Features of Runoff and Sediment Yield of Different Shrub-Grass Combination Modes for Highway Side Slope in Hilly Areas of Central Sichuan Province

[Objective] Indigenous plants with favorable water and soil conservation effects were screened for the shrub planting.[Method] Suining-Ziyang-Meishan Highway in the hilly areas of central Sichuan Province was taken for example,through sorting out plant species investigated in the route planning,3 indigenous shrub species(Neosinocalamus affinis,Vitex negundo and Coriaria nepalensis) and 3 indigenous herbaceous species(Setaria viridis,Miscanthus floridulus,Artemisia argyi) were selected.Rainfall simulation experiment was adopted to compare runoff and sediment yields of different combination modes and ratios under constant rainfall intensity(20 mm/min).[Result] Different combination modes under constant rainfall intensity all showed better water and soil conservation effects than that of control group did.For example,runoff appeared 1'-4'05"later,sediment yield reduced by 6.56-33.86 g respectively.Among all combination modes,runoff and sediment yield showed great difference after 20 min of constant rainfall,V.negundo+S.viridis had the lowest runoff(1,700 ml) and sediment yield(60.71 g);C nepalensis+A. argyi had the highest runoff(1,920 ml) and sediment yield(84.02 g).[Conclusion] Given the same planting conditions such as side slope and seeding quantity,and also the same planting techniques,in the hilly areas of central Sichuan Province,the combination of V.negundo and S.viridis can greatly improve the water and soil conservation capacity of highway.

Impacts of Climate Change on Spatial and Temporal Distribution of Runoff and Sediment Yield in Xixi Watershed of Jinjiang Basin

Based on meteorologic data in Xixi Watershed from 1972 to 1979, the SWAT model was applied to simulate the response of runoff and sediment yield in Xixi Watershed to climate change under 24 kinds of climate change scenarios, and then the spatial and temporal distribution of change rates of the runoff and sediment were analyzed. The results showed that the runoff yield would increase with the increase of precipitation or decrease of temperature, and the sediment yield would increase with the increase of precipitation or increase of temperature; the runoff would be more sensitive to variations in precipitation than to variations in temperature, and precipitation change would lead to more obvious change in the run- off yield; the temporal distribution of change rates of the runoff and sediment yield would be uneven in the 12 months, and the variation trends of the two change rates in the 12 months would be accordant; the spatial distribution of change rates of the runoff and sediment yield would be uneven in the sub-watersheds, and the change rate of the runoff yield would be bigger in the sub-watersheds where the runoff yield in the basic period would be smaller. This study can provide decision-making basis for sustainable development of Jinjiang Basin.

Modelling the Effects of Land-use Change on Runoff and Sediment Yield in the Weicheng River Watershed, Southwest China

As a major sediment area in the upper Yangtze River, Jialing River basin experienced substantial land-use changes, many water conservancy projects were constructed from the 1980 s onward to promote water and soil conservation. The water and sediment yield at the watershed outlet was strongly affected by these water conservation works, including ponds and reservoirs, which should be considered in the modelling. In this study, based on the observed data of the Weicheng River catchment, the relationships between precipitation, runoff, vegetation, topography and sediment yield were analyzed, a distributed runoff and sediment yield model(WSTD-SED) was developed, and the hydrological processes of different land-use scenarios were simulated by using the model. The main results are summarized as follows: 1) there is an alternating characteristic in river channels and reservoirs in the Jialing River hilly area, with scour occurring in wet years and deposit occurring in dry years. 2) Most of the sediment deposited in river channels and reservoirs is carried off by the largest flood in the year. 3) The model yielded plausible results for runoff and sediment yield dynamics without the need of calibration, and the WSTD-SED model could be usedto obtain qualitative estimates on the effects of land use change scenarios. 4) The modelling results suggest that a 10% increase in cropland(dry land) reforestation results in a 0.7% decrease in runoff and 1.5% decrease in sediment yield.

