Water Subsystems Research Articles

Coupled development of the urban water-energy-food nexus: A systematic analysis of two megacities in China's Beijing-Tianjin-Hebei area

Promoting the coupled development of water, energy, and food (WEF) subsystems is a critical step to enhance synergies and increase efficiencies in the WEF nexus. However, the evolution and obstacles of coupled development are largely ignored. This study developed a framework dividing links in the nexus to select indicators and integrated models for the degree of coordination and obstacle diagnosis to explore the coupled development of the WEF nexus from 2000 to 2020 in the water-scarce megacities of Beijing and Tianjin. The results show that the average coordination degree of the WEF nexus in Beijing (0.315) and Tianjin (0.317) is at a low level, indicating a limited interaction between the WEF subsystems, while the coordinated development degree of the WEF nexus is increasing. The order degree of the WEF subsystems shows a two-level hierarchical structure, indicating that both similarities and differences are included in place-specific characteristics. Furthermore, obstacle factors are identified from water and energy subsystems, in which environmental water use (W3) and the energy consumption per gross domestic production unit (E4) played the most significant roles and require a higher priority in policy response. The results in this paper complement obstacle factor analysis in WEF nexus practice, and provide operational indicators for nexus governance.

Evolution of the hydrogen-bonded network in methanol-water mixtures upon cooling

The hydrogen-bonded structure of methanol – water mixtures is investigated over the entire alcohol concentration range (from xMethanol = 0.1 to 1.0) at several temperatures, from 300 K down to the freezing point of the given mixture. Classical molecular dynamics simulations have been carried out, using the all-atom OPLS-AA force field for methanol and the TIP4P/2005 model for water molecules. Simulation trajectories (‘particle configurations’) obtained have been analyzed, in order to characterize the hydrogen-bonded network in the mixtures. The temperature and concentration dependence of the average hydrogen bond (H-bond) numbers between different types of molecules, the donor/acceptor roles of water and methanol molecules, and hydrogen bond number distributions have been revealed. The topology of the total system, as well as that of the water and methanol subsystems, has been investigated by calculating the cluster size distributions, the number of primitive rings, and ring size and ring type distributions. It has been found that upon cooling, the average number of H-bonded water molecules increases at every concentration and temperature investigated. As far as the connectivity of the hydrogen-bonded network is concerned, the percolation threshold has been shown to be above xM = 0.9 already at room temperature.

A comprehensive evaluation of the security of the water-energy-food systems in China

Water-energy-food (WEF) are the indispensable resources for achieving sustainable social-economic development, poverty reduction, and human well-being. An appropriate WEF security evaluation may help inform China's sustainable resource production and consumption. This study selects 27 indicators representing pressure-state-response (PSR) dimensions to evaluate the WEF security of 30 provinces in mainland China from 2010 to 2019 using the entropy weight method and matter-element extension (MEE) model. The results indicate that the security of the water subsystem is mostly under high risk, and is relative severe in the Beijing-Tianjin-Hebei region, Shanghai, Shandong, and Ningxia. Meanwhile, energy subsystem indicators like carbon emission and energy intensities have significantly improved. All food subsystem indicators have improved by varying degrees. Regionally, food security is high in the east, and low in the central and western regions. In terms of the performance of PSR dimensions, “Pressure” is the most optimistic, followed by “Response” and “State”. The “Response” in most provinces is getting better, which has promoted the overall improvement of WEF systems. Thus, while maintaining the subsystem with high security, the integrated system's security can be enhanced by addressing the shortcoming of other subsystems. This can help realise synergistic resource use and enhance their security.

