Integrating human food consumption choices into ecohydrological modelling
Illustrated chart showing what if food choices became the next BMP?
Authors: Ismail Jesna, Marali Kalra, Lisa Wainger, Raj Cibin
What is the issue?
Changes in human dietary preferences drive agricultural production systems. Transitioning to reduced meat consumption or shifts toward plant-based diets could reduce demand for livestock products and reshape agricultural production systems by reducing livestock and feed production and increasing food production. Reduction in livestock agriculture would have significant impacts on water quality. The Susquehanna River Basin, the largest tributary to the Chesapeake Bay, contributes more than 40% of the total nitrogen load to the Bay, with a disproportionate share originating from livestock-intensive agricultural regions in south-central Pennsylvania. These areas are characterized by concentrated animal operations, high manure production, and long-term nutrient surpluses that exceed local crop uptake capacity. Most nutrient reduction strategies in the Bay watershed focus on supply-side best management practices (BMPs) such as cover crops, buffers, and improved manure application timing. While these practices have reduced nutrient losses, progress has slowed and persistent manure surpluses continue to drive nutrient export from hotspot subbasins.
What did we find and why does it matter?
Diet-driven shifts in agricultural production substantially alter nutrient cycling and export in the SRB, with outcomes determined by changes in livestock systems. Two scenarios were evaluated relative to current conditions: an ovo-lacto vegetarian diet (plant-based foods plus dairy and eggs) and a vegan diet (entirely plant-based) scenario. Total caloric demand from the basin was held constant, with consumption shifts assumed to translate directly into proportional changes in basin-scale production and land use. Dietary change is assumed to occur across the food system, such that shifts in consumption are reflected in agricultural production rather than trade. Both scenarios reduced feed-crop demand and agricultural land area, but water-quality responses differed significantly.
The vegan scenario, which eliminated all livestock, yielded the largest improvements, reducing total nitrogen and total phosphorus loads by 21% and 38%, respectively (Figure 1). These reductions were driven by the removal of manure inputs, improved fertilizer–crop alignment, and conversion of former feed and forage lands to perennial prairie vegetation. The largest water quality improvements were estimated in high-loading sub-watersheds in Lancaster County and nearby regions, indicating that dietary transitions can directly reduce nutrient export from dominant source areas.
Figure 1. Average annual total (a) nitrogen and (b) phosphorus loads from the Susquehanna River Basin to the Bay under baseline, ovo-lacto vegetarian, and vegan dietary scenarios. Percent change is shown relative to baseline conditions.
In contrast, the ovo-lacto vegetarian scenario was estimated to yield limited or adverse water-quality responses. Despite a 10% reduction in cropland area and a 28% decline in total nitrogen inputs, nitrogen loads at the Susquehanna outlet decreased by only 2.6%, while phosphorus loads increased by 13.3% (Figure 1). Holding total caloric production constant, meat calories were replaced by increased dairy and egg production, expanding dairy and layer hen populations, and increasing manure generation by ~12%. Manure was applied based on crop nitrogen demand, which concentrated phosphorus inputs on a smaller cropland area, leading to increased phosphorus runoff despite reduced agricultural area.
These model simulation results highlight livestock production as a dominant control on watershed nutrient export. Dietary shifts that reduce meat consumption without addressing manure-intensive livestock systems may fail to improve—and can worsen—water quality, whereas strategies that substantially reduce or eliminate livestock can fundamentally reorganize nutrient cycling and export.
What did we do?
We used a watershed-scale ecohydrological modelling framework to link human dietary demand with land use, livestock production, and nutrient export. Three dietary scenarios: baseline, ovo-lacto vegetarian, and vegan, were translated into corresponding changes in crop area, pasture and hay extent, livestock populations, and manure availability within the Susquehanna River Basin. These changes were implemented in a previously calibrated and validated Soil and Water Assessment Tool (SWAT) model configured to represent current agricultural and hydrological conditions in the SRB. Land-use transitions, crop rotations, manure redistribution, and fertilizer inputs were modified directly in the model’s management schedules to ensure internally consistent nutrient cycling. Nutrient responses were evaluated at multiple spatial scales, including landscape-level nutrient fluxes, subbasin-scale spatial patterns, and total N and phosphorus loads delivered at the watershed outlet. This approach enabled direct comparison of how alternative dietary futures reshape agricultural systems and downstream water-quality outcomes.
Publications completed for this work
Jesna, I., Marali, K., Wainger, L., and Cibin, R. (in preparation). Is dietary transition the solution to improve water quality in the Chesapeake Bay? Integrating human food consumption choices into ecohydrological modelling.
Saha, A., Saha, G. K., Cibin, R., Drohan, P. J., White, C., Veith, T., Kleinman, P., and Spiegel, S. (2022). Evaluation of water quality benefits of manure-shed-based manure management in the Susquehanna River Basin. Journal of Environmental Quality. https://doi.org/10.1002/jeq2.20429
