Accuracy assessment and calibration of the impact of water content and structure of lake sediments on the XRF scanning data—A case study of Aweng Co in the Tibetan Plateau
Zhang Yuzhi, Zhang Jiawu, Mao Chunhui, Zhang Yanli, Zhou Shan, Yang Panpan
Key Laboratory of Western China's Environmental Systems, Ministry of Education, College of Earth and Environmental Sciences, Lanzhou University, Lanzhou 73000, Gansu
Abstract：X-ray fluorescence (XRF) scanning technology is widely used in determining the rough content of elements in sediments as it has advantages of rapid measurements, no damage to samples and high resolutions for environmental studies. However, the scanned intensities of some elements are often biased by water content and sedimentary structure of sediments, which need to be assessed and calibrated before being used in environmental researches. In order to evaluate the accuracy and reliability of the XRF scanning data, we chose core sediments from an alpine closed saline lake (salinity is 29.5 g/L and pH is 9.2), Aweng Co (32.70°~32.82°N, 81.63°~81.80°E; 4430 m a.s.l.), in western Tibet to compare the XRF scanning data and the traditional accurate XRF measurements for assessment and calibration. Two sediment cores, AWC2015A and AWC2015B (32.745°N, 81.757°E, 4430 m a.s.l, bedrocks in the catchment are Cretaceous granite and Jurassic metamorphosed sandstone), retrieved from the central part of the lake at a water depth of 6 m using a piston corer on a UWITEC platform in July 2015, were combined to a composite sequence of 445 cm in length. XRF scanning was conducted on one half of the sediment core using the Avaatech XRF core scanner at 2 mm resolution. The accuracy of the XRF scanning data are evaluated by comparing with the results of traditional XRF analyzer (Epsilon 3XL XRF analyzer) with 1 cm-resolution samples from section 130.5~189.5 cm of the core (58 samples) and another 19 samples distributed evenly along the core. The average of three XRF scanning data that cover one traditional XRF data are used to compare in this study. Then calibrations are conducted using three different methods, including the normalized polynomial-scaled (NPS) calibration, the multivariate log-ratio calibration (MLC), and the normalized median-scaled (NMS) calibration.
The results show that the XRF-scanned elemental intensities of Ti and Fe are significantly correlated with the measured elemental contents by traditional XRF equipment, indicating the intensities of Ti and Fe are reliable and thus can be used without calibrations. The intensities of Al, Si and K are affected by the water content, and the intensity of Ca is influenced by the cracks in the sediments, suggesting the intensities of Al, Si, K and Ca should be properly calibrated before being used for climatic and environmental change studies. Comparisons of the results calibrated by three different methods suggested that the performance of the NPS calibration is the best and it resulted in consistent variations of the calibrated Al, Si, K and Ca with their measured contents. Separate calibrations are recommended when the structures of the sediment surface changed (e.g. cracks) during the process of scanning, which may be caused by water loss after exposure in the air during the pretreatments.
张玉枝, 张家武, 毛春晖, 张延利, 周姗, 杨盼盼. 湖泊沉积物含水量和结构对XRF扫描结果影响的评估及校正——以西藏阿翁错为例[J]. 第四纪研究, 2020, 40(5): 1145-1153.
Zhang Yuzhi, Zhang Jiawu, Mao Chunhui, Zhang Yanli, Zhou Shan, Yang Panpan. Accuracy assessment and calibration of the impact of water content and structure of lake sediments on the XRF scanning data—A case study of Aweng Co in the Tibetan Plateau. Quaternary Sciences, 2020, 40(5): 1145-1153.
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2020, Vol. 40 
