System dynamics modeling of livestock and poultry manure supply chains in the water-energy-food-carbon-waste nexus

The utilization of livestock manure is a crucial area for reducing pollution and carbon emissions. However, current research focuses mainly on the impact of individual actors, overlooking a system view. This study uses system dynamics to develop a regional supply chain model for manure resource utilization, examining its overall effects through the water-energy-food-carbon emissions-waste Nexus. The main findings are as follows. (1) Within the Business-as-usual baseline scenario supply chain, comprising small- and medium-sized livestock and poultry farmers (SMS-LPFs), third-party companies (TPCs), and regional crop farmers, water, energy, food, and waste quantities all increase significantly over the simulation period. However, carbon emissions first decrease and then rise, underscoring the need for sustainable supply chain management. (2) Investing in water-saving facilities for manure treatment by SMS-LPFs can significantly reduce water use, energy consumption, carbon emissions, and waste. However, excessive investment may reduce livestock numbers and grain yield growth, whereas modest investment can improve the profits of SMS-LPFs. (3) There is no direct proportional relationship between manure treatment water-saving rates and the supply chain's carbon reduction. Although higher initial water savings enhance carbon reduction, further increases in water savings may eventually hinder carbon mitigation. (4) Improving the precision of government supervision reduces manure leakage and environmental pollution but can paradoxically lead to increased carbon emissions in the supply chain. These insights highlight the importance of adopting a system dynamics approach and integrated management strategies to promote sustainable manure resource use.