Framing a novel holistic energy subsystem structure for water-energy-food nexus based on existing literature (basic concepts)

It is interesting to note that the country of Iran is essential in terms of energy production and consumption, and the economy of Iran is mainly dependent on energy revenues. Therefore, thermal and hydropower plants consume water to produce various energy carriers. Considering that Iran is suffering from water stress, the nexus of water and energy becomes very important. This paper frames a comprehensive structure for Iran's energy subsystem within the Water, Energy, and Food (WEF) nexus system. The energy subsystem's supply and demand side in the proposed framework are formulated using data and physic-based equations. The presented framework addresses most interactions between WEF subsystems in a dynamic and adaptive setting. It is shown that through analysis of binding interactions between WEF, different management scenarios can boost the flexibility of the supply and demand side of the energy subsystem. In addition, by incorporating this framework, the water subsystem will manage the allocated and consumed water on the supply side and arrive at the most desirable outcome for the water sector. Also, the optimal cropping pattern could be evaluated based on energy consumption.

Neurodynamics-based distributed model predictive control of a low-speed two-stroke marine main engine power system

This article studies a steady operation optimization problem of a low-speed two-stroke marine main engine (LTMME) power system including a cooling water subsystem, a fuel oil subsystem and a main engine subsystem with input and state constraints. Firstly, a distributed model with coupling inputs and states is established for the LTMME power system according to laws of thermodynamics and kinetics. Further, an optimization problem of the LTMME power system is formulated to ensure the system to operate steadily, subjected to constraint conditions of the distributed model and the input and state bounds. Moreover, the optimization problem is rewritten as a quadratic programming problem, and an iterative distributed model predictive control (DMPC) scheme based on a primal–dual neural network (PDNN) method is used to obtain the optimal inputs within the constrained range. Finally, based on the actual data from an underway ocean vessel named Mingzhou 501 with an LTMME power system, a group of simulations are carried out to verify the effectiveness of the proposed approach.

A novel system integrating water electrolysis and supercritical CO2 cycle for biomass to methanol

In order to improve the efficiency of conventional biomass to methanol, a novel cogeneration system is designed that couples an electrolytic water subsystem with a s-CO2 cycle and a conventional biomass to methanol system. The novel cogeneration system uses syngas converted from biomass gasification and hydrogen obtained by water electrolysis for methanol synthesis, and it uses a supercritical CO2 cycle to improve its performance. The proposed process was modeled and calculated using Aspen Plus and MATLAB as the main simulation software to analyze its energy efficiency, exergy efficiency and economics, and to illustrate the advantages of the system compared with the conventional biomass to methanol system from a thermodynamic point of view. Taking a biomass with a mass flow rate of 2.78 kg/s for example, the energy efficiency of the new process was increased by 19.89% for the same biomass consumption conditions. The results show that the system has an energy efficiency of 67.98% and an exergy efficiency of 64.82%. The irreversibility comes from two main components: the gasifier and the electrolyzer. The project is expected to achieve a net present value of $22,948,830 over its 20-year life cycle.

Distributed Scheme for Main Engine Power Control Systems of Small and Medium Sized Container Ships Based on Nash Equilibrium

As a main force of ocean shipping, the energy consumption of container ships is considerably high due to the frequent load shifts of main engine and other disturbances. In this study, for engine room power systems in intelligent container ships, including cooling water subsystems, fuel oil subsystems, and main engine subsystems, a coordinated control scheme based on a correlation model and a distributed model predictive control approach was proposed to reduce continual fluctuations of control and output values through optimisation in a negotiated manner. The correlation model considers the interconnections among the subsystems, and the control approach achieves Nash equilibrium solutions. A comparative simulation was carried out between the proposed method and the decentralized model predictive control. The result shows that the proposed method works better than the decentralized one with less fluctuations. This study provides a theoretical basis for integrated designs of power control systems in intelligent container ships.

