Changes in Capacity for Water Quality Improvement (denitrification) through Sea Level-Induced Coastal Wetland Loss.

Coastal Louisiana is experiencing dramatic coastal land losses as a result of additive impacts of sea level rise and regional subsidence. Consequently, there is the potential of a concomitant decrease in ecosystem services with decreases in coastal wetland area. As part of a coastal restoration plan, Louisiana has planned to build several large, sediment diversions that will divert up to 70,000 cfs of Mississippi River water into the adjacent bays. There large sediment diversions will also divert high levels of nitrate into the open water-marsh bay complex. This study examined the effective change in ecosystem services associated with water quality improvement, a result of the conversion of vegetated marsh to an open water estuarine system. Previous studies have found that vegetated marsh soil can denitrify up to 18x faster than an equivalent area of bayou sediment. This study found that the denitrification rate significantly decreased as erosional processes scoured the previous marsh soil, eventually leading to the formation of primarily mineral bay bottom sediment, with little denitrification potential. Consequently, there is a change in N loss processes with sea-level induced coastal erosion, where denitrification and plant uptake, favored in emergent coastal marsh, changes to a plankton-dominated, open water estuarine removal with limited sediment denitrification.