Simulation of Runoff and Sediment Yield for a Himalayan Watershed Using SWAT Model

Watershed is considered to be the ideal unit for management of the natural resources. Extraction of water-shed parameters using Remote Sensing and Geographical Information System (GIS) and use of mathematical models is the current trend for hydrologic evaluation of watersheds. The Soil and Water Assessment Tool (SWAT) having an interface with ArcView GIS software (AVSWAT2000/X) was selected for the estimation of runoff and sediment yield from an area of Suni to Kasol, an intermediate watershed of Satluj river, located in Western Himalayan region. The model was calibrated for the years 1993 & 1994 and validated with the observed runoff and sediment yield for the years 1995, 1996 and 1997. The performance of the model was evaluated using statistical and graphical methods to assess the capability of the model in simulating the run-off and sediment yield from the study area. The coefficient of determination (R2) for the daily and monthly runoff was obtained as 0.53 and 0.90 respectively for the calibration period and 0.33 and 0.62 respectively for the validation period. The R2 value in estimating the daily and monthly sediment yield during calibration was computed as 0.33 and 0.38 respectively. The R2 for daily and monthly sediment yield values for 1995 to 1997 was observed to be 0.26 and 0.47.

Estimation of runoff and sediment yield in the Redrock Creek watershed using AnnAGNPS and GIS

Sediment has been identified as a significant threat to water quality and channel clogging that in turn may lead to river flooding. With the increasing awareness of the impairment from sediment to water bodies in a watershed, identifying the locations of the major sediment sources and reducing the sediment through management practices will be important for an effective watershed management. The annualized agricultural non-point source pollution(AnnAGNPS) model and newly developed GIS interface for it were applied in a small agricultural watershed, Redrock Creek watershed, Kansas, in this pilot study for exploring the effectiveness of using this model as a management tool. The calibrated model appropriately simulated monthly runoff and sediment yield through the practices in this study and potentially suggested the ways of sediment reduction through evaluating the changes of land use and field operation in the model for the purpose of watershed management.

Modeling and analysis of effects of precipitation and vegetation coverage on runoff and sediment yield in Jinsha River Basin

This paper focuses on the effects of precipitation and vegetation coverage on runoff and sediment yield in the Jinsha River Basin. Results of regression analysis were taken as input variables to investigate the applicability of the adaptive network-based fuzzy inference system （ANFIS） to simulating annual runoff and sediment yield. Correlation analysis indicates that runoff and sediment yield are positively correlated with the precipitation indices, while negatively correlated with the vegetation indices. Furthermore, the results of stepwise regression show that annual precipitation is the most important factor influencing the variation of runoff, followed by forest coverage, and their contributions to the variation ofrunoffare 69.8% and 17.3%, respectively. For sediment yield, rainfall erosivity is the most important factor, followed by forest coverage, and their contributions to the variation of sediment yield are 49.3% and 24.2%, respectively. The ANFIS model is of high precision in runoff forecasting, with a relative error of less than 5%, but of poor precision in sediment yield forecasting, indicating that precipitation and vegetation coverage can explain only part of the variation of sediment yield, and that other impact factors, such as human activities, should be sufficiently considered as well.

Impacts of precipitation variation and soil and water conservation measures on runoff and sediment yield in the Loess Plateau Gully Region, China

The Loess Plateau of China has experienced a lengthy drought and severe soil erosion.Changes in precipitation and land use largely determine the dynamics of runoff and sediment yield in this region. Trend and mutation analyses were performed on hydrological data(1981–2012) from the Yanwachuan watershed in the Loess Plateau Gully Region to study the evolution characteristics of runoff and sediment yield. A time-series contrasting method also was used to evaluate the effects of precipitation and soil and water conservation(SWC) on runoff and sediment yield. Annual sediment yield declined markedly from 1981 to 2012 although there was no significant change in annual precipitation and annual runoff. Change points of annual runoff and annual sediment yield occurred in 1996 and 1997,respectively. Compared with that in the baseline period(1981–1996), annual runoff and annual sediment yield in the change period(1997–2012)decreased by 17.0% and 76.0%, respectively, but annual precipitation increased by 6.3%. Runoff decreased in the flood season and normal season, but increased in the dry season, while sediment yield significantly declined in the whole study period. The SWC measures contributed significantly to the reduction of annual runoff(137.9%) and annual sediment yield(135%) and were more important than precipitation. Biological measures(forestland and grassland) accounted for 61.04% of total runoff reduction, while engineering measures(terraces and dams) accounted for 102.84% of total sediment yield reduction. Furthermore, SWC measures had positive ecological effects. This study provides a scientific basis for soil erosion control on the Loess Plateau.

