Abstract
BackgroundFlorida’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 (δ13C and δ15N) 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).ResultsCattail δ13C values decreased significantly from reference (–24.1‰), transition (–26.8‰) to the impacted sites (–28.2‰). In contrast, δ15N 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 13C enrichment (–26.0‰) and 15N depletion (0.2‰). By contrast, cattail grown in the canal sites with favorable hydropattern displayed 13C depletion (–27.6‰) and 15N enrichment (5.9‰) from the canal sites with more favorable hydrological condition.ConclusionsThe different patterns for the changes in δ13C and δ15N in cattail suggested that increased nutrients led to increased stomatal conductance and 13C fractionation during carbon uptake and decreased 15N fractionation with increasing nitrogen demand while poor hydrological condition coupled with low nutrients led to reduced plant growth indicated by higher δ13C and lower δ15N values. Findings from this study suggested that δ13C in emerged macrophytes such as cattail can be used as an indicator for environmental stress while δ15N is a robust indicator for wetland eutrophication.
Highlights
Florida’s Everglades is the largest subtropical peatland in the USA with its historic geochemistry and biological community characterizing an oligotrophic ecosystem (Richardson 2010)
Study sites at cell 3 and cell 4 of the Stormwater Treatment Areas (STAs)-1W, and E0 and F1 of WCA-2A that received direct Everglades Agricultural Area (EAA) discharges are highly enriched with total phosphorus (TP) (> 20 μg L−1)
Total N and dissolved inorganic N (DIN) concentrations were higher at the near inflow sites than the marsh interior sites, except for U3, the interior site of WCA-2A, which is enriched with ammonium and total N (TN)
Summary
Florida’s Everglades is the largest subtropical peatland in the USA with its historic geochemistry and biological community characterizing an oligotrophic ecosystem (Richardson 2010). A large portion of the Everglades peatland immediately south of Lake Okeechobee was converted into farmlands, i.e., Everglades Agricultural Area (EAA). Increased P loads have shifted portions of the ecosystem from oligotrophic to eutrophic states. The sawgrass in northern WCA-2A, an area that has received EAA discharge, has been replaced by cattail which was not present in large quantity in the historic Everglades (Sklar et al 2005). 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. Carbon and nitrogen stable isotopes (δ13C and δ15N) 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)
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