Here we use an analytical method to determine δ^13C in local plants and organic matter in the soils above Furong cave, Chong- qing, China. We also monitored d13C in dissolved inorganic carbon （DIC） of drip water, ...Here we use an analytical method to determine δ^13C in local plants and organic matter in the soils above Furong cave, Chong- qing, China. We also monitored d13C in dissolved inorganic carbon （DIC） of drip water, δ^13C of active deposits under the drip waters, and the concentration of air CO2 （PCO2）. Based on these, we preliminarily studied the transportation characteristics of stable carbon isotope （^13C） in cave system of the subtropical karst area. The average δ^13C value of 27 local plant samples, which belong to 16 families, was -32% and the weighted δ^13C for surface dry biomass was -33%0. We found that for 54 soil samples collected from 5 soil profiles, δ^13C of soil organic matters was -22%o, which could be attributed to the different trans- portation rates of stable carbon isotopes during the decomposition of plants and organic matters in soils. The relatively lighter 12C tended to transfer into gaseous CO2, which made the relatively heavier ^13C concentrated in the soils. On the basis of moni- toring of DIC- δ^13C in drip waters from July 2009 to June 2010, we found that values in winter months were heavier and values in summer months were lighter in general, the reason of which was that in summer months, both the temperature and the hu- midity were comparatively higher, resulted in more CO2 with lighter δ^13C generated from organic matters decomposition and plants respiration. The average DIC- δ^13C value was -11%o, about 11%o heavier than the δ^13C of organic matters in soils, which proved that part of DIC in cave drip water was sourced from dissolution of inorganic carbonate （host rock, with heavier δ^13C. As for the δ^13C of active deposits at five drip water sites in Furong cave, they had almost the same variation with relatively light values. In other words, these active speleothems were deposited at equilibrium conditions for isotopic fractionation. These results suggest that the carbon isotopic information of speleothems could be used to track the evolution of local vegetation in certain situations.展开更多
In this paper, the authors obtain the joint empirical likelihood confidence regions for a finite number of quantiles under negatively associated samples. As an application of this result, the empirical likelihood conf...In this paper, the authors obtain the joint empirical likelihood confidence regions for a finite number of quantiles under negatively associated samples. As an application of this result, the empirical likelihood confidence intervals for the difference of any two quantiles are also developed.展开更多
A technically transparent and freely available reference sample set for validation of global land cover mapping was recently established to assess the accuracies of land cover maps with multiple resolutions.This sampl...A technically transparent and freely available reference sample set for validation of global land cover mapping was recently established to assess the accuracies of land cover maps with multiple resolutions.This sample set can be used to estimate areas because of its equal-area hexagon-based sampling design.The capabilities of these sample set-based area estimates for cropland were investigated in this paper.A 30-m cropland map for China was consolidated using three thematic maps(cropland,forest and wetland maps)to reduce confusion between cropland and forest/wetland.We compared three area estimation methods using the sample set and the 30 m cropland map.The methods investigated were:(1)pixel counting from a complete coverage map,(2)direct estimation from reference samples,and(3)model-assisted estimation combining the map with samples.Our results indicated that all three methods produced generally consistent estimates which agreed with cropland area measured from an independent national land use dataset.Areas estimated from the reference sample set were less biased by comparing with a National Land Use Dataset of China(NLUD-C).This study indicates that the reference sample set can be used as an alternative source to estimate areas over large regions.展开更多
基金supported by Open Foundation of the Karst Dynamics Laboratory,China (Grant Nos.GKN0842008 and KDL2008-08)National Natural Science Foundation of China (Grant Nos.40802035,41030103,41172165 and 40971122)+1 种基金Open Foundation of the State Key Laboratory of Loess and Quaternary Geology,Institute of Earth Environment,CAS,China (Grant No. SKLLQG0907)Key Project of Special Research Foundation of Southwest University,China (Grant Nos. XDJK2009B016 and XDJK2009C106)
文摘Here we use an analytical method to determine δ^13C in local plants and organic matter in the soils above Furong cave, Chong- qing, China. We also monitored d13C in dissolved inorganic carbon （DIC） of drip water, δ^13C of active deposits under the drip waters, and the concentration of air CO2 （PCO2）. Based on these, we preliminarily studied the transportation characteristics of stable carbon isotope （^13C） in cave system of the subtropical karst area. The average δ^13C value of 27 local plant samples, which belong to 16 families, was -32% and the weighted δ^13C for surface dry biomass was -33%0. We found that for 54 soil samples collected from 5 soil profiles, δ^13C of soil organic matters was -22%o, which could be attributed to the different trans- portation rates of stable carbon isotopes during the decomposition of plants and organic matters in soils. The relatively lighter 12C tended to transfer into gaseous CO2, which made the relatively heavier ^13C concentrated in the soils. On the basis of moni- toring of DIC- δ^13C in drip waters from July 2009 to June 2010, we found that values in winter months were heavier and values in summer months were lighter in general, the reason of which was that in summer months, both the temperature and the hu- midity were comparatively higher, resulted in more CO2 with lighter δ^13C generated from organic matters decomposition and plants respiration. The average DIC- δ^13C value was -11%o, about 11%o heavier than the δ^13C of organic matters in soils, which proved that part of DIC in cave drip water was sourced from dissolution of inorganic carbonate （host rock, with heavier δ^13C. As for the δ^13C of active deposits at five drip water sites in Furong cave, they had almost the same variation with relatively light values. In other words, these active speleothems were deposited at equilibrium conditions for isotopic fractionation. These results suggest that the carbon isotopic information of speleothems could be used to track the evolution of local vegetation in certain situations.
基金supported by the National Natural Science Foundation of China under Grant Nos.1127108811361011+3 种基金11201088the Natural Science Foundation of Guangxi under Grant No.2013GXNSFAA0190042013 GXNSFAA 0190072013GXNSFBA019001
文摘In this paper, the authors obtain the joint empirical likelihood confidence regions for a finite number of quantiles under negatively associated samples. As an application of this result, the empirical likelihood confidence intervals for the difference of any two quantiles are also developed.
基金supported by the National Natural Science Foundation of China(Grant No.41301445)a research grant from Tsinghua University(Grant No.20151080351)
文摘A technically transparent and freely available reference sample set for validation of global land cover mapping was recently established to assess the accuracies of land cover maps with multiple resolutions.This sample set can be used to estimate areas because of its equal-area hexagon-based sampling design.The capabilities of these sample set-based area estimates for cropland were investigated in this paper.A 30-m cropland map for China was consolidated using three thematic maps(cropland,forest and wetland maps)to reduce confusion between cropland and forest/wetland.We compared three area estimation methods using the sample set and the 30 m cropland map.The methods investigated were:(1)pixel counting from a complete coverage map,(2)direct estimation from reference samples,and(3)model-assisted estimation combining the map with samples.Our results indicated that all three methods produced generally consistent estimates which agreed with cropland area measured from an independent national land use dataset.Areas estimated from the reference sample set were less biased by comparing with a National Land Use Dataset of China(NLUD-C).This study indicates that the reference sample set can be used as an alternative source to estimate areas over large regions.
