Comparing Carbon Sequestration Rates in Tropical and Temperate Wetlands Using Radiometric Dating

Wetlands constitute a large terrestrial carbon pool and play an important role in global carbon cycles as carbon sequestering systems. The goal of this study is to compare recent carbon sequestration rates in temperate and tropical flow-through wetlands using radiometric dating with 137-Cs, testing the hypothesis that tropical wetlands accumulate more carbon than do similar wetlands located in temperate climates. Soil cores were extracted from Old Woman Creek (OWC), a 56-ha freshwater estuarine wetland in Ohio, and from a similar 116-ha flow-through wetland (ELR) located at EARTH University in northeastern Costa Rica. OWC has a peak in 137-Cs concentration that indicated an accumulation of 16-18 cm of sediments in the last 42 years, whereas ELR accumulated 30-38 cm in that same period of time. Carbon content of these wetland soils was also determined. The carbon density of the sediment in OWC was on average 53 gC kg-1 soil, with 80% as organic carbon; in ELR the average carbon density was 110 gC kg-1 soil, with 91% of this as organic carbon. From these results, it is estimated that the temperate wetland accumulated 1.42 tonsC ha-1 yr-1, while the tropical wetland accumulated 2.57 tonsC ha-1 yr-1.