额济纳233年来胡杨树轮年表的建立 及其所记录的气象、水文变化*

通过胡杨树轮宽度的分析,建立了内蒙古额济纳地区过去233年来的STD,RES和ARS年表;并将树轮STD年表与采样点附近额济纳气象站的气温、降雨量以及狼心山水文站的地下水水位等记录进行了相关分析。结果表明,在额济纳地区显著影响该地胡杨生长的主要限制因子是地下水水位。胡杨树轮宽度年表与冬季及全年地下水水位相关性最高,分别为-0.808(p＜0.01)和-0.724(p＜0.05)。在此基础上,设计转换方程,重建了额济纳地区过去232年来冬季及全年地下水水位变化历史,冬季地下水水位重建方程的解释方差达76.3 % (调整自由度后为70.4 ％ ,n=11,r=0.874,F=12.881,p＜0.003),全年地下水水位重建方程的解释方差为72.8 ％ (调整自由度后为66.1 ％ ,n=11, r=0.854,F=10.731,p＜0.005)。

CLIMATIC AND HYDROLOGICAL CHANGES OF EJIN, INNER MONGOLIA, CHINA DURING THE PAST 233 YEARS RECORDED IN TREE-RINGS OF Populus euphratica

Trees of Populus euphratica are mainly distributed over desert region in West China. During their growth process they record climatic and hydrological variations, offering an important tool for the reconstruction of climate and hydrology of desert region where meteorological and hydrological data are generally lacking. In this paper we use tree rings of Populus euphratica to reconstruct past climate and hydrology variations in Ejin which is located in the northwest part of Inner Mongolia.The study region currently has typical continental climate which is characterized by drought, low precipitation, and great amount of evaporation. 30 increment cores of Populus euphratica trees were obtained in Ejin in 2004. All samples were dried, glued, mounted and sanded. Cross-dating was performed by the Skeleton Plot method and quality control was carried out by the COFECHA program. The standard (STD),residual (RES), and autoregressive standard (ARS) tree-ring chronologies up to 233 years were obtained by using the ARSTAN program. Correlation function analyses between STD chronology and temperature, precipitation, and groundwater level of the sampling site indicate that the variation of ring widths was mainly controlled by groundwater level. Temperature of March significantly affects the growth of tree. No apparent relationship has been found between ring width and precipitation in the region. The correlation between STD chronology and mean winter groundwater level is -0.808 (p＜0.01, n=11), and with mean annual groundwater level -0.724 (p＜0.05, n=11). This indicates that shallower groundwater level corresponds to wide rings and deeper groundwater level corresponds to narrow rings. On this base two multiple regression transfer functions are designed to reconstruct mean winter groundwater level and annual groundwater level of Ejin for the past 232 years. Considering lag effects, groundwater level of the previous year is regarded as one variable applied in the transfer functions. The explained variance of winter reconstruction is 76.3 ％ (and 70.4 ％ when adjusted for loss of degrees of freedom, n=11, r=0.874, F=12.881, p＜0.003), and the explained variance of annual reconstruction is 72.8 ％ (66.1 ％ when adjusted for loss of degrees of freedom, n=11, r=0.854, F=10.731, p＜0.005 ). The results show that tree ring variation is sensitive to winter groundwater level variation, and the reconstructed winter groundwater level is more reliable than the reconstructed annual groundwater level. Periods of relatively shallow annual groundwater level in Ejin during the past 232 years are 1781~1787a,1791~1806a,1846~1857a,1878~1910a,1953~1973a,1992~1997a, and periods of deep level are 1776~1780a,1809~1816a,1826~1845a,1858~1876a,1911~1952a,1980~1986a,1988~1991a.