Environmental stress and eutrophication in freshwater wetlands: evidence from carbon and nitrogen stable isotopes in cattail (Typha domingensis Pers.)

Florida’s Everglades is a vast freshwater peatland that has been impacted by the alterations of hydrological pattern and water quality which led to changes in plant species composition and biodiversity. In this study, carbon and nitrogen stable isotopes (δ 13 C and δ 15 N) in cattail ( Typha domingensis ) are evaluated as indicators of environmental changes in the Everglades wetlands along nutrient and hydrological gradients represented by reference sites with total phosphorus (TP) < 10 μg L −1 , transition sites with TP ≥ 10 μg L −1 < 20 μg L −1 and impacted sites with TP ≥ 20 μg L −1 which differed in hydrology or habitats (marsh and canal). Cattail δ 13 C values decreased significantly from reference (–24.1‰), transition (–26.8‰) to the impacted sites (–28.2‰). In contrast, δ 15 N values increased significantly from reference (–5.2‰), transition (2.4‰) to the impacted site (5.9‰). In response to a poor hydrological condition, cattail in marsh area displayed 13 C enrichment (–26.0‰) and 15 N depletion (0.2‰). By contrast, cattail grown in the canal sites with favorable hydropattern displayed 13 C depletion (–27.6‰) and 15 N enrichment (5.9‰) from the canal sites with more favorable hydrological condition. The different patterns for the changes in δ 13 C and δ 15 N in cattail suggested that increased nutrients led to increased stomatal conductance and 13 C fractionation during carbon uptake and decreased 15 N fractionation with increasing nitrogen demand while poor hydrological condition coupled with low nutrients led to reduced plant growth indicated by higher δ 13 C and lower δ 15 N values. Findings from this study suggested that δ 13 C in emerged macrophytes such as cattail can be used as an indicator for environmental stress while δ 15 N is a robust indicator for wetland eutrophication.