Nan Zhongren

Spatial Distribution of Selected trace Metals in Urban Soils of Lanzhou City, Gansu Province, Northwestern of China

Contamination of urban ecosystems with trace elements has become an important topic of investigation. A preliminary survey was conducted in Lanzhou city with an approximately 1.8 million inhabitants and a surface area of 1663 km. A total of 56 surface soil samples (0~15 cm) had been collected in the urban area according to the city planning districts, and each sample site was located by GPS, and the digestion soil total contents of copper, zinc, and lead had been determined using AAS with a graphite furnace. Results show that: 1the means of metal Zn and Pb were about 1.5 and 1.8 times more than the soil background contents, respectively; and contents of both metals showed wide ranges (Pb 7.6-96 mg/kg DW, Zn 33.9-282 mg/kg DW); 2Concentrations of selected metals Cu, Zn and Pb in most sites, 56% for Cu, 84% for Zn and 63% for Pb of total sample number, respectively; and3From maps made by means of GIS with kriging-interpolated method, it can be discovered that the heavy polluted soils were in the proximity of the motorway and streets with high traffic flows, especial near city crossroad or service station, and in sites of industrial region corresponding with areas of oil refineries where combustible deposit occurred. So, the following conclusion can be drawn that the urban soils studied has been affected by human activity resulted in a high accumulation of selected trace metals, and the topsoil metal contents clearly revealed an anthropogenic origin of contamination. Keywords-Urban soils of Lanzhou; Heavy metals Cu, Zn and Pb; Pollution; Spatial distribution

Effects of agro-activities on the soil organic carbon and soil properties in the middle reaches of Heihe river, Northwestern China

Knowledge about changes of SOC and other properties under influence of human activities in arid zone is very important for local cropland persistent management. In our study, SOC and selected soil properties had been investigated in the Linze country located in Hexi corridor, northern west China. The GIS tool was used to explain the causes resulted in SOC spatial distribution. The results indicated that the highest levels of SOC, humic acid, and fulvic acid presented in early cultivated plots, then in lately reclaimed cropland, and the lowest in desert soil. The remarkable increasing of soil CEC and clay content can been seen in arable land in contrast to desert land. Our findings may suggest that agricultural practices, such as irrigation, use of manure and fertilizer, return of crop residues, etc. protect SOC from loss and improve the soil fertility in arid area studied.

GIS-assisted modelling of the spatial distribution of Qinghai spruce (Picea crassifolia) in the Qilian Mountains, northwestern China

The aim of this study was to predict Qinghai spruce (Picea crassifolia) distribution at the regional scale, i.e., where the extent of the prediction was within the biogeographic range of Qinghai spruce in the study area. First, we selected the main resource variables such as mean July temperature, soil moisture and solar radiation. These variables were spatialized as functions of elevation and geographical coordinates or as functions of aspect and slope via a GIS. Second, the niche spaces of Qinghai spruce were determined by incorporating the spatially-distributed resource variables with the current distribution of the species, which came from remote sensing data (Landsat TM image). The niche spaces defined then were extrapolated over the study area. Third the distribution pattern was calibrated by field investigations. The results show the niche spaces of Qinghai spruce: the scope of mean July temperature ranging from 8.5 /spl deg/C to 13.5/spl deg/C, average annual precipitation from 370 mm to 660 mm, the soil moisture index from 2.3 m/sup 3//m yr to 4.5 m/sup 3//m yr and the shortwave radiation for an average July day from 3.8 mm m/sup -2/ day/sup -1/ to 7.8 mm m/sup -2/ day/sup -1/. According to the niche, the elevation range belonging to Qinghai spruce in Qilian Mountains was extracted from DEM, which was about from 2600 m to 3400 m. The result was consistent with other investigations. We found that the density of the species has higher value from 2650 m to 3100 m based on the field investigation, and from the height 3100 m the density decreased with elevation increase. The basal area of Qinghai spruce had the same trend as the density. That is, the suitable niche of the species ranged from 2650 m to 3100 m.

Relationship between vegetation distribution and groundwater level in the lower reaches of Heihe River basin, China

The relationship between vegetation coverage and groundwater level was built in the study area according to investigation data. The spatial and temporal variation of groundwater levels was simulated by FEFLOW from 1980 to 2010. Temporal-spatial distribution of Potential vegetation in the study area was estimated using the relationship combining with spatial distribution of groundwater level. The results of coverage estimated were validated by Landsat TM data.

Estimating Daily Evapotranspiration in Guanchuanhe River Basin Using Remote Sensing

The method used in the study is based on surface energy balance equation, i.e. Rn =lambdaET + H + G. By analyzing the spatial distribution of ET, we can draw that the spatial variation of ET is obvious. The estimated ET value ranges from 1.2 to 8.5 mm, with the average value of 4.7 mm on April 15, 2000. Spatially, it increased from north to south. The highest value is occurred at the source of the river, where is woodland distributing. The results have been validated by field data, and the root mean square error (RMSE) is 0.8. The errors are less than 0.7 mm in most of the stations except one. It proved that the method is feasible to estimate ET in the study area. The study enables us to better predict land surface hydrological cycle and lays a foundation for ecological restoration and application of distributed hydrologic model.