Potential nitrate removal from a river diversion into a Mississippi delta forested wetland

Abstract The objectives of this study were: (1) to carry out a baseline study of water quality parameters in the Maurepas forested wetland in Louisiana, USA; and (2) to estimate potential nitrate uptake of a proposed Mississippi River diversion into the wetland. Water sampling trips were carried out monthly from April to October 2000. Average water quality parameter concentrations and ranges were: nitrate 0.008 mg-N l −1 (non-detectable (n.d)-0.143 mg-N l −1 ); ammonium 0.007 mg-N l −1 (n.d-0.048 mg-N l −1 ); total nitrogen 0.577 mg-N l −1 (0.193–1.285 mg-N l −1 ); phosphate 0.034 mg-P l −1 (n.d-0.369 mg-P l −1 ); total phosphorus 0.055 mg-P l −1 (0.022–0.424 mg-P l −1 ); total suspended sediment 16 mg l −1 (4–101 mg l −1 ), salinity 3‰ (0–12‰), and chlorophyll a 11 μg l −1 (1–31 μg l −1 ). A UNET hydrodynamic model was constructed to predict hydrologic patterns as diverted water flowed through the Maurepas swamp. The study area was divided into 53 storage cells based on topographical features that mostly consisted of natural bayous and degraded artificial levees. Nitrate loading was high in the initial cells and removal efficiencies were on the order of 40–70%. Loading in subsequent cells was much lower and simulated nitrate retention was greater than 90%. Since most nutrients will be retained in the swamp, the proposed diversion of Mississippi River water should not cause adverse water quality conditions or extreme or persistent algal blooms in the Lake Maurepas.