainfalls and periods of high and low temperatures: days with heavy rainfall may cause a hydraulic overload of the sewerage systems; on hot days, the water demand increases significantly; on frost days, the risk of water pipe failure grows. The work aimed to summarise methods of weather risk management and propose indices that will help to protect the interests of the water supply and sewerage industry in Poland. Three indices were proposed: a daily precipitation index, frost day index, and hot day index. The frequency of reaching these indices in Poland was verified with the use of meteorological data from 1970–2019, for 19 locations. The non-parametric Mann-Kendall test was used to determine the climate change impact on the exceedance frequency of the proposed indicators. The results showed that the indexes were exceeded in the past once every 6 years, on average. The hot day index was exceeded the least often, but it was the only one with a clear (growing) trend observed. Full article
(This article belongs to the Special Issue Failure Risk Assessment in Water Supply System)
Show Figures

Figure 1

Article
Adsorption-Membrane Hybrid Approach for the Removal of Azithromycin from Water: An Attempt to Minimize Drug Resistance Problem
Water 2021, 13(14), 1969; https://doi.org/10.3390/w13141969 - 18 Jul 2021
Cited by 6 | Viewed by 1374
Abstract
In this study, activated carbon (AC) and magnetic activated carbon (MAC) were prepared from Dalbergia sissoo sawdust for the removal of antibiotic Azithromycin (AZM) from aqueous solution. The effect of initial concentration, contact time, pH, adsorbent dosage, and the temperature were investigated for [...] Read more.
In this study, activated carbon (AC) and magnetic activated carbon (MAC) were prepared from Dalbergia sissoo sawdust for the removal of antibiotic Azithromycin (AZM) from aqueous solution. The effect of initial concentration, contact time, pH, adsorbent dosage, and the temperature were investigated for both the adsorbents. The optimum AZM concentration, contact time, pH and adsorbents dosages were found to be 80 mg/L, 120 min, 6 and 7 (pH, respectively, for AC and MAC), and 0.1 g (for both AC and MAC), respectively. The isothermal data of both sets of experiments correlated well with the Langmuir isotherm model, while the kinetic data with the pseudo-second-order model. The adsorption of AZM on both adsorbents was found to be favorable, which is evident in the values of the thermodynamic parameters (ΔH = −26.506 and −24.149 KJ/mol, ΔS = 91.812 and 81.991 J/mol K, respectively, for AC and MAC). To evaluate the effect of AC and MAC on the membrane parameters, a continuous stirred reactor was connected with ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO) membranes. High % retention and improved permeate flux (around 90%) were obtained for AC/UF, AC/NF AC/RO, MAC/UF, MAC/NF, and MAC/RO treatments. The percent retention of AZM observed for AC/UF, AC/NF AC/RO was higher than MAC/UF, MAC/NF, and for MAC/RO hybrid processes due to greater surface area of AC than MAC. Full article
Show Figures

Figure 1

Review
Review of Historical Dam-Break Events and Laboratory Tests on Real Topography for the Validation of Numerical Models
Water 2021, 13(14), 1968; https://doi.org/10.3390/w13141968 - 17 Jul 2021
Cited by 5 | Viewed by 1310
Abstract
Dam break inundation mapping is essential for risk management and mitigation, emergency action planning, and potential consequences assessment. To quantify flood hazard associated with dam failures, flooding variables must be predicted by efficient and robust numerical models capable to effectively cope with the [...] Read more.
Dam break inundation mapping is essential for risk management and mitigation, emergency action planning, and potential consequences assessment. To quantify flood hazard associated with dam failures, flooding variables must be predicted by efficient and robust numerical models capable to effectively cope with the computational difficulties posed by complex flows on real topographies. Validation against real-field data of historical dam-breaks is extremely useful to verify models’ capabilities and accuracy. However, such catastrophic events are rather infrequent, and available data on the breaching mechanism and downstream flooding are usually inaccurate and incomplete. Nevertheless, in some cases, real-field data collected after the event (mainly breach size, maximum water depths and flood wave arrival times at selected locations, water marks, and extent of flooded areas) are adequate to set up valuable and significant test cases, provided that all other data required to perform numerical simulations are available (mainly topographic data of the floodable area and input parameters defining the dam-break scenario). This paper provides a review of the historical dam-break events for which real-field datasets useful for validation purposes can be retrieved in the literature. The resulting real-field test cases are divided into well-documented test cases, for which extensive and complete data are already available, and cases with partial or inaccurate datasets. Type and quality of the available data are specified for each case. Finally, validation data provided by dam-break studies on physical models reproducing real topographies are presented and discussed. This review aims at helping dam-break modelers: (a) to select the most suitable real-field test cases for validating their numerical models, (b) to facilitate data access by indicating relevant bibliographic references, and (c) to identify test cases of potential interest worthy of further research. Full article
Review
A Unified View of Nonlinear Resistance Formulas for Seepage Flow in Coarse Granular Media
Water 2021, 13(14), 1967; https://doi.org/10.3390/w13141967 - 17 Jul 2021
Viewed by 1246
Abstract
There are many studies on the nonlinear relationship between seepage velocity and hydraulic gradient in coarse granular materials, using different approaches and variables to define the resistance formula applicable to that type of granular media. On the basis of an analysis of the [...] Read more.
There are many studies on the nonlinear relationship between seepage velocity and hydraulic gradient in coarse granular materials, using different approaches and variables to define the resistance formula applicable to that type of granular media. On the basis of an analysis of the existing formulations developed in different studies, we propose an approach for comparing the results obtained by some of the most important studies on state-of-the-art seepage flow in coarse granular media. Full article
(This article belongs to the Special Issue Dam Safety. Overtopping and Geostructural Risks)
Show Figures

