Soil Organic Carbon and Its Fractions Across Vegetation Types:Effects of Soil Mineral Surface Area and Microaggregates

Soil organic carbon(SOC)can act as a sink or source of atmospheric carbon dioxide;therefore,it is important to understand the amount and composition of SOC in terrestrial ecosystems,the spatial variation in SOC,and the underlying mechanisms that stabilize SOC.In this study,density fractionation and acid hydrolysis were used to assess the spatial variation in SOC,the heavy fraction of organic carbon(HFOC),and the resistant organic carbon(ROC)in soils of the southern Hulun Buir region,northeastern China,and to identify the major factors that contribute to this variation.The results showed that as the contents of clay and silt particles(0–50μm)increased,both methylene blue(MB)adsorption by soil minerals and microaggregate contents increased in the 0–20 and 20–40 cm soil layers(P<0.05).Although varying with vegetation types,SOC,HFOC,and ROC contents increased significantly with the content of clay and silt particles, MB adsorption by soil minerals,and microaggregate content(P<0.05),suggesting that soil texture,the MB adsorption by soil minerals,and microaggregate abundance might be important factors influencing the spatial heterogeneity of carbon contents in soils of the southern Hulun Buir region.

Effect of reactive surface area of minerals on mineralization trapping of CO_2 in saline aquifers

The reactive surface area, an important parameter controlling mineral reactions, affects the amount of mineralization trapping of CO2 which affects the long-term CO2 storage. The effect of the reactive surface area on the mineralization trapping of CO2 was numerically simulated for CO2 storage in saline aquifers. Three kinds of minerals, including anorthite, calcite and kaolinite, are involved in the mineral reactions. This paper models the relationship between the specific surface area and the grain diameter of anorthite based on experimental data from literature （Brantley and Mellott, 2000）. When the reactive surface areas of anorthite and calcite decrease from 838 to 83.8 m^2/m^3, the percentage of mineralization trapping of CO： after 500 years decreases from 11.8% to 0.65%. The amount of dissolved anorthite and the amounts of precipitated kaolinite and calcite decrease significantly when the reactive surface areas ofanorthite and calcite decrease from 838 to 83.8 m2/m3. Calcite is initially dissolved in the brine and then precipitates during the geochemical reactions between CO2-H20 and the minerals. Different reactive surface areas of anorthite and calcite lead to different times from dissolution to precipitation. The pH of the brine decreases with decreasing reactive surface areas of anorthite and calcite which influences the acidity of the saline aquifer. The gas saturation between the upper and lower parts of the saline aquifer increases with decreasing reactive surface areas of anorthite and calcite. The mass density distribution of brine solution shows that the CO2^＋brine solution region increases with decreasing reactive surface areas ofanorthite and calcite.

Unraveling the size distributions of surface properties for purple soil and yellow soil

Soils contain diverse colloidal particles whose properties are pertinent to ecological and human health, whereas few investigations systematically analyze the surface properties of these particles. The objective of this study was to elucidate the surface properties of particles within targeted size ranges（i.e. 〉 10, 1-10, 0.5-1, 0.2-0.5 and 〈 0.2 μm） for a purple soil（Entisol） and a yellow soil（Ultisol） using the combined determination method. The mineralogy of corresponding particle-size fractions was determined by X-ray diffraction.We found that up to 80% of the specific surface area and 85% of the surface charge of the entire soil came from colloidal-sized particles（〈 1 μm）, and almost half of the specific surface area and surface charge came from the smallest particles（〈 0.2 μm）. Vermiculite,illite, montmorillonite and mica dominated in the colloidal-sized particles, of which the smallest particles had the highest proportion of vermiculite and montmorillonite. For a given size fraction, the purple soil had a larger specific surface area, stronger electrostatic field, and higher surface charge than the yellow soil due to differences in mineralogy.Likewise, the differences in surface properties among the various particle-size fractions can also be ascribed to mineralogy. Our results indicated that soil surface properties were essentially determined by the colloidal-sized particles, and the 〈 0.2 μm nanoparticles made the largest contribution to soil properties. The composition of clay minerals within the diverse particle-size fractions could fully explain the size distributions of surface properties.