Emerging Wetlands From River Diversions Can Sustain High Denitrification Rates in a Coastal Delta

It is assumed that to treat excess NO3- high soil organic matter content (%OM) is required to maintain high denitrification rates in natural or restored wetlands. However, this excess also represents a risk by increasing soil decomposition rates triggering peat collapse and wetland fragmentation. Here, we evaluated the role of %OM and temperature interactions controlling denitrification rates in eroding (Barataria Bay-BLC) and emerging (Wax Lake Delta-WLD) deltaic regions in coastal Louisiana using the isotope pairing (IPT) and N-2:Ar techniques. We also assessed differences between total (direct denitrification + coupled nitrification-denitrification) and net (total denitrification minus nitrogen fixation) denitrification rates in benthic and wetland habitats with contrasting %OM and bulk density (BD). Sediment (benthic) and soil (wetland) cores were collected during summer, spring, and winter (2015-2016) and incubated at close to in-situ temperatures (30 degrees C, 20 degrees C, and 10 degrees C, respectively). Denitrification rates were linearly correlated with temperature; maximum mean rates ranged from 40.1-124.1 mu mol m(-2) h(-1) in the summer with lower rates (<26.2 +/- 5.3 mu mol m(-2) h(-1)) in the winter seasons. Direct denitrification was higher than coupled denitrification in all seasons. Denitrification rates were higher in WLD despite lower %OM, lower total N concentration, and higher BD in wetland soils. Therefore, in environments with low carbon availability, high denitrification rates can be sustained as long as NO3- concentrations are high (>30 mu M) and water temperature is >10 degrees C. In coastal Louisiana, substrates under these regimes are represented by emergent supra-tidal flats or land created by sediment diversions under oligohaline conditions (<1 ppt).

Automated summary

This study evaluated denitrification rates in sediment and wetland habitats in coastal Louisiana, finding that high denitrification rates can be sustained in environments with low carbon availability as long as NO3- concentrations are high (>30 μM) and water temperature exceeds 10 degrees Celsius.