Cadmium in agricultural soils,vegetables and rice and potential health risk in vicinity of Dabaoshan Mine in Shaoguan,China

Soil cadmium(Cd)contamination resulted from mining and smelting is a major environmental concern,and health risk associated with Cd exposure to multi-media through muti-pathway is increasing.Cd concentrations in soils,vegetables and paddy rice were investigated,and potential non-carcinogenic and carcinogenic health risks exposure to Cd were estimated at six villages around the Dabaoshan Mine,South China.A total of 87 soil samples were found to exceed the China's maximum permission level(MPL)for Cd,while the highest value of 4.42 mg/kg was found near irrigation ditch associated with Hengshi River in Xinyi(XY)Village.Cd contents in vegetables and rice exceeded the maximum permissible concentration by more than five times in every village.Cadmium accumulation in plants is in the order of celery>lactuca sativa L>Chinese cabbage>Romaine lettuce>asparagus lettuce>mustard>cabbage mustard>cabbage.The mean hazard quotient(HQ)of all villages is in the range of [5.29,25.75],and the mean values of cancer risk for investigated areas are more than 10 times greater than the USEPA(2009)threshold limit value of 10-4.Moreover,human non-carcinogenic and carcinogenic risks are mainly attributable to paddy rice intake,followed by vegetables intake,soil ingestion,inhalation,and dermal contact.The results indicate that Cd has a huge potential risk on human health for the local residents.

Emission and Fixation of CO_2 from Soil System as Influenced by Long-Term Application of Organic Manure in Paddy Soils

The observations of 25-yr long-term experiment in Zhejiang paddy soils showed that the soil organic matter could increase continuously with applying organic manure, and the increase in rate enhanced along with the application rates of organic manure. By mathematical modeling, the soil organic matter increased by 22 kg when 1 t of fresh FYM was applied. The CO2 emission resulting from the mineralization of soil organic matter increased with the increase in the application rate of the organic manure as well as the increase in the root residues. It is expected that the CO2 emission will be at 10.04-21.61 t ha-1 yr-1 when 16.5-49.5 t ha-1 yr-1 of fresh FYM is applied. The soil organic carbon from mineralization and release of applied organic carbon (fresh FYM and root residues) will affect the CO2 concentration in the atmosphere. So, the higher the application rate of organic manure, the more is the fixed organic carbon. The CO2 fixation will be at 1.885-3.463 t ha-1 yr-1 when 16.5-49.5 t ha-1 yr-1 of fresh FYM is applied. Thus, the CO2 fixation will increase by 46.7 kg by applying 1 t fresh FYM. To apply organic manure continuously in rice fields may reduce the contribution to the increase of CO2 concentration in the atmosphere.

Enhanced soil moisture improves vegetation growth in an arid grassland of Inner Mongolia Autonomous Region, China

Climate change impacts on grasslands that cover a quarter of the global land area, have become unprecedented during the 21~(st) century. One of the important ecological realms, arid grasslands of northern China, which occupy more than 70% of the region's land area. However, the impact of climate change on vegetation growth in these arid grasslands is not consistent and lacks corresponding quantitative research. In this study, NDVI(normalized difference vegetation index) and climate factors including temperature, precipitation, solar radiation, soil moisture, and meteorological drought were analyzed to explore the determinants of changes in grassland greenness in Inner Mongolia Autonomous Region(northern China) during 1982–2016. The results showed that grasslands in Inner Mongolia witnessed an obvious trend of seasonal greening during the study period. Two prominent climatic factors,precipitation and soil moisture accounted for approximately 33% and 27% of grassland NDVI trends in the region based on multiple linear regression and boosted regression tree methods. This finding highlights the impact of water constraints to vegetation growth in Inner Mongolia's grasslands. The dominant role of precipitation in regulating grassland NDVI trends in Inner Mongolia significantly weakened from 1982 to 1996, and the role of soil moisture strengthened after 1996. Our findings emphasize the enhanced importance of soil moisture in driving vegetation growth in arid grasslands of Inner Mongolia, which should be thoroughly investigated in the future.

