森林干扰对大兴安岭北部森林小流域径流情势的影响

为了解大兴安岭森林流域水文过程对森林干扰的响应,利用近配对流域方法,排除了气候变量的时空差异,对比研究了森林干扰后大兴安岭北部典型森林小流域(100 km2)洪峰径流(High flow)和枯水径流(Low flow)径流情势(Flow regimes)的变化趋势。结果表明,森林干扰对枯水径流情势影响显著,与对照流域(小北沟流域)相比,森林干扰(占流域总面积的6.74%)使老沟河流域平均枯水径流流量降低了26.58%,平均枯水径流变异系数值增加了36.77%,并且差异达到极显著水平(P0.01)。另一方面,森林植被的干扰相对增加了森林小流域的洪峰流量、历时和变异性,但与对照流域相比差异均未达到统计显著水平,说明小面积的森林植被干扰未能引起流域洪峰径流情势的显著变化。进一步对配对流域的径流浮动系数(Flashiness Index)的分析发现,森林干扰显著增加了森林小流域的径流浮动性,研究时段内干扰流域的径流浮动系数为0.078,是对照流域(0.057)的1.37倍。大兴安岭北部森林小流域的天然径流情势(Natural flow regimes)对森林干扰比较敏感,在与水文循环联系紧密的区域(例如河岸带),小范围的森林干扰便可以引起径流情势的显著变化,这在未来该地区森林和水资源的管理中需要特别注意。

The effects of forest disturbance on flow regimes of a small forested watershed in northern Daxing'anling, China

The natural flow regimes of rivers have been threatened by climate change and increased human activities, which could consequently affect their heath and integrity. Forest disturbance and climate variability are two of the most critical drivers affecting hydrological processes in forested watersheds. Despite an increased understanding of the relationship between climate change and flow regimes, few investigations have been conducted on how forest disturbance influences flow regimes. Moreover, existing researches have not accounted for the effects of climate variability on flow regimes when assessing the effects of forest disturbance. In the present study, the paired watersheds approach, which can account for temporal and spatial variations of climate, was applied to a typical small forested watershed (<100 km²) in northern Daxing''anling to investigate the effects of forest disturbance on flow regimes. The results showed that low-flow regimes were more sensitive than high-flow regimes to forest disturbance. Even though the area of forest disturbance was only 6.74% of the total watershed area (Laogouhe watershed), the average magnitude (0.47 mm) of low flows was lower by 26.58% and the average variability (0.39) of low flows was higher by 36.77% than those of low flows (0.60 mm and 0.28, respectively) in the control watershed (Xiaobeigou watershed). Besides, the differences in low flow magnitude and variability between the paired watersheds were statistically significant (P<0.01). In contrast, the magnitude, duration, and variability of high flows in the disturbed watershed were greater than those in the control watershed, but no statistical significance was found, suggesting that the small forest disturbance did not significantly affect the flow regimes of high flows in the study region. Based on the results of the flashiness index, the flashiness of flows was significantly increased by forest disturbance. The flashiness index in the disturbed watershed was 0.078 during the whole study period, which is 1.37 times larger than that of the control watershed (0.057). These results indicate that the natural flow regimes of small forested watersheds in northern Daxing''anling are sensitive to forest disturbance. Since small-scale disturbance in the study area can lead to significant changes in flow regimes, more focus should be applied to forest disturbance and water resources in future management.