We thank Arnbjerg-Nielsen and co-authors for their constructive contribution. We endorse their key comments and suggestions on how to increase awareness of and action on water quality interactions in the water–energy–food (WEF) nexus. Here, we advance the discussion, commenting on the scope of water quality to embrace ecosystem as well as human needs, and the importance of transdisciplinarity and focusing at the city/aquifer/drainage basin scale in WEF nexus hotspots in ensuring that water quality is considered in WEF nexus approaches. We also identify how recent global events, the COVID-19 pandemic and the 26th Conference of the Parties to the UN Framework Convention on Climate Change (UNFCCC COP 26), may intensify the WEF nexus and its water quality interlinkages, highlighting the need to weave WEF considerations into addressing the United Nations Sustainable Development Goals and the climate and biodiversity emergencies.

Sustainable and resilient food systems depend on sustainable and resilient water management. Resilience is characterised by overlapping decision spaces and scales and interdependencies among water users and competing sectors. Increasing water scarcity, due to climate change and other environmental and societal changes, makes putting caps on the consumption of water resources indispensable. Implementation requires an understanding of different domains, actors, and their objectives, and drivers and barriers to transformational change. We suggest a scale-specific approach, in which agricultural water use is embedded in a larger systems approach (including natural and human systems). This approach is the basis for policy coherence and the design of effective incentive schemes to change agricultural water use behaviour and, therefore, optimise the water we eat.

Energy conservation is a clear function of torpor. Although many studies imply that torpor is also a water-saving strategy, the experimental evidence linking water availability with torpor is inconclusive. We tested the relative roles of water and energy shortages in driving torpor, using the Siberian hamster Phodopus sungorus as a model species. To account for the seasonal development of spontaneous heterothermy, we used male hamsters acclimated to short (8L:16D, SP; n = 40) and long (16L:8D, LP; n = 36) photoperiods. We continuously measured body temperature (Tb) during consecutive 32 h of complete removal of water, food, or both, separated by 7.5 d recovery periods. We predicted that all deprivation types would increase the frequency of spontaneous torpor in SP, and induce torpor in LP-acclimated hamsters. Individuals underwent each deprivation type twice in random orders. Food and water deprivation did not induce torpor in LP-acclimated P. sungorus. Patterns of torpor expression varied among deprivation types in SP individuals. Torpor frequency was significantly lower, but bouts were ∼2 h longer and 2.5 °C deeper, during water deprivation compared to food and food-and-water deprivation. Heterothermic responses to all deprivation types were repeatable among individuals. Different torpor patterns during water and food deprivation suggest that water and energy shortages are distinct physiological challenges. Deeper and longer bouts during water deprivation likely led to higher energy and water savings, while shorter and shallower bouts during fasting may reflect a trade-off between energy conservation and food-seeking activity. The lack of a difference between food- and food-and-water-deprived hamsters suggests a higher sensitivity to food than water shortage. This supports the traditional view that energy conservation is the major function of torpor, but suggests that water shortages may also modulate torpor use. The high repeatability of thermoregulatory responses to resource deprivation suggests that these may be heritable traits subject to natural selection.

In this work we demonstrate that the synergistic combination of organic molecules extracted from food waste can empower different types of carboxylated gold nanoparticles (Au NPs) in removal of Cr(VI) species from both milliQ and real water solutions. In particular, chitosan extracted from shrimp’s shell and dissolved in an acidic active medium based on a 1:3 M mixture of ascorbic and citric acid allows citrate-capped Au NPs to improve their abatment efficiency from 18.4 to > 99% in milliQ and 80.6% in drinking water. When citrates are exchanged with 3-mercaptopropionic or 11-mercaptoundecanoic acids, the efficiency reaches 100% in both milliQ and drinking water. 11-mercaptoundecanoic acid is found to be the best capping agent in terms of efficiency and stability. Crossing of cyclic voltammetry and UV–Vis data enabled to define the main role of each individual component in abatment of Cr(VI). This study further advances research on the rational design of hybrid nanoparticle/polymer systems for environmental remediation, inspired by criteria of circular economy and environmental sustainability.

