Ecohydrological Characteristics And Climate Change Responses Of Artificial Bamboo Forests In Typical Watershed

It is of great significance for the comprehensive management and evaluation of regional water resources to deeply understand the ecohydrological characteristics of river basin and to clarify the temporal and spatial variation trend of hydrological process,especially the ecohydrological response under the condition of climate change.In order to reveal the ecohydrological characteristics and climate change response mechanism of artificial bamboo forests in typical watershed,soil core method combined with Win RIHZO root analysis system was used to analyze the root index of each deep layer of artificial bamboo forests to reveal the growth characteristics and distribution law of root system.By comparing the characteristics of fine roots in the same depth in summer and winter,the dynamic difference of fine roots in the year was analyzed.Based on the observed soil moisture data in a typical watershed,the temporal and spatial distribution and dynamic variation of soil moisture and the temporal stability of soil moisture in each soil profile of a typical small watershed were studied.The temporal and spatial variation of soil moisture in artificial bamboo forests were recognized by classical statistics and temporal stability of soil moisture.Based on the observed runoff and soil moisture data of a typical watershed,through the combination of field sampling,laboratory experiment and Hydrus-1D model,the soil moisture and other hydrological characteristics of artificial bamboo forests were simulated by Hydrus-1D model.According to different climate change scenarios,the ecohydrological process of the study period was determined,the response of the artificial bamboo forests to climate change was evaluated,and the relationship between ecohydrological process and climate change were revealed.The main conclusions are as follows:(1)In the vertical direction,the total roots of bamboo were mainly distributed at0-20 cm,accounting for about 63.94%of the total underground roots.The fine roots were mainly concentrated in the 0-10 cm soil layer,accounting for about 45%of the underground fine roots,about 62%of underground fine roots in 0-20 cm soil layer,and less than 10%of fine roots below 50 cm.It showed a decreasing power function of the vertical distribution of the root system of bamboo.The total and fine roots of bamboo decreased rapidly in 0-20 cm soil layer.When the depth was more than 20 cm,the root change was relatively gentle.There were seasonal dynamic differences in the vertical distribution of bamboo root system.The significant difference of root system in summer and winter was mainly reflected in the change from 0-10 cm to 10-20 cm soil layer,while the difference was not significant in the adjacent soil layer over 20cm.(2)The spatial distribution of soil moisture in different soil profiles in typical small watershed was similar,mainly as follows:Although the coefficient of variation of soil moisture in different soil profiles varies with depth,the variation coefficient of soil moisture in deeper soil layer was small,and the variation range was small,which was medium variation,that is,the soil moisture in deeper soil layer was low stable.The change of soil water content was relatively active in the range of 0-30 cm soil profile,while it was relatively stable in the soil profile below 30 cm.Maybe due to the combined effect of atmospheric precipitation,soil evaporation,vegetation transpiration and water infiltration,0-30 cm soil moisture in the watershed fluctuated severely.By analyzing the time stability of soil moisture in typical small watershed,the specific performance was as follows:the representative soil depth of No.1,No.2,No.3,No.6,No.8 and No.9 points are 50 cm,90 cm,30 cm,80 cm,140 cm and 50 cm respectively,and the time stability of soil moisture in deep layer(>30 cm)was stronger than that in shallow layer(0-30 cm).(3)The results of simulation,coefficient of determination(~2),relative error(),root mean square error()and Nash-Sutcliffe model efficiency()showed that the model could greatly reflect the temporal and spatial variation characteristics of soil moisture,and there was a certain correlation between simulated runoff and observed runoff.The results showed that the Hydrus-1D model was suitable for the simulation of ecohydrological process in a typical small watershed.The dynamic variation of hydrological variables in the results showed that the transpiration accounts for 78.72%of the total evapotranspiration during the study period,which indicated that the vegetation transpiration was the main way of soil water resources consumption.The total runoff(surface runoff and bottom drainage)formed by the total precipitation in the watershed was relatively large,accounting for74.48%of the total evapotranspiration,and soil water storage was in deficit.(4)By setting different climate change scenarios,the response of artificial bamboo forests to climate change was analyzed.In the whole study period,evaporation and transpiration increased with the increase of temperature under different climate change scenarios,with the precipitation unchanged and the temperature increased by 2℃,that is,the increase of evaporation and transpiration was controlled by temperature;the trend of runoff change was consistent with precipitation,but opposite to temperature,it was more sensitive to the change of precipitation,in which runoff was the most sensitive to the decrease of precipitation and the increase of temperature.The change of soil moisture storage was consistent with runoff,and was obviously affected by precipitation.The change of air temperature had little effect on soil moisture storage,and the soil moisture storage was most sensitive to the decrease of precipitation and the increase of temperature.The monthly variation showed that soil evaporation and vegetation transpiration had the same monthly variation trend,that is,the increase rate in winter was greater than that in summer;when the temperature was constant,the change of precipitation has more influence on summer runoff,and the increase and decrease rate of summer runoff was tens of times of that in winter.Only when the temperature changes,the winter runoff was more easily affected.In addition,the increase of precipitation can offset part of the impact of temperature rise,and maintain a slight increase in runoff;the impact of precipitation on soil water storage in summer was greater than that in winter,and the impact of temperature was more obviously on the fluctuation of soil water storage in winter.Coupled with temperature and precipitation,the soil water storage overall was more obviously affected in winter.