近百年来西居延海湖泊水位变化的湖岸林树轮记录

Water Level Change of the West Juyan Lake in the Past 100 Years Recorded in the Tree Ring of the Shrubs in the Lake Banks

通过对西居延海柽柳树轮年表与气象、水文要素进行相关分析,结果表明:标准年表和西河下游5～8月平均地下水位变化呈显著正相关,而且这一相关具有明确的生物学意义.利用标准化年表和地下水位的相关关系,重建了西居延海近100a以来5～8月的水位变化,检验表明重建结果是可靠的.结合西居延海在1960—1962年干涸的史实和重建水位变化曲线,将湖岸林柽柳树轮年表涵盖的近百年分为湖水水位和地下水水位变化两个时期.其中湖水水位上升阶段为1932—1952、1956—1958年,下降阶段为1920—1932、1952—1956、1958—1960年,持续时间分别为20a、2a、12a、5a和2a;地下水水位上升阶段为1974—1981、1996—1997年,下降阶段为1961—1973、1981—1995、1997—2002年,持续时间分别为8a、1a、13a、15a和5a.

West Juyan Lake is one of the terminal lakes of the Heihe River, which has been dried since 1960. There are three sandbar banks on the southwest of the lake, in the area of 42°20′15.56″～42°21′8.81″ N and 100°41′50.945″～100°42′30.63″ E. The shrubs in the banks of the West Juyan Lake are mainly Tamarix romasisima, which invaded along with the lake degradation. There are 53 samples taken from the banks. All the samples were sanded, polished and cross-dated with the dendrochronological methods. Tree ring width is measured with microscope in 0.01 mm precision. The COFECHA program checked the result of cross-date; the ARSTAN program achieved the standard chronology. Based on the correlation analysis, which includes the tree ring standard chronology of the West Juyan Lake and the elements of meteorology and hydrology in the Ejina Banner, Inner-Mongolia, it is found that the standard chronology has a positive correlation with the average grounder-water level in the lower reaches of the West River from May to August. Saltcedar (also named phreatophyte) on the condition without frequent floods to inundate mainly lives on the deep groundwater. So, the correlation of the tree ring chronology and the grounder-water level change has a definite biological significance. A regression model was found using the correlation. Upon it, the water level change of the West Juyan Lake from May to August was reconstructed for the past 100 years. Through verification with the historical documents, the instrument records of the river runoff and the precipitation, the reconstructed result of the water level change is credible. Combined with the historical fact that the West Juyan Lake had dried during 1960—1962, and the reconstructed water-level change curve, the 100 years can be divided into water level change and groundwater level change phases. Among them, the water level rising stages were 1932—1952 and 1956—1958, the water level declining stages were 1916—1932, 1952—1956 and 1958—1960, with the intervals of 20, 2, 12, 5 and 2 years; The groundwater level rising stages were 1973—1981 and 1992—1999, the groundwater level declining stages were 1960—1973, 1981—1992 and 1999—2002, with the intervals of 8, 1, 13, 15 and 5 years.