The Changes in Guilin Paddy Soil Organic Matter and Rice Yield under Long-Term Fertilization

Rational fertilization is an important measure to increase crop yield and soil fertility. Through analysis,this paper aims to master the change characteristics of soil organic matter and rice yield under different fertilizer treatments,in order to provide an important reference for the sustainable use of soil and effective fertilization. Long-term( 19 years) rice crop rotation experiments in waterloggogenic paddy soil were conducted to investigate the change trend of crop grain yield and soil organic matter with time,reveal the dynamic characteristics and relationship between main fertility factors and crop yields using comparative analysis at three sites with conventional fertilization and non-fertilization in Guilin. The results showed that compared with previous years,the rice yield increased by 53% under the fertilization treatment and degreased by 66% under the control. Over the years,the average soil organic matter( SOM) content under fertilization treatment was 23% higher than under CK treatment. This indicates that chemical fertilizer and organic manure application can increase the rice yield and soil organic matter,and high rice yield can be attributed to the SOM increase.

Influence of Climate on Soil Organic Carbon in Chinese Paddy Soils

Soil organic carbon(SOC) is a major component of the global carbon cycle and has a potentially large impact on the greenhouse effect. Paddy soils are important agricultural soils worldwide, especially in Asia. Thus, a better understanding of the relationship between SOC of paddy soils and climate variables is crucial to a robust understanding of the potential effect of climate change on the global carbon cycle. A soil profile data set(n = 1490) from the Second National Soil Survey of China conducted from 1979 to 1994 was used to explore the relationships of SOC density with mean annual temperature(MAT) and mean annual precipitation(MAP) in six soil regions and eight paddy soil subgroups. Results showed that SOC density of paddy soils was negatively correlated with MAT and positively correlated with MAP(P < 0.01). The relationships of SOC density with MAT and MAP were weak and varied among the six soil regions and eight paddy soil subgroups. A preliminary assessment of the response of SOC in Chinese paddy soils to climate indicated that climate could lead to a 13% SOC loss from paddy soils. Compared to other soil regions, paddy soils in Northern China will potentially more sensitive to climate change over the next several decades. Paddy soils in Middle and Lower Yangtze River Basin could be a potential carbon sink. Reducing the climate impact on paddy soil SOC will mitigate the positive feedback loop between SOC release and global climate change.

Effects of Vegetation Restoration in Different Types on Soil Nutrients in Southern Edge of Mu Us Sandy Land

In order to explore effects of vegetation on nutrients in soils, nutrients characters of soils under natural grass, closed grass, abandoned lands, forest lands returned from farmlands and fixed sandy areas in Mu Us Desert were researched. The results indicated that vegetations in varied types have different effects on organic matter, total N, available N and available P, among which the first three were all higher in soils under closed grass, forest lands returned from farmlands, and fixed sandy lands than those under natural grass and abandoned lands. This was totally contrary with contents of available P in soil. In addition, nutrients in soils at 0-20 cm were more influenced by vegetation, than those at 20-60 cm, and Caragana Korshinskii proved better in improving nutrients in soils.

Spatial-Temporal Changes of Soil Organic Carbon During Vegetation Recovery at Ziwuling, China

To probe the processes and mechanisms of soil organic carbon (SOC) changes during forest recovery, a 150-yearchronosequence study on SOC was conducted for various vegetation succession stages at the Ziwuling area, in the centralpart of the Loess Plateau, China. Results showed that during the 150 years of local vegetation rehabilitation SOC increasedsignificantly (P < 0.05) over time in the initial period of 55-59 years, but slightly decreased afterwards. Average SOCdensities for the 0-100 cm layer of farmland, grassland, shrubland and forest were 4.46, 5.05, 9.95, and 7.49 kg C m-3,respectively. The decrease in SOC from 60 to 150 years of abandonment implied that the soil carbon pool was a sink forCO2 before the shrubland stage and became a source in the later period. This change resulted from the spatially variedcomposition and structure of the vegetation. Vegetation recovery had a maximum effect on the surface (0-20 cm) SOCpool. It. was concluded that vegetation recovery on the Loess Plateau could result in significantly increased sequestrationof atmospheric CO2 in soil and vegetation, which was ecologically important for mitigating the increase of atmosphericconcentration of CO2 and for ameliorating the local eco-environment.

