Multivariate-statistical assessment of heavy metals for agricultural soils in northern China.

The study evaluated eight heavy metals content and soil pollution from agricultural soils in northern China. Multivariate and geostatistical analysis approaches were used to determine the anthropogenic and natural contribution of soil heavy metal concentrations. Single pollution index and integrated pollution index could be used to evaluate soil heavy metal risk. The results show that the first factor explains 27.3% of the eight soil heavy metals with strong positive loadings on Cu, Zn, and Cd, which indicates that Cu, Zn, and Cd are associated with and controlled by anthropic activities. The average value of heavy metal is lower than the second grade standard values of soil environmental quality standards in China. Single pollution index is lower than 1, and the Nemerow integrated pollution index is 0.305, which means that study area has not been polluted. The semivariograms of soil heavy metal single pollution index fitted spherical and exponential models. The variable ratio of single pollution index showed moderately spatial dependence. Heavy metal contents showed relative safety in the study area.

[Impact of land-use type changes on soil nitrification and ammonia-oxidizing bacterial community composition].

A comparative study was conducted to determine nitrification potentials and ammonia-oxidizing bacterial (AOB) community composition in 0-20 cm soil depth in adjacent native forest,natural grassland, and cropland soils on the Tibetan Plateau, by incubation experiment and by denaturing gradient gel electrophoresis (DGGE) of 16S rDNA, respectively. Cropland has the highest nitrification potential and nitrate concentration among the three land-use types (LUT), approximately 9 folds and more than 11 folds than that of the forests and grasslands, respectively. NO3(-) -N accounted for 70%-90% of inorganic N in cropland soil, while NH4(+) -N was the main form of inorganic N in forest and grassland soils. Nitrification potentials and nitrate concentrations showed no significant difference between native forest and grassland soils. The native forest showed the lowest nitrification potentials and the lowest AOB diversity and community composition among the three LUT. Conversions from natural grasslands to croplands remarkably decreased the AOB diversity and composition, but croplands remain high similarity in AOB community composition compared with grasslands. The minimal and the lowest diversity of AOB in native forests directly resulted to the lowest nitrification potentials compared to natural grasslands and croplands. From the fact of the highest nitrification potentials and nitrate concentrations in croplands indicated that there were the most substantial AOB with higher activity and priority. The results provide evidence that changes of land-use type can affect both soil nitrogen internal cycling process, the diversity, community and activity of AOB, which further affect soil environment quality and the long-term sustainability of ecosystems.

An investigation on magnetic susceptibility of hazardous saline-alkaline soils from the contaminated Hai River Basin, China.

Magnetic susceptibility can provide rich environmental information, especially for hazardous heavy metals and saline-alkaline in the contaminated soils. Magnetic susceptibility in four vertical profiles from saline-alkaline soils in lower Hai River basin was investigated. Soil sites were extended from alluvial fan to coastal plain areas. They are aligned along a latitudinal strip. Magnetic parameters including low/high frequency susceptibility, frequency-dependent susceptibility was measured. Moreover, some standard pedological parameters such as pH value and organic matter content were also determined. The results showed that low frequency magnetic susceptibility values is very high at the surface and decreases with the profile to a low value. In all profiles from alluvial fan frequency-dependent susceptibility greater than 3% may suggest the presence of relatively more super-paramagnetic particles. Magnetic susceptibility showed obvious vertical distribution in alluvial fan higher than coastal plain. No significant correlations between organic matter, pH and low frequency magnetic susceptibility were found, while there is a negative correlation between organic matter and frequency-dependent susceptibility. A positive correlation between pH and frequency-dependent susceptibility was found in the study areas.

An investigation on the distribution of eight hazardous heavy metals in the suburban farmland of China.

Understanding spatial variability of hazardous soil heavy metals is an important precondition for suitably monitoring and evaluating eco-environment quality in the primary agricultural production zone. One hundred topsoils were sampled from the urban-rural transition zone in Taihang Piedmont Plain, China. The contents of eight heavy metals Cu, Zn, Cr, Ni, Pb, Cd, Hg and As were tested for each soil sample, and their spatial patterns were analyzed by the semivariogram approach of geostatistics and geographical information system (GIS) technology. Results showed that Cd concentration exceeded its background level. The local pollution from Cd attributed to the anthropogenic influence. The concentrations of eight hazardous heavy metals are relatively lower than the critical values of the national soil quality standard. The correlation distance of soil heavy metals ranged from 3.28 to 11.63 km, with the eight heavy metals having moderate spatial dependence. Cu, Cr, Ni, Pb and As are associated with and controlled by parent material. The results are helpful for improving agricultural and forest ecosystem in the arid and semiarid region.

The spatial variability of heavy metal distribution in the suburban farmland of Taihang Piedmont Plain, China.