Downscaling global land-use/cover change scenarios for regional analysis of food, energy, and water subsystems

Integrated assessment models (IAMs) capture synergies between human development and natural ecosystems that have important implications for the food-energy-water (FEW) nexus. However, their lack of fine-scale representation of water regulatory structure and landscape heterogeneity impedes their application to FEW impact studies in water-limited basins. To address this limitation, we developed a framework for studying effects of global change on regional outcomes for food crops, bioenergy, hydropower, and instream flows. We applied the new methodology to the Columbia River Basin (CRB) as a case study. The framework uses the Demeter land-use and land-cover change (LULCC) downscaling tool, which we updated so that water rights are spatially integrated in the land allocation process. We downscaled two LULCC scenarios (SSP2-RCP 4.5 and SSP5-RCP 8.5) under three levels of irrigation expansion: no expansion (historical extent), moderate expansion (all land presently authorized by a water right is irrigated), and maximum expansion (new water rights are granted to cover all irrigable land). The downscaled scenarios were evaluated using a hydrology-cropping systems model and a reservoir model coupled in a linear fashion to quantify changes in food and bioenergy crop production, hydropower generation, and availability of instream flows for fish. The net changes in each sector were partitioned among climate, land use, and irrigation-expansion effects. We found that climate change alone resulted in approximately 50% greater production of switchgrass for bioenergy and 20% greater instream flow deficits. In the irrigation-expansion scenarios, the combination of climate change and greater irrigated extent increased switchgrass production by 76% to 256% at the cost of 42% to 165% greater instream flow deficits and 0% to 8% less hydropower generation. Therefore, while irrigation expansion increased bioenergy crop productivity, it also exacerbated seasonal water shortages, especially for instream use. This paper provides a general framework for assessing benchmark scenarios of global LULCC in terms of their regional FEW subsystem outcomes.

Urban ecosystem services supply-demand assessment from the perspective of the water-energy-food nexus

To facilitate sustainable urban development, a pressing issue is how to integrate the water-energy-food nexus (WEF-Nexus) into the assessment of supply and demand of urban ecosystem services (UESs). This study proposed a conceptual framework for the supply-demand assessment of UESs from the WEF-Nexus perspective. Taking the city of Suzhou, China, as an example, the relationships between UESs and WEF-Nexus were identified by the correlation and regression analyses based on the total supply of each urban ecosystem service and evaluation value of each subsystem of WEF-Nexus. Then the supply-demand matching of UESs was evaluated by the supply-demand matching degree and z-score standardization. The results indicated that the water and energy subsystems were positively correlated with water yield/soil retention, and negatively correlated with carbon storage/food production. The food subsystem showed significant positive correlations with carbon storage/food production. Three UESs related to WEF-Nexus, carbon storage, soil retention and food production, were always in short supply, while water yield has shifted to oversupply. The supply-demand spatial mismatches of carbon storage/food production became more pronounced, showing a trend of spreading from urban central areas to the periphery. Therefore, this study provides a scientific basis for proposing supply-demand management strategies of UESs from the WEF-Nexus perspective.

Exploring the relationship between water-energy-food nexus sustainability and multiple ecosystem services at the urban agglomeration scale

The current perception of how ecosystem services (ES) affect the water-energy-food nexus sustainability (hereafter, nexus sustainability) is still unclear. Here, we proposed an analytical framework to explore the relationship between nexus sustainability and multiple ES. This study took the Yangtze River Delta Urban Agglomeration (YRDUA) as an example. Firstly, a nexus sustainability evaluation index system was established to evaluate the sustainability of water-energy-food nexus and its three subsystems. Then various models were utilized to quantify the four ES (water yield, carbon storage, soil retention, and food production). Finally, the coupling coordination degree model and correlation analysis were applied to explore the relationship between nexus sustainability and multiple ES. The results show that the coordination between nexus sustainability and water yield gradually improved, while that between nexus sustainability and food production declined significantly, especially in the southern regions of the YRDUA. There were obvious spatial heterogeneities in the coordination between nexus sustainability and carbon storage/soil retention, characterized by a coordination state in the southern regions and an incoordination state in the northern regions. A complex relationship between nexus sustainability and multiple ES existed. Water subsystem sustainability had significant and positive linear correlations with water yield/carbon storage, and a significant and positive nonlinear correlation with soil retention. There was also a significant and positive nonlinear correlation between food subsystem sustainability and food production. The nonlinear correlations between energy subsystem sustainability and four ES were not significant in most years. Therefore, relationship-based and location-based management measures, such as ecological protection and restoration, strictest water resources management and cross-city cooperation, were proposed to facilitate the sustainable and coordinated development of nexus sustainability and multiple ES. This study can also provide references for the coordinated development of nexus sustainability and multiple ES in other urban agglomerations within and beyond China.

