Will hydrologic restoration of Mississippi River riparian wetlands improve their critical biogeochemical functions?

Abstract

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 wetlands have been hydrologically disconnected from the Mississippi River by a vast system of levees, altering the ecosystem services provided by these riparian zones. Efforts are underway to restore these ecosystem services, however previous research demonstrated that the statutory requirements guiding wetland restoration do not adequately consider soil biogeochemical cycling. We examined soil properties and biogeochemical indicators of nitrogen cycling to assess soil recovery in a recently hydrologically restored riparian wetland. This restored wetland, reconnected with the river for approximately two years, was compared to a nearby reference wetland where the river connection has been constant. Seasonal measurements included bulk density, total carbon, nitrogen and phosphorus, microbial biomass nitrogen, potentially mineralizable nitrogen (PMN) and potential denitrification. There were significant differences found for nearly all measured soil properties with higher bulk density and lower total C, total N, microbial biomass, PMN and potential denitrification at the restored compared to the reference site. The PMN and potential denitrification at the restored site plots were 27–46% and 2% (respectively) of the values measured at the reference site. This clearly demonstrates that while the regulatory indicators of success are improving, some critical biogeochemical functions of the restored sites are significantly lower than the reference site two years after hydrologic restoration.