Distribution characteristics, source identification, and risk assessment of heavy metals in surface sediments of the salt lakes in the Ordos Plateau, China

Salt lakes have a significant effect on the regional climate, environment, and ecology in semi-arid regions characterized by lower rainfall and high evaporation. However, under the stresses of global change and human disturbance, anthropogenic pollution is the main factor threatening the lake ecological environment. Surface sediment samples collected from four salt lakes in the Ordos Plateau were used to investigate the salinity, concentration, pollution status, potential sources of heavy metals, and influencing factors. The surface sediments of Beida Pond and Gouchi Pond were weakly alkaline (pH < 9) owing to Na2SO4, whereas those of Chaigannaoer and Hongjiannao were strongly alkaline (pH > 9) owing to Na2CO3. The concentration range of Cr, Ni, Cu, Zn, As, Cd, and Pb in the sediment samples collected from the salt lake in the Ordos followed the order of Cr > Zn > Ni > Pb > Cu > As > Cd. The Cr values were higher in Chagannaoer and Hongjiannao, but the Ni, Cu, and Zn values were higher in Beida Pond and Gouchi Pond. The geoaccumulation index (Igeo) and enrichment factor (EF) consistently indicated that Cr posed the greatest potential ecological risk and that Ni, Cu, and Zn pollution was more severe in Beida Pond and Gouchi Pond than in Chagannaoer or Hongjiannao. However, Er and RI indicated these heavy metals were a low risk to the environment. Risk assessment code (RAC) revealed that Pb and Cr exhibited no mobility and had low potential bioavailability risk, although Zn, Ni, and As were categorized as medium risk. Cu had the highest mobility and high risk. Principal component analysis for Beida Pond and Gouchi Pond revealed that the source of Ni, Cu, Zn, Cd, and Pb might be associated with water - soluble elements in aqueous migration, and the source of Cr, Pb, and As might be lithospheric minerals carried by dust storms. Ni, Cu, Zn, Cd, Cr, and Pb in Chagannaoer and Hongjiannao may be derived from surface runoff, and chemicals from these sources may eventually accumulate in sediments. Pearson’s correlation analysis indicated that pH was the main environmental factor controlling the distribution of heavy metals in Chagannaoer and Hongjiannao.

Distribution characteristics, source identification, and risk assessment of heavy metals in surface sediments of the salt lakes in the Ordos Plateau, China

Salt lakes have a significant effect on the regional climate, environment, and ecology in semi-arid regions characterized by lower rainfall and high evaporation. However, under the stresses of global change and human disturbance, anthropogenic pollution is the main factor threatening the lake ecological environment. Surface sediment samples collected from four salt lakes in the Ordos Plateau were used to investigate the salinity, concentration, pollution status, potential sources of heavy metals, and influencing factors. The surface sediments of Beida Pond and Gouchi Pond were weakly alkaline (pH < 9) owing to Na2SO4, whereas those of Chaigannaoer and Hongjiannao were strongly alkaline (pH > 9) owing to Na2CO3. The concentration range of Cr, Ni, Cu, Zn, As, Cd, and Pb in the sediment samples collected from the salt lake in the Ordos followed the order of Cr > Zn > Ni > Pb > Cu > As > Cd. The Cr values were higher in Chagannaoer and Hongjiannao, but the Ni, Cu, and Zn values were higher in Beida Pond and Gouchi Pond. The geoaccumulation index (Igeo) and enrichment factor (EF) consistently indicated that Cr posed the greatest potential ecological risk and that Ni, Cu, and Zn pollution was more severe in Beida Pond and Gouchi Pond than in Chagannaoer or Hongjiannao. However, Er and RI indicated these heavy metals were a low risk to the environment. Risk assessment code (RAC) revealed that Pb and Cr exhibited no mobility and had low potential bioavailability risk, although Zn, Ni, and As were categorized as medium risk. Cu had the highest mobility and high risk. Principal component analysis for Beida Pond and Gouchi Pond revealed that the source of Ni, Cu, Zn, Cd, and Pb might be associated with water - soluble elements in aqueous migration, and the source of Cr, Pb, and As might be lithospheric minerals carried by dust storms. Ni, Cu, Zn, Cd, Cr, and Pb in Chagannaoer and Hongjiannao may be derived from surface runoff, and chemicals from these sources may eventually accumulate in sediments. Pearson’s correlation analysis indicated that pH was the main environmental factor controlling the distribution of heavy metals in Chagannaoer and Hongjiannao .

Distribution characteristics, source identification, and risk assessment of heavy metals in surface sediments of the salt lakes in the Ordos Plateau, China