Forecasting of Runoff and Sediment Yield Using Artificial Neural Networks

Runoff and sediment yield from an Indian watershed during the monsoon period were forecasted for differ-ent time periods (daily and weekly) using the back propagation artificial neural network (BPANN) modeling technique. The results were compared with those of single- and multi-input linear transfer function models. In BPANN, the maximum value of variable was considered for normalization of input, and a pattern learning algorithm was developed. Input variables in the model were obtained by comparing the response with their respective standard error. The network parsimony was achieved by pruning the network using error sensitiv-ity - weight criterion, and model generalization by cross validation. The performance was evaluated using correlation coefficient (CC), coefficient of efficiency (CE), and root mean square error (RMSE). The single input linear transfer function (SI-LTF) runoff and sediment yield forecasting models were more efficacious than the multi input linear transfer function (MI-LTF) and ANN models.

Simulation of Runoff and Sediment Yield for a Kaneri Watershed Using SWAT Model

Watershed as an entry point acts as a beginning to address the issues of sustainable rainwater management for improving livelihoods. Extraction of watershed parameters using Geographical Information System (GIS) and use of simulation models is the current trend for hydrologic evaluation of watersheds. In the present study, the open Source Tool Quantum GIS 2.2.0 was used for preparation of maps to verify the spatial extent of the area. The Soil and Water Assessment Tool (SWAT) having an interface with Arc-View GIS software (ArcGIS 10.1 with Arc SWAT 2012 extension) was selected for the estimation of runoff and sediment yield from Kaneri watershed, located in Western Maharashtra region. The coefficient of determination (R2) for the monthly and yearly runoff was obtained as 0.849 and 0.951 respectively for the calibration period 1979 to 2000 and 0.801 and 0.950 respectively for the validation period 2001-2013. The R2 value in estimating the monthly and yearly sediment yield during calibration period was computed as 0.722 and 0.788 respectively. The R2 for monthly and yearly sediment yield values for validation period was observed to be 0.565 and 0.684 respectively.

Path Analysis on Environmental Factors Controlling Runoff and Sediment Yields in Shelter Forests in Three Gorges Reservoir Region

Effects of environmental factors such as climate,topography,vegetation and soil in shelter forests in Three Gorges Reservoir Region on runoff and sediment yields were monitored to identify dominant environmental factors controlling runoff and sediment yields in 15 runoff plots in study area by soil sampling,laboratory analysis,stepwise regression analysis and path analysis,and to establish the main control environmental factors that affect runoff and sediment yields. The results showed that soil bulk density,herbaceous cover,slope,and canopy density were the significant factors controlling runoff,and the direct path coefficient of each factor was ranked as canopy closure(-0. 628) > litter thickness(-0. 547) > bulk density( 0. 509) > altitude( 0. 289). The indirect path coefficient was ranked as soil bulk density( 0. 354) >litter thickness(-0. 169) > altitude( 0. 126) > canopy closure(-0. 104). Therefore,canopy closure and litter thickness mainly had direct effects on runoff,while soil bulk density mainly had indirect effects through their contributions to other factors. Herbaceous cover,litter thickness,slope,canopy density,and altitude were the significant factors controlling sediment yields. The direct path coefficient of each factor was ranked as herbaceous cover(-0. 815) > litter thickness(-0. 777) > canopy closure(-0. 624) > slope( 0. 620). The indirect path coefficient was ranked as slope( 0. 272) > litter thickness(-0. 131) > canopy closure(-0. 097) > herbaceous cover(-0. 084). Therefore,herbaceous cover and litter thickness mainly had direct effects on sediment yields,while slope mainly had indirect effects through their contributions to other factors. All the selected environmental factors jointly explained 85. 5% and 78. 3% of runoff and sediment yield variability,respectively. However,there were large values of remaining path coefficients of other factors influencing runoff and sediment yields,which indicated that some important factors are not included and should be taken into account.

