| In recent years,China has experienced significant Land use and land cover change（LUCC）with the continuous promotion of Grain for Green Project and the accelerated urbanization process.For the Loess Plateau region,where soil erosion is frequent,the study of soil and water conservation effects of LUCC is very meaningful.In this study,the soil and water conservation effects of LUCC from 2000 to 2020 were investigated and evaluated preliminarily in Chengguan District,Lanzhou City.In the study,two cultivated land plots,lily land（N1）and peony land（N2）,two forest land plots,mixed forest land of Pinus tabulaeformis and Platycladus orientalis（L1）and mixed forest land of Robinia pseudoacacia and Platycladus orientalis（L2）,three grassland plots,abandoned land（C1）,alfalfa land（C2）and natural grassland（C3）,and three unused land plots,dug plot（W1）,filled plot 1（T1）and filled plot 2（T2）,were selected to investigate the soil and water conservation performance of different land use and land cover was measured.The selected soil and water conservation performance indicators include soil anti-erodibility,soil anti-scourability and soil infiltration capacity.Soil anti-erodibility was obtained by dry-wet sieving of undisturbed soil samples to derive the proportion of different grain classes and calculate mean weight diameter of soil water-stable agglomerates（MWDw）,geometric mean diameter of soil water-stable agglomerates（GMDw）,fractal dimension of soil water-stable agglomerates（Dw）,percentage of aggregates destruction（PAD）,and the percentage of water-stable agglomerates>0.25 mm[Mw（>0.25）],samples were taken at every 5 cm layer in the soil layer from 0 to 30 cm depth.Soil anti-scourability was determined by using an indoor water flushing method for surface undisturbed soil samples to obtain the amount of soil loss weight（Ms）for each sample and to calculate the soil anti-scourability coefficient（AS）.Soil infiltration capacity index soil saturated hydraulic conductivity（Ks）was determined using a single-ring dual-head infiltrator.Soil and water conservation performance indicators values were then calculated for four types of land use and land cover:cultivated land,forest land,grassland,and unused land,the values of indicators related to soil and water conservation performance of construction land were also estimated.Then the LUCC 2000-2020 in Chengguan District,Lanzhou City,was analyzed by remote sensing and GIS methods,and the LUCC soil and water conservation effects were calculated using the concept of land use and land cover conversion index,combined with different land use and land cover soil and water conservation performance data.The main results were as follows.（1）The surface soil anti-erodibility of each land use and land cover in Chengguan District,Lanzhou City,was as follows:MWDw showed that forest land and grassland were significantly larger than cultivated land and unused land;GMDw showed that forest land>grassland>cultivated land>unused land,with significant differences among land use and land cover;Dw showed that forest land was significantly smaller than grassland and cultivated land,and unused land was the largest;PAD showed that forest land and grassland were significantly smaller than cultivated land,and unused land was the largest;Mw（>0.25）showed that the largest was forest land,followed by grassland and cultivated land,and the smallest in unused land.The soil anti-scourability showed that Ms of unused land was significantly larger than that of cultivated land,forest land and grassland;AS showed that grassland>forest land>cultivated land>unused land,and the value of AS of grassland was 36.29 L/g,while that of unused land was only 0.32 L/g.The soil infiltration capacity index Ks showed that forest land>grassland>cultivated land>unused land,and the values were 0.19,0.12,0.10 and 0.10cm/min,respectively,with good significance of the differences between forest,cultivated and unused land.（2）Soil organic matter and plant roots were significantly correlated with soil anti-erodibility index and soil infiltration capacity index;soil anti-scourability index was significantly correlated with soil organic matter,and soil anti-scourability tended to increase with the increase of root biomass.Soil electrical conductivity was highly significant negative correlated with soil anti-erodibility,soil anti-scourability and soil infiltration capacity.The correlation between alkaline nitrogen and soil anti-erodibility,soil anti-scourability and soil infiltration capacity was significantly positive,because alkaline nitrogen is easily absorbed by plants,which is particularly important for the accumulation of plant biomass.A higher accumulation of soil organic matter will result in a looser soil structure,greater porosity,smaller capacity and increased infiltration capacity.（3）The LUCC in Chengguan District of Lanzhou City from 2000 to 2020 mainly shows the decrease of grassland,the increase of construction land and unused land,as well as the decrease of cultivated land and the increase of forest land.Among them,the increase area and increase rate of construction land are at the highest level,with values of 25.96 km2 and 46.15%,and the decrease of grassland area is the largest,and the decrease rate is also larger,with values of 27.68 km2 and 28.88%.The transfer of grassland to construction land is the largest with 12.05 km2,followed by the transfer of grassland to unused land with 10.02 km2,and the transfer of cultivated land and forest land to construction land is also large with 7.42 km2 and 7.12 km2 respectively.（4）The soil and water conservation effect of LUCC in Chengguan District of Lanzhou City from 2000 to 2020 is mainly manifested by the enhancement of overall soil anti-erodibility,the weakening of overall soil anti-scourability and the weakening of overall soil infiltration capacity,and the changes in the area of grassland,construction land and unused land play a major role in this.The urban expansion project is the main aspect affecting the soil and water conservation effect of LUCC in Chengguan District,Lanzhou City. |
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