Global Nitrogen Market Disruptions Reshape Local Critical Zone Dynamics

Human management of nutrients plays a central role in shaping processes within the Critical Zone, yet economic decision-making remains weakly integrated into its analysis. This study presents a coupled modeling framework that links global economic dynamics with spatially explicit land, water, and nutrient processes to examine how nitrogen use mediates interactions between human systems and the Critical Zone. Farmers are represented as adaptive agents who adjust nitrogen application, land allocation, and water use in response to prices, policies, and local constraints, allowing global demand and trade to influence local resource use. We evaluate a set of nitrogen price and supply shock scenarios to assess their impacts on food security, environmental outcomes, and market dynamics. Price-based shocks produce moderate and spatially heterogeneous responses, with limited changes in crop prices, malnutrition, and nitrogen leaching, as production and trade adjust across regions. In contrast, a global reduction in nitrogen manufacturing capacity generates large, system-wide effects, including substantial increases in crop prices and malnutrition, alongside sharp reductions in nitrogen use and trade. Regional results show that responses vary with baseline input intensity and substitution capacity, with stronger yield impacts in high-input systems and greater reliance on land and water adjustments under constrained nitrogen availability. These findings highlight the importance of distinguishing between price and quantity shocks in shaping global agricultural and environmental outcomes. More broadly, the results demonstrate that nitrogen response functions as a key human-controlled flux within the Critical Zone, linking economic behavior to nutrient cycling, water use, and land dynamics. Integrating socio-economic processes into Critical Zone analysis provides a pathway for understanding how global market forces and local decision-making jointly determine patterns of resource use and environmental change.