Quantifying Tillage and Vetiver Grass (Vetiveria nigritana Stapf) Strips Spacing Effects on Runoff, Soil Loss and Maize Yield in Southern Guinea Savanna of Nigeria

Soil erosion induced by inappropriate tillage remains a serious problem on many agricultural fields in the humid tropics. Studies were conducted between 2004 and 2006, on an Alfisol in Ogbomoso in the Southern Guinea Savanna of Nigeria to evaluate the effectiveness of Vetiver Grass(Vetiveria nigritana) Strips(VGS) under different tillage systems. The experiment was split-plot laid out in a randomized complete block design with two replications on 6% slope with 18 runoff plots. Main plot treatments were tillage systems; Manual Clearing(MC), Ploughing(P) and Ploughing plus Harrowing(PH). Subplot treatments were VGS spaced at intervals of 5 m(eight strips) and 10 m(four strips) with the control(no-vetiver). Runoffs and soil losses were collected after each major storm. Chemical analyses of eroded sediments and runoff were determined. Data were analyzed using ANOVA at p<0.05. The results showed that tillage had no significant reduction in runoffs and soil losses, but they were reduced with MC compared with P and PH. Mean total runoff on 5 and 10 m VGS plots were significantly(p<0.05) lower than that of the control by 74.4% and 45.0%, respectively. Corresponding soils loss on 5 and 10 m VGS plots were 27.1% and 53.5%, respectively. Mean NO3-N levels in runoff water were lower under PH plots than those under MC plots by 79.0% and 66.5%, respectively in 2004 and 2006 growing seasons. VGS spaced at 5 m significantly(p<0.05) reduced NO3-N loss than the control by 108.8% in 2004. Nutrients loads of eroded sediments were consistently higher for the control(no-vetiver) plots and least for 5 m VGS plot. Carbon, nitrogen and phosphorus contents of eroded sediments were 90%-92.4%, 83%-83.6% and 97%-97.8%, respectively, and were lower on 5 m than other treatments. Maize grain yield was significantly(p<0.05) affected by both tillage and VGS spacing only in 2005 growing season. P plot produced higher grain yield than MC and PH by 79.9% and 99.1%, respectively. Also, grain yield on VGS plot was significantly(p<0.05) higher on 5 and 10 m VGS plots than the control by 82.2% and 85.4%, respectively. The significant beneficial effect of PH in producing higher yields was dwarfed by the potential danger of soil erosion in the absence of a soil erosion control measure. The results showed that a balance needed to be struck between mechanical clearance and protective measure against soil erosion.

工程堆积体产流产沙及水沙效益对植被近地表特征的响应

针对陡坡工程堆积体水土流失严重的问题,通过野外模拟降雨试验开展植被不同近地表特征对堆积体产流产沙和蓄水减沙效益特征影响的定量研究。选择土石混合堆积体(10%砾石质量分数,坡度30°)作为工程侵蚀下垫面的典型代表,并以裸坡(bare slope,BS)为对照,定量分析了植被在3种近地表特征条件下(完整植株(intact grass,IG),不含叶(not leaf,NL),只含根系(only root,OR)对堆积体产流产沙特征和蓄水减沙效益影响。结果表明:1)植被在IG条件下延缓坡面径流发生使其较BS滞后,效益达50.74%~188.98%,但不完整植被(NL、OR)会加速径流发生使其较BS提前2.19%~70.12%;2)植被在NL和OR下的瞬时径流率比IG增大0.20%~185.58%,在降雨强度1.8 mm/min的瞬时径流率甚至比BS高1.20%~169.10%;植被在IG和NL条件下瞬时侵蚀速率比BS减少0.91%~98.71%,但在降雨强度达到1.8 mm/min时OR条件下甚至增大侵蚀使其比BS高6.76%~75.63%;3)随降雨强度增大,植被在NL和OR条件下的减沙效益由95.18%和68.31%分别递减至46.58%和-68.13%,但对IG下的减沙效益影响小(效益差异<2%),平均蓄水效益随降雨强度增大而减小。不同堆积体水沙呈显著线性相关(R^(2)在0.40~0.88),且径流率达到4 L/min会显著改变植被对堆积体坡面防护效益。提出开展堆积体生态修复时选择冠层丰富的植被,同时要避免外部因素对植被造成损害。研究结果对于揭示植被防护扰动边坡侵蚀机制具有重要意义,可为堆积体植被修复提供实践指导。

