Carbon Storage along with Soil Profile: An Example of Soil Chronosequence from the Fluvial Terraces on the Pakua Tableland, Taiwan

Abstract

A well-dated soil chronosequence may allow exploration of the accumulation of soil carbon over time. There are multiple levels of river terraces on the Pakua tableland in Central Taiwan. Unlike many of the reddish or lateritic soils in Taiwan, these soils were recently dated, with absolute ages in the range of 19–400 kyr. This information allowed us to develop an ideal soil chronosequence, with time constraints, through which it is possible to explore soil organic carbon (SOC) storage and its changes over time. In this study, we attempted to establish an SOC time series, and to give an estimate of long-term accumulation of the SOC storage in the red soils of Taiwan. The data on these soils used in this study were taken from the soil profiles presented in our previous studies. Two additional soil profiles were sampled for those soils for which data were not available from the previous studies. The total carbon stock (TCS) for each soil profile was measured and assessed based on the depth categories of 0–30, 30–50, and 50–100 cm. Weighted carbon stock (WCS) measurements were further derived by the total thickness of the soil profile, for better comparison. The overall carbon stocks of the soils in the Pakua tableland were in the range of 2.8–3.2 Tg for TCS and WCS, respectively. In addition, the SOC tended to be highest in the surface soil horizons and decreased with the soil depth. The continuous pattern of the carbon content, in terms of its vertical distribution, was considered in terms of a negative exponential function, which showed that the SOC was highest in the shallowest soil layers and decreased rapidly with the soil depth. This trend was mitigated at a depth of 50–100 cm, which approached a fixed value, denoted as the carbon sequestration value (CSV), below a certain depth. We show here that the values of the CSV, as approximated by exponential fitting, are closely related to soil age. The CSV linearly decreases with age. These findings point to the potential of using carbon storage for chronometric applications.