Spring Nutrient Flux to the Gulf of Mexico and Nutrient Balance in the Mississippi River Basin.

Annual total nitrogen and phosphorus load reductions are considered necessary to reduce hypoxia in the Gulf of Mexico. States along the Mississippi River have or are developing nutrient loss reduction strategies in response to federal and state agency guidance and recommendations. Although annual load reductions are important, spring flux of nitrogen and phosphorus may be more important in the annual summertime development of hypoxia in the northern Gulf of Mexico. May flux of nutrients in particular may deserve greater nutrient loss mitigation attention. Relationships between the flux of total nitrogen and phosphorus, nitrate-nitrogen and orthophosphate-P and hypoxia were explored, as well as nitrogen and phosphorus balances in the Mississippi River Basin since 1985. Spring nutrient flux and hypoxia may respond to appropriate 4R nutrient management options and technologies when coupled with optimum in-field and edge-of-field conservation planning. Greater Certified Crop Adviser and agricultural retailer involvement in state-based action plans, and water quality protection will be needed to further address local and downstream water quality challenges.