Water — Open Access Journal

Choosing a model that suitably represents the characteristics of a watershed to simulate low flows is crucial, especially in watersheds whose main source of baseflow generation depends on groundwater storage and release. The goal of this investigation is to study the performance and representativeness of storage-release process modeling, considering aspects such as the topography and geology of the modeled watershed through regional sensitivity analysis, in order to improve low-flow prediction. To this end, four groundwater storage-release structures in various watersheds with different geological (fractured and sedimentary rock) and topographic domains (steep and gentle slopes) were analyzed. The results suggest that the two-reservoir structure with three runoff responses is suitable (better) for simulating low flows in watersheds with fractured geological characteristics and rugged or steep topography. The results also indicate that a one-reservoir model can be adequate for predicting low flows in watersheds with a sedimentary influence or flat topography. Full article

The removal of trace metals (TM), dissolved organic carbon (DOC), mineral nitrogen (N_min.), and polycyclic aromatic hydrocarbons (PAHs) from the water of Lake Baikal and its tributaries was evaluated. The contaminant removal rate (CRR) and the contaminant removal capacity (CRC) were used as water self-purification parameters. The CRR was calculated as the difference between contaminant mass flow rates at downstream and upstream gauging stations. The CRC was calculated as the quotient of the CRR and the change in water discharge between downstream and upstream gauging stations. Whether the CRR and CRC have positive or negative values depends on whether contaminant release or removal occurs in the water body. The CRR depends on the size of the water body. The lowest and the highest CRRs observed for Baikal were equal to −15 mg/s (PAHs) to −7327 g/s (DOC), whereas the highest PAH and DOC removal rates observed for Selenga River (the major Baikal tributary) in summer were equal to −9 mg/s and −3190 g/s correspondingly. The highest PAH and DOC removal rates observed for small tributaries were equal to 0.0004 mg/s and −0.7 g/s respectively. The amplitude of annual CRR oscillations depends on contaminant abundance. The highest amplitude was typical for most abundant contaminants such as N_min. and DOC. In unpolluted sections of the Selenga River the highest rates of N and C removal (−85 g/s and −3190 g/s, respectively) were observed in summer and the lowest rates (4 g/s and 3869 g/s, respectively) were observed in the spring. The lowest amplitude was typical for PAHs and some low-abundance TM such as V and Ni. The highest summer rates of V and Ni removal were equal to −378 mg/s and −155 mg/s respectively, whereas lowest spring rates are equal to 296 mg/s and 220 mg/s. The intermediate CRR amplitudes were typical for most abundant TM such as Sr, Al, and Fe. The spatial CRR variability depends on water chemistry and the presence of pollution sources. The lowest (up to 38 g/s) rates of N_min. removal was observed for polluted lower Selenga sections characterized by low water mineralization and high DOC concentrations. The highest rates (−85 g/s) were observed for unpolluted upper sections. Seepage loss from the river to groundwater was also recognized as an important means of contaminant removal. The CRC values depend mostly on water residence time. The DOC removing capacity value of Baikal (−26 g/m³) were lower than those of Selenga in summer (−35 g/m³) but higher than the CRCs of all tributaries during the other seasons (from 30 mg/m³ to −10 g/m³⁾. Full article

Hydrodynamic conditions are considered to be very important in the control of algal blooms. Weekly or daily measurements may miss some important events in the hydrodynamic process, resulting in inaccurate evaluations of the impacts of hydrodynamics on phytoplankton. In this study, high-frequency (15-min interval) measurements were used to analyze the effect of water column stability on surface chlorophyll a (Chl a) and lag time under different nutrient backgrounds during a cyanobacterial bloom in the Three Gorges Reservoir, China. Cross-correlation analysis between the relative water column stability (RWCS) and Chl a was performed at different stages. The results showed that the RWCS above the euphotic depth influenced the surface Chl a concentration most significantly. A lower RWCS (<20) limited the increase in the Chl a concentration, and a higher RWCS caused a significant increase in Chl a only when nutrients were not limited (TN/TP < 29) and light and temperature conditions were suitable. It took a short time for a higher RWCS to significantly increase the surface Chl a concentration compared with a lower RWCS. When the waterbody had a very low Chl a concentration (almost 0), approximately 2 days were needed to significantly increase the Chl a concentration, while approximately only half an hour was needed when the background concentration of Chl a was slightly higher. During the bloom period, a decline in the RWCS significantly decreased the Chl a in a very short time (approximately half an hour). Reducing the water column stability could be a good approach to control cyanobacterial blooms. Full article

