Landslides and organic carbon erosion: Reassessing the role of landslides as transient carbon stores in the western Southern Alps, New Zealand.

Abstract

Landslides erode large amounts of particulate organic carbon (POC) over short periods of time and therefore are thought to play an important role in local carbon cycles. However, the onward fate of POC is poorly constrained, particularly with respect to storage on hillslopes in landslide deposits, which may protect biospheric organic carbon (OCbio) from oxidation and act as short-term stores of CO2. It is also crucial to constrain the source of the eroded organic carbon, with only OCbio able to sequester CO2 from the atmosphere. Understanding the fate of eroded OCbio will help to better infer the consequences of landsliding on the carbon cycle.

This thesis contributes to this research gap by quantifying the mass of OCbio eroded by 10 individual landslides in the Southern Alps, New Zealand, and then determining the carbon storage potential for each landslide deposit. I collected 191 samples from landslide deposits, riverbeds, and undisturbed soil profiles, and quantified total organic carbon content and stable isotope ratios (δ13C and δ15N) using an elemental analyser coupled to isotope ratio mass spectrometer. The mass of OCbio mobilised by each landslide, calculated using soil organic carbon stocks and mapped landslide areas, ranged from 0.32 ± 0.1 tC to 360 ± 100 tC. To find the deposit storage potential, these values were compared to estimates of the mass of OCbio stored in each landslide deposit (0 tC to 3900 ± 3000 tC). This was derived using a binary mixing model, deposit volume, bulk density and organic carbon content. This study found that deposit carbon storage potential was variable across the ten landslides, possibly as a result of landslide type and the processes occurring during and following the initial erosion. Future research should better constrain the factors controlling landslide deposit carbon storage potential, such as bulk density, vegetation and post-landslide erosion