Investigating the use of macrophyte stable C and N isotopic ratios as indicators of wetland eutrophication: Patterns in the P-affected Everglades
Inglett, Patrick W., and K. Ramesh Reddy
Limnol. Oceanogr., 51(5), 2006, 2380–2387

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 d¹⁵N (~4‰ and 6‰, respectively) in affected areas, with live leaves of Typha showing elevated d¹⁵N up to 7 km from nutrient inflows. In contrast, changes in d¹³C 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 d¹³C of both plants and the d¹⁵Nof Typha, and a greater importance of N content in determiningd¹⁵N of Cladium. These results support the use of macrophyte biomass d¹³C and d¹⁵N 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.