Hydrological Responses Of Vegetation Restoration In The Lianshui River Of Xingguo,Jiangxi Province

Before the 1980s,Xingguo County in Jiangxi Province experienced a series of movements such as steel making and land reclamation.After vegetation was cut down,soil erosion was extremely serious.In 1983,Xingguo County was identified by the country as a key national water and soil erosion control area,and a series of small watershed harnessing activities were carried out,mainly including measures such as returning farmland to forests,afforestation,and closing mountains and afforestation.In this study,the reclaimed Lianshui River Basin in Jiangxi Province was used as the research area.The basic geographical data such as topography,soil,meteorology,vegetation and hydrology in the Lianshui River Basin were collected and integrated.Statistical analysis and a distributed hydrological model were applied to the study.The response status of water and sediment under different vegetation recover areas in the Lianshui River Basin from 1967 to 2015 was discussed to further clarify the response of the hydrological process to the land cover change.In order to effectively evaluate the management of soil erosion and the effectiveness of ecological restoration and reconstruction projects in the hilly areas of southern China,it provides relevant theoretical basis and technical support for the protection of the ecological environment of the river basin and the coordinated management of vegetation and water resources.The research contents and results of this paper are as follows:(1)Using remote sensing technology to obtain land use data from the period from 1976 to 2015 in the Lianshui River Basin.In the early period of afforestation from 1976 to 1987,the area of bare land in the river basin was greatly reduced and turned into the sparse forest land.During the period of vegetation protection from 1987 to 1993,the area of forest land increased by 97.08 km2,and the area of bare land continued to decrease.In the 1993-2002 years of tea and orchard planting period,the area of sparse forest land increased,the area of woodland decreased and the reduction in bare land has become smaller.In the past 2002-2015years,due to the growth of vegetation,the area of sparse forest land was converted into forest land,resulting in a substantial increase in the woodland area.The area of cultivated land was reduced by 34.06 km2,and the area of bare land continued to decrease,leaving only 5.6km2.Throughout the study period from 1976 to 2015,the vegetation coverage in the river basin increased from 310.35 km2 to 465.98 km2,and the area increased by 50.15%.The area of cultivated land was reduced by 67.3 km2 with a decrease of 45.38%,and the area of bare land was reduced by 100.73 km2 with a decrease of 94.72%.Part of the reduction of cultivated land and bare land were basically transformed into forest land.With the support of the national and local governments,the Lianshui River Basin has been effective in ecological restoration projects over the years,and the vegetation coverage has increased significantly.(2)Using statistical and hydrological methods to analyze the hydrological data from 1967 to 2015 in the Lianshui River Basin,the coefficient of variation of the multi-year runoff,surface runoff,underground runoff,and sediment yield was increased after vegetation restoration.It shows that the interannual variation of flow and sediment yield after vegetation change is more significant.Based on the flow duration curve analysis,the annual change of runoff,surface runoff,and sediment production in the basin tends to be uniform under the condition of vegetation restoration,and the degree of change in underground runoff during the year increases slightly.The average multi-year runoff coefficient decreased after vegetation restoration.During the flood season,the proportion of runoff,surface runoff,underground runoff,and the amount of sediment production were lower than before the restoration of vegetation.The rate of surface runoff reduction was the largest,and the effect of vegetation on reducing the water yield and sediment yield in flood season is obvious.Before and after the change of vegetation,when the daily precipitation conditions are equivalent,the ability of vegetation to intercept the peak runoff is obvious.Trend and mutation detection showed that before vegetation restoration,the trend of runoff,surface runoff,and underground runoff did not change significantly,showing a slight upward trend;after vegetation restoration,although the amount of change did not reach significant level,it declined slightly.The sediment production showed a significant decrease.In the 49 years before and after vegetation restoration,there were no abrupt changes in runoff,underground runoff,and surface runoff in the Lianshui River Basin.The annual sediment production had abrupt changes before and after 2002,and the relative change rate of average annual sediment yield before and after the mutation was 67.3%.(3)The SWAT model was used to simulate the runoff,surface runoff,underground runoff and sediment yield in the Lianshui river basin.Both the simulated and measured values of water and sediment keep the same trend in annual and monthly time scales.The simulation results were better.The runoff R2 and Ens are all above 0.85,the relative error is less than 10%,the sediment production R2 and Ens are all above 0.7,and the relative error is less than 20%.With the increase of forest vegetation area,the annual average runoff,surface runoff and sediment yield of the river basin showed a gradual decrease trend,but the impact on runoff was small.The annual average runoff reduction rate was only 2.08%throughout the study period,and the surface runoff decrease of 47.43%and a decrease in sediment yield by 47.8%.Underground runoff has an increasing trend,an increase of 46.38%.In the flood season,the proportion of runoff gradually decreases,and the proportion of runoff in the dry season increases gradually.Vegetation reduces flood peak flow and increases the effect of dry runoff.The runoff coefficient decreased with the increase of the proportion of vegetation area,showing a negative correlation.The subsurface runoff index increases with the increase of vegetation area,showing a positive correlation.For every 10%increase in the average vegetation area,the runoff coefficient of the watershed decreased by 0.64%,and the underground runoff index increased by 8.08%.The actual evapotranspiration in the basin increases with the increase of vegetation area,which is one of the possible reasons for the reduction of runoff in the basin.Vegetation has a well-developed root system.By improving the soil structure and increasing the coarse porosity of the soil,it increases the infiltration of precipitation,and increases the amount of underground runoff,further reduces surface runoff,while the decrease in surface runoff reduces the erosion of the soil.