Processing tomato is one of the most important economic crops in Xinjiang, China, which was constrained with severe water shortage and extreme arid climate. Alternate partial root-zone irrigation (APRI) may provide an effective way to increase irrigation water use efficiency (iWUE) without yield reduction. However, limited studies concerned about applying APRI in processing tomato plantation have been done, especially combined with drip irrigation to further control the irrigation and improve iWUE. Therefore, the two-year pot experiments were conducted to study the effects of different irrigation treatments, including three APRI treatments (irrigation quota of 67.5, 51.6, and 43.7 mm, respectively), fixed partial root-zoon drip irrigation (FPRI, 67.5 mm) and conventional drip irrigation (CDI, 67.5 mm). The results indicated that APRI was an appropriate irrigation method in processing tomato plantation in arid desert area such as Xinjiang, as high irrigation quota of APRI (APRIH) significantly improved its yield without fruit quality reduction in comparison with those of CDI. However, the yield without fruit quality of FPRI significantly decreased. Even if the irrigation quota of APRI decreased to the medium level (APRIM, 51.6 mm), iWUE by increased 31.8–32.7% on the contrary, as irrigation water was saved by 23.6%; while keeping the yield and fruit quality. Therefore, APRIM is recommended for processing tomato plantation in arid northwest China, to increase plant growth, fruit quality, yield, and iWUE synergistically. Full article

Coastal freshwater resources are commonly under high risk of being contaminated from seawater. The main processes that affect seawater intrusion are groundwater overexploitation, land use change, and climate change effects. In this context coastal lagoons represent the more sensitive environments prone to seawater intrusion. Numerical modelling is a useful tool to understand and predict seawater intrusion. In this study, a three-dimensional SEAWAT model is employed to simulate the seawater intrusion to coastal aquifers of Variconi Oasis (Italy). The present simulation was divided into a calibration and a validation model, then the model was used to predict the salinization trend up to 2050. Results show the role of the sea in salinizing the beach front, while the retrodunal environment is characterized by transitional environments. Future seawater intrusion scenarios considering only climate data showed no significative differences in respect to the actual situation. The same happens considering also a low sea level rise prediction. On the contrary, the worst scenario (high sea level rise prediction), depicts a quite different situation, with a saline intrusion in the Variconi oasis that will severely affect the fragile transitional ecosystem. This modelling framework can be used to quantify the effects of climate changes in similar coastal environments. Full article

Downpours are increasing in frequency and severity due to climate change. Cities are particularly susceptible to flooding from downpours because of their large share of impervious surfaces. Minimising pluvial flood risk requires all involved stakeholders to collaborate and overcome various barriers. Although an increase in citizen engagement in climate adaptation is generally preferred, experiences with inclusive decision-making are often limited. The aim of this paper is to obtain a deeper understanding of how the capacity to govern pluvial flood risk can be developed through citizen engagement. We scrutinised the capacity of local actors to govern pluvial flood risk in the city of Utrecht, the Netherlands. For the analysis of Utrecht’s problem-solving capacity, the Governance Capacity Framework provided a consistent assessment of the key governance components. The results indicate that Utrecht’s capacity to govern pluvial flooding is relatively well-developed. Collaboration between public authorities is advanced, sufficient financial resources are available, and smart monitoring enables high levels of evaluation and learning. However, citizen awareness and engagement in policy making is rather low. Accordingly, citizens’ willingness to pay for flood adaptation is limited. Stimulating flood risk awareness by combining financial incentives with more advanced arrangements for active citizen engagement is key for Utrecht and other cities. Full article

