Existing wetland conservation programs miss nutrient reduction targets

Abstract Increasing coastal hypoxia results largely from riverine export of excess nutrients used for fertilization of row crops1–4 and has the potential to fundamentally change marine habitats over the next millennium5. Nutrient-rich runoff from agricultural lands in the Mississippi/Atchafalaya River Basin must decline by half to begin reducing hypoxia in the Gulf of Mexico6,7. Nutrient mitigation measures should target hot-spots of excess fertilizer application or manure production8,9 and numerous studies10–15 identify wetland restoration as capable of achieving these targets. Here, process-based physical modeling evaluated the efficacy of existing wetland conservation programs to reduce nutrient export to the Gulf of Mexico. We show that full adoption of two programs meet 10% to 60% of nutrient reduction targets for agriculture, lower reductions than prior estimates16,17 due primarily to refined estimates of subsurface storage and geographic disconnect between restorable lands18 and heavily fertilized croplands. Daily model resolution captured the seasonal and stormflow dynamics inhibiting wetland nutrient removal due to peak wetland effectiveness being asynchronous with nutrient inputs19. Considering these limitations, and large legacy pools of nitrate in groundwater20,21, efforts should balance measures that limit new inputs and maximize treatment across all hydrologic flowpaths from field margins, through groundwater, and ultimately to rivers.