Disparities in nitrogen and phosphorus management across time and space: a case study of the Chesapeake Bay using the CAFE framework
Efficient management of nitrogen (N) and phosphorus (P) is imperative for sustainable agriculture, resource conservation, and reducing environmental pollution. Despite progress in on-farm practices and urban wastewater treatment in the Chesapeake Bay (CB) watershed, limited attention has been given to nutrient transport, use, and handling beyond farms. This study introduces the hierarchical CAFE (Cropping system, Animal-crop system, Food system, and Ecosystem) framework to evaluate the nutrient management performances within the watershed. We first develop a three-decade county-level nutrient budget database (1985-2019), then analyze the spatiotemporal patterns of N and P budgets and use efficiencies within the four CAFE hierarchies. Results indicate a sizable increase in potential N and P losses beyond crop fields (at the Animal-crop system, Food system, and Ecosystem), surpassing those on cropland in over 90% of counties. To address these system-wide trade-offs, we estimate the nutrient resources in waste streams beyond croplands, which could theoretically offset synthetic fertilizer inputs in over 60% of counties. Additionally, the growing imbalance in excess N and P across systems that increases the N:P ratio of potential losses could pose risks to downstream aquatic ecosystems. By utilizing a systematic approach, this novel application of the CAFE framework reveals trade-offs and synergies in nutrient management outcomes that transcend agro-environmental and political boundaries, underscore the disparities in N and P management, and identify unique opportunities for enhancing nutrient management across systems within the CB watershed.