青海湖现代沉积物的元素分布特征

Distribution Characteristics of Elements in Modern Sediments of Qinghai lake

青海湖目前已进入湖泊半咸化的发育阶段，水位下降，湖体缩小，湖水趋于咸化，引起了人们的普遍关注。我们根据湖底现代沉积物中的元素分布特征和变化规律，利用沉积物中介质性质指标、可溶盐指标以及表征气候干湿的元素及其组合关系指标等特点，阐述了青海湖距今３５００年以来的演化规律，说明青海湖的发展总趋势是水质由淡向咸变化。但最近１２０年来，表征干旱气候元素降低，潮湿气候元素有所增加，有反向发展的征兆，可能预示青海湖区域气候从干冷向温湿转变，故湖水不会在近期内干涸。

Great concerns have been put on the prospect of the Qinghai Lake for its water body′s violent change and continuous shrinkage.To discuss the developing tendency of the lake,We have studied the distribution characteristics of elements,sampled from the modern sediments of the lake,in time and space and their variation law.There are 34 elements in the sediments,which can be classified into four genetic assemblages,that is,detritus element,bio element,spersive and sparse element and soluble salt aedimentary element. The regional climate and variation feature of water medium of Qinghai Lake have been determined comprehensively through those indexes.Some 2 000 years(equivalent to 1￣0 m thick sediments),the content of ion Cl and B,Which stand for the salinity of Water medium,reach their peak values.Whereas the Al coefficient(Al 2O 3/SiO 2) and carbonate coefficient (CaO+MgO)/SiO 2 ,Which reflect the climate change,are located in the value showing the climate changed from cold to warm,especially on the sediment surface is nearly up to the limit of wet and hot.In the past 2 900￣3 400 years,the Water medium was fresh and the climate tended to warm and wet,indicatining that the general developing tendency of the lake is from fresh to salty.But in recent 120 years,there are signs showing the reverse developing tendency,that is,the element distribution in the uppermost sediments show that the content of dry climate element reduce and,in contrast,the content of wet climate element increase,which may indicate that the climate of Qinghai lake begin to change from dry cold to much warmer and wet.Seeng that the small variation cycles of climate from dry to wet have frequently occurred in the west China since Meso Cenozoic,we can see the local climate of the lake has the possibility to change reversely,and the lake water could not dry up in a short period. In addition,we have calculated the salinity of the water body.It can be seen that the salinity of sediments in 1 m deep rise from 4.38% to 7.9%,that is,the rising rate is 1.21%.If this rate keeps,the present salinity of Qinghai lake evolutes to that of the present climate and hydrology conditions,at least 18 000￣36 000 years are needed,so the prospect of Qinghai lake is optimistic and the Qinghat Lake could not dry up in at least 10 000 years.