基于随机森林算法的冻融期土壤蒸发预报模型研究

以山西省晋中盆地大田土壤蒸发实测数据和气象站监测资料为例,采用2017~2018年冻融期土壤蒸发实测数据作为因变量、影响冻融期土壤蒸发的9个因素作为自变量,利用随机森林算法构建了冻融期土壤蒸发预报模型,并对冻融期三个阶段影响土壤蒸发的因素进行了重要度评价。结果表明,冻融期土壤蒸发的预测值与实测值的平均相对误差为5.7%,均方误差为0.055,模型预测精度较高,拟合效果较好,所建立的模型适用于冻融期土壤蒸发的预报;不稳定冻结期对土壤蒸发影响较大的为地表土壤含水率和太阳辐射,稳定冻结期为降水和地表土壤含水率,消融解冻期为降水、地表土壤含水率和水面蒸发量。     

那曲流域季节冻土区土壤水热动态变化分析

鉴于青藏高原冻土区土壤水热动态变化过程对高寒区气候变化、植被演替及退化等方面的研究意义重大。基于2019年9月10日～2020年8月10日那曲流域4个监测站点分层土壤温度和湿度数据,探讨了冻融过程中土壤水热的变化规律及土壤水分和温度间的互作效应。结果表明,那曲流域季节冻土区在冻结过程期、完全冻结期、融化过程期、完全融化期土壤含水率呈现降低—稳定—升高—波动的变化趋势。冻结过程中,土壤水在温度梯度的作用下开始向冻结锋面运移并补充冻结锋面以下的土壤水分,各层土壤含水率均有所下降;融化过程中季节冻土呈现双向消融特征,各层土壤含水率上升,小唐古拉山、措玛乡、那曲大桥、香茂乡分别在20、35、10、50cm土壤水分高值区。土壤在冻结过程中处于放热状态,表层土壤温度较深层小,而融化过程处于吸热状态,表层土壤温度较深层大。随着土层深度增加,气温对土壤温度的影响越来越小,表层土壤温度变化速率均较深层大。5、10、20、35、50cm土层土壤温度与土壤含水率呈正相关关系,确定性系数R2分别为0.596、0.500、0.499、0.304、0.414。研究结果为及时明晰青藏高原土壤水热动态变化状况提供了一定的理论依据。     

河北平原区土壤水分空间变异特征研究

以河北平原区望都灌溉试验站为例,选取210m×210m的正方形田块进行试验,在该范围内布置64个测点,分别测量0~30、30~50、50~80cm三个深度的土壤含水率信息。利用经典统计和地统计方法分析了田间土壤含水率的空间变异结构,并采用协同克里格插值技术得到了该区域土壤含水率的空间分布状况。结果表明,0~30cm土层及50~80cm土层的土壤含水率具有中等空间相关性,其相关距离分别为66.4、75.7m,而30~50cm土层表现出了强烈的空间相关性,相关距离为88.2m,研究结果可为实现灌区精准灌溉和土壤墒情预测提供科学的理论指导。     

青藏高原土壤冻融对地表辐射特征的影响分析

利用黄河源区气候与环境综合观测研究站.2006年10月1日～2007年4月30日的辐射和5cm土壤温度和湿度资料研究了土壤冻融对地表辐射特征的影响,结果表明:土壤冻结降低了土壤中的液态水含量,致使冻结阶段地表反照率大于冻结前的值,也大于土壤融化后的值;受总辐射和地表反照率共同作用,整个冻融过程中反射辐射可区分为两个比较明显的阶段;土壤冻结减缓了地表温度降低的速率,相应地减缓了地表长波辐射和大气逆辐射降低的速率;整个冻融过程中净辐射变化与总辐射的变化比较相近,在冻结阶段,地表反照率大于冻结前的值,也大于融化后的值,因此冻结阶段的净辐射值也更小一些。     

