Hydrologic connectivity and backswamp water quality during a flood in the Atchafalaya Basin, USA

The Atchafalaya River Basin (ARB) is the largest distributary basin of the Mississippi River and contains the largest tract of forested wetlands in North America. However, hydrologic manipulations for flood control, logging, and mineral extraction have altered how water flows through the ARB and have led to widespread stagnation and hypoxia. To address this, the State of Louisiana has developed a hydrologic restoration plan to increase connectivity between the Atchafalaya River and backswamp areas on the floodplain. Here, we report on water quality changes in the forested wetlands of the ARB during a flood pulse as part of a prerestoration monitoring programme. Monitoring stations were set up in the backswamp to collect data on water levels, dissolved oxygen, turbidity, temperature, and specific conductance. We found that when water levels were high enough to overtop bayou banks and spoil banks, north-to-south flow patterns were reinstated and water quality in the backswamp was improved. Specifically, hypoxic conditions, which had been common before the flood, were alleviated whereas the swamps were receiving flowing, oxygenated river water. The magnitude and duration of dissolved oxygen improvement was dependent on the length of time a site received river water. Our results suggest that stagnation and hypoxia can be alleviated in the ARB by increasing the amount of time river water can access to floodplain swamps.