This paper presents a new data-driven method for leak localization in water distribution networks. The proposed method relies on the use of available pressure measurements in some selected internal network nodes and on the estimation of the pressure at the remaining nodes using Kriging spatial interpolation. Online leak localization is attained by comparing current pressure values with their reference values. Supported by Kriging; this comparison can be performed for all the network nodes, not only for those equipped with pressure sensors. On the one hand, reference pressure values in all nodes are obtained by applying Kriging to measurement data previously recorded under network operation without leaks. On the other hand, current pressure values at all nodes are obtained by applying Kriging to the current measured pressure values. The node that presents the maximum difference (residual) between current and reference pressure values is proposed as a leaky node candidate. Thereafter, a time horizon computation based on Bayesian reasoning is applied to consider the residual time evolution, resulting in an improved leak localization accuracy. As a data-driven approach, the proposed method does not need a hydraulic model; only historical data from normal operation is required. This is an advantage with respect to most data-driven methods that need historical data for the considered leak scenarios. Since, in practice, the obtained leak localization results will strongly depend on the number of available pressure measurements and their location, an optimal sensor placement procedure is also proposed in the paper. Three different case studies illustrate the performance of the proposed methodologies. Full article

Most concrete dams have seepage problems to some degree, so it is a common strategy to maintain ongoing monitoring and take timely repair measures. In order to grasp the real operation state of dam seepage, it is vital to analyze the measured data of each monitoring indicator and establish an appropriate prediction equation. However, dam seepage states under the load and environmental influences are very complicated, involving various monitoring indicators and multiple monitoring points of each indicator. For the purpose of maintaining the temporal continuity and spatial correlation of monitoring objects, this paper used a multi-indicator grey clustering analysis model to explore the grey correlation among various indicators, and realized a comprehensive evaluation of a dam seepage state by computation of the clustering coefficient. The case study shows that the proposed method can be successfully applied to the health monitoring of concrete dam seepage. Full article

With climate change prevailing around the world, understanding the changes in long-term annual and seasonal rainfall at local scales is very important in planning for required adaptation measures. This is especially true for areas such as the Awash River basin where there is very high dependence on rain- fed agriculture characterized by frequent droughts and subsequent famines. The aim of the study is to analyze long-term trends of annual and seasonal rainfall in the Awash River Basin, Ethiopia. Monthly rainfall data extracted from Climatic Research Unit (CRU 4.01) dataset for 54 grid points representing the entire basin were aggregated to find the respective areal annual and seasonal rainfall time series for the entire basin and its seven sub-basins. The Mann-Kendall (MK) test and Sen Slope estimator were applied to the time series for detecting the trends and for estimating the rate of change, respectively. The Statistical software package R version 3.5.2 was used for data extraction, data analyses, and plotting. Geographic information system (GIS) package was also used for grid making, site selection, and mapping. The results showed that no significant trend (at α = 0.05) was identified in annual rainfall in all sub-basins and over the entire basin in the period (1902 to 2016). However, the results for seasonal rainfall are mixed across the study areas. The summer rainfall (June through September) showed significant decreasing trend (at α ≤ 0.1) over five of the seven sub-basins at a rate varying from 4 to 7.4 mm per decade but it showed no trend over the two sub-basins. The autumn rainfall (October through January) showed no significant trends over four of the seven sub-basins but showed increasing trends over three sub-basins at a rate varying from 2 to 5 mm per decade. The winter rainfall (February through May) showed no significant trends over four sub-basins but showed significant increasing trends (at α ≤ 0.1) over three sub-basins at a rate varying from 0.6 to 2.7 mm per decade. At the basin level, the summer rainfall showed a significant decreasing trend (at α = 0.05) while the autumn and winter rainfall showed no significant trends. In addition, shift in some amount of summer rainfall to winter and autumn season was noticed. It is evident that climate change has shown pronounced effects on the trends and patterns of seasonal rainfall. Thus, the study contribute to better understanding of climate change in the basin and the information from the study can be used in planning for adaptation measures against a changing climate. Full article