秸秆和生物炭对紫色土坡耕地产流产沙与氮素流失的影响

[目的]探究不同添加量的秸秆和生物炭对紫色土坡耕地的具体改良效果,从而为合理防治三峡库区水土流失提供理论参考。[方法]采用人工模拟降雨的方法,以裸坡为对照,研究了紫色土中添加水稻秸秆(施用量4,7,10 t/hm^(2))和生物炭(含量13,39,65 t/hm^(2))对紫色土坡耕地产流产沙与氮素流失的影响。[结果](1)高强度降雨条件下,紫色土混掺生物炭加快了坡面产流进程,而施加碎混秸秆能延长起始产流时间、削减产流速率;(2)紫色土添加生物炭后累积产沙量较对照增加了0.64%~66.29%,而施加碎混秸秆后减少了42.58%~70.27%,且施加碎混秸秆对坡面产沙的抑制效应远强于对坡面产流的控制作用;(3)地表径流中氮素流失过程以NO-3-N为主,且TN,NO-3-N和NH+4-N的流失量和养分流失模数整体表现为生物炭处理最大,碎混秸秆处理最小。[结论]紫色土坡耕地施加碎混秸秆能促渗阻流、有效控制水土及养分流失,而短期施加生物炭可能会产生负面影响。

滇西蒲缥河流域侵蚀性降雨及产流产沙特征研究

采用径流小区观测法获取蒲缥河流域2018—2022年的降雨及水土流失数据,利用判别聚类法对侵蚀性降雨进行分类识别。结果表明:研究区月降雨量和侵蚀性降雨量随时间的变化呈先增后减的趋势,表现为单峰型,雨季是研究区防治水土流失的关键时期,其侵蚀性降雨量占总量的86.89%;研究区侵蚀性降雨类型主要有3种,其中Ⅰ型降雨特征为高频率、中雨量、短历时、中雨强,Ⅱ型降雨特征为中频率、中雨量、中历时、小雨强,Ⅲ型降雨特征为低频率、大雨量、长历时、小雨强;Ⅰ型降雨产流产沙量远大于Ⅱ和Ⅲ型降雨,是引起蒲缥河流域坡面水土流失的主要雨型,且不同土地利用类型下,坡面产流产沙量以裸地和橘子地最为明显;研究区各降雨影响因子对不同土地利用类型径流深和产沙量的影响存在较大差异,影响程度总体表现为降雨侵蚀力最大,其次为降雨量和I30,平均降雨强度和降雨历时最小。滇西蒲缥河流域侵蚀性降雨主要发生在雨季,雨型及下垫面是影响坡面产流产沙特征的主要因素,植被的高覆盖率和实施沟垄耕作是减少研究区坡面产流产沙的有效措施。

鲁中南山区侵蚀性降雨及典型作物对坡面产流产沙影响研究

为研究降雨量、降雨历时、降雨强度等降雨因素及典型作物对坡面产流产沙的影响,基于K-均值聚类分析法对山东省泰安市东周小流域2014-2020年77次侵蚀性降雨进行分类,并进一步分析不同降雨类型下不同作物产流产沙特征及对各降雨指标的响应.结果表明:①研究区侵蚀性降雨可以分为Ⅰ型(小雨量、短历时、大雨强)、Ⅱ型(大雨量、长历时、小雨强)、Ⅲ型(中雨量、中历时、小雨强)3类.各降雨频率为67.53%,3.9%,28.57%,占研究期内总降雨量的44.2%,14.02%,41.78%.②各径流小区产流和土壤流失量从大到小依次为大豆、裸地、地瓜、花生,花生和地瓜对径流和泥沙的削减效果相对较好.在Ⅱ型条件下,各小区产流产沙量最大,Ⅲ型次之,Ⅰ型最小;但当Ⅰ型和Ⅲ型雨频率较高时,产流产沙量也较大.③对坡面产流产沙影响最大的因素为降雨量,当作物种类不同时,影响次之的因素有所差别.径流对降雨因素的响应程度高于土壤流失量,控制产流发生可在一定程度上有效降低土壤流失量.