Figure 1

Article
The Management of Na-Tech Risk Using Bayesian Network
Water 2021, 13(14), 1966; https://doi.org/10.3390/w13141966 - 17 Jul 2021
Cited by 1 | Viewed by 973
Abstract
In the last decades, the frequency and severity of Natural-Technological events (i.e., industrial accidents triggered by natural phenomena or Na-Techs) increased. These could be more severe than simple technological accidents because the natural phenomenon could cause the prevention/mitigation/emergency systems fail. The dynamic assessment [...] Read more.
In the last decades, the frequency and severity of Natural-Technological events (i.e., industrial accidents triggered by natural phenomena or Na-Techs) increased. These could be more severe than simple technological accidents because the natural phenomenon could cause the prevention/mitigation/emergency systems fail. The dynamic assessment of the risk associated with these events is essential for a more effective prevention and mitigation of the consequences and emergency preparation. The main goal of this study is the development of a fast and dynamic tool for the risk manager. An approach supporting the management of the consequence is presented. It is based on the definition of a risk-related index, presented in the form of a discrete variable that combines frequency and magnitude of the events and other factors contributing to the worsening of Na-Tech. A properly designed Geographical Information System (GIS) allows the collection and processing of territorial information with the aim to create new data contributing to the quantification of the Na-Tech risk index. A Bayesian network has been built which efficiently lends in including within the model multiple elements with a direct or indirect impact on the distribution of risk levels. By means of this approach, a dynamic updating of the risk index is made. The proposed approach has been applied to an Italian case-study. Full article
(This article belongs to the Section Hydrology)
Show Figures

Figure 1

Article
Karst Recharge Areas Identified by Combined Application of Isotopes and Hydrogeological Budget
Water 2021, 13(14), 1965; https://doi.org/10.3390/w13141965 - 17 Jul 2021
Cited by 1 | Viewed by 771
Abstract
The identification of recharge areas in karst aquifers allows us to perform sustainable management of these groundwater resources. Stable isotopes (δ18O and δ2H) have been largely used to provide information about recharge elevation in many mountainous regions. In this [...] Read more.
The identification of recharge areas in karst aquifers allows us to perform sustainable management of these groundwater resources. Stable isotopes (δ18O and δ2H) have been largely used to provide information about recharge elevation in many mountainous regions. In this paper, an improved version of a recent “isotope-driven model”, for the identification of recharge areas, was applied to Capodacqua di Spigno Spring (south of the Latium region). The model upgrade consists of a preliminary check procedure to estimate the degree of influence of the rainfall’s isotopic variability on the spring water. This additional procedure gives us an indication of the reliability of the model and its applicability conditions. Moreover, the dataset of the spring was updated to analyze the degree of reliability of the isotope-driven model. The purpose of this study was to combine the previously mentioned isotope-driven model with hydrogeological tools. A quantitative study of the basin, based on the estimation of the average monthly infiltration volume, was performed by using the inverse hydrogeological water budget. In this way, the qualitative model for the recharge areas’ estimation was validated by a quantitative hydrogeological tool. Both models show that, for karst mountain basins, the recharge areas decrease as the average recharge elevations increase, including areas at high altitudes. Full article
(This article belongs to the Special Issue Isotope Hydrology)
Show Figures

Figure 1

Article
Oxygen Transfer in Two-Stage Activated Sludge Wastewater Treatment Plants
Water 2021, 13(14), 1964; https://doi.org/10.3390/w13141964 - 17 Jul 2021
Cited by 1 | Viewed by 929
Abstract
Aeration is an energy-intensive process of aerobic biological treatment in wastewater treatment plants (WWTP). Two-stage processes enable energy-efficient operation, but oxygen transfer has not been studied in depth before. In this study, α-factors were determined with long-term ex situ steady-state off-gas measurements in [...] Read more.
Aeration is an energy-intensive process of aerobic biological treatment in wastewater treatment plants (WWTP). Two-stage processes enable energy-efficient operation, but oxygen transfer has not been studied in depth before. In this study, α-factors were determined with long-term ex situ steady-state off-gas measurements in pilot-scale test reactors (5.8 m height, 8.3 m3) coupled to full-scale activated sludge basins. A two-stage WWTP with more than 1 Mio population equivalent was studied over 13 months including rain and dry weather conditions. Operating data, surfactant concentrations throughout the two-stage process, and the effect of reverse flexing on pressure loss of diffusers were examined. The values of αmean, αmin, and αmax for design load cases of aeration systems were determined as 0.45, 0.33, and 0.54 in the first high-rate carbon removal stage and as 0.80, 0.69, and 0.91 in the second nitrification stage, respectively. The first stage is characterized by a distinct diurnal variation and decrease in α-factor during stormwater treatment. Surfactants and the majority of the total organic carbon (TOC) load are effectively removed in the first stage; hence, α-factors in the second stage are higher and have a more consistent diurnal pattern. Proposed α-factors enable more accurate aeration system design of two-stage WWTPs. Fouling-induced diffuser pressure loss can be restored effectively with reverse flexing in both treatment stages. Full article
(This article belongs to the Section Wastewater Treatment and Reuse)
Show Figures

Figure 1

Previous Issue
Next Issue
Back to TopTop