Search Results (13)

This study assesses the functioning of the karst aquifer system located on the Croatian coast of the Adriatic Sea, where saltwater intrusion often presents a major problem for freshwater supply. We use two years of sensor data collected from two coastal springs to conduct a range of time-invariant and time-variant statistical analyses over various timescales. We perform separate analyses of the within-day and longer-term variation in the data as well as the interactions between the spring levels, salinity, rainfall, and sea levels. Such comprehensive analyses provide a greater understanding into the inner functioning of the intricate, heavily karstified aquifers. Time-invariant time-series analyses of the hourly data indicate that the spring levels and salinity are strongly controlled by sea levels. Furthermore, time-variant wavelet analyses demonstrate that the variation in spring levels in both springs has two modes defined by flow regime. Increases in the delay of the spring response to sea level indicate that aquifer diffusivity decreases in low flow conditions. Analyses facilitated the development of a conceptual model of the karst subsurface in the discharge zone. Using daily data, we constructed a linear mixed model of the spring levels. This model identified long-term sea level changes, rainfall from previous weeks, and seasonal recharge patterns as the primary factors influencing longer-term spring dynamics. Full article

Solar desalination systems turn saltwater water into freshwater, which helps to overcome water scarcity. In this study, the effects of direct (contact) and indirect (non-contact) interactions with water in solar desalination were evaluated. The emphasis was on changing water depths to better understand the performance variances. Contact systems have a direct interface between thermal absorption materials and water, whereas non-contact systems avoid material–water contact to increase longevity. The experiments at two elevated water depths (3 cm and 4 cm) were conducted in a single-slope solar desalination system. The productivity of both touch and non-contact systems was investigated in June, August, and October 2024 to gather sufficient data for the training and testing of various machine learning models used to predict the distillate. Surprisingly, the non-contact structure system produced 15% and 8% more distillate than the contact system at 3 and 4 cm water depths, respectively. This insightful result will aid in building efficient and sustainable solar desalination technologies. The comparative study gives information on the trade-off between contact and non-contact techniques, with implications for future advances in solar-powered desalination technology. Among all the machine learning techniques, random forest regression achieved the highest coefficient determination (R² train of 0.89 and R² test of 0.95 for the non-contact structure system and R² of train 0.85 and R² test of 0.98 for the contact structure system). Machine learning techniques improve solar desalination by allowing for predictive insights and efficient maintenance, ultimately leading to sustainable water production. Full article

This study investigates enclosed water bodies to understand the intricate interactions among physical, chemical, and biological processes. A one-dimensional model, integrating sediment and ecosystem components, was developed to analyze oxygen depletion, nutrient dynamics, and the influence of sediment organic matter on oxygen concentrations due to stratification. Oxygen and nutrient concentrations were derived by combining results from a one-dimensional vertical diffusion model with the ecosystem model. The dissolution, adsorption, and desorption of inorganic substances in bottom mud react differently under anaerobic and aerobic conditions, necessitating separate formulations for reduction and oxidation reactions in the bottom mud model. In Lake Biwa, Japan’s largest lake, dissolved oxygen levels have decreased despite regulatory efforts since the 1970s, prompting an investigation into the causes of oxygen-depleted water masses. The model was thus applied to examine oxygen consumption in Lake Biwa’s deep sediments, shedding light on anoxia in enclosed water bodies. This study emphasizes the significance of bottom sediments in water quality models and their implications for ecosystems. Furthermore, the adaptive nature of this model allows for its application in various water bodies, including freshwater reservoirs, lakes, and saltwater bays. Full article