Cross-County Characteristics of Water–Ecology–Economy Coupling Coordination in the Wuding River Watershed, China

Investigating the coupling coordination relationship between water resources, ecology and the economy is the basis process for watershed governing to achieve sustainable development. Taking the Wuding River watershed (one of the largest tributaries of the Yellow River) as an example, we used the coupling coordination model to analyze the coupling coordination relationship of the water–ecology–economy system between 2001 and 2020, and then used grey correlation and partial correlation analyses to explore the main influencing factors and cross-county characteristic of the coupling coordination. The results show that the water, ecology and economy subsystems changed slightly before 2007. After 2007, the economy developed rapidly, while the water and ecology increased for a short time and then decreased after 2013. The water–ecology–economy coupling coordination was on the verge of dysfunctional decline. Water and ecology were the main influencing factors on the coupling coordination. The coupling coordination showed a cross-county characteristic. Water and ecology in upstream counties had significant positive correlations with the coupling coordination in downstream counties. The economy subsystem in upstream counties, however, had significant negative correlations with water and ecology in downstream counties. Our findings provide an empirical mode to measure transregional characteristics of coupling coordination and could support the construction of a coordination governance mode in the Wuding River watershed.

Energy simulation modeling for water-energy-food nexus system: a systematic review.

Since essential nexus variables were not considered in the energy subsystem, this study focused on the role of energy in the Water, Energy, and Food nexus (WEF nexus) system. The energy subsystem interacts with water and food on the supply and demand sides. The WEF nexus-based energy model has not been reviewed recently. This study provides a systematic review of 459 articles regarding energy simulation modeling issues relating to the WEF nexus system. The keyword ("energy" AND "simulation" AND "nexus") as well as "water" OR "food" OR "climate" OR "land" OR "carbon" OR "environment" is used for searching WEF nexus documents for energy simulation. The review highlighted that the energy subsystem is modeled online (One-way) and offline (Two-way), and the energy simulation struggles to represent its system boundary with the water and food subsystems in different spatial scales (household to global). The energy subsystem of the WEF nexus did not address return flow from cooling towers and crop energy consumption comprehensively. In the research, the supply and demand section of the energy subsystem demonstrated that a comprehensive simulation model for energy can be developed using the nexus system approach. The energy subsystem's supply, primarily power plants, interacts with the water subsystem, and the energy generation policy is based on water use. The WEF nexus system assesses renewable energy effects to reduce tradeoffs. In addition, energy demand is related to energy consumption, so the energy consumption for each crop can be calculated and explained the appropriate cultivation pattern based on it.

Sustainability and efficiency of water-land-energy-food nexus based on emergy-ecological footprint and data envelopment analysis: Case of an important agriculture and ecological region in Northeast China