Soil moisture of different vegetation types on the Loess Plateau

Water stored in deep loess soil is one of the most important resources regulating vegetation growth in the semi-arid area of the Loess Plateau, but planted shrub and forest often disrupt the natural water cycle and in turn influence plant growth. The purpose of this study was to examine the effects of main vegetation types on soil moisture and its inter-annual change. Soil moisture in 0-10 m depth of six vegetation types, i.e., crop, grass, planted shrub of caragana, planted forests of arborvitae, pine and the mixture of pine and arborvitae were measured in 2001,2005 and 2006. Soil moisture in about 0-3 m of cropland and about 0-2 m of other vegetation types varied inter-annually dependent on annual precipitation, but was stable inter-annually below these depths. In 0-2 m, soil moisture of cropland was significantly greater than those of all other vegetation types, and there were no si nificant differences among other vegetation types. In 2-10 m, there was no significant mois- ture difference between cropland and grassland, but the soil moistures under both of them were significantly higher than those of planted shrub and forests. The planted shrub and forests had depleted soil moisture below 2 m to or near permanent wilting point, and there were no significant moisture differences among forest types. The soil moisture of caragana shrub was significantly lower than those of forests, but the absolute difference was very small. The results of this study implicated that the planted shrub and forests had depleted deep soil moisture to the lowest limits to which they could extract and they lived mainly on present year precipitation for transpiration.

Effects of Vegetation Restoration on Soil Organic Carbon in China:A Meta-analysis

Vegetation restoration has been proposed as an effective method for increasing both plant biomass and soil carbon(C) stocks. In this study, 204 publications(733 observations) were analyzed, focusing on the effects of vegetation restoration on soil organic carbon(SOC) in China. The results showed that SOC was increased by 45.33%, 24.43%, 30.29% and 27.98% at soil depths of 0–20 cm, 20–40 cm, 40–60 cm and > 60 cm after vegetation restoration, respectively. Restoration from both cropland and non-cropland increased the SOC content. The conversion of non-cropland was more efficient in SOC accumulation than the conversion of cropland did, especially in > 40 cm layers. In addition, the conversion to planted forest led to greater SOC accumulation than that to other land use did. Conversion period and initial SOC content extended more influence on soil C accumulation as the main factors after vegetation restoration than temperature and precipitation did. The SOC content significantly increased with restoration period after long-term vegetation restoration(> 40 yr), indicating a large potential for further accumulation of carbon in the soil, which could mitigate climate change in the near future.

Seasonal dynamics of soil water content in the typical vegetation and its response to precipitation in a semi-arid area of Chinese Loess Plateau

Soil water content is a key limiting factor for vegetation growth in the semi-arid area of Chinese Loess Plateau and precipitation is the main source of soil water content in this area.To further understand the impact of vegetation types and environmental factors such as precipitation on soil water content,we continuously monitored the seasonal dynamics in soil water content in four plots(natural grassland,Caragana korshinskii,Armeniaca sibirica and Pinus tabulaeformis)in Chinese Loess Plateau.The results show that the amplitude of soil water content fluctuation decreases with an increase in soil depth,showing obvious seasonal variations.Soil water content of artificial vegetation was found to be significantly lower than that of natural grassland,and most precipitation events have difficulty replenishing soil water content below a depth of 40 cm.Spring and autumn are the key seasons for replenishment of soil water by precipitation.Changes in soil water content are affected by precipitation,vegetation types,soil evaporation and other factors.The interception effect of vegetation on precipitation and the demand for water consumption by transpiration are the key factors affecting the efficiency of soil water replenishment by precipitation in this area.Due to artificial vegetation plantation in this area,soil will face a water deficit crisis in the future.