High-resolution water quality monitoring indicates recurring elevation of stream phosphorus concentrations during low-flow periods. These increased concentrations may exceed Water Framework Directive (WFD) environmental quality standards during ecologically sensitive periods. The objective of this research was to identify source, mobilization, and pathway factors controlling in-stream total reactive phosphorus (TRP) concentrations during low-flow periods. Synoptic surveys were conducted in three agricultural catchments during spring, summer, and autumn. Up to 50 water samples were obtained across each watercourse per sampling round. Samples were analysed for TRP and total phosphorus (TP), along with supplementary parameters (temperature, conductivity, dissolved oxygen, and oxidation reduction potential). Bed sediment was analysed at a subset of locations for Mehlich P, Al, Ca, and Fe. The greatest percentages of water sampling points exceeding WFD threshold of 0.035 mg L⁻¹ TRP occurred during summer (57%, 11%, and 71% for well-drained, well-drained arable, and poorly drained grassland catchments, respectively). These percentages declined during autumn but did not return to spring concentrations, as winter flushing had not yet occurred. Different controls were elucidated for each catchment: diffuse transport through groundwater and lack of dilution in the well-drained grassland, in-stream mobilization in the well-drained arable, and a combination of point sources and cumulative loading in the poorly drained grassland. Diversity in controlling factors necessitates investigative protocols beyond low-spatial and temporal resolution water sampling and must incorporate both repeated survey and complementary understanding of sediment chemistry and anthropogenic phosphorus sources. Despite similarities in elevation of P at low-flow, catchments will require custom solutions depending on their typology, and both legislative deadlines and target baselines standards must acknowledge these inherent differences. Full article

The transformation of land-use and land cover in Nakhon Ratchasima province, Thailand has rapidly changed over the last few years. The major factors affecting the growth in the province arise from the huge expansion of developing areas, according to the government’s development plans that aim to promote the province as a central business-hub in the region. This development expansion has eventually intruded upon and interfered with sub-basin areas, which has led to environmental problems in the region. The scope of this study comprises three objectives, i.e., (i) to optimize the Cellular Automata (CA) model for predicting the expansion of built-up sites by 2022; (ii) to model a linear regression method for deriving the transition of the digital elevation model (DEM); and (iii) to apply Geographic Weighted Regression (GWR) for analyzing the risk of the stativity of flood areas in the province. The results of this study show that the optimized CA demonstrates accurate prediction of the expansion of built-up areas in 2022 using Land use (LU) data of 2-year intervals. In addition, the predicting model is generalized and converged at the iteration no. 4. The prediction outcomes, including spatial locations and ground-water touch points of the construction, are used to estimate and model the DEM to extract independent hydrology variables that are used in the determination of Flood Risk Susceptibility (FRS). In GWR in the research called FRS-GWR, this integration of quantitative GIS and the spatial model is anticipated to produce promising results in predicting the growth and expansion of built-up areas and land-use change that lead to an effective analysis of the impacts on spatial change in water sub-basin areas. This research may be beneficial in the process of urban planning with respect to the study of environmental impacts. In addition, it can indicate and impose important directions for development plans in cities to avoid and minimize flood area problems. Full article

The spatial distribution of antibiotics in alluvial aquifers presents a large variability caused by the joint action of several factors including hydrology, land use, and groundwater properties. In this study, the influences of these factors on the spatial variability of antibiotics is evaluated based on an extensive database of 47 wells located in the Baix Fluvià alluvial aquifer (NE Catalonia). Statistical methods such as redundancy and variation partitioning (VP) analyses, which are not commonly used in hydrogeological studies, are herein tested and used to estimate the effects of environmental factors on the observed antibiotic occurrence. Using VP, the total explained variation of the antibiotic distribution only reaches 18% of the total variability, meaning that the whole set of explanatory parameters is insufficient or inadequate to describe the occurrence of antibiotics and their concentration. The results point out that groundwater properties are the most representative parameters, while those related to antibiotic sources and aquifer susceptibility have lower influences. Omitting solute transport parameters that actually govern antibiotic fate (i.e., sorption coefficients and degradation rates) from the statistical analysis limited the success of the VP results. VP thus highlights the importance of researching antibiotic transport in groundwater by determining the reactive properties of these pollutants above other hydrogeochemical variables. We conclude that the present capacity to predict antibiotic existence at a specific location—for instance, a supply well—based on field data is still poor and unrepresentative, being an impediment for groundwater pollution management. Full article