Ecological security and efficient utilization of resources in the water-land-energy-food (WLEF) nexus are important strategic needs. Therefore, this study developed an emergy ecological footprint using the super-efficiency Slacks-Based Measure-Data Envelopment Analysis (SBM-DEA) to comprehensively evaluate the ecological security and efficiency of the WLEF nexus from 2006 to 2019 in the Songnen-Sanjiang Plain in Northeast China. Our findings indicated that: 1) Ecological security had improved from 2006 to 2019, with an average ecological carrying capacity supply and demand balance index of 3.301 and 2.723 in 2006 and 2019, respectively. 2) The average concordant index in the Songnen Plain and Sanjiang Plain was 1.258 and 1.358 respectively, indicating that the Sanjiang Plain had better ecological security than the Songnen Plain. 3) The efficiency of the water and energy subsystems demonstrated an increasing trend over time, with the overall land subsystem increasing before 2016 but decreasing afterwards. 4) The efficiency of the Songnen-Sanjiang Plain's water, land, energy, and food subsystems varied greatly on temporal and spatial scales. The water efficiency in the Songnen-Sanjiang Plain was higher in the middle and low all around. 5) From 2006 to 2019, the WLEF nexus efficiency in the Sanjiang Plain was higher than in the Songnen Plain, and in 2019, the WLEF nexus efficiency in 50% of the cities did not reach the Songnen-Sanjiang Plain production frontier. Therefore, to achieve regional sustainable development, additional efforts are required to ameliorate the ecological conditions of the middle part of the Songnen Plain and improve the resource utilization efficiency of each subsystem, especially the water resources of the WLEF nexus.

Reactive nitrogen budgets in human-nature coupling system in lakeside area with insufficient data - A case study of Mwanza, Tanzania

Nitrogen (N) is an essential nutrient element for life, and also a major element involved in the composition of greenhouse gases, surface water pollutants, air pollutants, etc. Quantifying and evaluating the nitrogen budget of a region is very important for effectively controlling the nitrogen discharge and scientifically managing the nitrogen cycle. In this paper, the urban Rural Complex N Cycling (URCNC) model was used to analyze the nitrogen budget of Mwanza region, a typical lakeside area with insufficient data, and the nitrogen flow process of livestock subsystem, cropland subsystem, human subsystem and landfill subsystem was clearly described and the nitrogen input sources of atmospheric subsystem and surface water subsystem were clarified. And the results demonstrated: (1) the cropland subsystem was the subsystem with the largest nitrogen flux, and the input, output and accumulation of nitrogen were 33,116 t of N, 31,925 t of N and 1191 t of N, respectively. Livestock subsystem was the second largest subsystem of nitrogen flux, and the input, output and accumulation of nitrogen were 31,013 t, 30,183 t and 830 t, respectively. The nitrogen flux of the human subsystem was also large, and the nitrogen input, output and accumulation were 17,905, 17,125 and 780 t, respectively. The nitrogen input, output and accumulation of the landfill subsystem were 3700 t, 770 t and 2930 t, respectively. (2) 8093 t of N, 6864 t of N, 3959 t of N, and 758 t of N emitted into the atmospheric subsystem from the livestock subsystem, cropland subsystem, human subsystem, and landfill subsystem, respectively. (3) The total Nr input of surface water subsystem increased from 18,545 t of N in 2010 to 20,174 t of N in 2020, with an increase of 8.78 % in the past decade. It was estimated that by 2030, the total Nr input of the surface water subsystem would reach 24,946 t of N with an increase of 23.65 % compared with 2020. The livestock subsystem was the largest source, the cropland subsystem was the second largest source and human subsystem was an important source. (4) Population growth, economic development and urbanization are the main nitrogen driving factor. (5) Technology and policy together have important contributions to the reduction of nitrogen pollution in surface water.

Research on the competitive and synergistic evolution of the water-energy-food system in China

