This SGER project will examine how river flood pulsing controls freshwater residence time in coastal wetland basins of Louisiana, and how this control regulates biogeochemical processing of nitrogen (N). The central hypothesis is that the pulsed event of river floods will decrease N retention and removal by wetlands (via denitrification) by drastically decreasing water residence times in entire wetland basins. This, in turn, will lead to increased N loading to the Gulf of Mexico, where anthropogenic N loading has long been implicated in coastal hypoxia and the Northern Gulf Dead Zone. It will take advantage of The Mississippi River flood of 2008, which will be one of the largest pulses of freshwater for wetlands in coastal Louisiana in almost a century. This study will use managed river diversions into the study basins to examine this relationship between freshwater inputs and nitrogen retention.
This research will provide ecosystem managers, who manage valuable, large wetland systems like the Mississippi River Delta and the Florida Everglades, with critical water quality information. One management goal is to prevent excess N from reaching the coastal ocean where many economically important fisheries are located and where excess N causes toxic algal blooms, low dissolved oxygen, and massive fish kills. This experiment will also provide important data on how well coastal wetlands respond to very large pulses of freshwater.
