关键词: 嫩江上游, 树轮, 兴安落叶松, 1～3月径流量, 多带谱分析

Abstract: Nenjiang River is one of the most important rivers in northeast China. It has critical significance for forestry management and agriculture and livestock production to understand the longterm hydrological regime in this region. A total of 115 treering cores of Larix gmelinii were collected at four sites (A'li River, Gan River, Keyi River and Nuomin River) in the upper Nenjiang River, the northern Daxing’an Mountains, China. All cores were visually crossdated under the binocular microscope. Treering widths were measured to the nearest 0.001 mm with a Velmex measurement system. The crossdated treering sequences were quality checked by COFECHA program. ARSTAN program was used to detrend the ringwidth sequences with a negative exponential curve or a straight line with negative slope (or a horizontal line) and four chronologies were developed. Response analysis between four treering chronologies and monthly climatic factors (mean temperature and total precipitation) were conducted. The results show that treering chronologies in the four sites are negatively correlated with temperature in all months of a whole year, while which are positively correlated with precipitation in growing season and negatively correlated with precipitation in nongrowing season. These results indicate that water availability is the major limiting factor of tree growth in this region. Therefore, an average treering chronology for four sites was developed to reconstruct the history of streamflow variation for the Nenjiang River. Simple correlations between the average treering chronology and monthly streamflow data show that the average chronology of four sites is significantly correlated with mean January-March streamflow. Therefore, mean January-March streamflow in the upper Nenjiang River since 1804 was reconstructed. In addition, the reconstructed drought and flood periods are relatively identical with the historical records of hydrological variation in Heilongjiang province. The major periods of reconstructed dry conditions include AD 1808-1809, 1821-1822, 1827-1833, 1852-1875, 1906-1919, 1932-1954 and 1987-2004, while the significant wetter periods are AD 1810-1820, 1823-1826, 1834-1851, 1876-1905, 1920-1931 and 1955-1986. The fluctuation amplitude of the reconstructed streamflow is relatively small from the beginning of nineteenth century to the beginning of twentieth century, while which was larger in the middle and late twentieth century. MultiTaper Methods spectral analysis of reconstructed streamflow series indicate that the upper streamflow variations of the Nenjiang River exhibited 60, 4.3-4.0, 3.4-3.2, 3.1-2.9 and 2.3 years dominant periodicities. The factors that affect the cyclical changes of JanuaryMarch streamflow in this area need to be further studied.

Key words: the upstream of Nenjiang River, tree rings, Larix gmelinii, mean JanuaryMarch streamflow, MultiTaper methods