长江中下游典型湖泊近代环境变化研究

Modern Environmental Changes of Typical Lakes along the Middle and Lower Reaches of Yangtze River Basin

选择长江中下游的典型湖泊洪湖、巢湖、石臼湖和太湖,采集了沉积柱样,测定了总有机碳、总氮、总磷,并采用210Pb和137Cs定年以研究湖泊近代环境演变。根据洪湖137Cs蓄积峰得到过去50a里洪湖沉积速率经历了一个由慢到快再变慢的过程,1963～1986年之间沉积速率最大,达0.174cm/a,这可能是因为当时湖区大规模开垦有关。巢湖钻孔核素的研究发现20世纪70年代以来随着深度的减少,巢湖钻孔中沉积通量在增加,可能与流域内水土流失逐步加重有关。对营养盐的分析表明,洪湖50年代以来沉积物中营养元素急剧增加,巢湖70年代以来营养元素开始增加,在太湖中体现为80年代,石臼湖中则为近百年来营养元素开始快速增加。从营养盐增加的幅度来看,草型湖的洪湖、石臼湖要大于藻型的巢湖以及太湖藻型区域。本文尝试利用总有机碳、总磷获取了湖泊环境变化的速率。研究表明总有机碳和总磷的变化速率存在波动性,这可能与湖泊的自我调节有关。而总有机碳的变化速率在最近时间阶段内基本呈正值,对于洪湖来说在80年代初,石臼湖在1970年左右,太湖在80年代初,巢湖在60年代。总有机碳、总磷变化速率的振荡幅度与周期也许对理解当今湖泊处于何种位置,由此采取何种湖泊管理手段提供重要认识。

Sedimentary samples were collected from typical lakes such as the Honghu Lake, Chaohu Lake, Lake Taihu and Shijiu Lake along the the Middle and Lower Reaches of Yangtze River Basin for analysis of total organic carbon （TOC）, total nitrogen （TN）, and total phosphorus （TP）. ^210Pb and ^137Cs dating method was used to study recent environmental change of lakes. ^137Cs cumulative peak value of Honghu Lake indicates that the depositional rate of Honghu Lake gradually slowed down during the past 50 years, with a largest depositional rate of up to 0. 174 cm/a between 1963 and 1986. This probably results from human activity such as reclamation at that time. The drilling core of Caohu Lake found that since the 1970s, depositional flux has increased with increasing depth, which is probably attributed to worsening of soil erosion around this area. Organic analysis also shows that since the 1950s, organic matter in sediment of the Honghu Lake has increased dramatically, the Caohu Lake started to deposit in the 1970s and the Taihu Lake started to increase in the 1980s, but the Shijiu Lake started to deposit rapidly in this one hundred year. Viewed from increasing amount, the Honghu Lake and Shijiu Lake, belonging to macrophytic lake, increases faster than the Caohu Lake and Taihu Lake, which belong to algae lake. This study tried to take use of TOC and TP to obtain the rate of environmental change of lake. The research shows that the change of TOC and TP is probably related to self-adjusting of lakes. Rates of TOC changes showed positive trends in the early 1980s at Honghu and Taihu, 1970s at Shijiu and 1960s at Chaohu. The range and periodical of rates of TOC and TP change may help us understand lake evolution in current days, which provides us with an important understanding that what means will be used to treat and manage lakes.