Soil carbon fractionation as a tool to monitor coastal wetland rehabilitation
Pestheruwe Liyanaralalage Iroshaka Gregory Marcelus Cooray, Gareth Chalmers, David J. Chittleborough, Zeinab Ghasemzadeh
Abstract
Coastal wetland rehabilitation can provide nature-based solutions for climate change mitigation. The high carbon accumulation rate and carbon secured, potentially for several millennia, as soil organic carbon (SOC), is among the reasons. Measuring SOC storage and accrual over time are the main tools to understand rehabilitation success. However, SOC is partitioned among different organic matter fractions with varying physio-chemical properties and stabilities. In this research, we separated different organic matter fractions based on density (free light fraction: f-LF, occluded light fraction: o-LF and heavy fraction: HF) and solubility (dissolved fraction: DF) from soils taken from a wetland under rehabilitation and a pristine mangrove forest in Queensland, Australia. The f-LF and o-LF contain particulate organic carbon (POC f-LF and POC o-LF ), whereas HF consists of mineral-associated organic carbon (MAOC HF ). Mangroves are superior to wetlands under rehabilitation and terrestrial forests in terms of C storage in each fraction. Soils from both mangroves and wetlands under rehabilitation are dominated by MAOC HF . However, MAOC HF from mangrove soils are relatively physio-chemically stable, while wetlands under rehabilitation are leaching aged-SOC (>1000 years) from the HF to DF as dissolved organic carbon (DOC DF ). Therefore, reducing the risk of mobilisation of aged-SOC can be a key to achieve rehabilitation success. • Mineral-associated organic carbon (MAOC) fraction dominates coastal wetland soils. • Some particulate organic carbon (POC) is protected via occlusion within soil aggregates. • MAOC dissolution produces aged (>1000 years) dissolved organic carbon (DOC) at depths. • Aged DOC is present in disturbed or restoring coastal wetland soils. • Mangrove soils have relatively stable MAOC complexes.