Figure 3.

Ordinary least squares regressions for total organic carbon content against black carbon across seagrass and mangrove sediments. With the exception of Little Swanport estuary seagrass sediments, the regressions are constructed from measurements of black carbon (BC) as isolated via chemothermal oxidation (CTO), concentrated nitric acid oxidation (NAO), and dilute chromic acid oxidation (CAO) down seagrass and mangrove sediment cores along a sand-to-mud gradient of (○) the tropical lagoon Salut–Mengkabong, (●) the temperate estuary Little Swanport, and (▲) the surface sediments of the subtropical Shantou wetlands. For Little Swanport seagrass sediments, the amount of BC isolated via NAO was calculated from regressions of loss on ignition of TOC vs total organic matter, and black organic matter vs BC, constructed across the seagrass and mangrove sediments of Salut–Mengkabong (Supplementary Figures S3 and S4). The regressions represent the sum of a proportional increase in BC associated with soil carbon washout and BC supply to the sediment from aeolian transport, as measured by the intercept. The difference between the mangrove regressions (ANCOVA) from Salut–Mengkabong and the Shantou wetlands (d) were not statistically different (P = 0.15 of being the same). There was no evidence of serial correlation between the residuals; and so, the 95% confidence estimators (dotted lines) may be considered reasonable (see Supplementary Table S1 for regression equations and estimator parameters).