Thermal groundwater is relatively abundant in the deep-seated bedrock underlying the Beijing plain area. The main geothermal reservoir is composed of dolomites of the Wumishan Group of the Meso–Neoproterozic Jixian System. The thermal groundwater has been developed and utilized since the 1970s and significant declines in groundwater levels were observed. A 3D unsteady flow model of an anisotropic karst-fissure aquifer based on the equivalent continuum is used to describe the flow of thermal groundwater and heat transport. The heat transportation is described by the governing equation including convection and dispersion. The simulation of this paper aims to solve such problems as uneven distribution and thinness of the aquifer, insufficient initial monitoring data, and poor knowledge of the properties of the horizontal boundary. They are solved by considering vertical stratification of the aquifer with equal thickness, replacing initial water level data by surface elevation, and choosing natural boundary far away from the exploitation areas. Through a trial–error procedure, the simulated and measured groundwater level and temperature in the simulation period are well fitted. Three exploitation schemes are proposed to predict the spatial and temporal changes in groundwater level and temperature of the thermal groundwater in the study area. The prediction results show that the reinjection can effectively slow the decline in the thermal groundwater levels. Except for the Dongnanchengqu, Xiaotangshan, and Liangxiang subgeothermal fields, the other six subgeothermal fields have the potential for further development of thermal groundwater. Full article

Improving current understanding of hydrodynamics and sediment dynamics in complex tidal embayments is of major importance to face future challenges derived from climate change and increasing human pressure. This work deepens the knowledge of the hydro-morphodynamics of complex creek networks that connect basins with different characteristics, identifying their morphodynamic trends and the potential impacts of channel deepening. We selected two tidal creeks which flow through salt marshes and tidal flats of the Cádiz Bay (SW Spain) in a singular network due to their double connection to the Atlantic Ocean and the inner bay. We study the interactions between tidal waves that penetrate into the creeks from these two different bodies of water, analyzing the tidal asymmetry and the morphodynamic tendencies of the system. For the analysis, we set up a hydro-morphodynamic model specifically developed for areas with very shallow and complex channels. Results show that the tidal wave penetrates within the tidal network both from the inner Bay and the open ocean with different amplitudes, phases and flow velocities. There is also an asymmetric pattern for the tidal flows caused by the deformation of the dominant astronomical tidal constituents, M2 and M4, due to the non-linear interaction of tidal currents with the irregular creek geometry and bottom topography. Tidal asymmetry promotes the progressive infilling of the area where the tidal waves meet closing the connection between the open ocean and the inner bay, such an infilling trend being accelerated by human interventions. Full article

During the last several decades, Earth´s climate has undergone significant changes due to anthropogenic global warming, and feedbacks to the water cycle. Therefore, persistent efforts are required to understand the hydrological processes and to engage in efficient water management strategies under changing environmental conditions. The twenty-four contributions in this Special Issue have broadly addressed the issues across four major research areas: (1) Climate and land-use change impacts on hydrological processes, (2) hydrological trends and causality analysis faced in hydrology, (3) hydrological model simulations and predictions, and (4) reviews on water prices and climate extremes. The substantial number of international contributions to the Special Issue indicates that climate change impacts on water resources analysis attracts global attention. Here, we give an introductory summary of the research questions addressed by the papers and point the attention of readers toward how the presented studies help gaining scientific knowledge and support policy makers. Full article

Grazing management practices can be erosion abatement actions for lowering soil loss and the subsequent sediment pollution of surface water bodies. Process-based Geographic Information Systems models provide the opportunity to identify critical areas and hence better target such actions across the landscape. This study implemented the SWAT (Soil Water Assessment Tool) hydrologic and catchment management model to estimate the soil loss vulnerability of the nearly pristine but highly erodible Greek island of Samothraki in the North Aegean Sea, with a typical Mediterranean climate and steep topography. Model parameterization and evaluation were carried out by taking advantage of previous modeling experience on areas with data limitations. Inter-annual and intra-annual soil loss variability and the most critical areas (subbasins) of soil loss to waters were adequately identified and grazing management scenarios, including livestock reductions by 50% and 100%, grazing period reduction, and a combination of them, were formulated and applied to investigate the degree to which soil loss could be reduced. The annual reduction results varied between scenarios in the range of 10% to 25% for the entire island, and in wider ranges for its individual subbasins, showing a high potential for reducing the vulnerability of the most pressured ones. However, due to the high importance of the natural factors of rainfall and land slopes, the erosion vulnerability of the island overall could be significantly altered only if grazing management was integrated within a vegetation regeneration plan that included reforestation. Full article