Changes in vegetation and soil properties during recovery of a subtropical forest in South China

Secondary forests account for a large amount of subtropical forest due to persistent anthropogenic disturbance in China.The interaction between vegetation and soil during recovery process is rather complex and dependent on forest conditions.Understanding how vegetation and soil properties changes and how their relationship develops in secondary forests is key to effective forest restoration and management.Here we explored the patterns of vegetation and soil properties as well as their correlations during forest recovery process in a subtropical forest in south China.Plots of three forest types,i.e.,broadleaf-conifermixedforest,broadleaved forest and old growth stand,were established to represent the recovery stages.The results showed that diversity patterns in the tree,shrub and herb layers were different:in the tree layer the species diversity peaked at the intermediate stage,while in the understory layers it decreased chronologically.Most of the soil factors showed an increasing trend,and different effects of soil factors were found for the three layers as well as for the two spatial scales.Together,our results suggested that vegetation and soil might be interdependent during the recovery course.Further studies are needed on exploring how vegetation interplays with soil at different scales and how nutrient limitations affects the vegetation development in a chronosequence.

Soil physicochemical properties and vegetation structure along an elevation gradient and implications for the response of alpine plant development to climate change on the northern slopes of the Qilian Mountains

Elevation is one of key factors to affect changes in the environment, particularly changes in conditions of light, water and heat. Studying the soil physicochemical properties and vegetation structure along an elevation gradient is important for understanding the responses of alpine plants andtheir growing environment to climate change. In this study, we studied plant coverage, plant height, species richness, soil water-holding capacity, soil organic carbon(SOC) and total nitrogen(N) on the northern slopes of the Qilian Mountains at elevations from2124 to 3665 m. The following conclusions were drawn:(1) With the increase of elevation, plant coverage and species richness first increased and then decreased, with the maximum values being at 3177 m.Plant height was significantly and negatively correlated with elevation(r=–0.97, P<0.01), and the ratio of decrease with elevation was 0.82 cm·100 m-1.(2) Both soil water-holding capacity and soil porosity increased on the northern slopes of the Qilian Mountains with the increase of elevation. The soil saturated water content at the 0-40 cm depth first increased and then stabilized with a further increase of elevation, and the average ratio of increase was2.44 mm·100 m-1. With the increase of elevation, the average bulk density at the 0-40 cm depth first decreased and then stabilized at 0.89 g/cm3.(3) With the increase of elevation, the average SOC content at the 0-40 cm depths first increased and then decreased,and the average total N content at the 0-40 cm depth first increased and then stabilized. The correlation between average SOC content and average total N content reached significant level. According to the results of this study, the distribution of plants showed a mono-peak curve with increasing elevation on the northern slopes of the Qilian Mountains. The limiting factor for plant growth at the high elevation areas was not soil physicochemical properties, and therefore,global warming will likely facilitate the development of plant at high elevation areas in the Qilian Mountains.

不同种植年限水稻土有机碳矿化对周期性变温的响应

为了探讨陕北中部黄土丘陵沟壑区不同种植年限水稻土有机碳矿化对周期性温度变化的响应,以陕北南泥湾水稻种植基地不同种植年限(78 a、30 a、3 a)的稻田土壤为研究对象,基于室内35 d培养试验与矿化动态模型研究方法,解析温度变化对土壤有机碳矿化的影响。结果表明:恒温以及周期性变温处理的土壤累积矿化量在前7 d增加较快,达到整个培养期的39.2%~47.6%,7 d后至培养结束时增加缓慢。培养前7 d,土壤有机碳矿化速率快速下降,直至21 d时趋于稳定状态。78 a、30 a、3 a水稻土和玉米地的累积矿化量分别为3126.75、2737.63、2547.42和2173.88 mg/kg,水稻土累积矿化量比玉米地高28.94%。变温条件下的有机碳累积矿化量较恒温条件下增加4.95%。变温条件下,0~20 cm和20~40 cm土壤有机碳矿化量比恒温下分别高5.69%和4.20%。水稻土在周期性变温条件下14 d的微生物生物量碳(MBC)下降幅度(41.49%)高于恒温培养(32.22%),35 d的MBC下降幅度(50.20%)低于恒温培养(54.23%),溶解性有机碳(DOC)下降幅度规律与之相反。0~20 cm和20~40 cm土壤潜在矿化量占总有机碳的比例(C 0/SOC)均表现为15℃/35℃高于25℃恒温,说明表层土壤易于矿化,土壤碳固存能力随温度周期性改变而降低。变温与恒温的土壤有机碳矿化速率、累积矿化量、潜在可矿化有机碳量无明显差异,说明在本试验条件下,在积温相同的情况下,周期性变温对土壤有机碳的矿化无显著影响。

