Will Hydrologically Restored Mississippi River Wetlands Promote Critical Biogeochemical Function?.

Riparian wetlands are essential components of the landscape providing critical functions including buffers for floodwaters, wildlife habitat, and improvement of surface water quality.  Many riparian areas have been functionally removed from the landscape by emplacement of levees alongside the Mississippi River and its distributaries.  Recent restoration efforts along the Mississippi River, in southern Arkansas, include reconnecting the river with the riparian alluvial fringe.  Now that the hydrologic connection has been re-established, we are investigating several microbial-mediated wetland soil biogeochemical processes including ammonification and the important nitrate removal process of denitrification.  We established sampling stations at newly restored wetland sites and at an adjacent control wetland that has been continually flooded by river water.  Soil and microbial processes measured include bulk density, organic matter, total carbon, nitrogen (N) and phosphorus, microbial biomass, potentially mineralizable N and potential denitrification.   Higher soil bulk density and lower soil organic matter, total C, total N, and microbial biomass were observed for the restored site.  The mineralizable N rates were 21.4 ± 7.9 and 85.8 ± 22.0 mg N kg^-1 d^-1 for the restored and control wetland soils, respectively.  The denitrification rate of the restored wetland soils were 7.94±7.44 and 459±60.6 mg N₂O-N kg^-1 d^-1 in the control wetland.  This result suggests that while the hydrologic function of the riparian wetland has been restored, the biogeochemical function of the wetland is substantially lower than that of the control, ranging from four times lower mineralizable N to 58 times lower potential denitrification at the restored site. One possible remedy for speeding up the rate of “biogeochemical restoration” would be the addition organic matter to the restored site to more quickly restore the microbial-mediated biogeochemical functions.