Technical note: Comparison of radiometric techniques for estimating recent organic carbon sequestration rates in inland wetland soils

Abstract

For wetlands to serve as natural climate solutions, accurate estimates of organic carbon (OC) sequestration rates in wetland sediments are needed. Dating using cesium-137 (137Cs) and lead-210 (210Pb) radioisotopes is commonly used for measuring OC sequestration rates in wetland sediments. 137Cs radioisotope dating is relatively simple, with calculations based on a single point representing the onset (1954) or peak (1963) of the 137Cs fallout. 210Pb radioisotope dating is more complex, as the calculations are based on multiple points. Here, we show that reliable dating of sediment cores collected from wetlands can be achieved using either 137Cs or 210Pb dating or their combination. However, 137Cs and 210Pb profiles along the depth of sediment cores need to be screened, analyzed, and interpreted carefully to estimate OC sequestration rates with high precision. To this end, we propose a decision framework for screening 137Cs and 210Pb profiles into high- and low-quality sediment profiles, and we compare dating using the 1954 and 1963 time markers, i.e., the rates of sedimentation and, consequently, OC sequestration over the past ĝ1/4 60 years. Our findings suggest that 137Cs- and 210Pb-based OC sequestration rates are comparable, especially when using the 1963 (vs. 1954) time marker.