Nitrogen discharge in the Gulf of California from wastewater, agriculture, livestock, and aquaculture

ABSTRACT Excessive nitrogen inputs from agriculture, urban wastewater, livestock, and aquaculture are disrupting coastal ecosystems in the Gulf of California through eutrophication, hypoxia, and harmful algal blooms. This study quantifies nitrogen discharges from these four major sources across 29 coastal municipalities using spatially explicit data on land use, demographics, and wastewater infrastructure. Results show that agricultural runoff is the dominant contributor, accounting for 72.7% of total nitrogen loads, followed by urban wastewater (12.2%), livestock (9.4%), and shrimp aquaculture (5.7%). Nutrient hotspots are concentrated in Mexicali, Ahome, Guasave, and Culiacán, where irrigation, population density, and aquaculture intensity converge. Wastewater emerges as a strategically manageable source, with targeted investments of $586.16 million USD estimated to close treatment gaps. The findings provide a first-order spatial diagnosis of nutrient pollution in the region, supporting science-based prioritization of mitigation efforts to safeguard marine ecosystems and coastal livelihoods.