Effect of NaCl and Typha angustifolia L. on marsh community establishment: A greenhouse study

Post-restoration wetland sites often do not resemble natural wetlands in diversity or richness of native species, in part due to the influence of Stressors such as excess contaminant loads and invasive species. Road salt and the salt-tolerant invasive Typha augustifolia are potential wetland Stressors for which little is known, although it is thought that high salt contaminant loads can lead to invasion of a plant community by T. angustifolia. To understand how an establishing freshwater wetland community responds to NaCl, with regard to both direct and indirect effects (indirect mediated by competition with T. angustifolia), an assemblage of native marsh species was grown from seed in greenhouse microcosms and subjected to treatments of NaCl (0, 100, 250, 500, and 1000 mg·L^-1 solutions) and T. angustifolia (with and without T. angustifolia seed additions) for 194 days. Direct effects of NaCl on final biomass of the native assemblage were observed in the 500 and 1000 mg·L^-1 NaCl treatments. Indirect effects of NaCl on final biomass were observed in the 1000 mg·L^-1 NaCl treatment. Diversity and species richness decreased slightly with increasing NaCl concentration. Evenness increased slightly with increasing NaCl concentration. Individual species responded differently to NaCl and T. angustifolia, suggesting that species composition plays an important role in determining the extent to which NaCl and T. angustifolia influence native community establishment. Results from this experiment suggest that road salt runoff should be considered a Stressor during site selection and that restoration of sites exposed to high levels of NaCl may be less diverse or contain an assemblage of species different than that intended.