Investigating the use of macrophyte stable C and N isotopic ratios as indicators of wetland eutrophication: Patterns in the P-affected Everglades

Abstract

We investigated the use of stable C and N isotopic ratios as indicators of shifts in nutrient limitation of aquatic macrophytes in native Typha (Typha domingensis Pers.) and Cladium (Cladium jamaicense Crantz) communities growing along the well-established phosphorus enrichment gradient of Water Conservation Area 2A of the Florida Everglades. Both Typha and Cladium had significantly different δ15N (∼4‰ and 6‰, respectively) in affected areas, with live leaves of Typha showing elevated δ15N up to 7 km from nutrient inflows. In contrast, changes in δ13C were inconsistent, with an ∼2‰ increase in Typha and a corresponding 2‰ decrease in Cladium of nutrient-affected areas. The isotopic patterns of live leaves were well represented in standing dead leaves of Cladium, but not for Typha, indicating a significant alteration of isotopic signature during senescence for this emergent species. Correlations of isotopic values with tissue nutrients (total C, N, and P) indicated a greater effect of P on the δ13C of both plants and the δ15N of Typha, and a greater importance of N content in determining δ15N of Cladium. These results support the use of macrophyte biomass δ13C and δ15N as an indicator of eutrophication and shifts between N and P limitation. However, the results also highlight potential pitfalls arising from differences in species-specific response to nutrient enrichment. © 2006, by the American Society of Limnology and Oceanography, Inc.