As an enduring Chinese freshwater aquaculture product, the Eriocheir sinensis has a high economic value and is characterized by a catadromous life style that undergoes seawater–freshwater migration. However, little is known about their gut microbial status as they move from saltwater to freshwater acclimatization. Here, we sampled and cultivated Eriocheir sinensis megalopa from three aquaculture desalination ponds and investigated their gut microbiota diversity, community structures and biotic interactions from megalopa stage to the first juvenile stage after desalination for 9 days. Our results revealed that during the transition from megalopa to the first juvenile in Eriocheir sinensis, a significant change in gut microbial composition was observed (for instance, changes in relative abundance of dominant phyla), which was, however, not influenced by different sampling sites. The species diversity (such as the richness) of the gut microbiota showed a hump-shaped pattern along the succession. However, the compositional differences of the gut microbes showed constantly increasing patterns during the succession after freshwater adaption for all three sampling sites. Further co-occurrence analysis also showed that the complexity of the ecological networks in gut microbes was significantly enhanced during the development, such as increasing numbers of network links, connectivity and modularity, and was confirmed by decreasing average path length and proportions of negative links. Taken together, the differences in community structures and biological interactions of gut microorganisms were more pronounced in Eriocheir sinensis megalopa during desalination than in diversity and species compositions. This implies that the gut microbes of Eriocheir sinensis megalopa would become more robust and adaptive during the developmental process. Full article

Currently, microplastic pollution poses a great threat to diverse ecosystems. Microplastics can potentially change soil characteristics and impact soil microorganisms, and then affect the production of CO₂, CH₄ and other greenhouse gases. However, experimental study on different ecological soils is lacking. Herein, we experimentally analyzed the CO₂ and CH₄ production potential affected by four types of microplastics in freshwater (Poyang Lake in Jiangxi province, paddy soil in Hunan province) and saltwater (Salt marsh in Shandong province, mangrove soil in Fujian province) ecosystems. Microplastics promoted CO₂ production, of which polyethylene terephthalate (PET) had the greatest impact. In our study, the microplastics that had the greatest impact on CH₄ concentration emissions were high-density polyethylene (1276 umol·g⁻¹·L⁻¹), followed by polyvinyl chloride (384 umol·g⁻¹·L⁻¹), polyethylene terephthalate (198 umol·g⁻¹·L⁻¹), and polyamide (134 umol·g⁻¹·L⁻¹). In addition, the largest impact on CO₂ concentration emissions was displayed by polyethylene terephthalate (2253 umol·g⁻¹·L⁻¹), followed by polyvinyl chloride (2194 umol·g⁻¹·L⁻¹), polyamide (2006 umol·g⁻¹·L⁻¹), and high-density polyethylene (1522 umol·g⁻¹·L⁻¹). However, the analysis results based on one-way ANOVA showed that CO₂ emission was most significantly affected by soil properties rather than microplastics types. In comparison, the influencing factor on CH₄ production changed from soil types to the interaction between soil types and microplastics, and finally to the microplastics with the increase in incubation time. Further, by comparing CO₂ and CH₄ production and Global Warming Equivalent (GWE) affected by microplastics, freshwater ecosystems were more sensitive than saltwater. For all the soil types used in this study, high-density polyethylene had the greatest impact on CH₄ production potential. In conclusion, our study provided basic data for further understanding the effects of microplastics on soil greenhouse gas emissions from different sources. Full article

The interaction effects of organic ligand ethylene diamine tetra-acetic acid (EDTA) and oxide nanoparticles (magnetite Fe₃O₄-NPs and copper CuO-NPs) were investigated during a 72 h period on two green algal species—Chlamydomonas reinhardtii under freshwater conditions and Chlamydomonas euryale under saltwater conditions. Fe₃O₄-NPs had larger agglomerates and very low solubility. CuO-NPs, having smaller agglomerates and higher solubility, were more toxic than Fe₃O₄-NPs in freshwater conditions for similar mass-based concentrations, especially at 72 h under 100 mg L⁻¹. Furthermore, the effect of EDTA increased nanoparticle solubility, and the salinity caused a decrease in their solubility. Our results on C. euryale showed that the increase in salinity to 32 g L⁻¹ caused the formation of larger nanoparticle agglomerates, leading to a decrease in the toxicity impact on algal cells. In addition, EDTA treatments induced a toxicity effect on both freshwater and saltwater Chlamydomonas species, by altering the nutrient uptake of algal cells. However, C. euryale was more resistant to EDTA toxicity than C. reinhardtii. Moreover, nanoparticle treatments caused a reduction in EDTA toxicity, especially for CuO-NPs. Therefore, the toxicity impact caused by these environmental factors should be considered in risk assessment for metallic nanoparticles. Full article