Zooplankton is crucial for the transfer of matter, energy, and pollutants through aquatic food webs. Primary and secondary consumers contribute to the abundance and standing stock biomass, which both vary seasonally. By means of taxa- and size-specific carbon and nitrogen stable isotope analysis, the path of pollutants through zooplankton is traced and seasonal changes are addressed, in an effort to understand pollutant dynamics in the pelagic food web. We analyzed zooplankton plurennial changes in concentration of polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethane and its relatives (DDTs) and in taxa-specific δ¹⁵N signatures in two size fractions, ≥450 µm and ≥850 µm, representative of the major part of zooplankton standing stock biomass and of the fraction to which fish predation is mainly directed, respectively. Our work is aimed at verifying: (1) A link between nitrogen isotopic signatures and pollutant concentrations; (2) the predominance of size versus seasonality for concentration of pollutants; and (3) the contribution of secondary versus primary consumers to carbon and nitrogen isotopic signatures. We found a prevalence of seasonality versus size in pollutant concentrations and isotopic signatures. The taxa-specific δ¹⁵N results correlated to pollutant concentrations, by means of taxa contribution to standing stock biomass and δ¹⁵N isotopic signatures. This is a step forward to understanding the taxa-specific role in pollutant transfer to planktivores and of zooplankton enrichment in PCBs and DDTs. Full article

In recent years, a dramatic decline in Poyang Lake water levels and a shrinking water surface have raised concerns about water security and the wetland ecosystem. Changes in bottom topography due to sand mining activities in the lake was supposed to be one of the influencing factors of these changes. In response to this issue, the current study analyzed the change of lake bottom topography from observed digital elevation model (DEM) data, and quantitatively assessed the spatial and temporal responses of lake hydrology based on the framework of the neural network and the sediment effect was examined afterward. Results showed a total volume of 11.54 × 10⁸ m³/year (about 0.96 × 10⁸ m³/year or 1.58 × 10⁸ t/year sediment) in net change of lake bottom topography in recent years, among which 97% was directly exported by commercial sand mining. During the study period, 2000–2011, intensive sand mining extended the central part of Poyang Lake and widened and deepened the outflow channel of the northern lake. This great change of lake bottom topography caused an average annual increase of 182.74 m³/s of lake outflow and a decline of 0.23 m–0.61 m in water levels across the lake. However, lake water levels are not consistent and show remarkable spatial and seasonal differences. The effects of changes in lake bottom topography on lake hydrological processes continue to grow as sand mining activities in the lake continue. More research on the environmental impacts is required for sustainable management of the lake ecosystem. Full article

The spatiotemporal variation in meiofaunal assemblages were investigated for the first time in the Cabras Lagoon, the largest transitional system in the Sardinian Island (W-Mediterranean Sea). Two main environmental (salinity and trophic) gradients highlighted a significant separation of the three study sites across the lagoon, which were consistent through time. The environmental variability and habitat heterogeneity of the Cabras Lagoon influenced the meiofauna. In particular, salinity and dissolved oxygen, primarily, shaped the meiofaunal assemblage structure at the seaward site which was significantly different from both the riverine and the organically enriched sites. On the other hand, the trophic components (e.g., organic matter, Chlorophyll-a, and phaeopigments) and the different degrees of confinement and saprobity among sites were the secondary factors contributing mostly to the separation between the latter two sites. The lack of significant differences in the temporal comparison of the meiofaunal assemblage structure along with the very low contribution of temperature to the meiofaunal ordination indicated that this assemblage was more affected by spatial rather than by temporal variation. This pattern was also supported by significant differences between the three sites in several univariate measures, including total number of individuals, number of taxa, Pielou’s evenness, and the ratio between nematodes and copepods. Thus, the present study corroborates the hypothesis that meiofaunal organisms are good indicators of the spatial heterogeneity in transitional waters (TWs) and could have a greater species richness than that expected. Indeed, the Cabras Lagoon overall showed one of the highest meiofaunal richness values found from both Mediterranean and European TWs. Full article