| Middle altitude region of south slope of Qingling belongs to forest region of water conservation. The forest plays a huge role in ensuring regional water balance, water security and water supply and other aspects in the Region. So it has the importance of self-evident. With the mid-route project of south to north water transfer construction, hydrology ecological role of Qinling forest is more prominent.But in recent years, because of the impact of air pollution and a lot of lead- zinc mine mining in the surrounding area of Qinling, water quality of precipitation has acidification and heavy metal pollution. Forest in the region belongs to middle-aged forest, and appeared growth retardation and severe differentiation phenomenon. So it is urgent need to take thinning. rational thinning. But we did not know that thinning intensity how to influence water balance components, different levels of water quality effects and water conservation functions.These questions belongs to major issues which local government and relevant researchers who urgently need to understand. In this study, we selected representative species pine(Pinus armandii)of Qinling as study object and set five thinning intensity of 5%, 10%, 15%, 20% and 0%. We explored abovementioned problems by a combination method of field observations and laboratory experiments. Finally, select a thinning intensity which has the best water regulation functions.Meanwhile provide a scientific basis which aim at sustainable management of forest resources.Conclusions are as follows:1)When precipitation were greater than 4.8mm, Pinus armandii forest may produce stem-flow.With increased rainfall, stemflow increased by linear function, canopy and litter interception increased by logarithmic function. Stemflow, canopy interception and litter interception of plots had the maximum values in September, respectively between 11.82 mm and 5.49 mm, between 59.18 mm and 66.85 mm,between 30.42 mm and 39.96 mm.With thinning intensity increased,stemflow showed a increase trend, canopy interception and litter interception showed a decreasing trend.2)Soil evaporation and plant transpiration of plots mainly in July, August and September. The maximum value of Soil evaporation appeared in August, were between 26.18 mm and 35.68 mm. The maximum value of plant transpiration appeared in July, were between 41.62 mm and 46.93 mm. With thinning intensity increased, soil evaporation raised, transpiration vegetation decreased. The maximum value of soil runoff appeared in September,were between 89.21 mm and 109.86 mm.With thinning intensity increased, the soil runoff tended to increase.3)Water output of plots had no Significant differences. Forest evapotranspiration is the main form of water output In Pinus armandii ecosystem.It accounted for between 72.02% and 76.44% of the total expenditure. Thinning did not change the total water budget, but to change the proportion of the components of the water balance in the distribution of Precipitation. With increasing thinning intensity, canopy interception, litter interception and vegetation transpiration accounting for the proportion of Precipitation were decreased; and soil water storage, soil runoff and soil evaporation accounts for the proportion of Precipitation showed increasing trend. The plot of thinning 20%, soil runoff and changes in soil water storage were the greastest. From the perspective of water supply, Pinus armandii should take 20% thinning.4)Canopy layer and litter layer of Pinus armandii can raise the p H of precipitation, can reduce Cd, Pb and Zn amount of precipitation. With the increase of thinning intensity, the p H of throughfall and litter drainage were decreased, the Cd, Pb and Zn amount of precipitation were increased. From the water quality effect of canopy and litter layer, Pinus armandii should take low intensity Thinning.5)The soil of Pinus armandii can raise and maintain the p H of precipitation. On the whole,the p H of soil leachate showed an increasing trend. With the increase of the p H and concentrations of heavy metals of precipitation, the p H of soil leachate both showed an increasing trend. With the increase of thinning intensity, the p H of soil leachate both showed an upward trend under the simulated precipitation of different p H and concentrations of heavy metals. The soil of Pinus armandii can not only absorb Cd, Pb and Zn of precipitation, but also resolve them. In general, with the increase of the p H and concentrations of heavy metals of precipitation, concentrations of heavy metals of soil leachate showed a decreasing trend. With the increase of thinning intensity, the concentrations of heavy metals of soil leachate both showed an downward trend under the simulated precipitation of different p H and concentrations of heavy metals. The water quality of soil leachate were the best under 20% thinning. From the water quality effects of soil layer, Pinus armandii should take 20% thinning.6)Thinning can reduce the litter amount,water holding capacity and water holding rate of litter, but this effect were little. Their order respectively showed 0%> 5%> 20%> 10%> 15%, 0%> 5%> 20%> 15%> 10% and 0%> 5%> 15%> 20%> 10% under different thinning intensity.7)Thinning can reduce soil bulk density, soil water holding capacity and can increase soil permeability. With thinning intensity increased,soil bulk density were decreased, soil capillary capacity and non-capillary water holding capacity were increased, initial infiltration rate and stable infiltration rate were raised.8)Thinning can improve water conservation functions of forests for a long time. With increasing thinning intensity, water conservation function of forest was enhanced. This study showed that: 20% thinning had the best water conservation function, followed by 15% thinning. |
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