An integrated research approach consisting of hydrogeologic and geochemical methods was applied to a coastal aquifer in the Ostia Antica archaeological park, Roma, Italy, to describe freshwater–saltwater interactions. The archaeological park of Ostia Antica is located on the left bank of the Tevere River delta which developed on a morphologically depressed area. The water monitoring program included the installation of multiparametric probes in some wells inside the archaeological area, with continuous measurement of temperature, electrical conductivity, and water table level. Field surveys, water sampling, and major elements and bromide analyses were carried out on a seasonal basis in 2016. In order to understand the detailed stratigraphic setting of the area, three surface boreholes were accomplished. Two distinct circulations were identified during the dry season, with local interaction in the rainy period: an upper one within the archaeological cover, less saline and with recharge inland; and a deeper one in the alluvial materials of Tevere River, affected by salinization. Oxygen and carbon isotopic signature of calcite in the sediments extracted from the boreholes, along with major elements and Br concentration, allowed us to recognize the sources of salinity (mainly, local interaction with Roman salt pans and agricultural practices) and the processes of gas–water–rock interaction occurring in the area. All these inferences were confirmed and strengthened by PCA analysis of physicochemical data of groundwater. Full article

The association between fish consumption and new-onset type 2 diabetes is inconsistent and differs according to geographical location. We examined the association between the total and types of fish consumption and type 2 diabetes using individual participant data from 28 prospective cohort studies from the Americas (6), Europe (15), the Western Pacific (6), and the Eastern Mediterranean (1) comprising 956,122 participants and 48,084 cases of incident type 2 diabetes. Incidence rate ratios (IRRs) for associations of total fish, shellfish, fatty, lean, fried, freshwater, and saltwater fish intake and type 2 diabetes were derived for each study, adjusting for a consistent set of confounders and combined across studies using random-effects meta-analysis. We stratified all analyses by sex due to observed interaction (p = 0.002) on the association between fish and type 2 diabetes. In women, for each 100 g/week higher intake the IRRs (95% CIs) of type 2 diabetes were 1.02 (1.01–1.03, I² = 61%) for total fish, 1.04 (1.01–1.07, I² = 46%) for fatty fish, and 1.02 (1.00–1.04, I² = 33%) for lean fish. In men, all associations were null. In women, we observed variation by geographical location: IRRs for total fish were 1.03 (1.02–1.04, I² = 0%) in the Americas and null in other regions. In conclusion, we found evidence of a neutral association between total fish intake and type 2 diabetes in men, but there was a modest positive association among women with heterogeneity across studies, which was partly explained by geographical location and types of fish intake. Future research should investigate the role of cooking methods, accompanying foods and environmental pollutants, but meanwhile, existing dietary regional, national, or international guidelines should continue to guide fish consumption within overall healthy dietary patterns. Full article

Groundwater resources are facing increasing pressure especially in semi-arid regions where they often represent the main freshwater resource to sustain human needs. Several aquifers in the Mediterranean basin suffer from salinization and quality degradation. This study provides an assessment of Grombalia coastal aquifer (Tunisia) based on multidisciplinary approach that combines chemical and isotopic (δ²H, δ¹⁸O, ³H, ¹⁴C and δ¹³C) methods to characterize the relation between groundwater quality variation and aquifer recharge. The results indicate that total dissolved solids exceed 1000 mg/L in the most of samples excepting the recharge area. In addition to water–rock interaction, evaporation and nitrate pollution contributing to groundwater mineralization, the reverse cation exchange process constitute an important mechanism controlling groundwater mineralization with enhancing risk of saltwater intrusion. Environmental isotope tracers reveal that groundwater is evolving within an open system to close system. A significant component of recent water that is recharging Grombalia aquifer system is confirmed by applying correction models based on the δ¹³C values and ¹⁴C activities and tritium contents. However, this recharge, which is mainly associated to the return flow of irrigation water, contributes to the groundwater salinization, especially for the shallow aquifer. Full article

In this study, numerical simulations were conducted in order to understand the role of wave-current interactions in wave deformation. The wave-current interaction mechanisms, wave reflection and energy loss due to currents, the effect of incident conditions on wave-current interactions, the advection-diffusion characteristics of saltwater, and the effect of density currents on wave-current interactions were discussed. In addition, the effect of saltwater–freshwater density on wave-current interactions was investigated under a hypopycnal flow field via numerical model testing. Turbulence was stronger under the influence of wave-current interactions than under the influence of waves alone, as wave-current interactions reduced wave energy, which led to decreases in wave height. This phenomenon was more prominent under shorter wave periods and higher current velocities. These results increase our understanding of hydrodynamic phenomena in estuaries in which saltwater–freshwater and wave-current pairs coexist. Full article