Salt lakes have a significant effect on the regional climate, environment, and ecology in semi-arid regions characterized by lower rainfall and high evaporation. However, under the stresses of global change and human disturbance, anthropogenic pollution is the main factor threatening the lake ecological environment. Surface sediment samples collected from four salt lakes in the Ordos Plateau were used to investigate the salinity, concentration, pollution status, potential sources of heavy metals, and influencing factors. The surface sediments of Beida Pond and Gouchi Pond were weakly alkaline (pH < 9) owing to Na2SO4, whereas those of Chaigannaoer and Hongjiannao were strongly alkaline (pH > 9) owing to Na2CO3. The concentration range of Cr, Ni, Cu, Zn, As, Cd, and Pb in the sediment samples collected from the salt lake in the Ordos followed the order of Cr > Zn > Ni > Pb > Cu > As > Cd. The Cr values were higher in Chagannaoer and Hongjiannao, but the Ni, Cu, and Zn values were higher in Beida Pond and Gouchi Pond. The geoaccumulation index (Igeo) and enrichment factor (EF) consistently indicated that Cr posed the greatest potential ecological risk and that Ni, Cu, and Zn pollution was more severe in Beida Pond and Gouchi Pond than in Chagannaoer or Hongjiannao. However, Er and RI indicated these heavy metals were a low risk to the environment. Risk assessment code (RAC) revealed that Pb and Cr exhibited no mobility and had low potential bioavailability risk, although Zn, Ni, and As were categorized as medium risk. Cu had the highest mobility and high risk. Principal component analysis for Beida Pond and Gouchi Pond revealed that the source of Ni, Cu, Zn, Cd, and Pb might be associated with water - soluble elements in aqueous migration. For Cr, Pb, and As, it was indicated that the source of these heavy metals might be lithospheric minerals carried by dust storms. Ni, Cu, Zn, Cd, Cr, and Pb in Chagannaoer and Hongjiannao may be derived from surface runoff, and chemicals from these sources may eventually accumulate in sediments. Pearson’s correlation analysis indicated that pH was the main environmental factor controlling the distribution of heavy metals in Chagannaoer and Hongjiannao.

Distribution characteristics, source identification, and risk assessment of heavy metals in surface sediments of the salt lakes in the Ordos Plateau, China

Salt lakes have a significant effect on the regional climate, environment, and ecology in semi-arid regions characterized by lower rainfall and high evaporation. However, under the stresses of global change and human disturbance, anthropogenic pollution is the main factor threatening the lake ecological environment. Surface sediment samples collected from four salt lakes in the Ordos Plateau were used to investigate the salinity, concentration, pollution status, potential sources of heavy metals, and influencing factors. The surface sediments of Beida Pond and Gouchi Pond were weakly alkaline (pH < 9) owing to Na2SO4, whereas those of Chaigannaoer and Hongjiannao were strongly alkaline (pH > 9) owing to Na2CO3. The concentration range of Cr, Ni, Cu, Zn, As, Cd, and Pb in the sediment samples collected from the salt lake in the Ordos followed the order of Cr > Zn > Ni > Pb > Cu > As > Cd. The Cr values were higher in Chagannaoer and Hongjiannao, but the Ni, Cu, and Zn values were higher in Beida Pond and Gouchi Pond. The geoaccumulation index (Igeo) and enrichment factor (EF) consistently indicated that Cr posed the greatest potential ecological risk and that Ni, Cu, and Zn pollution was more severe in Beida Pond and Gouchi Pond than in Chagannaoer or Hongjiannao. However, Er and RI indicated these heavy metals were a low risk to the environment. Risk assessment code (RAC) revealed that Pb and Cr exhibited no mobility and had low potential bioavailability risk, although Zn, Ni, and As were categorized as medium risk. Cu had the highest mobility and high risk. Principal component analysis for Beida Pond and Gouchi Pond revealed that the source of Ni, Cu, Zn, Cd, and Pb might be associated with water - soluble elements in aqueous migration. For Cr, Pb, and As, it was indicated that the source of these heavy metals might be lithospheric minerals carried by dust storms. Ni, Cu, Zn, Cd, Cr, and Pb in Chagannaoer and Hongjiannao may be derived from surface runoff, and chemicals from these sources may eventually accumulate in sediments. Pearson’s correlation analysis indicated that pH was the main environmental factor controlling the distribution of heavy metals in Chagannaoer and Hongjiannao.

Water Source of Six Woody Plants in Different Habitats on Desertified Land of Ordos Plateau, Semi-Arid China

Water and soil erosion and sandy desertification are two mainly land desertification types on eastern and southern Ordos Plateau, north China. Hippophae rhamnoides, Armeniaca sibirica and Pinus tabuliformis are three woody plants for soil and water conservation on loess slope. Sabina vulgaris, Artemisia ordosica and Salix psammophila are three shrubs for sand control on sand dune. Water source of six woody plants were investigated by stable isotope technology. The results showed that the δ18O of shallow soil water was similar to that of rainwater in July and September in two habitats. Both of six woody plants in two habitats mainly used shallow soil water in May. However, three shrubs on sand dune mainly used both of shallow and deep soil water in July and September. Three woody plants on loess slope mainly used rainwater or deep soil water in July and September. Therefore, six woody plants utilized different depths of soil water or rain water based on their availability in different seasons, which is an adaptive strategy to the semiarid climate on Ordos Plateau.

Cellulose δ18O of Tree Rings Reflects Vapour Pressure Variations in the Ordos Plateau

In arid and semi-arid regions, a better understanding of the effect of climate change mechanisms on environmental evolution can be used to guide regional ecological conservation and to improve water resource availability. Increased aridity in arid and semi-arid regions considerably affects the physiological functions of plants and the exchange of carbon and water with the environment. We collected Pinus tabuliformis Carr. samples from Ordos, Inner Mongolia, and measured their δ18O variations. Vapour pressure (VP) was the main factor dominating δ18O variations from July to August, indicating the regulatory role of plant leaf stomata. Based on the δ18O series in the Ordos region, we reconstructed VP variations for July–August (VPJA) for the past 205 years. Spatial analysis showed the reconstruction as spatially highly representative. VP variations in the Ordos region mainly reflected precipitation variations and did not show a significant correlation with temperature. Since the late 1950s, VP has been decreasing, which is related to the weakening of the Asian monsoon. The results of reconstruction decomposed using ensemble empirical mode decomposition showed that El Niño–Southern Oscillation may affect VP in the study area, and the effect of sea surface temperature on the central and eastern Pacific Ocean in the Ordos region may lead to an increase in the drought.