内蒙古中部草原区光伏电站对土壤水分及其脉冲响应的作用机制

针对内蒙古草原地区光伏电站对降雨的再分配作用下土壤水分空间变异规律及其对降水事件的脉冲响应特征,对草原地区光伏组件下的土壤水分时空特征进行持续观测,并确定光伏组件干扰下的气象因子与土壤水分的关系,最终通过参数估计厘清光伏组件对土壤水分脉冲响应的作用机制。结果表明：光伏组件前檐下方的土壤总储水量整体高于组件下方和未架设组件区域的土壤储水量;光伏组件前檐的各土层储水量对降水的响应均较强,光伏组件下各层土壤储水量对降水无明显响应过程;光伏组件下大气湿度与0~10、10~20和20~30 cm土层储水量的相关系数分别为0.889、0.579和0.414;光伏组件前檐10、20和30 cm土层的含水量对降水量的脉冲响应方程R²分别为0.875、0.938和0.957,降水量的补给对0~30 cm土层的脉冲事件均产生促进作用。未架设组件区域的20 cm土层含水量对自然降水有较好的响应过程。     

饱和溶液电导率法在滨海高盐土壤水盐运移规律分析中的应用

分析海涂围垦区土壤水盐运移规律对改良滨海区域盐碱地有着重要意义。而在高盐土壤中实现含水率和可溶解盐分浓度的连续测量是掌握海涂围垦区土壤水盐运移规律的关键,因此以江苏如东海涂围垦试验区内的重度盐土为研究对象,利用耐盐度较好的土壤水分—盐分传感器连续监测土壤含水率、表观电导率变化,以土壤饱和溶液电导率■为盐分当量指标,分析受降雨、蒸发影响的水盐运移规律。结果表明,■可用以指示土壤中最大可溶解盐分含量。此外,土壤盐分在年内呈显著的季节性变化,即在冬季土壤中盐分较高,春季土壤脱盐,夏季土壤盐分波动剧烈,秋季土壤积盐明显。在蒸发和降雨过程中,■可有效指示不同埋深处土壤盐分的变化特征,结合土壤水分运移规律可直观佐证“盐随水走”的运移特征。     

青藏高原冻融过程期划分及发展趋势研究

鉴于冻融循环是高寒地区土壤的基本特征,对地表能量平衡、植被生长、工程建设等有重要影响。基于青藏高原分布在高寒干旱区、半干旱区、湿润区3个气候区、海拔跨度在3 400～4 900m间的58个监测站点2011～2015年逐日表层土壤温度、湿度数据,分析了青藏高原不同气候区不同海拔冻结过程期、完全冻结期、融化过程期、完全消融期的分布特点及演变特征。结果表明,高寒干旱区土壤含水率长期低于4%,土壤中水分稀少,难以冻结,水分的变化主要由于降水和蒸发,表层土壤一直处于融化状态,基本不发生冻融循环;高寒半干旱区、湿润区,降水等补给充足,土壤内的水分随温度的升高或降低,发生显著地融化或冻结在海拔3 400～3 500m处,融化过程期始于3月上旬,完全消融期始于4月上旬,冻结过程期始于11月中旬;完全冻结期始于12月中旬;当海拔上升至4 800～4 900m,融化过程期始于4月上旬,完全消融期始于5月中旬,冻结过程期始于10月下旬,完全冻结期始于11月中旬,随着海拔升高,融化过程期和完全消融期开始的时间延后,冻结过程期和完全冻结期开始的时间提前;气候变暖对青藏高原短期环境特征变化的影响尚未确定,但气温升高可能导致融化过程期和完全消融期开始时间提前,缩短冻结过程期和完全冻结期。研究结果有利于明晰青藏高原表层土壤水热变化规律,为应对气候变化提供坚实的理论基础。     

一维土柱非饱和蒸发试验与数值分析

为揭示在蒸发条件下非饱和土中水分的运动规律,进行了一维土柱非饱和蒸发室内试验,并采用湿/热耦合的非等温渗流方程对蒸发条件下土壤水分的运动规律进行了数值模拟,通过将数值计算结果与试验结果进行对比,验证了湿/热耦合的非等温渗流方程的可靠性,同时发现干土层的形成是引起土壤水分运动形式发生转变的根本原因,即在干土层形成前,土壤内水分的运动以液态流动形式为主;在干土层形成后,干土层以下土壤的水分仍以液态流动形式向上运移,在干土层内则是以水蒸气扩散的形式向大气运动。     

