[Effect of Ca Modified Biochar on the Chemical Speciation of Soil Phosphorus and Its Stabilization Mechanism].

To control of phosphorus release from soil after farmland inundation around the lake and reservoir， calcium modified biochar （Ca-BC） was prepared using the coprecipitation method. Through X-ray photoelectron spectroscopy （XPS）， X-ray polycrystalline powder diffraction （XRD）， adsorption experiments， and simulated culture experiments， the effects of Ca-based biochar on the fraction of soil phosphorus （P） and its stabilization mechanism were studied. The results showed that the adsorption process of Ca-based modified biochar conformed to Langmuir （R2 = 0.940） and the first-order adsorption kinetic model （R2 = 0.961）， indicating that the P adsorption was a single-layer adsorption dominated by chemical action， and the maximum adsorption capacity was 267.93 mg·g-1. The simulated culture experiment indicated that when the modified biochar was 1%， the exchangeable fraction of phosphorus in the soil decreased from 7.42% to 4.59%. The XRD results demonstrated that Ca3（PO4）2 and hydroxyapatite absorption peaks appeared after adsorbed phosphorus on biochar， which proved that phosphate formed a relatively stable crystal precipitation. As shown in the XPS spectrum analysis， the carbonyl functional groups participated in the phosphorus fixation process， which improved the adsorption capacity of biochar for phosphorus. In general， when the concentration of Ca-based modified biochar was greater than 1%， it had a good fixation capacity for phosphorus release and had potential application value for controlling phosphorus release in soil.

[Speciation Distribution and Risk Assessment of Heavy Metals in Sediments from the Yitong River City Area].

The total content and chemical speciation of Cd, Cr, Cu, Ni, Pb, and Zn in seven short cores sampled from the Yitong River from Changchun City were analyzed to assess the pollution levels and potential ecological risks of heavy metals in the sediments. The results demonstrated that the total contents of Cd, Cr, Cu, Ni, Pb, and Zn in sediments were 0.10-1.18, 23.57-66.35, 11.27-43.95, 10.78-29.82, 15.02-60.81, and 54.27-175.83 mg·kg-1, respectively. The acid-soluble fraction of Cd varied from 42.1% to 51.28%, whereas Cr, Ni, and Zn were mainly found in the residual fraction; their mass fractions were 63.54%-79.91%, 35.16%-53.75%, and 27.55%-57.55%, respectively. The vertical results of pollution degree and ecological risk assessment indicated that the studied sediment was polluted by Cd, Cu, Pb, and Zn, and the ecological risk of Cd was the highest, followed by Zn and Cu. Each group of metals in each core showed a similar vertical variation, and the ecological risk of metals in sediment of 4-8 cm depth was relatively high. Cd, Zn, and Pb in the sediments of Yitong River were mainly from industrial pollution and municipal sewage discharge, and Cu could be attributed to both natural processes and human activities, whereas Cr and Ni may be attributed to natural processes.