石臼湖近代环境演化历史

RECENT ENVIRONMENTAL EVOLUTION OF SHIJIUHU LAKE INFERRED FROM LAKE SEDIMENTS

以2007年在石臼湖采集的浅岩芯钻孔(SJH07-C1)研究近代石臼湖湖泊环境演化历史以及人类活动的影响。运用核素^(210)Pb和^(137)Cs进行定年,^(210)Pb的CRS模式定年结果与^(137)Cs方法获得的年代具有较好的可比性。同时分析了岩芯沉积物的理化指标,包括烧失量、总磷、金属元素和磁化率。分析表明:1955年以前地球化学指标表明石臼湖湖泊沉积物中人类活动信息较弱,但总磷和有机质(烧失量)开始出现增加,湖泊营养水平开始升高。1955～1969年,湖泊沉积物磁化率较高,重金属(包括铜、铅、锌和汞)含量快速增加,可能与该期开始大量使用化肥、农药有关,导致入湖污染物增加。1969～1997年期间,1969～1979年时段湖泊沉积物磁化率最高,重金属含量比较稳定,在石臼湖进行了大规模的围垦;1979～1997年,湖泊沉积物磁化率较高但呈减少趋势,重金属含量再次快速增加,总磷增加较快,说明该阶段入湖污染物增加,湖泊营养水平也在增加。1997～2007年,磁化率较低,重金属含量保持在高水平,总磷快速增加,显示该阶段湖泊营养水平较高,但入湖物质通量在减少。

Shijiuhu Lake is a relatively large（ A = 210.4km2） and shallow water body with an average depth of 4.08 m. It is located at the southern boundary between Anhul and Jiangsu Provinces, China and connected to the Yangtze River. A sedimentary core named SJH07 -C1 was collected from the western Shijiuhu Lake （31°27′22.2″N, 118°50′49.2″E） using gravity corer in 2007. The core, 29.5cm long, was sectioned at 0.5cm intervals for the top 10cm and 1.0cm intervals for the lower part. LOI（Loss on ignition）, phosphorus, susceptibilities, elements were analyzed. The aim is to obtain environmental evolution of Shijiuhu Lake and human impacts. The sediment age of 210pb CRS method was consistent with the result based on the onset of 137Cs. The average sedimentation rate was calculated to be 0.24cm/a in the past near eighty years. Combined with the age of 210Pb and 137Cs method, the results indicated that the environment evolution succession of the historical period can be divided into four stages since 1925. 1925 , 1955 ： TP（total phosphorus）and organic matter began to increase indicating the increase of lake trophic level; 1955 - 1969： Lake sediment low frequency susceptibilities were high, and heavy metals including copper, lead, zinc and mercury enhanced sharply, which was possibly due to the intensive use of chemical fertilizer and pesticide in this period. The subsequent reclamation between 1.969 and 1979 caused the continual shrinkage of Shijiuhu Lake. In this period, sediment low frequency susceptibilities were the highest in the profile, and the content of heavy metals kept stable. 1979 - 1997 ： The lake sediment was characterized with increasing of heavy metals and nutrients, demonstrating a high productivity of lake and serious heavy metal pollution. The accumulation of these metals and nutrients was considered to be the discharge of sewage water from multiple sources and cultivation of the lake. In 1997 and 2007, heavy metals and nutrients kept their high levels but low frequency susceptibilities showed a decrease tendency, indicating that although heavy metal and nutrient load was high the inlet of sediment flux decreased.