| The hydrological effect of land use change is the hotspot of current research on t he environmental impact of human activities.The expansion of citrus orchards is the most important land use change in the Xunwu watershed in the past 20 years.This arti cle uses data from land use,meteorology and hydrology,DEM,and soil in the Xunwu watershed to analyze the spatial distribution characteristics of citrus orchard expansio n in the watershed,status of soil erosion on different terrain and fruit-age plots,charac teristics of precipitation,runoff and sediment transport from 2009 to 2018,and combin ed with SWAT model to simulate the characteristics of watershed runoff and sediment transport in three different periods of land use,and analyze the impact of land use cha nge on runoff and sediment transport.The main results are as follows:(1)The total area of citrus orchards has a net increase of 402.69km~2 from 1990 t o 2015.The fastest and most increasing area is between 300-400m and 8°-25°.The net increase of orchard area within the range of 300-400m elevation was 216.02km~2,a nd the net increase of orchard area within the slope range of 8°-25°was 283.08km~2,accounting for about 70.32%of the total area increase.From 2008 to 2015,more than88%of the orchards were distributed below 500m above sea level,and the area of orc hards above 600m was less than 4%of the total area.The orchard area increased the most between 8°-25°,with a net increase of 33.54km~2,and 91%of the orchard area distribution slope was less than 25°.(2)The erosion area in the basin is about 292.58km~2,accounting for 29.68%of t he total area of the basin,light erosion mainly accounts for about 90.93%of the total e rosion area;In terms of terrain,soil erosion is mainly distributed at an altitude of 300-500m and a slope of 8°-25°.The range of elevation and slope distribution is consiste nt with the main expansion of the orchard area,indicating that the cultivation of citrus fruit trees has aggravated water and soil to a certain extent.From 2013 to 2015,the to tal area of the orchard was slowly increasing,and the area of light and moderate erosi on was proportional to it.The area of strong and above erosion intensity decreased wit h the increase of the area of the orchard.This is because the newly planted plots are se verely damaged by the surface vegetation,which increases the erosion intensity,and with the growth of fruit trees and the restoration of underlying vegetation,the soil eros ion intensity will gradually weaken.(3)Correlation analysis was performed on the time scales of annual and monthly time scales for the meridional flow,sediment transport and rainfall in the river basin.I n the annual scale analysis,R>00.93;and R>0.78 in the analysis of the time scale of t he month,indicating that the three have a strong correlation;Double accumulation cur ve analysis of runoff and sediment transport,the two have strong consistency.In 2010,the slope of the cumulative curve increased,turning points appeared;(4)The research results show that the SWAT model has a better effect on simulati ng runoff(Re=-0.05;R~2=0.79;Ens=0.72),the simulation results of sediment trans port are also within a reasonable range(Re=0.75;R~2=0.8;Ens=0.71);from 1990 t o 2015,the forest land area in the Xunwu watershed decreased by 36.83%,the orchar d area increased by 42.48%,and the change rates of runoff and sediment transport wer e 2.57%and 4.27%,respectively;the relationship between the area of newly cultivate d orchards and the amount of sediment transported by the river is not significant,beca use the sediment transport of the river is not only related to soil erosion,but also to th e location relationship between the soil erosion block and the river.At the same time,soil and water loss in the orchard was effectively controlled by the water conservation measures such as the reverse slope level. |
PDF Full Text Request