The vulnerability of environmental systems to human activities depends on the type and magnitude of the anthropogenic stresses, and on the ability of the natural system to adapt to them. This vulnerability is especially acute in low-lying deltaic systems such as the Mississippi River Delta, subject to the influence of a continental-scale river basin, coastal processes, and intensive human use and development. Delta restoration (system design toward a resilient, self-sustaining delta) is a generic environmental problem worldwide in which human and natural dynamics are strongly and inherently coupled. The urgent need for wetland restoration and rehabilitation at large spatial scales have been addressed through the diversion of riverine water from the Mississippi River. Large river diversions have been proposed that can result in self-sustaining deltaic landscapes under different scenarios of sea level rise and subsidence.  Modeling results demonstrate the adaptation of deltaic wetlands to climate and land use constraints.  The challenge to develop bold new ideas of such river management diversions to reintroduce sediment to the coast are further complicated by how the chemistry of the river has changed over the last four decades. Role of denitrification in these emerging restored deltaic landscapes is critical to reducing risks to impaired coastal waters. The combination of water residence time and soil organic matter in rehabilitated wetlands controls the fate of nitrate.  
Results/Conclusions

The Mississippi River delta faces another round of human control through expanded public work projects following the catastrophic realities of hurricanes in 2005 and 2008. Urgent solutions to post-Katrina issues in the Mississippi River delta involve providing increased protection to communities while expanding river processes to restore wetland landscapes, which will also require changing approaches to agricultural land use to reduce nitrogen load and risks of eutrophication. The challenge is even greater with complex interactions of land use change throughout the catchment and the coast with projected sea level rise that must be resolved to accommodate bold new river management plans. Changes in sediment and nutrient chemistry of major river systems complicate the restoration of deltaic regions around the world as restoration programs to restore wetlands are constrained by potential problems with coastal eutrophication. However, projects to restore river-dominated deltas have to consider major diversions to provide the resources for wetlands to adapt to a changing climate.