Distribution and accumulation of biogenic silica in the intertidal sediments of the Yangtze Estuary

Sedimentary biogenic silica is known to be all important parameter to understand biogeochemical processes and paleoenviromental records in estuarine and coastal ecosystems. Consequently, it is of great significance to investigate accumulation and distribution of biogenic silica in sediments. The two-step mild acid-mild alkaline extraction procedure was used to leach biogenic silica and its early diagenetic products in intertidal sediments of the Yangtze Estuary. The results showed that total biogenic silica(t-BSi)in the intertidal sediments varied from 237. 7-419. 4 μmol Si/g. while the mild acid leachable silica(Si-HCl)and the mild alkaline leachable silica(Si-Alk)were in the range of 25. 1-72. 9μmol Si/g and 208. 1-350. 4 μmol Si/g. respectively. Significant correlations were observed for the grain size distributions of sediments and different biogenic silica pools in intertidal sediments. This confirms that grain size distribution Can significantly affect biogenic silica contents in sediments. Close relationships of biogenic silica with organic carbon and nitrogen Were also found, reflecting that there is a strong coupling between biogenic silica and organic matter biogeochemical cycles in the intertidal system of the Yangtze Estuary. Additionally, the early diagenetic changes of biogenic silica in sediments are discussed in the present study.     

环境空气质量新标准对珠三角区域站空气质量评价的影响

利用粤港珠三角区域空气质量监控网中天湖、金果湾与万顷沙3个区域站2010年全年SO₂、NO₂、PM₁₀、O₃、PM_2.5与CO自动监测的数据,分析了实施环境空气质量新标准(GB 3095—2012)对这3个子站空气质量评价的影响。研究发现,若采用新标准,万顷沙的NO₂、PM₁₀和PM_2.5年均浓度将不同程度超标。这3个子站空气质量达标率下降7~28个百分点,空气污染指数从91%~99%下降至63%~91%;O₃的引入是导致空气质量达标率下降的最主要的原因;O₃将取代PM₁₀成为最主要的首要污染物,出现频率大于50%,且O₃(8 h)平均浓度的影响大于O₃ (1 h)浓度的影响。PM_2.5的纳入也是导致空气质量达标率下降的重要因素,其超标率为3%(金果湾)~16%(万顷沙)。NO₂标准的收严未对天湖与金果湾空气质量评价造成影响,但导致万顷沙NO₂的超标率从2%上升至10%,且NO₂作为首要污染物的比例达24%。