IN SITU NON-INVASIVE SOIL CARBON ANALYSIS: SAMPLE SIZE AND GEOSTATISTICAL CONSIDERATIONS.
I discuss a new approach for quantitative carbon analysis in soil based on INS. Although this INS method is not simple, it offers critical advantages not available with other newly emerging modalities. The key advantages of the INS system include the following: (1) It is a non-destructive method, i.e., no samples of any kind are taken. A neutron generator placed above the ground irradiates the soil, stimulating carbon characteristic gamma-ray emission that is counted by a detection system also placed above the ground. (2) The INS system can undertake multielemental analysis, so expanding its usefulness. (3) It can be used either in static or scanning modes. (4) The volume sampled by the INS method is large with a large footprint; when operating in a scanning mode, the sampled volume is continuous. (5) Except for a moderate initial cost of about $100,000 for the system, no additional expenses are required for its operation over two to three years after which a NG has to be replenished with a new tube at an approximate cost of $10,000, this regardless of the number of sites analyzed. In light of these characteristics, the INS system appears invaluable for monitoring changes in the carbon content in the field. For this purpose no calibration is required; by establishing a carbon index, changes in carbon yield can be followed with time in exactly the same location, thus giving a percent change. On the other hand, with calibration, it can be used to determine the carbon stock in the ground, thus estimating the soil's carbon inventory. However, this requires revising the standard practices for deciding upon the number of sites required to attain a given confidence level, in particular for the purposes of upward scaling. Then, geostatistical considerations should be incorporated in considering properly the averaging effects of the large volumes sampled by the INS system that would require revising standard practices in the field for determining the number of spots to be sampled. It is highly desirable to assess properly the sampled volume for reporting the absolute value of the measured carbon. At the same time, increasing the number of detectors surrounding the NG can reduce error propagation. In the present work, only the volume irradiated by the neutrons was estimated. It should be pointed that the carbon yield is also affected by the neutron energy spectrum that changes with depth. Thus, all these considerations must be considered carefully when evaluating the detectors' configuration and the resulting counting efficiency. In summary, INS system is a novel approach for non-destructive carbon analysis in soil with very unique features. It should contribute in assessing soil carbon inventories and assist in understanding belowground carbon processes. The complexity of carbon distribution in soil requires a special attention when calibrating the INS system, and a consensus developed on the most favorable way to report carbon abundance. Clearly, this will affect the calibration procedures.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States)
- Sponsoring Organization:
- DOE/SC (US)
- DOE Contract Number:
- AC02-98CH10886
- OSTI ID:
- 15015227
- Report Number(s):
- BNL-73892-2005-BC; R&D Project: EE-536-EEBA; KP1202020; TRN: US0502531
- Resource Relation:
- Other Information: PBD: 1 Apr 2005; Related Information: SOIL CARBON SEQUESTRATION AND GLOBAL CLIMATE CHANE: MITIGATION POTENTIAL OF LATIN AMERICA
- Country of Publication:
- United States
- Language:
- English
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