基于GRNN的冻融期土壤蒸发预测

基于2017～2018年冻融期实测大田土壤蒸发数据和日气象数据,采用主成分分析法与广义回归神经网络(GRNN)相结合的方法对土壤蒸发量进行预测。即先利用主成分分析法提取影响冻融期土壤蒸发的7个主要因子,将其作为GRNN模型的输入变量,土壤蒸发量作为输出变量;再利用10折交叉验证法选取的最佳光滑因子建立GRNN土壤蒸发预测模型。结果表明,GRNN模型预测值与实测值拟合程度较高,R~2为0.982、均方根误差为0.014mm/d、平均相对误差为5.281%、平均绝对误差为0.010mm/d,模型模拟精度较高,可用于冻融期土壤蒸发预测。     

五道沟地区土壤水分动态变化规律及模拟研究

以五道沟地区实测土壤含水率与气象要素为基础,分别从年、月和季节尺度上分析了土壤含水率在时间与垂向分布上的变化特征,选择不同的典型年和降水场次,探讨了土壤水分在不同降水强度下的响应规律,并运用Hydrus-1D模型模拟了土壤水的运动。结果表明,土壤水分受到降水和蒸发的共同作用,降水强度影响土壤水分的持续下渗时间与下渗深度,浅层土壤的响应程度更大。各层土壤模拟效率系数均超过0.6,表明Hydrus-1D模型在五道沟地区具有较强的适用性,可用于该地区土壤水分运动的模拟研究。     

基于VIC模型的淮河中上游地区水量空间分布研究

研究淮河流域的水文循环过程及水量空间分布对合理开发利用水资源具有重要意义,采用VIC模型对淮河中上游地区各种水量要素(降水、蒸散发、地表径流、地下径流、植被截留水量、土壤含水率、截留水蒸发、植物散发、裸地及水面蒸发、降雪日的积雪深、积雪覆盖面积比等)的空间分布进行模拟。结果表明,模型反映的水量分布与实际的流域下垫面物理机制相符。流域的沙壤土和壤土地区的蒸散发量较大,而地表径流量较小。在有大面积水体或水库的区域,蒸散发量、植被截留水量很小,而地下径流量、深层土壤含水率较大。降雪日中流域的西北部更容易形成较大的积雪深。     

Microbial changes during the on-farm storage of canola (oilseed rape) straw bales and pellets

The effect of on-farm storage on microbial growth on baled and pelletised Brassica napus (oilseed rape/canola) straw was investigated. Canola straw collected in 2008 and 2009 was stored baled in an open shed for 3, 4, 7, 10 and 20 months in 2008 and for 1 and 3 months in 2009. Pellets were produced from straw stored for 3, 7, and 10 months in 2008 and straw stored for 3 months in 2009, and stored for up to 48 weeks.The moisture content (MC), water activity (a_w), bacterial and fungal colony-forming units (CFU), and carbon-to-nitrogen ratio (C:N) of canola straw bales and pellets were measured during storage. In addition, temporal environmental conditions (ambient temperature and relative humidity) and bale temperature were monitored. The moisture content showed a tendency to stabilise during storage, with an equilibrium moisture content of approximately 155 g kg⁻¹ total weight for straw bales and 110 g kg⁻¹ total weight for straw pellets. Consequently, the water activity of canola straw bales remained below 0.8 and that of pellets below 0.66 during storage, providing an explanation for relatively low microbial growth. The number of bacterial and fungal CFU present in the straw bales and pellets followed the trend of ambient relative humidity and no correlation was found with the C:N ratio of the biomass. Canola straw pellets were considered a superior combustion fuel to straw bales due to lower moisture content and less microbial deterioration during storage.     

