A Systems Approach To Assess Trade Dependencies in U.S. Food-Energy-Water Nexus

Investigating a microbial approach to water conservation: Effects of Bacillus subtilis and Surfactin on evaporation dynamics in loam and sandy loam soils

Semi-arid regions faced with increasingly scarce freshwater resources must manage competing demands in the food-energy-water nexus. A possible solution modifies soil hydrologic properties using biosurfactants to reduce evaporation and improve water retention. In this study, two different soil textures representative of agricultural soils in Kansas were treated with a direct application of the biosurfactant, Surfactin, and an indirect application via inoculation of Bacillus subtilis. Evaporation rates of the wetted soils were measured when exposed to artificial sunlight (1000 W/m2) and compared to non-treated control soils. Experimental results indicate that both treatments alter soil moisture dynamics by increasing evaporation rates by when soil moisture is plentiful (i.e., constant rate period) and decreasing evaporation rates by when moisture is scarce (i.e., slower rate period). Furthermore, both treatments significantly reduced the soil moisture content at which the soil transitioned from constant rate to slower rate evaporation. Out of the two treatments, inoculation with B. subtilis generally produced greater changes in evaporation dynamics; for example, the treatment with B. subtilis in sandy loam soils increased constant rate periods of evaporation by 43% and decreased slower rate evaporation by 49%. In comparing the two soil textures, the sandy loam soil exhibited a larger treatment effect than the loam soil. To evaluate the potential significance of the treatment effects, a System Dynamics Model operationalized the evaporation rate results and simulated soil moisture dynamics under typical daily precipitation conditions. The results from this model indicate both treatment methods significantly altered soil moisture dynamics in the sandy loam soils and increased the probability of the soil exhibiting constant rate evaporation relative to the control soils. Overall, these findings suggest that the decrease in soil moisture threshold observed in the experimental setting could increase soil moisture availability by prolonging the constant rate stage of evaporation. As inoculation with B. subtilis in the sandy loam soil had the most pronounced effects in both the experimental and simulated contexts, future work should focus on testing this treatment in field trials with similar soil textures.

Redundancy, Diversity, and Modularity in Network Resilience: Applications for International Trade and Implications for Public Policy

Sustainability is increasingly concerned with the complex interactions between nature and society, and we need to seek solutions towards the challenges that threaten humanity's collective wellbeing. Towards this end, it is critical to advance the application of research examining the dynamic interactions of the components of complex social-ecological systems and their emerging properties. A key research area is on advancing tools and strategies relevant to the evaluation and strengthening of resilience. Redundancy, diversity, and modularity are important characteristics of resilience with a high potential for application in various critical social-ecological systems. This paper provides a critical overview of the theoretical underpinnings of modularity and redundancy and their application in measuring resilience of trade networks with implications for public policy and institutional design.

The Water Footprint of the United States

This paper commemorates the influence of Arjen Y. Hoekstra on water footprint research of the United States. It is part of the Special Issue “In Memory of Prof. Arjen Y. Hoekstra”. Arjen Y. Hoekstra both inspired and enabled a community of scholars to work on understanding the water footprint of the United States. He did this by comprehensively establishing the terminology and methodology that serves as the foundation for water footprint research. His work on the water footprint of humanity at the global scale highlighted the key role of a few nations in the global water footprint of production, consumption, and virtual water trade. This research inspired water scholars to focus on the United States by highlighting its key role amongst world nations. Importantly, he enabled the research of many others by making water footprint estimates freely available. We review the state of the literature on water footprints of the United States, including its water footprint of production, consumption, and virtual water flows. Additionally, we highlight metrics that have been developed to assess the vulnerability, resiliency, sustainability, and equity of sub-national water footprints and domestic virtual water flows. We highlight opportunities for future research.

Analysis and vulnerability of the international wheat trade network

Wheat is one of the three basic cereals providing the necessary calorific intake for most of the world's population. For this reason, its trade is critical to many countries in order to fulfil their internal demand and strategic stocks. In this paper, we use complex network analysis tools to study the international wheat trade network and its evolving characteristics for the period 2009-2013. To understand the vulnerability of each country's dependence on the imports of this crop we have performed different analyses, simulating shocks of varying intensities for the main wheat producers, and observed the population affected by the production drop. As a result, we conclude that globally the network is slightly more resilient than four years previously, although at the same time some developing countries have slipped into a vulnerable situation. We have also analysed the effects of a global shock affecting all major producers, assessing its impact on every country. Some comments on the COVID-19 outbreak and the political decisions taken by governments following the pandemic declaration are included, observing that given their capital-intensive characteristics, no negative effects should currently be expected in the wheat market.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12571-020-01117-9.

What Induces the Energy-Water Nexus in China's Supply Chains?

Given energy and water scarcity, it is necessary to develop an in-depth understanding of the energy-water nexus in China for its sustainable development. Previous studies have focused on nexus accounting, synergy conservation, and system optimization, but its induction mechanism along the supply chains has not been uncovered. This paper proposes a top-down structural path analysis (SPA) and combines it with an environmental input-output model (EIOM) to identify the critical final demand, consumption sectors, and supply chain paths inducing the energy-water nexus. The results show that the largest final demand of water for energy production (WFE) is capital formation, while the largest final demand of energy for water supply (EFW) is urban consumption. The distribution of WFE at different production layers shows an inverted U shape. Most WFE is indirectly consumed by other sectors, such as construction, through three-step supply chain paths. In contrast, the distribution of EFW shows a L shape, and most EFW is directly consumed by the final demand. In addition, some critical supply chain paths inducing more WFE and EFW are identified. Finally, some policies targeting the energy-water nexus management are proposed, which are conducive to resource conservation and the sustainable supply of energy and water.