Loss‐on‐Ignition Method to Assess Soil Organic Carbon in Calcareous Everglades Wetlands

Abstract

Measurement of soil carbon (C) is important for determining the effects of Everglades restoration projects on C cycling and transformations. Accurate measurement of soil organic C by automated carbon–nitrogen–sulfur (CNS) analysis may be confounded by the presence of calcium carbonate (CaCO3) in Everglades wetlands. The objectives of this study were to compare a loss‐on‐ignition (LOI) method with CNS analysis for assessment of soil C across a diverse group of calcareous Everglades wetlands. More than 3168 samples were taken from three soil depths (floc, 0–10, 10–30 cm) in 14 wetlands and analyzed for LOI, total C, and total calcium (Ca). The LOI method compared favorably to CNS analysis for LOI contents ranging from 0 to 1000 g kg−1 and for soil total Ca levels from 0 to 500 g Ca kg−1. For all wetlands and soil depths, LOI was significantly related to total C (r2 = 0.957). However, LOI was a better predictor of total C when LOI exceeded 400 g kg−1 because of less interference by CaCO3. Total C measurement by CNS analysis was problematic in soils with high total Ca and low LOI, as the presence of CaCO3 confounded C analysis for LOI less than 400 g kg−1. Inclusion of total Ca in regression models with LOI significantly improved the prediction of total C. Estimates of total organic C by CNS analysis were obtained by accounting for C associated with CaCO3 by calculation, with results being similar to total organic C values obtained from LOI analysis. The proportion of C in organic matter measured by the LOI method (51%) was accurate and applicable across wetlands, soil depths, and total Ca levels; thus LOI was a suitable indicator of total organic C in Everglades wetlands.