砾石作用下松散红壤堆积体坡面产流产沙特征

为了探究松散红壤工程堆积体在不同降雨条件下的径流产沙特性,基于野外调查统计结果构建堆积体试验槽模型,通过模拟降雨试验研究不同降雨强度下纯土和20%砾石含量堆积体的径流产沙的差异。结果表明:(1)砾石作用延缓堆积体坡面径流发生时间的平均滞后效益为299.56%;2种堆积体径流率随产流历时呈递增变化,随降雨强度增大,平均径流率递增34.48%~244.83%,土石混合堆积体平均径流率相较于纯土减少6.54%~45.83%,平均流速减少13.76%~30.54%。(2)降雨强度≤1.5 mm/min时堆积体侵蚀速率随产流历时总体缓慢递增或趋于稳定,土石混合堆积体平均侵蚀速率比纯土减少80.39%~84.95%;但在强降雨条件下(2.0 mm/min)纯土堆积体侵蚀速率呈快速增大后递减变化,土石混合堆积体侵蚀速率波动递增,且土石混合堆积体平均侵蚀速率比纯土增大20.04%。(3)降雨强度和砾石均会改变堆积体坡面径流产沙和流速,差异显著(P<0.05)且呈“水大沙多”的特点。研究结果可为堆积体水土流失防治措施布设提供指导,为建立工程堆积体土壤侵蚀预测模型提供基础数据。

表层土壤结构对红壤坡耕地产流及产沙过程的影响

针对南方红壤区坡耕地水土流失严重与表层结构退化的现状,采用室内模拟降雨的方法,分析表层土壤结构和雨强对降雨再分配、坡面产流及产沙过程的影响。结果表明:(1)表层土壤结构显著改变降雨的再分配过程,深耕作层可以降低地表径流比例,增加壤中流比例,60和90 mm·h^(-1)雨强下,随耕作层深度增加,地表径流平均比例依次为70.5%,62.9%和56.8%,壤中流平均比例依次提升为7.1%,12.3%和18.1%;(2)土壤流失率随雨强增加而增大,90 mm·h^(-1)雨强下土壤流失率为60 mm·h^(-1)雨强下的4.4倍,土壤流失率随耕作层深度增加而显著减小,依次为36.8、21.1和13.1 g·m^(-2) min^(-1);(3)雨强和表层土壤结构显著影响坡面侵蚀形态的演变,随耕作深度增加坡面侵蚀由细沟侵蚀逐渐转变为面蚀。表层土壤结构显著改变坡耕地降雨-径流关系和侵蚀过程,合理增加耕作层深度,对降低地表侵蚀、促进土壤水分的深层下渗、增加土壤深层持水量具有积极作用。

短历时强降雨对喀斯特玉米坡地产流产沙的影响

[目的]研究短历时强降雨对喀斯特坡耕地产流产沙的影响,揭示喀斯特坡耕地土壤侵蚀特征机理,为解决喀斯特坡耕地土壤侵蚀和保障粮食生产提供科学依据。[方法]通过人工模拟降雨试验,以喀斯特裸坡地和玉米坡地为研究对象,研究短历时强降雨对喀斯特坡耕地产流产沙的影响。[结果](1)裸坡地和玉米地地表产流产沙模数随坡度的增大而增大,当坡度相同时,玉米地地表产流产沙模数显著小于裸坡地(p<0.05);随着降雨历时的增加,裸坡地和玉米地地表产流模数呈现出先增大后保持稳定的趋势,而地表产沙模数则是先增大后减小。(2)裸坡地和玉米地各壤中流产流模数随坡度的增大而增大;当坡度相同时,玉米地各壤中流产流量显著小于裸坡地(p<0.05),其中坡度为20°时,玉米地壤中流(15—25 cm)总产流量相对裸坡地减少了62.59%。(3)当坡度不变时,玉米地地下产沙量和产沙模数显著小于裸坡地(p<0.05);随着降雨历时的增加,裸坡地与玉米地地下产流模数呈现出不断增大的趋势,其变化趋势基本保持一致,而地下产沙模数呈现先增大后减小的趋势,在20~30 min之间达到最大产沙模数。(4)比较不同坡度裸坡地与玉米地各产流产沙之间的相关性,发现玉米地相比裸坡地地下产沙与地表产流、地下产流、地表产沙之间相关性增强,而地表产沙与地表产流、地下产流之间的相关性减弱。[结论]强降雨下玉米坡地能够增加入渗,具有阻控和缓蚀的作用,其中地表产流产沙模数和壤中流产流模数随坡度的增大而增大,而地下产流模数随降雨历时增加呈不断增大的趋势,地下产沙模数呈先增大后减小的趋势。

