Yugang Wang

Integrated assessment of heavy metal contamination in sediments from a coastal industrial basin, NE China.

The purpose of this study is to investigate the current status of metal pollution of the sediments from urban-stream, estuary and Jinzhou Bay of the coastal industrial city, NE China. Forty surface sediment samples from river, estuary and bay and one sediment core from Jinzhou bay were collected and analyzed for heavy metal concentrations of Cu, Zn, Pb, Cd, Ni and Mn. The data reveals that there was a remarkable change in the contents of heavy metals among the sampling sediments, and all the mean values of heavy metal concentration were higher than the national guideline values of marine sediment quality of China (GB 18668-2002). This is one of the most polluted of the world’s impacted coastal systems. Both the correlation analyses and geostatistical analyses showed that Cu, Zn, Pb and Cd have a very similar spatial pattern and come from the industrial activities, and the concentration of Mn mainly caused by natural factors. The estuary is the most polluted area with extremely high potential ecological risk; however the contamination decreased with distance seaward of the river estuary. This study clearly highlights the urgent need to make great efforts to control the industrial emission and the exceptionally severe heavy metal pollution in the coastal area, and the immediate measures should be carried out to minimize the rate of contamination, and extent of future pollution problems.

Hidden carbon sink beneath desert

For decades, global carbon budget accounting has identified a “missing” or “residual” terrestrial sink; i.e., carbon dioxide (CO2) released by anthropogenic activities does not match changes observed in the atmosphere and ocean. We discovered a potentially large carbon sink in the most unlikely place on earth, irrigated saline/alkaline arid land. When cultivating and irrigating arid/saline lands in arid zones, salts are leached downward. Simultaneously, dissolved inorganic carbon is washed down into the huge saline aquifers underneath vast deserts, forming a large carbon sink or pool. This finding points to a direct, rapid link between the biological and geochemical carbon cycles in arid lands which may alter the overall spatial pattern of the global carbon budget.

Storage/Turnover rate of inorganic carbon and its dissolvable part in the profile of saline/alkaline soils.

Soil inorganic carbon is the most common form of carbon in arid and semiarid regions, and has a very long turnover time. However, little is known about dissolved inorganic carbon storage and its turnover time in these soils. With 81 soil samples taken from 6 profiles in the southern Gurbantongute Desert, China, we investigated the soil inorganic carbon (SIC) and the soil dissolved inorganic carbon (SDIC) in whole profiles of saline and alkaline soils by analyzing their contents and ages with radiocarbon dating. The results showed that there is considerable SDIC content in SIC, and the variations of SDIC and SIC contents in the saline soil profile were much larger than that in the alkaline profile. SDIC storage accounted for more than 20% of SIC storage, indicating that more than 1/5 of the inorganic carbon in both saline and alkaline soil is not in non-leachable forms. Deep layer soil contains considerable inorganic carbon, with more than 80% of the soil carbon stored below 1 m, whether for SDIC or SIC. More importantly, SDIC ages were much younger than SIC in both saline soil and alkaline soil. The input rate of SDIC and SIC ranged from 7.58 to 29.54 g C m-2 yr-1 and 1.34 to 5.33 g C m-2 yr-1 respectively for saline soil, and from 1.43 to 4.9 g C m-2 yr-1 and 0.79 to 1.27 g C m-2 yr-1respectively for alkaline soil. The comparison of SDIC and SIC residence time showed that using soil inorganic carbon to estimate soil carbon turnover would obscure an important fraction that contributes to the modern carbon cycle: namely the shorter residence and higher input rate of SDIC. This is especially true for SDIC in deep layers of the soil profile.

Effect of Land Use History and Pattern on Soil Carbon Storage in Arid Region of Central Asia

The purpose of this study is to investigate variations in soil organic carbon (SOC) in arid areas due to differences in the cultivation history, land use, and soil salinization. The study area is the lower Sangong River basin on the piedmont of the northern TianShan mountains, which experiences heavy land-use activities. In 1982 and 2005,127(152) and 74 (161) samples in old (new) oasis were collected from each site at the surface soil (i.e., 0–20 cm). The data reveal that the mean value of the surface soil organic carbon content of the old oasis was higher than that of the new oasis by 4.01 g/kg in 1982 and 3.79 g/kg in 2005. Additionally, the soil organic carbon content decreased more rapidly in the newly reclaimed oasis than in the old oasis from 1982 to 2005. The spatial pattern of the SOC content was correlated with the exploitation time in the new oasis, the agricultural land use history, and the SOC content. The decreasing trend is clearer in the high SOC content area than in the low SOC content area. Farmland is the largest carbon pool in both the new and old oases. The carbon density of the old oasis was higher than that of the new oasis by 4.01 and 3.79 g/kg in 1982 and 2005 respectively. The loss of SOC in the agricultural watershed of the arid region in NW China is obvious. Improvements of land management practices, such as no tillage, straw returning to soil, and balanced fertilization techniques, should be adopted to increase the SOC content.