Abstract:
During the anthropocene land use change has exacerbated erosion of the Soil Organic Carbon (SOC) rich topsoil in the Oporae Valley. As well as reducing the SOC content of the contemporary topsoil, the large scale redistribution of sediment has created a quantifiable long-term SOC sink in paleosols. Using contemporary native forest soils as a proxy, pasture covered topsoils contain
~40% less SOC (a loss of 5,338 T/[square kilometer] SOC). The pre-human paleosol at ~200 cm, an average 32 cm thickness, contains 9180 T/[square kilometer]. Significantly more SOC buried at depth than what currently exists in the contemporary topsoil indicates the relative importance of paleosols as C stores and the role of land use change on SOC. The preservation characteristics of a paleosol in the Oporae Valley are determined by slope angle and the relative position they hold in relation to the
inter-fingering of the alluvial toeslope with the colluvial footslope. Groupings of [radioisotope carbon-14] ages in and above the pre-human paleosol allow for calculation of terrestrial sedimentation rates. At ~0.9 mm yr^-1 the terrestrial pre-human sedimentation
rate averaged over the valley floor is approximately half (0.53) of the corresponding pre-human lake rate of ~1.7 mm yr^-1. As a proportion of the lake's anthropogenic sedimentation rate at ~4.8 mm yr^-1, the terrestrial anthropogenic sedimentation rate has slightly increased to ~2.8 mm yr^-1 (0.58 of the lake sedimentation rate). These initial findings demonstrate the potential for further research in this area, so that ongoing land-use change can be accurately incorporated into terrestrial carbon accounting.
