Rapid carbon accumulation in soil rapidly forming in the Southern Alps of New Zealand
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Date
2021-11-17
Journal Title
Journal ISSN
Volume Title
Publisher
Australian Nuclear Science and Technology Organisation
Abstract
Biota contribute 3-7 orders of magnitude more potential energy to landscapes than climate or tectonics alone. This potential energy is quantified as the system’s net primary productivity (NPP), i.e., the net gain of photosynthetically sourced carbon. The effects of biological energy on landscape evolution is likely highly non-negligible, yet, has proven difficult to properly quantify in the past. Current methods for quantifying NPP vary in accuracy and can involve careful and costly study over the course of many years. The associated costs are often prohibitive for geomorphic studies. Therefore, NPP is not a commonly included measurement made in such studies. While relating biological to geomorphic processes in rapidly forming soils could help increase the predictive ability of current geomorphic models, a more suitable method for quantifying NPP is required to make this possible.
Here, we present a novel method combining uranium and carbon isotopes that can be used for quantifying soil NPP. The study was carried out on a rapidly forming, New Zealand soil. The uranium isotope composition of the soil was used to derive a soil age of 178 years. Given the soil’s age, the soil production rate is 1.7 mm yr-1 which is one of the most rapid every quantified. Geomorphic models fail to predict such rapid soil production by a factor of ~2. Carbon-14 (14C) was also isolated from the same soil and quantified by AMS. The 14C measurements allow for the soil organic carbon (SOC) mean residence time (MRT) to be calculated. Utilizing a commonly employed biogeochemical model, the MRT allows for the calculation of the concentration of SOC as a function of time. In the rapidly forming soil, we measured a SOC content of 536 g-C m-1. Employing MRT and SOC to calculate the expected age of soil yielded a predicted soil age of 408 years. The discrepancy in MRT predicted age and the observed soil age indicates that the biogeochemical model fails to predict the rate of carbon accretion in the rapidly forming soil by a factor of ~2. The work presented here is the first biogeochemical characterization of a soil forming more rapidly than current geomorphic models can accurately determine. Both the observed soil NPP and the soil formation rate exceed current model predictions. It is possible that a causal relationship exists, however, further cocharacterization of biological energy input rates and soil formation rates is needed to test this hypothesis. © The Authors
Description
Keywords
Carbon, Soils, Alps, New Zealand, Tectonics, Isotopes, Uranium isotopes, Hypothesis
Citation
Raines, E., Hua, Q., Dosseto, A., Lukens, E. E., Deslippe, J. R., & Norton, K. P. (2021). Rapid carbon accumulation in soil rapidly forming in the Southern Alps of New Zealand. Paper presented to the 15th International Conference on Accelerator Mass Spectrometry. ANSTO Sydney, Australia. November 15th – 19th, 2021, (pp. 83). Retrieved from: https://ams15sydney.com/wp-content/uploads/2021/11/AMS-15-Full-Program-and-Abstract-Book-R-1.pdf