贡嘎山峨眉冷杉林原生扰动土壤溶质运移的持续降雨模拟研究

A Continuous Rainfall Simulation on the Solute Movement Through the Disturbed Primary Soil of an Abies fabri Forest in Gongga Mountain,China

以人工持续 (5 d)降雨模拟方式研究了贡嘎山峨眉冷杉林原生土壤地表覆被层破坏后土壤中矿质元素与营养盐的迁移输出动态与规律。模拟降雨采用当地最为常见的小到中雨雨型 (5 .7～ 2 6mm/h)。壤中流以垂直入渗为主 ,并滞后于降雨 0 .2～ 4.2 h。通过模拟实验发现 ,降雨总量和降雨事件的持续时间对壤中流产生量的影响比单位时间降雨强度的影响更为明显。在持续降雨影响下 ,主要离子 (Mg2 +,Ca2 +,Cl- ,SO2 - 4和 Na++K+)和营养盐 (NH+4 -N、NO- 3-N和活性磷酸盐 )在短期内急剧流失。模拟降雨的第 1天 ,壤中流结束时离子浓度仅为初始时浓度的 2 9% ,营养盐浓度为初始浓度的2 1 %～ 5 5 %。至第 3天 ,上述离子和营养盐输出浓度趋于恒定 ,约为首日降雨壤中流初始浓度的 1 %～ 1 5 %。在主要矿质元素流失后 ,原生土壤内过程转为有机质控制的 HCO- 3输出过程。伴随着土壤矿质养分的输出 ,土壤缓冲能力下降。壤中流 p H值由 6.1降为 5 .2。研究结果表明 ,贡嘎山区峨眉冷杉林原生土壤系统十分脆弱 ,养分易于流失 ,对人类活动的敏感性很高。

The Gongga Mountain,located on the southeastern fringe of the Qinghai\|Tibet Plateau,is vulnerable and sensitive to climatic change.The fragility of mountain forest ecosystems in this region is mainly resulted from steep slopes,thinness of soil layer and un\|harmony among the hydro\|thermal factors.The surface cover of primary forest has been highly disturbed by human activities,such as tourism and deforestation.The objective of this study was to study the occurrence of subsurface runoff and the movement of mineral elements through the disturbed primary soil by an indoor rainfall simulation.The disturbance was simulated by removal of vegetation,moss and debris. The soil was collected from the slope wash in the deglaciation slash of the subalpine dark coniferous forest zone,in which Abies fabri forest community reaches climax.The soil is loose and porous with high infiltration and categorized as subalpine dark brown forest soil.Four columns were packed with soil sampled from the corresponding horizons to a similar bulk density.From the top down,there are 4 layers;A0,4cm,vegetation,moss and debris were removed and replaced by washed and calcined quartz sand;A horizon,18 cm,soil;B horizon,20cm,soil;C horizon,8cm,filled with gravel of diameter 3～8cm.Three columns were set as treatments by precipitation of simulated rainfall and one for control by distilled water.The subsurface runoff collection holes were drilled at the both sides of corresponding horizons.Before rainfall start,four columns were gradually wetted to the stable water capacity (20%) with simulated rainfall.Small\|moderate rain intensity (5.7~26 mm/h),which is common in the experimental region during May\|June,was adopted with 5 days of duration.Once the subsurface runoff began,the runoff was sampled every certain interval and the main ions and nutrients in the runoff were analyzed. No significances exist between the runoff output behaviors of treatments and control column.Under the influence of small\|moderate rain intensity,the runoff mode in the Abies fabri primary soil was dominated by subsurface runoff.It mainly flowed from C horizon with a time lag of 0.2～4.2 h after the rainfall start.After the rainfall stopped,the subsurface runoff continued to leach from soil and showed “tailing' phenomenon.The results suggest that the subsurface runoff output chiefly depends on the total rainfall amount and duration,not significantly correlated to the rainfall intensity.With the rainfall duration,the output rates of subsurface runoff increased.Under the influence of continuous rainfall,the main ions (Mg 2+ ,Ca 2+ ,Cl -,SO 2- 4 and Na ++K +) and nutrients (NH + 4\|N,NO - 3\|N and total reactive phosphorus) quickly lost from the disturbed primary soil.The main ions show different preferential migration sequence in different soil columns.The HCO - 3 concentrations in the runoff fluctuate more widely and increasingly output from the primary soil with rainfall duration.On the 1st day of rainfall simulation,the concentrations of main ions at the end of flow were about 29% of those of the beginning period,and the nutrient concentrations accounted for 21%～55% of the initial.On the 3rd day,the output concentrations of ions and nutrients are only 1%～15% of the initial concentrations.After large quantity losses of mineral ions,the dominated anions in the subsurface runoff turned from SO 2- 4 to HCO - 3.The above results suggest that the subsurface processes in the disturbed primary soil mainly depend on the carbon cycle controlled by organic matter (humus).Affected by the continuous rainfall,the mineral elements and nutrients largely run off,the soil buffering capacity decreased dramatically and the pH value of subsurface runoff declined sharply from 6.1 to 5 2.The results show that the primary soil of Abies fabri forests in Gongga Mountain is a weak and sensitive system to anthropogenic disturbance.The common small\|moderate rainfall distribution strongly affects the transport and output of main mineral elements.The element loss