The formation of societies is based on the dynamics of spatial clustering, which optimizes economies of scale in the management of the water–energy–food (WEF) nexus. Energy and food are determinant measures of prosperity. Using the WEF nexus as an indicator, we evaluate the social impacts of the current (2022) conflict and in particular the economic sanctions on Russia. As Russia and Ukraine are major global suppliers of energy sources, food, and fertilizers, new threats arise by their limitations and the rally of prices. By analyzing related data, we show the dramatic effects on society, and we note that cities, which depend on a wider area for energy and food supplies, are extremely vulnerable. This problem was substantially worsened due to the large-scale urbanization in recent decades, which increased the distance from food sources. We conjecture that the Western elites’ decision to sanction Russia dramatically transformed the global WEF equilibrium, which could probably lead to the collapse of social cohesion.

The formation of societies is based on the dynamics of spatial clustering, which optimizes economies of scale in the management of the water–energy–food (WEF) nexus. Energy and food are determinant measures of prosperity. Using the WEF nexus as an indicator, we evaluate the social impacts of the current (2022) conflict and in particular the economic sanctions on Russia. As Russia and Ukraine are major global suppliers of energy sources, food, and fertilizers, new threats arise by their limitations and the rally of prices. By analyzing related data, we show the dramatic effects on society, and we note that cities, which depend on a wider area for energy and food supplies, are extremely vulnerable. This problem was substantially worsened due to the large-scale urbanization in recent decades, which increased the distance from food sources. We conjecture that the Western elites’ decision to sanction Russia dramatically transformed the global WEF equilibrium, which could probably lead to the collapse of social cohesion.

Data availability: Data will be made available on request. | Supplementary materials are available online at https://www.sciencedirect.com/science/article/pii/S0043135422007916?via%3Dihub#sec0017 . | Copyright © 2022 The Author(s). The Multi-Sectoral Water Circularity Assessment (MSWCA) is a methodological framework developed for circularity assessment of the Water-Energy-Food-Ecosystems nexus. It involves five methodological steps and includes an indicators list for the selection of case-specific indicators. This study expands the MSWCA to provide a systematic approach for selecting indicators, considering system's circular actions and multi-functionality, the capture of implemented changes, the three CE principles and the sustainable development goals. Furthermore, this study differentiates between benchmark and dynamic circularity assessment and applies the expanded MSWCA in a water system of the HYDROUSA H2020 project. The benchmark assessment indicates that the HYDROUSA system achieves a 75% increase of water circularity, 76–80% increase of nutrients circularity and 14% reduction of operational `carbon footprint compared to the baseline scenario. The dynamic assessment highlights that additional measures can improve the system's circularity performance (e.g. water circularity can reach 94%) and mitigate risks occurring from uncontrollable changes. | This research was supported by the Horizon 2020 Research and Innovation Program HYDROUSA (Grant Agreement No 776643).

The safety of the water–energy–food (WEF) system in the China–Pakistan Economic Corridor (CPEC) is critical to the sustainable development of resources, the economy, and society in the region. This paper uses the projection pursuit model of a real-code accelerated genetic algorithm (RAGA-PP) to comprehensively evaluate the WEF system security of the CPEC for the period 2000–2016. The results show that from 2000 to 2016, the projection value of the WEF system was reduced from 2.61 to 0.53, and the overall system security showed a downward trend. Moreover, the CPEC increased by 6.13 × 10⁷ people, resulting in a rapid decrease in per capita water resources and decreased security of the water resources subsystem. With the rising social and economic development in recent years, the per capita energy consumption has likewise risen, leading to a decline in the energy subsystem. At the same time, the per capita grain output in the study area has increased from 185 to 205 kg, and the safety of the food subsystem has been enhanced. However, the significant increase in irrigated areas (from 1.82 × 10¹⁰ to 1.93 × 10¹⁰ hectares) has further highlighted the contradiction between the supply and demand of surface water resources, and the number of tube wells increased by 7.23 × 10⁵, resulting in the consumption of a large amount of electricity and diesel resources. The water–energy (WE) subsystem also became less safe. With the implementation of water resources management policies over the past few decades, the proportion of agricultural water consumption dropped from 95.06% in 2000 to 93.97% in 2016, and the safety of the water–food (WF) subsystem increased. Unfortunately, agricultural irrigation consumes a large amount of power resources, leading to a reduction in the security of the energy–food (EF) subsystem. The research results from the present study could provide a scientific basis for the coordinated development of WEF systems across the CPEC region.