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China's terrestrial ecosystems have functioned as important carbon sinks. However, previous estimates of carbon budgets have included large uncertainties owing to the limitations of sample size, multiple data sources, and inconsistent methodologies. In this study, we conducted an intensive field campaign involving 14,371 field plots to investigate all sectors of carbon stocks in China's forests, shrublands, grasslands, and croplands to better estimate the regional and national carbon pools and to explore the biogeographical patterns and potential drivers of these pools. The total carbon pool in these four ecosystems was 79.24 ± 2.42 Pg C, of which 82.9% was stored in soil (to a depth of 1 m), 16.5% in biomass, and 0.60% in litter. Forests, shrublands, grasslands, and croplands contained 30.83 ± 1.57 Pg C, 6.69 ± 0.32 Pg C, 25.40 ± 1.49 Pg C, and 16.32 ± 0.41 Pg C, respectively. When all terrestrial ecosystems are taken into account, the country's total carbon pool is 89.27 ± 1.05 Pg C. The carbon density of the forests, shrublands, and grasslands exhibited a strong correlation with climate: it decreased with increasing temperature but increased with increasing precipitation. Our analysis also suggests a significant sequestration potential of 1.9-3.4 Pg C in forest biomass in the next 10-20 years assuming no removals, mainly because of forest growth. Our results update the estimates of carbon pools in China's terrestrial ecosystems based on direct field measurements, and these estimates are essential to the validation and parameterization of carbon models in China and globally. [ABSTRACT FROM AUTHOR]

Though numerous studies have evaluated the effect of prediction method on soil organic carbon (SOC) spatial distribution, the influence of prediction method on detecting the temporal evolution of SOC has rarely been reported. This study was conducted in Yujiang County, Jiangxi Province, China using 174 and 257 samples collected in 1982 and 2007, respectively. The SOC spatial distributions for those 2 years and the associated temporal evolution were predicted via ordinary kriging (OK) and kriging combined with soil types and land-use (KSTLU) patterns. Results showed that KSTLU had better spatial prediction accuracy than OK for both years. The mean absolute errors (MAEs) of OK for 1982 and 2007 were 2.45 and 5.99 g kg, and the root mean square errors (RMSEs) were 3.37 and 7.23 g kg, respectively. Meanwhile, the MAEs of KSTLU for 1982 and 2007 were 1.99 and 3.23 g kg which are 19 and 46% lower than those of OK, respectively. The RMSEs were 2.76 and 3.97 g kg which were 18 and 45% lower than those of OK, respectively. Moreover, the result of temporal evolution from the KSTLU prediction showed that the area of increasing SOC (70%) is remarkably larger than the area of decreasing SOC (30%). The KSTLU prediction was more consistent with the statistical results than the OK prediction. Furthermore, the contours of SOC temporal evolution from KSTLU had a more detailed description for local change of SOC than OK. Thus, the prediction methods greatly affect the detection of SOC temporal evolution. Results of this study indicated that KSTLU is more efficient and rational than OK in studying the SOC temporal evolution in the Hilly Red Soil Region of South China. [ABSTRACT FROM AUTHOR]

Purpose: Mercury (Hg) accumulation and transfer in soil ecosystems has been altered on local, regional, and even global scales, and their environmental risk has increasingly been a concern to the public and the scientific community. Materials and methods: A county level region in Zhangjiagang County, the Yangtze River Delta (YRD) region of China and a factory with Hg-contaminated wastewater discharging within the region were selected to study the accumulation, bioavailability, and transfer of Hg from different sources in soils and crops under rapid industrialization, urbanization, and intensive agricultural activities. Regional soil samples close to and away from factories and local soil and crop samples around a typical factory were collected in the YRD region of China. Soil and crop Hg and basic soil properties were examined. Results and discussion: Significant soil Hg accumulation was found in soils away from factories regardless of Cambosols (Entisols) and Anthrosols (Inceptisols), while the mobile HCl-extractable Hg (HCl-Hg) were greater in soils closer to factories due to a decrease and increase in soil pH and organic matter. A high level of soil total Hg (T-Hg) was found around the factory, and soil and crop Hg accumulation in the vicinity of the factory was localized with an exponential decrease as distance away from the wastewater discharge outlet increased. Although Hg accumulated in these soils, the T-Hg levels at only a few sampling sites in acidic Anthrosols area were found to exceed the second most stringent critical value of Chinese Environmental Quality Standards for Soils. Conclusions: Considering the cessation of Hg-containing agrochemicals and limitation of effects of industrial activities on Hg accumulation, more attention should be paid to the changes in soil properties and crop rotations than controlling the pathways of Hg entering soils because the current environmental risk is mobilization of accumulated soil Hg. [ABSTRACT FROM AUTHOR]

