湖泊沉积物蓄积的磷在湖泊环境发生变化(如pH值、Eh改变)时,往往能释放到水体,形成湖泊内源释放,造成湖泊富营养化。因此了解湖泊沉积物磷的蓄积特征,对于湖泊环境的治理和保护有重要意义。通过长江中游龙感湖不同部位钻孔的 ²¹⁰ Pb、沉积物磷和其他环境指标分析表明,近百年来东部湖区沉积速率明显大于西部湖区,北部湖区略大于南部湖区,人类活动在20世纪50年代后期主要通过修建水库和闸坝,改变龙感湖水系结构,也改变了龙感湖的物源供给,因而西部湖区沉积速率略有放缓,东部湖区变化不明显。龙感湖沉积物磷的浓度空间上表现为东部高于西部,这与不同物源磷的背景值相关,时间序列上近百年来呈上升趋势,上世纪50年代以来上升趋势更为明显。在确定沉积物磷背景值的基础上,由于人类活动导致的磷的增加量表明,20世纪50年代开始人类活动导致沉积物磷的增加量持续上升,20世纪70年代末开始增加幅度更大,这一特征与人类活动的方式有关。

Phosphorus in lake sediments is generally regarded as an internal nutrient source that will cause aquatic plant flourishing and algae blooming when it is released into the water column due to changes in the lake environment(e.g. changes in pH and Eh).It is therefore crucial to understand the process of phosphorus accumulation in lake sediments for the restoration and protection of lakes.Longgan Lake,a large shallow lake,is located in the middle reaches of the Yangtze River.Previous studies on nutrient accumulation and the associated human impacts were confined to the northwestern bay of the lake,which cannot demonstrate the overall status of trophic conditions in the lake.Six sediment cores were recovered from different parts of Longgan Lake in this study and analyzed for ²¹⁰ Pb activity and phosphorus content to reveal the spatial and temporal distribution of phosphorus in the lake sediments.The data indicate that the sedimentation rate(SR)in the eastern lake is higher than in the western part,and SR in the northern lake is slightly higher than in the southern part.The phosphorus in the lake sediments is more abundant in the eastern lake than in the western part,presumably denoting differences in the phosphorus content in source materials.The average phosphorus content in 52 soil and rock samples collected from the north bank of the lake is 437.2mg/kg,while 26 soil samples from the Taibai Lake region yields an average phosphorus content of 383.3mg/kg,suggesting that different sources of materials transported to the lake result in the difference in the spatial distribution of phosphorus in the lake sediments.In the later 1950s,reservoirs were constructed in the upper reaches of lakes in China,dams were built in the lower reaches,and lacustrine plains were reclaimed.Such intensive human activities altered the hydrological structure of the Longgan Lake catchment,leading to changes in the nature and supply of source materials.Phosphorus in the lake sediments has exhibited an obvious trend of increases in the content since 1950s,implying the effect of human activities on the phosphorus content.The increment of the phosphorus content resulting from human activities(anthropogenic phosphorus,AP)was estimated by subtracting the background content,calculated according to the relationship between the contents of Al,Fe,Ti and P in the samples,from the measurements.As a result,AP shows greater increases in the western lake than in the eastern part.Since 1950s,AP has increased due to the utilization of phosphoric fertilizer,and the increment has been heightened since the end of 1970s when phosphoric fertilizers were directly used to improve the growth of aquatic plants in the lake for fishery.AP reached its maximum of 298.2mg/kg in LL4 sediment core around 1997.