Water, energy, and food are essential and strategic resources for human well-being and socio-economic development and form the water-energy-food (WEF) system with competition and synergy. The competitive and synergistic evolution model was developed to remedy the limitations in quantitatively analyzing the tradeoffs and synergies of the WEF system. Firstly, an assessment model was developed for measuring the synergy and competition of the WEF system based on the order degree of each subsystem (That is, the development degree of each subsystem) and synergy theory. Then the synergy evolution model (SEM), with the help of a logistic model and accelerated genetic algorithm (AGA) model, was developed to measure and identify the steady-state. Furthermore, an empirical study was conducted with 30 provinces in China as examples. The results indicated that the food subsystem had the highest average order degree (0.347), followed by the energy subsystem (0.305), and the water subsystem had the lowest (0.281). The degree of order of the three subsystems exhibited an upward trend in time and has differences in the spatial distribution. Also, the results showed that synergistic, restrictive, and competitive relationships exist within the WEF system. Areas with competitive and restrictive relationships are mainly located in South China and North China, respectively, within the relationship between the water and energy subsystems. The entire country showed a restrictive relationship between the water and food subsystems. The energy and food subsystems showed that the eastern regions with relationship, while the western regions with competitive and restrictive relationship. Finally, effective measures (e.g., optimize the industrial structure, continuing to implement the strategy of “storing grain in the land and technology”, and to hold the arable land minimum) are suggested to achieve the WEF system coordinated and sustainable development. We believe that the assessment model is also applicable to assess the other complex and dynamic system worldwide that involve multiple factors.

Will city cluster cope with water dilemma?

The study focuses on whether city cluster as an urbanization development mode can solve the problem of stable water system development that cannot be solved at the city level. This study selects the Jing-Jin-Ji city cluster and the Yangtze River Delta city cluster as the research objects for comparative analysis. First, the coupling index system of urbanization and water was constructed, then the urbanization subsystem and the water subsystem were evaluated by the Comprehensive Gravity-Gram Schmidt Orthogonalization coupling model (CG-GSO) and the entropy weight method. Second, the coordinated development between urbanization and water was explored based on the coupling coordination degree model, and its driving factors were analyzed. The results showed: (1) the overall trends of urbanization development were on the rise in both city clusters; (2) whether in the water-deficient Jing-Jin-Ji city cluster or the water-abundant Yangtze River Delta city cluster, the water pollution dimension and the water supply and use dimension alternately occupied the largest proportion in the water subsystem; (3) in the urbanization subsystem and the water subsystem, the driving factors promoting the coordinated development in the coupling system were demographic urbanization dimension and water supply and use dimension in the Jing-Jin-Ji city cluster, and social urbanization dimension and water supply and use dimension in the Yangtze River Delta city cluster. Overall, as the development mode, city cluster did solve the problem of uncoordinated development of the coupling urbanization and water system in inner cities, and the coordination degrees were upward from unbalanced to balanced development, which were from 0.1278 to 0.4118 in the Jing-Jin-Ji city cluster and from 0.1770 to 0.5001 in the Yangtze River Delta city cluster. The study framework could provide ideas for other regions to solve the problem of coordinated development between water and urbanization.

Where Will ‘Water-Energy-Food’ Research Go Next?—Visualisation Review and Prospect

Research on water, energy, and food (WEF) is gradually becoming a global research hotspot in response to threats caused by the overexploitation of resources. In this study, 13,202 documents were selected from the WoS database and CiteSpace to judge frontier development in WEF research. In this study, visualisation research was carried out in 1547 papers that are most relevant to WEF research. The results show that WEF research has gradually increased during the research period, especially since 2015. The Food and Agriculture Organisation of the United Nations, Hoff, and Bazilian have the greatest influence on the promotion of WEF research and there is significant cooperation between institutions and countries. The United States, China, and the United Kingdom were the main contributors. The WEF nexus has become the most important hotspot in WEF research. In this case, 823 papers focused on the WEF nexus were selected to demonstrate the research contents, frontiers and clusters, and methods of the WEF nexus. Applied researches on the WEF nexus, such as security issues and multi-objective optimisation are current frontiers. Some new topics such as the pandemic and geopolitics have not attracted enough attention relative to their potential importance. A comprehensive data platform for the inter-department of water, energy, and food subsystems should be constructed in the near future.

Development and synergetic evolution of the water-energy-food nexus system in the Yellow River Basin.

