Freshwater wetlands contain 33% of the global pool of soil carbon – a disproportionately high contribution given that such habitats occupy a mere 6–8% of the land surface. As the world seeks to capitalise on new biosequestration opportunities to reduce atmospheric CO2 levels, interest is growing in restoring wetlands for carbon offset purposes.
Here we investigated whether rehabilitating wetlands can increase soil carbon density and carbon sequestration capacity in the central Murray region of south-eastern Australia. The study took advantage of the region’s 20-year legacy of wetland rehabilitation to assess wetland soil carbon changes with increasing time since rehabilitation and other site specific factors.
From an initial nine different wetlands, we established an average sediment accretion rate and carbon accumulation rates. Sediment core samples were collected and analysed for 19 wetlands in the region to quantify soil organic carbon.
Wetland rehabilitation significantly improves soil organic carbon over time and explains 19% of the variation in the data. The underlying soil organic carbon at deeper depths explained another 29% of the variation in the data, likely representing site specific differences between wetlands (e.g. frequency of water inundation, vegetation type, soil type).
These results provide vital information for landowners and management agencies seeking to understand the soil carbon storage capacity of rehabilitating wetlands. With growing interest in wetlands within national and international carbon markets, assessment of the effectiveness of rehabilitation activities in storing additional carbon is vital to implement these programs on the ground in the future.