The groundwater from shallow coastal aquifers in Nigeria has been reported to be under intense stress resulting from both natural and anthropogenic impacts ranging from saltwater intrusion, effluent-related contamination and pollution to oil spillage, gas flaring, municipal, industries and agriculture. Here we characterised the hydrostratigraphy and hydraulic characteristics of the shallow coastal aquifers of the Niger Delta basin and assessed the resilience of groundwater to both natural and anthropogenic impacts. Fifty-two borehole logs were analysed from which lithological sections were used to generate cross-sections along with four profiles. The system was more complex than previously reported: a unit of silty sand was observed in the western part of the basin that thins out leaving the eastern part of the basin as an unconfined aquifer underlain by multiple thin beds of the sand aquifer. A layered sand aquifer occurs in the northern parts of the basin, which holds freshwater in this area, and is interbedded by clay layers which serve as aquitards. The relatively higher hydraulic conductivity of the Benin Formation units compared to those of the Deltaic Formation leave it with weaker climate change resilience and more vulnerable to pollution and contamination. While groundwater remains the dominant source of fresh water in the northern part of the basin, a strategic approach is needed to access potable water from the southern part where contaminated surface water appears to directly interact with groundwater of the uppermost unconfined aquifer. Management of waste and effluent related to oil spillage, municipal, industries and agricultural in this area should be engineered to protect the groundwater resources of this aquifer. Full article

This study focuses on the salinization of the coastal aquifer in the Mazandaran Province (Iran) within four different sites. Many factors can lead to declining groundwater quality, but this study focuses on the seawater intrusion area. Therefore, locating the interface between saltwater and freshwater is very important. For this purpose, three characterization methods with different accuracies have been employed: the Verruijt equation, vertical resistivity sounding, and an electromagnetic survey. Vertical resistivity sounding and the electromagnetic survey were performed near existing exploration boreholes and were used to determine the saltwater interface. The results showed that the Verruijt equation provides a reliable localization in two of the sites, but in the other two sites, the determined interface is lower than the observed data. The geoelectrical method showed acceptable results, but often this method cannot distinguish between the saltwater and saline aquitard boundary. The electromagnetic method showed a high accuracy in all the study sites and proved to be the most reliable method compared with the other techniques employed in this study. The results from this study are useful in helping to identify the most suitable technique for locating the freshwater/saltwater interface, especially in those sites where a detailed characterization via multilevel sampling is not feasible for technical or economic reasons. Full article

Aquifer over-exploitation may increase coastal seawater intrusion by reducing freshwater availability. Fractured subsurface formations commonly host important freshwater reservoirs along sea coasts. These water resources are particularly vulnerable to the contamination due to seawater infiltration occurring through rapid pathways via fractures. Modeling of density driven fluid flow in fractured aquifers is complex, as their hydrodynamics are controlled by interactions between preferential flow pathways, 3D interconnected fractures and rock-matrix porosity distribution. Moreover, physical heterogeneities produce highly localized water infiltrations that make the modeling of saltwater transport in such aquifers very challenging. The new approach described in this work provides a reliable hydrogeological model suitable to reproduce local advancements of the freshwater/saltwater wedge in coastal aquifers. The proposed model use flow simulation results to estimate water salinities in groundwater at a specific depth (1 m) below water table by means of positions of the Ghyben-Herzberg saltwater/freshwater sharp interface along the coast. Measurements of salinity in 25 boreholes (i.e., salinity profiles) have been used for the model calibration. The results provide the groundwater salinity map in freshwater/saltwater transition coastal zones of the Bari (Southern Italy) fractured aquifer. Non-invasive geophysical measurements in groundwater, particularly into vertical 2D vertical cross-sections, were carried out by using the electrical resistivity tomography (ERT) in order to validate the model results. The presented integrated approach is very easy to apply and gives very realistic salinity maps in heterogeneous aquifers, without simulating density driven water flow in fractures. Full article