Changes in duration of rhizome cold storage and manipulation of the growing environment to promote field establishment of Miscanthus giganteus

Miscanthus biomass yield can be limited by poor rhizome establishment and this is linked to rhizome age and storage conditions prior to planting. To avoid poor establishment, best practice recommends field planting directly after rhizome division. Operations avoiding rhizome storage, and utilising favourable climatic conditions at planting, may be climatologically and logistically challenging when large areas are planted at high rhizome densities. Our aim is to evaluate storage regimes to maintain rhizome viability and maximise establishment when planted under optimal conditions. To achieve this we have compared differences in site pre-planting management (level of soil cultivation) strategies, along with post-planting treatments (irrigation and soil mulching with compost), against differences in storage regime (temperature) and duration. The results from a rhizome establishment bioassay showed viability at lifting in early March was high, while cold storage of rhizomes had no negative influence on viability and growth. There were no negative impacts of storage temperature on rhizome mineral or carbohydrate concentrations. Increases in air temperature enhanced rhizome and culm final biomass and rate of establishment. Application of irrigation, or compost mulch, to field rhizome plantings improved establishment increasing soil moisture levels in early May through August. In conclusion, cold storage of rhizomes is achievable and effective in maintaining rhizome viability and can be used to extend the planting time. Soil moisture and application of supplementary irrigation was important during establishment. Also important was the avoidance of weed competition. Achieving the most appropriate conditions for optimal establishment will be critical in regions where spring/summer rainfall is restrictive.     

Investigation of heat and moisture migration in unsaturated soil under natural boundary conditions

Theoretical and experimental investigations were conducted to determine the heat and moisture migration in unsaturated soil under natural surface boundary conditions. Theoretically, a new model of heat and moisture migration in unsaturated porous media was developed, in which the gradients of volume water content, temperature, and partial vapor pressure were considered as the main driving forces which influence the process of heat and moisture migration in unsaturated soil. A set of coupled, nonlinear, partial differential equations were developed, which are related dynamically to the surface boundary conditions. Heat and moisture migration in sandy soil under solar radiation and air convection were studied experimentally. Temperature, volume water content, and water table evaporation were measured under unsteady conditions. The predictions are in good agreement with experimental data from a fairly sandy soil. © 1999 Scripta Technica, Heat Trans Asian Res, 28(1): 3–17, 1999     

不同自然降雨雨型下红壤坡地地表径流和壤中流输出特征

我国南方红壤丘陵区受降雨和土壤性状影响,洪涝灾害与季节性干旱等问题并存,研究坡地降雨过程中径流输出特征具有重要意义。为此,利用江西省水土保持生态科技园内大型土壤渗漏装置,研究了3年期间32场天然次降雨下植草覆盖、干草敷盖和裸露3种不同处理的红壤坡地径流输出特征。结果表明,小雨雨型下,研究区红壤坡地均不产生地表径流;中雨雨型下,植草覆盖、干草敷盖、裸露处理的壤中流所占地表径流和壤中流总量比例分别为58%、80%和12%;对于促进降雨入渗,干草敷盖最优。大雨及以上雨型下,植草覆盖和干草敷盖处理以壤中流为主,占比分别为63%和64%,裸露处理以地表径流为主,占比93%。在红壤坡地开发中除栽种植物加强植被覆盖外,辅以敷盖措施能起到更好的保水保墒效果。     

Study of heat and moisture transfer in soil with a dry surface layer

Mathematical model for describing simultaneous heat and moisture transfer in the porous soil with a dry surface layer was developed by using the volume-averaging method. Numerical simulation was conducted to investigate water evaporation, transient distributions of temperature and moisture in the porous soil at environmental conditions, which might be useful for agricultural application. In order to validate the mathematical model and numerical method, an experiment was conducted under natural environmental conditions. An additional experiment was conducted in a closed-loop wind tunnel to investigate the temperature effect on soil moisture transport. Theoretical and experimental results indicate that the dry surface layer has an important effect on heat and moisture migration in soil and the influence of temperature on moisture transport in unsaturated soil is significant.