陕北中部黄土区不同种植年限水稻田有机碳矿化对温度的响应

为了探讨陕北中部黄土区不同种植年限水稻田有机碳矿化对温度的响应,以陕北南泥湾水稻种植基地不同种植年限(3、30、78 a)的稻田土壤为研究对象,基于室内35 d培养试验与矿化动态模型研究方法,解析温度对土壤有机碳矿化的影响。结果表明:土壤有机碳累积矿化量和矿化速率均表现为78 a水稻田>30 a水稻田>3 a水稻田>玉米田。土壤累积矿化量、矿化速率、潜在可矿化有机碳含量(C 0)和潜在可矿化有机碳占总有机碳的比值(C 0/SOC)均表现为30℃处理>20℃处理>10℃处理。水稻田矿化累积量均表现为10℃处理(2015.14 mg·kg^(-1))显著低于20℃(2799.20 mg·kg^(-1))和30℃处理(3078.47 mg·kg^(-1))(P<0.05),但20℃与30℃处理之间无显著差异。玉米田累积矿化量在不同培养温度间没有达到显著差异水平。0~20 cm土层累积矿化量是20~40 cm土层的1.18倍。供试土壤在温度从10℃升高到20℃时的温度系数(Q 10)值(1.38)均高于从20℃升高到30℃时的Q 10值(1.14),土层间的Q 10值大小关系为0~20 cm>20~40 cm。潜在可矿化有机碳含量C 0与总有机碳、易氧化有机碳及溶解性有机碳含量之间均呈正相关关系,C 0与微生物生物量碳含量间呈正相关关系但未能达到显著水平。C 0/SOC随水稻种植年限的增加而降低,说明土壤有机碳的固存能力随水稻种植年限的增加而增强。

长白山地区土壤水蚀时空演变特征及驱动因素分析

探讨长白山地区受极端降水、地形复杂、植被破坏等因素影响造成的土壤侵蚀状况,可以研判该地区水土流失情况,为当地水土生态保护提供科学参考。利用修正的通用土壤流失方程(RUSLE)、趋势及相关分析法,定量分析长白山地区土壤水蚀的空间格局及时空分布特征,并探究土壤水蚀与气候、植被覆盖度及地形驱动因子的关系。结果表明:2000-2020年长白山地区土壤水蚀模数均值总体呈“西南高,东北低”的空间格局。相较于其他地类,草地、未利用地、林地更易发生土壤水蚀。近21 a来,土壤水蚀模数平均以0.0255 t/(hm^(2)·a)的速度上升,土壤水蚀模数表现为上升趋势的地区占研究区总面积的68.3%,侵蚀等级总体以微度和轻度为主,且轻度侵蚀比例也呈增加趋势,表明该地区土壤侵蚀状况趋于好转,未来吉林市中北部和延边州部分地区的水土流失风险较高。土壤水蚀与降水、海拔高度及坡度具有较为显著的正相关关系,而与气温、植被覆盖度的相关性以负相关为主。海拔大于1000 m或坡度大于20°的草地、林地区域是水土防治的重点地形区。

