Variation and distribution of evaporated salt under different landscape units in the playa of Lake Ebinur, Xinjiang Province

Abstract

盐尘暴是由干旱、半干旱区尾闾湖干涸湖底及其附近盐质荒漠风蚀所导致的一种灾害性极强的天气现象.盐尘主要来自风蚀过程中干涸湖底盐分的释放.由于干涸湖底不同的植被覆盖状况,导致风蚀过程中盐分损失不同.为了解风蚀过程中不同景观单元下盐分分布与变化特征,选择艾比湖干涸湖底自然状态下典型的6种景观单元(胡杨林带(Landscape 1,简写为L1)、乔本结合带(L2)、草本结合带(L3)、芦苇荒漠带(L4)、梭梭荒漠带(L5)、无植被覆盖(L6)),于2011年6月初和10月初2次采集沉积物样品,运用方差分析方法,研究各个景观单元下盐分的分布与季节变化特征.结果表明:1)2次采样不同景观单元0~30 cm和30~60 cm处阳离子Na⁺、K⁺、Mg²⁺含量均存在显著差异,其中Na⁺含量存在极显著差异且含量最高,而不同景观单元0~30 cm和30~60 cm处阴离子Cl^-、SO₄^2-含量均存在显著差异,CO₃^2-、HCO₃^-含量甚微;2)干涸湖底沉积物的主要盐分类型是NaCl,其次是CaSO₄,其它盐分含量较小,且不同景观单元相同深度沉积物盐分含量存在显著差异.无论是盐分离子组成还是含量,L5均最高,其次是L6,而L2均最低.随着深度的增加,不同景观单元沉积物中的盐分含量均呈现降低的趋势.随着时间变化,景观单元L2、L3、L4、L5、L6盐分含量有不同程度的增加,而L1盐分含量减少;3)在小尺度范围内,局地气候条件相对均一,地下水矿化度、地下水埋深及沉积物性质差别不大,不同景观类型是影响盐分表聚的主要因素.;Salt dust storm which mainly released from the dry lakebed is an extremely disastrous weather phenomenon caused by wind erosion of playa in arid and semi-arid land. Due to different kinds of vegetation covered in the dry lakebed, the salt loss amount is different during wind erosion process. In order to understand the distribution and variation of the salt content under different landscape units, six typical landscape units under natural state were selected as research objects in the dry lakebed of Lake Ebinur. In early June and early October 2011, sediment samples were collected twice. Mathematical statistical methods were used to study the distribution and seasonal variation of salt composition and content. The results showed that the Na⁺ contents in sediments of the same two depths from 0 cm to 60 cm were significantly different among the six different landscape types(L1 to L6, characterized with decreasing vegetation coverage) in early June and early October, so do K⁺ and Mg²⁺. In addition, Na⁺ had a highly significant difference with the highest content. The contents of Cl^-, SO₄^2- from 0 cm to 30 cm were significantly different among different landscape units, this result is the same as samples from 30 cm to 60 cm, although the CO₃^2- and HCO₃^- contents were low. The main type of salt in sediments was NaCl, followed by CaSO₄, and other types of salt were in very low concentrations. There was a significant difference among the salt contents of sediments from the same depth under different landscape units. In term of the ionic composition and salt content, the content of L5 was the highest, followed by L6, and L2 was the lowest. With increasing depth, the salt contents of sediments from different landscape units showed a decreasing trend. Over time, the salt contents of landscape units L2, L3, L4, L5, L6 increased in varying degrees, only L1 turned out reduce. It is suggested that different landscape units was the main factor affecting the salt accumulation in the range of small-scale of which the local climate conditions, groundwater salinity, groundwater depth and sediment properties are relatively homogeneous.