Time: 15:00-17:00, 24th October (Wednesday)
Venue: Lecture Hall 221, Institute of Surface-Earth System Science (Building No. 16), Tianjin University
Lecture I: DOM affects the bioaccumulation of heavy metals by fresh algae
Speaker: Prof. LI Feili, Zhejiang University of Technology
Abstract: Dissolved organic matter is widely existed in water and affects the bioaccumulation of heavy metals by freshwater algae, which will reduce the accuracy of predicting the bioavailability of heavy metals by water quality prediction models. From the view of molecular weight, main functional groups and polarity of DOM, the behavior characteristics of chlorella Pyrenoidosa in the enrichment of heavy metals Cu and Pb in the presence of various DOM were studied. It has been found that the concentration of free metal ions in water was decreased by the complexation of DOM, which inhibited the enrichment of heavy metals by algae. However, when the ternary complexes of DOM - metal ions - algae were formed, the accumulation of heavy metals by algae can be increased by times or even orders of magnitude. Among various DOM extracted and separated from Taihu Lake, F1 with the largest carboxyl percentage (molecular weight < 500da) and the transitional TPHA with the largest concentration of carboxyl groups can promote the enrichment of heavy metals in algae, compared with other DOM with larger molecular weight and hydrophobicity. SEM and TEM observations showed that a large amount of Pb is enriched on the cell wall surface of algae in ternary system. The formation mechanism of ternary complexes is concluded that metal ions plays a bridging role in the ternary complexes, and the proper concentration ratio of metal ions to DOM is the key to the formation of ternary complexes. This study provides a scientific basis for accurately understanding the migration and transformation of heavy metals in aquatic ecosystems and for effectively carrying out the control of heavy metal pollution in freshwater.
Lecture II: Combining chemical characteristics with stable isotopes to determine nitrate sources of precipitation at typical cities, SE China
Speaker: Prof. JIN Zanfang, Zhejiang University of Technology
Abstract: The contribution of NO3- in precipitation to surface water and acid rain is increasing. The hydrochemistry and stable isotopes (δ2H, δ18O, δ15N-NO3 and δ18O-NO3) of precipitation were analyzed to determine the chemical characteristics and the sources of NO3- in precipitation at typical cities, SE China. The slope and intercept of LMWL (δ2H = 8.87δ18O + 25.95, R2 = 0.90, n = 157) in the whole region were higher than the GMWL and the China LMWL. Based on the HYSPLIT model, the air masses of precipitation in spring, autumn and winter coming from the north Asian continent and near-sources caused higher δ2H and δ18O values, while those in summer from the low latitudes of the South China Sea and the western Pacific Ocean caused lower δ2H and δ18O values. The increase of desulphurizing systems in coal combustion and more motor vehicle resulted in a lower [SO42-]/[NO3-] ratio of precipitation, indicating mixed acid rain in Hangzhou and Huzhou. δ15N-NO3 values variations was demonstrated the multiple sources of NO3- and regional differences in the contribution of the main NO3- sources in precipitation in Hangzhou and Huzhou. Higher levels of traffic emissions in Hangzhou were responsible for the spatial variations in δ15N-NO3 values between Hangzhou and Huzhou. The seasonal variation of δ15N-NO3 values was influenced by the changing contributions of the main NO3- sources in precipitation collected from the study areas: soil emissions increased in summer and coal consumption emissions increased because of coal consumption for winter heating from northern China in Hangzhou and Huzhou. The different NO2 oxidation pathways are particularly important in seasonal variation of δ18O-NO3. Due to the oxidation of NO2 via O3 forming HNO3 in the N2O5 pathway, the highest δ18O-NO3 values were observed in the winter. The lowest δ18O-NO3 values were explained by the NOx oxidation forming HNO3 via the OH pathway in the summer. The results showed that nitrate sources of precipitation could be identified effectively by combining chemical components with stable isotopes. Effective measures, such as, simultaneous desulfurization and denitrification, decreasing traditional fuel vehicles, promoting electric vehicles, should be used to reduce NOX emissions and improve air quality in Hangzhou City and Huzhou City.