2000-2021年新疆植被覆盖度变化及驱动力

[目的]探讨2000—2021年新疆植被覆盖变化及其驱动力的分析,为新疆地区环境监测提供理论依据。[方法]借助GEE平台获取由NASA提供的NDVI数据,利用趋势分析、Hurst指数法对新疆地区2000—2021年植被覆盖变化进行动态分析,结合气象等数据,采用Mann-Kendall、偏相关分析法等对植被覆盖变化与气候、地表因素的响应进行分析。[结果](1)2000—2021年新疆地区NDVI年际变化总体以0.0014/a的速率波动式增长;年内变化总体呈倒U型,草甸植被的NDVI月均值波动最大。(2)2000—2021年新疆地区NDVI年均值77.9%在0~0.3波动,在空间分布表现为北部和西北部高,南部和东南部低。(3)2000—2021年新疆地区总体slope值在-0.036~0.052波动,主要变化趋势为基本不变和轻微改善,结合Hurst指数,新疆植被主要未来趋势变化为改善到退化。(4)22年间新疆地区的气温总体呈上升趋势,降水、土壤湿度和径流总体呈下降趋势。NDVI年均值与气温、降水、土壤湿度和径流呈显著负相关性的像元数占比均大于正相关性的像元数占比,且存在明显的空间地域特征。[结论]新疆植被覆盖变化总体呈上升趋势,但未来趋势不容乐观,需要重点关注新疆地区的环境监测等保护措施。

水田改旱地和菜地后红壤酸度和养分变化特征

【目的】以红壤区典型县域祁阳为例,分析不同母质发育的水田改为旱地和菜地后土壤酸度和养分含量变化特征,为该区合理利用土地防治酸化提供科学依据。【方法】选取18个点位,采集水田及相邻的旱地和菜地,分析土壤pH、交换性酸、交换性盐基离子、有机质、阳离子交换量和养分含量的变化及其相互关系。【结果】碱性母质发育的土壤pH均显著高于酸性母质发育的土壤。酸性母质发育的水田改为菜地后土壤pH降低了0.48个单位;碱性母质发育的水田改为旱地和菜地后土壤pH分别降低了0.74和0.53个单位。双直线模型拟合分析表明,当水田、旱地和菜地的土壤pH分别低于5.88、5.78和5.63时,土壤交换性铝含量快速升高,且降低一个pH单位土壤交换性铝含量分别增加1.09、2.33和2.93 cmol(+)·kg^(-1)。酸性母质发育的水田改为旱地土壤有机质和全氮含量分别降低了11.06和0.42 g·kg^(-1),而菜地无显著变化;碱性母质发育的水田改为旱地和菜地后土壤有机质和全氮含量均显著下降,降幅分别为13.88—17.28和0.57—0.71 g·kg^(-1)。碱性母质发育的水田改为旱地和菜地后土壤有效氮含量分别降低了47.66和42.34 mg·kg^(-1)。两种母质发育的水田改为菜地后土壤全磷、有效磷含量均显著增加,增幅分别为0.41—0.48 g·kg^(-1)和26.79—28.69 mg·kg^(-1)。两种母质发育的水田改为旱地和菜地土壤全钾含量无显著变化;碱性母质发育的水田改为旱地和菜地后土壤有效钾含量显著升高,分别升高了36.69和65.76 mg·kg^(-1)。相关分析表明,土壤pH与土壤交换性钙和镁、阳离子交换量、有机质含量和全氮含量呈显著正相关(P<0.01);土壤交换性酸和铝与有效磷含量显著正相关(P<0.05),与土壤交换性钙和镁、阳离子交换量、有机质含量和全氮含量呈显著负相关(P<0.01)。【结论】酸性母质和碱性母质发育的水田改为旱地后土壤有机质、全氮含量均显著降低,而土壤全磷、有效磷含量呈增加趋势;酸性母质发育的水田只有改为菜地后土壤才酸化,而碱性母质发育的水田改为旱地和菜地后土壤均酸化;水田改为旱地和菜地后土壤硝化作用增强和盐基离子淋失增加可能是其酸化的主要原因之一。