递增式连续降雨条件下典型山区坡面径流产沙水动力学特征

山区复杂的下垫面条件导致了山区小流域水文响应过程的复杂性,山区坡面作为山区小流域水文响应的基本单元,研究其不同下垫面条件下径流产沙水动力特征具有重要意义。为明晰山区坡面不同下垫面条件下径流水沙水动力特征,该研究选用官山河小流域作为研究对象,基于室内模拟递增式连续降雨试验方法,研究了坡度、土层厚度分布和土层底部透水性等山区坡面下垫面特性共同作用下的坡面径流产沙水动力学特征。结果表明:1)连续降雨条件下,雷诺数、水流剪切力和径流功率随着产流时间和雨强增加呈现增加趋势,Darcy-Weisbach阻力系数呈降低趋势。2)雨强增加使雷诺数均值和径流功率均值显著增加(P<0.05),设计雨强60、90、120 mm/h时的雷诺数均值、径流功率均值分别比30 mm/h的雷诺数均值、径流功率均值增加了130%、276%、366%和171%、328%、435%;坡度增加使水流剪切力均值和径流功率均值显著增加(P<0.05),坡度15°、25°的水流剪切力均值分别比坡度5°的增加了135%和187%,坡度15°、25°的径流功率均值分别比坡度5°的均值增加了224%和357%;土层厚度分布对阻力系数均值和土层底部透水的雷诺数均值、径流功率均值有显著影响(P<0.05),土层底部透水性仅对土层厚度分布为上薄下厚的雷诺数均值和水流剪切力均值有显著影响(P<0.05)。3)雨强是影响坡面产流产沙水动力特征的主导因素,对雷诺数的方差贡献率高达83.11%,水流剪切力主要受到雨强和坡度的影响,累计贡献率达67.64%,径流功率主要受到雨强和坡度的影响,累计贡献率达80.58%。在单一雨强条件下,坡度和土层厚度分布是影响水动力参数的主要因素,土层厚度分布和坡度的交互作用、土层底部透水性和土层厚度分布的交互作用对水动力参数也有一定影响。因此,在研究坡面产流产沙规律时,除考虑雨强和坡度外,还应兼顾考虑土层厚度分布和土层底部透水性及其交互作用的影响。该研究结果可为山区坡面复杂下垫面条件下的坡面产流产沙机理提供一定的理论支撑,并为改进山区小流域水文过程分布式模拟提供参数率定依据。

控释氮肥减量对作物产量、氮素吸收与径流损失的影响

玉米蔬菜轮作是我国南方丘陵山地农区一种主要的旱地种植方式。为指导施肥,减少农业面源污染,于2020—2021年持续开展定位试验,探究控释氮肥及减氮处理对玉米小白菜轮作体系作物产量、氮素吸收残留、氮素径流损失的影响。试验共设置6个处理:CK,不施氮肥;U,常量施用普通尿素;CRU,施用等氮量的控释氮肥;90%CRU,施用控释氮肥,并较常量减氮10%;80%CRU,施用控释氮肥,并较常量减氮20%;70%CRU,施用控释氮肥,并较常量减氮30%。结果表明,与U处理相比,玉米在减氮20%条件下未显著减产,小白菜在减氮30%时均未显著减产。与U处理相比,合理施用控释氮肥可使总氮流失量显著(P<0.05)降低25.3%~43.5%,以70%CRU处理的总氮流失量最少。径流水中的氮素流失主要以颗粒氮为主,占比60.0%~67.0%。与U处理相比,除70%CRU处理外,其他施用控释氮肥处理的玉米地上部氮素积累量无显著差异;80%CRU处理的氮肥利用率显著提高9.4百分点。与U处理相比,施用控释氮肥0~80 cm各土层的总氮、铵态氮、硝态氮含量均未显著增加,不会提高土壤无机氮的流失风险。综上,在该试验条件下,与U处理相比,80%CRU处理可以在确保产量不降低的同时,减少氮素投入,降低氮素径流损失,提高肥料利用率,是试验条件下较为合理的施肥方式。