Quantifying methane emissions from rice fields in the Taihu Lake region, China by coupling a detailed soil database with biogeochemical model

As China has approximately 22% of the world's rice paddies, the regional quantification of CH<sub>4</sub> emissions from these paddies is important in determining their contribution to the global greenhouse gas effect. This paper reports the use of a biogeochemical model (DeNitrification and DeComposition or DNDC) for quantifying CH<sub>4</sub> emissions from rice fields in the Taihu Lake region of China. For this application, the DNDC model was linked to a 1:50 000 soil database derived from 1107 paddy soil profiles compiled during the Second National Soil Survey of China in the 1980s–1990s. The simulated results showed that the 2.3 Mha of paddy rice fields in the Taihu Lake region emitted the equivalent of 5.7 Tg C from 1982–2000, with the average CH<sub>4</sub> flux ranging from 114 to 138 kg C ha<sup>−1</sup> y<sup>−1</sup>. As for soil subgroups, the highest emission rate (660 kg C ha<sup>−1</sup> y<sup>−1</sup>) was linked to gleyed paddy soils accounting for about 4.4% of the total area of paddy soils. The lowest emission rate (91 kg C ha<sup>−1</sup> y<sup>−1</sup>) was associated with degleyed paddy soils accounting for about 18% of the total area of paddy soils. The most common soil in the area was hydromorphic paddy soils, which accounted for about 53% of the total area of paddy soils with a CH<sub>4</sub> flux of 106 kg C ha<sup>−1</sup> y<sup>−1</sup>. On a regional basis, the annual averaged CH<sub>4</sub> flux in the Taihu Lake plain soil region and alluvial plain soil region were higher than that in the low mountainous and hilly soil region and the polder soil region. The model simulation was conducted with two databases using polygons or counties as the basic units. The county-based database contained soil information coarser than the polygon system built based on the 1:50 000 soil database. The modeled results with the two databases found similar spatial patterns of CH<sub>4</sub> emissions in the Taihu Lake region. However, discrepancies exist between the results from the two methods. The total CH<sub>4</sub> emissions generated from the polygon-based database is 2.6 times the minimum CH<sub>4</sub> emissions generated from the county-based database, and is 0.98 times the maximum CH<sub>4</sub> emissions generated from the county-based database. The average value of the relative deviation ranged from −20% to 98% for most counties, which indicates that a more precise soil database is necessary to better simulate CH<sub>4</sub> emissions from rice fields in the Taihu Lake region using the DNDC model

Plant elemental composition and portable X-rayfluore scence (pXRF) spectroscopy:quantification under differentanalytical parameters

Emergence of portable X-ray fluorescence (pXRF) systems presents new opportunities for rapid, low-cost plant analysis, both as a lab system and in situ system. Numerous studies have extolled the virtues of using pXRF for a wide range of plant applications, however, for many such applications, there is need for further assessment with regards to analytical parameters for plant analysis. While pXRF is a potential powerful research tool for elemental composition analysis, its successful use in plant analysis is made more likely by having an understanding of X-ray physics, calibration process, and ability to test a variety of homogenous and well-characterized materials for developing a matrix-specific calibration. Because potential pXRF users may often underestimate the complexity of proper analysis, this study aims at providing a technical background for plant analysis using pXRF. The focus is on elemental quantification under different analytical parameters and different methods of sample presentation: direct surface contact under vacuum, placement in a sample cup with prolene as a seal, and without the aid of a vacuum. Direct analysis on the surface of a pXRF provided highest sensitivity and accuracy (R2 > 0.90) for light elements (Mg to P). Sulfur, K, and Ca can be reliably measured without the aid of a vacuum (R2 > 0.99, 0.97, and 0.93 respectively), although lower detection limits may be compromised. pXRF instruments provide plant data of sufficient accuracy for many applications and will reduce the overall time and budget compared with the use of conventional techniques. Sensitivity and accuracy are dependent on the instrument's settings, make, and model. © 2015 The Authors. X-Ray Spectrometry published by John Wiley & Sons, Ltd

Elemental quantification, chemistry, and source apportionment in golf course facilities in a semi-arid urban landscape using a portable X-ray fluorescence spectrometer

This study extends the application of the portable X-ray fluorescence (PXRF) spectrometry to the examination of elements in semi-arid urban landscapes of the Southern High Plains (SHP) of the United States, focusing on golf courses. The complex environmental challenges of this region and the unique management practices at golf course facilities could lead to differences in concentration and in the chemistry of elements between managed (irrigated) and non-managed (non-irrigated) portions of these facilities. Soil samples were collected at depths of 0–10, 10–20, and 20–30 cm from managed and non-managed areas of seven different facilities in the city of Lubbock, Texas, and analyzed for a suite of soil properties. Total elemental quantification was conducted using a PXRF spectrometer. Findings mostly indicated no significant differences in the concentration of examined elements between the managed and non-managed areas of the facilities. However, strong positive relationships (<i>R</i> = 0.82&minus;0.91, <i>p</i> < 0.001) were observed among elements (e.g., Fe on the one hand and Cr, Mn, Ni, and As on the other; Cu and Zn; As and Cr) and between these elements and soil constituents or properties such as clay, calcium carbonate, organic matter, and pH. The strengths of these relationships were mostly higher in the non-managed areas, suggesting a possible alteration in the chemistry of these elements by anthropogenic influences in the managed areas. Principal component and correlation analyses within the managed areas suggested that As, Cr, Fe, Mn, and Ni could be of lithogenic origin, while Cu, Pb, and Zn could have anthropogenic influences. Only one possible, likely lithogenic, source of the elements was identified within the non-managed areas. As evidenced by the study, the PXRF spectrometer can be a valuable tool for elemental quantification and rapid investigation of elemental interaction and source apportionment in semi-arid climates