Soil Carbon Sequestration Potential and Linkages with General Flooding and Erosion Issues, Gisborne/East-Cape Region, North Island, New Zealand

Abstract

The global carbon cycle has been significantly modified by increased human demand and consumption of natural resources. Billions of tonnes of carbon moves between the Earth’s natural spheres in any given year, with anthropogenic activities adding approximately 7.1 gigatonnes (Gt) of carbon (C) to this flux. On a global basis, the sum of C in living terrestrial biomass and soils is approximately three times greater than the carbon dioxide (CO2) in the atmosphere; with the current soil organic carbon (OC) pool estimated at about 1500 Gt (Falkowski et al. 2000). With total global emissions of CO2 from soils being acknowledged as one of the largest fluxes in the carbon cycle, ideas and research into mitigating this flux are now being recognised as extremely important in terms of climate change and the reduction of green house gases (GHG) in the future. Additional co-benefits of increasing carbon storage within the soil are improvements in a soil’s structural and hydrological capacity. For example, increasing organic carbon generally increases infiltration and storage capacity of soil, with potential to reduce flooding and erosion. There are several management options that can be applied in order to increase the amount of carbon in the soil. Adjustments to land management techniques (e.g. ploughing) and also changes to cropping and vegetation type can increase organic carbon content within the subsurface (Schlesinger & Andrews, 2000). If we are able to identify specific areas of the landscape that are prone to carbon losses or have potential to be modified to store additional carbon, we can take targeted action to mitigate and apply better management strategies to these areas. This research aims to investigate issues surrounding soil carbon and the more general sustainability issues of the Gisborne/East-Cape region, North Island, New Zealand. Maori-owned land has a large presence in the region. Much of this land is described as being “marginal” in many aspects. The region also has major issues in terms of flooding and erosion. Explored within this research are issues surrounding sustainability, (including flooding, erosion, and Maori land) with particular emphasis on carbon sequestration potential and the multiple co-benefits associated with increasing the amount of carbon in the soil. This research consists of a desktop study and field investigations focusing on differences in soil type and vegetation cover/land use and what effects these differences have on soil OC content within the subsurface. Soil chemical and physical analysis was undertaken with 220 soil samples collected from two case-study properties. Particle size analysis was carried out using a laser particle sizer (LPS) to determine textural characteristics and hydraulic capacity. Soil organic carbon (OC) content was determined following the colorimetric method, wet oxidation (Blakemore et al. 1987), with results identifying large difference in soil OC quantification between sampled sites. National scale data is explored and then compared with the results from this field investigation. The direct and indirect benefits resulting from more carbon being locked up in soil may assist in determining incentives for better land-use and land management practices in the Gisborne/East-Cape region. Potentially leading to benefits for the land-user, the environment and overall general sustainability.