RESUMEN

Southern China and Southeast Asia witnessed some of their most significant economic and social changes relevant to human land use during the Late Holocene, including the intensification and spread of rice agriculture. Despite rice growth being associated with a number of earth systems impacts, how these changes transformed tropical vegetation in this region of immense endemic biodiversity remains poorly understood. Here, we compile a pollen dataset incorporating ∼150,000 identifications and 233 pollen taxa to examine past changes in floral biodiversity, together with a compilation of records of forest decline across the region using 14 pollen records spanning lowland to mountain sites. Our results demonstrate that the rise of intensive rice agriculture from approximately 2,000 y ago led not only to extensive deforestation but also to remarkable changes of vegetation composition and a reduction in arboreal diversity. Focusing specifically on the Tertiary relic tree species, the freshwater wetland conifer Glyptostrobus (Glyptostrobus pensilis), we demonstrate how key species that had survived changing environmental conditions across millions of years shrank in the face of paddy rice farming and human disturbance.

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RESUMEN

A filtered Rayleigh scattering system is developed and applied to measure the mole fraction of methane in a methane-air swirl flow through a transparent conical quartz quarl. Light scattering from the location where the laser beam is incident on the surface of the quarl is orders of magnitudes larger than Rayleigh scattering from the gas mixture of interest. This diffusive scattering is suppressed using molecular absorption by an iodine cell and using spatial filtering by an optical aperture. Residual stray light accounted for up to 5% of the total signal and had to be removed for accurate measurements. The flow consisted of a nonpremixed mixture of methane and air in the central jet surrounded by a strong swirling air flow. Measurements were conducted at a height of 4 mm from the fuel tube's exit for six different conditions of the swirl flow to demonstrate the ability of the instrument to study the effects of swirl strength and fuel flow rate on the mixing process. By using a four-leg pulse stretcher to allow higher laser energies in the probe volume, large collection optics and a reference iodine cell to monitor laser wavelength variations, standard deviations of ∼0.006 in air and ∼0.012 in a laminar methane flow were achieved for mole fraction measurements.

RESUMEN

This paper focuses on the study on continuous XRF (X-Ray Fluorescence) scanning elements of a 39 m core from Fuzhou Basin. The XRF scanning result is used to recognize the different sedimentary environment before the discussion of the element variation of different deposit in transitional zone between land and ocean. There are five sedimentary facies in the study area from the late Pleistocene: lacustrine-fluvial-estuary (mud tidal flat)-mixed tidal flat-fluvial. The XRF result from the 5 sedimentary stages shows that the high concentration of Co, Fe, Ti, Si are controlled largely by grain size. The average element intensity of layers with similar grain size indicates that Ca, Ti, Mn, Fe and Co from the marine (tidal flat) deposit is 3~10 times bigger than those from terrestrial (fluvial) deposit, with higher content of Si coinciding with terrestrial deposit. It is indicated that except grain size, the deposit environment is an important factor for element concentration. In this study, Ca, Ti, Mn, Fe and Co are relatively better indicator elements for marine sediments while Si is good and K, Rb and Sr have some indication for terrestrial sediments. The study result shows XRF continuous scanning can help to identify the subtle variation of elements, as to the determination of the sediment facies. Thus, XRF scanning is an important supplement to sediment facies identification. This study also provides an application example of XRF in a typical transitional zone between land and ocean.