Advancing circular nutrient economy to achieve benefits beyond nutrient loss reduction in the Mississippi/Atchafalaya River basin

Since the establishment of the US Hypoxia Task Force (HTF) in 1997, billions of dollars have been invested in Nutrient Reduction Strategy (NRS) implementation in the Mississippi and Atchafalaya River basins (MARB) to reduce the Gulf of Mexico hypoxic zone size to less than 5,000 km2 (1,930 mi2) by 2035 (USEPA 2022). However, after 25 years of continuous efforts, substantial improvement in water quality has yet to be achieved. The largest hypoxic zone measured was 22,730 km2 (8,776 mi2) in 2017, more than four times the targeted goal (NOAA 2022). Farmers’ adoption of best management practices proposed by state NRS and collaboration among diverse stakeholders are vital to achieving the HTF goals because the majority of nutrient pollution is from agricultural sources (USEPA 2022; Robertson and Saad 2021). Therefore, reorienting the strategy to implement NRS more effectively and motivate farmers’ involvement has been a top priority at the scientific and policy levels. A circular nutrient economy encom- passes responsible nutrient management practices for the reduction of nutrient losses and increased recovery of nutrients from waste streams for reuse in agricultural production. The concept is based on the principles of the circular economy, which seeks to decouple economic growth from resource consumption and environmental degradation. Some countries (e.g., Netherlands and Singapore) have been pioneers in implementing circular nutrient economy practices to close nutrient loops, such as the Phosphate Platform and Singapore's NEWater program. In this viewpoint, we suggest that a circular nutrient economy in the MARB could accelerate NRS implementation and achieve benefits beyond nutrient loss reduction.