Predicting soil organic carbon (SOC) content distribution accurately from limited soil samples has received a great deal of attention recently in an effort to support soil fertility mapping and to improve our understanding of carbon sequestration variability. Kriging methods combined with auxiliary variables are frequently used at present. However, studies using categorical information, such as soil type and land use, which are closely related to local trends in SOC spatial variation, as auxiliary variables are seldom conducted. In the present investigation, a total of 254 surficial soil samples were collected in the study area, Yujiang county in the hilly red soil region of South China, and a comparison of performance of four kriging approaches was conducted, ordinary kriging (OK), kriging combined with soil-type information (KST), land use (KLU) and combined land use–soil type information (KLUST). Results of the assessment were based on 85 validation samples. The results indicate that the best correlation between the measured and predicted values for validation location was obtained with KLUST ( r = 0.854), whereas the lowest was obtained using OK ( r = 0.383). Furthermore, the root mean square error (RMSE) from KLUST (3.47 g kg−1) is the lowest, whereas the one obtained using OK (6.49 g kg−1) is the highest. The correlation coefficient and RMSE from KST ( r = 0.784, RMSE = 4.15 g kg−1) and KLU ( r = 0.795, RMSE = 3.95 g kg−1) are the second and third most correlated, respectively. Comparing the SOC distribution maps generated by the four prediction approaches, the KLUST rendering best reflects the local change associated with soil types and land uses, whereas the map from the OK is the least representative. The results demonstrate that soil type and land use have an important impact on SOC spatial distribution, and KLUST, which reduces their influence as a local trend, is an efficient and practical prediction approach for the hilly red soil region of South China. [ABSTRACT FROM AUTHOR]

We have investigated the storage and spatial distribution of soil nitrogen (N) in China based on a data set of 2480 soil profiles and a map of Chinese soil types at a spatial resolution of 1:1,000,000. Our estimate indicates that the total N storage in China is 8.29 × 1015 g, representing 5.9–8.7% of the total global N storage. The total N storage in China is on average or slightly above the average of its share in the global N storage, even though low nitrogen content soils cover a large area in China. N density varies substantially with soil types and regions. Peat soils in the southeast of Tibet, southwest China, show the highest averaged N density with a value of 7314.9 g/m³ among all soil types. This is more than 30 times of the lowest N density of brown desert soils in the western desert and arid region. The highest N storages among all the soil types are the felty soil in southeast of Tibet, dark-brown earths in northeast China, and red earths in southeast China with values of 921.1, 611.4, and 569.6 Tg, respectively. N density also varies with land cover types in China. Wetlands in southwest China exhibit the highest N density at 6775.9 g/m³ and deserts in northwest China have the least at 447.5 g/m³. Our analysis also indicates that land cover types are poor predictors of N content. Further research is needed to examine how transformation from organic agriculture to increased use of fertilizers and pesticides has influenced N storage in China. [ABSTRACT FROM AUTHOR]

We have investigated the pools and distributions of soil phosphorus (P) in the top 50 cm of soil in China by using a combination of total and available P information from more than 2400 soil profiles and a map of soil types at a resolution of 1:1,000,000. Our estimates indicate that the average total P density and available P density in China are about 8.3 × 10² g/m³ and 5.4 g/m³, respectively. The total national soil P pool in the surface half meter is 3.5 Pg (1015 g). The available P density ranges from 0.7 g/m³ in the Lithosols to 16.7 g/m³ in the Irrigated Silting Soils. The total P density ranges from 1.2 × 10² g/m³ in the Lithosols to 19 × 10² g/m³ in the Frigid Desert Soils. The ratio of available P to total P density ranges from 0.6 × 10-3 in Aeolian Soils to 21.6 × 10-3 in Coastal Solonchaks. The available P content and its vertical distribution show a complex pattern among soil orders of different development stages, possibly indicating the important role of biota's control over soil available P content. There are large variations of P content in different climatic regions. The tropical and subtropical region has the lowest available P density (4.8 g/m³) and the second lowest total P density (8.2 × 10² g/m³) among all climatic regions. The large variation in the soil P content suggests that further study is needed to investigate climatic and land-use controls over the soil P content. [ABSTRACT FROM AUTHOR]

Southern China has abundant natural resources and is a major region of agricultural production. However, soil erosion is increasingly threatening the agricultural productivity of this region. Increases in soil erosion are caused by improper land use practices with soils of high rainfall erosivity. Much of the area prone to accelerated erosion was previously forested and subsequently logged four times since the 1920s. This paper discusses the effects of biological control practices on soil erosion according to erosion types, soil properties, and terrain. [ABSTRACT FROM PUBLISHER]