The water-energy-food nexus is a complex system where balancing the trade-offs across water, energy, and food sectors is especially difficult in resource-deficient areas. The Yellow River Basin is an area in which water shortages lead to conflicts among water, energy, and food resources. Thus, investigating the evolution state and spatial characteristics of the water-energy-food nexus in the Yellow River Basin is essential for the management of resources and sustainable development orientation of the region's water-energy-food nexus system. This study proposed an integrated assessment framework by using synergy theory and the integrated index system method. The improved Lotka-Volterra symbiotic model was used to elucidate the development and synergy evolution status of the water-energy-food nexus system in prefecture-level cities in the Yellow River Basin between 2004 and 2019. The results show that the order degree of the water and energy subsystems in the Yellow River Basin increased by an average of 0.12 and 0.42, on average respectively, from 2004 to 2019, whereas that of the food subsystem only increased by an average of 0.004 compared to the initial year. Furthermore, most prefecture-level cities experienced subsystem degradation of one or two subsystems during the evolution of the water-energy-food nexus system. Based on the uniqueness and evolution process of each city, there are eight possibilities for system evolution and three types of feedback state between each pair of subsystems, which may lead to a certain spatial aggregation. Additionally, the interaction and competition states are more common than synergy states in the water-energy-food nexus system of the Yellow River Basin. This study provides an important basis and suggestions for the internal relationship and sustainable orientation of water-energy-food nexus systems in such water-deficient areas.

A review on water simulation models for the WEF Nexus: development perspective.

The primary impediment to adopting the Water, Energy, and Food (WEF) Nexus is a lack of a comprehensive and user-friendly simulation model. According to our search on Google Scholar and the Scopus databank, WEF Nexus studies can be divided into three broad categories: (1) studies about the nexus concept, (2) studies related to nexus modeling and software development, and (3) case studies. Given that the present study's objective is to review various solutions for WEF Nexus modeling and also to prepare a checklist of available models to find a better model for nexus simulation, we excluded papers and studies which were related to the nexus concept. After that, we split up other papers that talked about nexus and software development into (1) integrated and (2) compiled approaches. Then, it was attempted to identify the shortcomings in each approach. It was shown that the existing integrated WEF Nexus models (such as MUSIASEM, NexSym, CLEW, and ANEMI) had some significant drawbacks compared to compiled alternatives. Several of the major shortcomings of existing integrated models include the following: (1) They did not cover all spatial scales; (2) they included only a limited number of interactions across WEF subsystems; and (3) some of these models were unavailable. Therefore, as a general result of the current study, it was shown that compiled approach is generally preferable compared to available integrated models. In this regard, we tried to find the best water simulation models to implement in the nexus concept. We searched for papers about water simulation models and defined water subsystem requirements in the nexus concept. So, we evaluated each water simulation model based on its ability to cover water subsystem requirements. This work illustrates the capability of a suitable water simulation model to be utilized in the nexus concept and provides a holistic checklist to choose the preferred water simulation model based on the needs of each issue.

Contributions for the Understanding of the São Pedro do Sul (North of Portugal) Geohydraulic and Thermomineral System: Hydrochemistry and Stable Isotopes Studies

São Pedro do Sul thermomineral aquifer system is located in the North of Portugal. Hydrogeochemistry and isotopic studies were conducted in order to improve knowledge of this groundwater system, known since ancient Roman times for their therapeutic properties. One thermomineral spring (NT) and three boreholes (AC1, SDV1 and SDV2) have a mean temperature around 68 °C. Currently, these waters are mainly used in thermal spas and for geothermal energy supply. Major cations and anions were used to identify and characterize different water types and sub-systems. Stable isotopes composition, δ18O and δ2H, have been used to determine the origin and have been used as a first approach to estimate the mean preferential recharge altitude of thermomineral water. The results suggest a single aquifer system with a relative composition of cations and anions and similar mineralization values. δ18O and δ2H values indicate a meteoric origin with no significant evaporation before infiltration. Besides, the isotopic composition points to recharge areas located at altitudes of about 1000 m a.s.l. This suggests a recharge area in the Freita/Arada mountains located NW of the thermomineral poles.