Proceedings of the 2022 Mississippi Water Resources Conference

Year: 2022 Authors: Sample A., Ervin G., Turnage G.

Increased nutrient inputs into the Mississippi River resulting from extensive agricultural activity and loss of wetlands in the Lower Mississippi Alluvial Valley (LMAV) can be mitigated via wetland restoration initiatives. The goal of this study was to establish a model system for studying the effects of species invasion and eutrophication on floodplain wetlands in the southeastern US. A multi-year mesocosm study was developed in which two regionally non-weedy emergent macrophyte species—Juncus effusus (Common Rush) and Schoenoplectus tabernaemontani (Softstem Bulrush)—and two common weedy emergent macrophyte species—Typha latifolia (Broadleaf Cattail) and Phragmites australis (Common Reed)—were chosen as model species. The first year of the mesocosm study was aimed at determining baseline growth and nutrient removal from the water column for each species, grown in a monoculture setting, under a standardized flooding and nutrient availability regimen based on water quality studies and flood duration data from the LMAV. Results from the first year showed clear differences in growth patterns between the weedy and non-weedy species. As expected, the weedy species exhibited faster radial spread and reached taller maximum heights than the non-weedy species. The non-weedy species also showed relatively consistent growth rates through the growing season, whereas the weedy species displayed relatively short bursts of rapid growth prior to flowering. Despite those differences in growth, we saw no differences in nutrient removal from the water column based on species or species designation (weedy or non-weedy), with over 50% removal of total nitrogen by all species. This work will be followed by simulated scenarios of species invasion in the second year (monoculture and mixed species mesocosms) and eutrophication (mixed species mesocosms with baseline and increased nitrogen concentrations) in the third year. The results of this work should be useful for wetland managers regarding species selection for project design and in planning adaptive management strategies considering these two major wetland management challenges.