土地利用变化对土壤类型的影响——以太仓和昆山两市为例

选取江苏省太仓市和昆山市作为研究区域,结合当前土地利用方式和历史土壤图资料,通过室内分析确定土地利用方式的变化区域,并设置典型的调查样点,通过野外踏勘确定土地利用方式改变对土壤类型的潜在影响。结果表明:近40年来,太仓和昆山的主要土地利用变化方式是水改旱(即由水田转变为水浇地、旱地、园地、林地和草地等),这一变化分别占据了两市土地利用方式变化的98.92%和98.15%。这种显著的土地利用变化对土壤类型产生了明显影响,导致土壤性质发生改变,包括水稻土的犁底层逐渐减少,甚至消失,使其失去了典型的水稻土特征。研究区内土壤类型变化规则的确定主要由土壤质地和人为土地改造方向所影响。值得注意的是,水改旱后如继续旱作,土壤类型可能会由水稻土转为其他类型土壤(如潮土等),但这需要进一步的研究来验证其效果。

晋西黄土区典型造林整地措施对土壤水分动态的影响

【目的】探究晋西黄土区典型造林树种和水平阶整地措施对0~180 cm土层土壤水分动态的影响,为植被恢复及流域综合治理提供参考依据。【方法】以晋西黄土残塬区蔡家川流域典型工程措施水平阶以及主要造林树种刺槐Robinia pseudoacacia和侧柏Platycladusorientalis为研究对象,于2019年5—9月生长季开展土壤水分定位监测,并采用配对试验,对自然坡面刺槐林地与侧柏林地土壤水分进行同步观测,分析不同植被和水平阶整地综合影响下的土壤水分特征及对降雨事件的响应,评价典型工程措施对不同植被土壤含水量的影响。【结果】生长季不同植被类型、水平阶整地前后的土壤含水量的变化与降雨量的变化密切相关,不同样地平均土壤含水量由高到低依次为水平阶侧柏林地(18.68%)、自然坡面侧柏林地(16.19%)、水平阶刺槐林地(16.10%)、自然坡面刺槐林地(15.42%)。较之自然坡面,水平阶整地措施能够分别提高侧柏林地和刺槐林地土壤含水量15.38%、4.41%。根据土壤水分垂直变化特征,水平阶整地可以提升土壤水分的活跃层、次活跃层深度:水平阶侧柏林地活跃层、次活跃层深度范围为0~80 cm,相对于自然坡面侧柏林地提升深度33%;水平阶刺槐林地活跃层、次活跃层深度范围为0~140 cm,相对于自然坡面刺槐林地提升深度40%。【结论】土壤含水量的动态变化与降雨量、工程措施、植被作用关系密切,水平阶是开展黄土残塬小流域生态恢复的有效工程措施,且水平阶侧柏林地提升效果要优于水平阶刺槐林地。图3表3参37.

渭河流域植被覆盖变化趋势及其对土壤干湿状况的响应

随着全球气候的快速变化以及渭河流域地区城市的快速发展,渭河流域植被生态系统面临许多挑战,研究区域内植被的时空变化以及对土壤干湿状况的响应有着重要意义。基于2001—2020年的MODIS的归一化植被指数(NDVI)与地表温度(LST)数据,对渭河流域的土壤干湿状况数据进行反演,通过线性回归、残差分析和贡献度分析了2001—2020年渭河流域生长季植被覆盖时空特征及土壤干湿状况的驱动与贡献。结果表明:(1)2001—2020年渭河流域生长季NDVI均值总体呈现波动增加趋势,平均趋势率为0.47×10^(-2)·a^(-1),植被呈恢复趋势,其中2012—2016年生长季NDVI均值受到人类活动的抑制作用呈现下降趋势。(2)土壤干湿状况和人类活动对渭河流域生长季NDVI的影响迥异,土壤干湿状况的影响主要表现为影响较弱与缓慢增长,人类活动的影响主要以促进植被恢复为主。(3)土壤干湿状况和人类活动对渭河流域生长季NDVI均值变化的贡献均主要集中于同向贡献,其中负向贡献只来源土壤干湿状况,占比19.77%,同向高贡献主要来源人类活动,说明渭河流域中人类活动是植被覆盖变化的主要驱动力。(4)渭河流域植被整体受到土壤干湿状况和人类活动的双重促进作用;抑制作用主要集中于汾渭盆地农业生态区,属于人类活动的同向高贡献率分布区,说明目前人类活动是抑制植被覆盖增长的主要原因。研究结果可为渭河流域生态保护以及可持续发展提供更加精确的科学依据。