The understanding of the spatial variability of soil heavy metals is an important precondition for suitably monitoring and evaluating eco-environment quality in a primary agricultural production zone. 100 topsoils were sampled from the Zhengding County of the urban-rural transition zone in Taihang Piedmont Plain, China. The contents of eight heavy metals Cu, Zn, Cr, Ni, Pb, Cd, Hg and As were tested for each soil sample, and their spatial patterns were analyzed by using the semivariogram approach of geostatistics, with which the kriging method was used to estimate the unobserved points. Then GIS technology was employed to produce spatial distribution maps of the 8 elements. The results showed that the concentration of Cd exceeded its background level. The local pollution from Cd was attributed to the anthropogenic influence. The concentrations of the eight heavy metals are relatively lower than the critical values of the national soil quality standard. The correlation distance of soil heavy metals ranged from 3.28 to 11.63 km, with the eight heavy metals having moderate spatial dependence. Cu, Cr, Ni, Pb and As were associated with and controlled by parent material. The spherical model was fitted to the semivariograms of Cu, Cr, Cd, Hg, Pb and As, and the Zn and Ni were fitted with the Gaussian model and the linear model, respectively. The results are helpful for improving agricultural and forest ecosystem in the region.

[Spatial variability of farmland heavy metals contents in Qianan City].

By the methods of geostatistics and GIS, this paper studied the spatial variability of Cu, Zn, Ni, Cr As, Hg, Cd and Pb contents in the farmland topsoil (0 -20 cm) of Qianan City, Hebei Province. The results showed that the average contents of test metals were under the secondary standard of environmental quality standard for soil (GB 15618-1995), and belonged to moderate variability. The theoretical models of semi-variance of Cu, Zn, Ni, Cr and As contents fitted exponential models, and their spatial correlations were strongly spatial dependence; while the theoretical models of Hg and Cd contents fitted spherical models, and their spatial correlations were moderately spatial dependence. The Pb content had pure nugget effect, and was weakly spatial dependence. In whole research scale, Pb content had lasting variability, while the other seven heavy metals contents had the spatial variability mainly caused by their spatial correlation parts. The ranges of heavy metals spatial correlations were about 11 km to 20 km. The Kriging' s interpolation of Cu, Zn, Ni, Cr, Hg, As and Cd contents showed that their contents were higher in northern mountainous area, but lower in mid basin.

[Effects of stress duration and non-toxic ions on heavy metals toxicity to Arabidopsis seed germination and seedling growth].

The study on the toxicity of heavy metals Hg2+, Cd+, Cu2+ and Pb2+ to Arabidopsis se d germination and seedling growth showed that the test heavy metals had a stronger toxicity on seedling growth than on seed germination. The toxicity on seedlings was in order of Cu2+ > Hg2+ > Cd2+ /Pb2+, while on seeds was Hg2+ > Cd2+ > Pb2+/Cu2+. Seed germination rate was decreased with increasing stress duration, and different heavy metals showed different toxicity at different stress duration. For example, Hg2+ displayed a stronger toxicity at 12 - 24 h stress, while Cd2+ was at 0 - 12 h stress. It seemed that seed coat played an important role in seed tolerance to heavy metals. The interaction between non-toxic ions and heavy metal ions on seed germination showed that Ca2+, Mg2+, K+ and Na+ at 5 mmol x L(-1) could enhance the toxicity of Hg2+, but did not affect Cd2+ toxicity. For seedling growth, Ca2+, Mg2+, K+ and Na+ might enhance the toxicity of Hg2+, Ca2+ might alleviate the toxicity of Cd2+ but enhance the toxicity of Cu2+ , and K+ might alleviate Pb2+ toxicity. The mechanism of heavy metals injury was discussed in the paper.

[Nitrogen, phosphorus and potassium cycling and balance in farmland ecosystem at the piedmont of Taihang].

The feature and change trend of N, P and K cycling and balance in farmland ecosystem of Luancheng County at the piedmont of Taihang were analyzed. The status of nutrient balance was appraised, and the rational way to apply fertilizer was put forward. The result indicated that N balance went through a process from slight deficit to surplus during 1985-2000, changing from deficit of 1.4% in 1985 to surplus of 48.6% in 2000. Potassium balance changed gradually from serious deficit of 82% to slight surplus of 4.6%, but was still deficit in many fields. P budget was surplus ever since 1985. Comparing with the output of nutrients, the inputs of N and P were excessive, but the K input was short. Under the current soil fertility and crop planting structure, the countermeasure to control the application amount of N and P and to increase the application rate of K should be carried out, so that, there would be no significant surplus N emitting or leaching from soil into environment. The technique to return crop straw into farmland should be extended to increase the nutrient recycling rate.

[Spatial variability of farmland soil nutrients at Taihang piedmont].

By the method of geostatistics, this paper studied the spatial variability of soil nutrients in 30,490 hm2 crop field in Luancheng region and in 15 hm2 experimental field in Luancheng Ecological Agriculture Station of Chinese Academy of Sciences. The results showed that the variation of soil nutrient contents differed obviously, and the semivariograms could be simulated by Gaussian and spherical models with some nugget variances. The limit distance of spatial correlation was 4.2-15.6 km and 112-223 m in Luancheng region and in experimental field, respectively, and the spatial variability of soil organic matter, N, P and K was of semivariance structure. It revealed that there existed a spatial correlation in soil nutrient contents under relatively large-block scale, which made it possible to develop regionalized soil nutrient precision management.