THE WATER BALANCE OF AN AGRICULTURAL CATCHMENT. I. ESTIMATION OF EVAPORATION FROM SOIL WATER RECORDS

Errors of measurement of soil water content with the neutron probe can be made small enough for most water balance studies; and apart from the possible damage resulting from access tube implacement, they can be readily specified. A more important problem is estimating how much water is lost from soil by drainage. A simple, graphical method is described to distinguish between drainage and evaporation from soil, based upon identification of the maximum depth at which measurable quantities of water are extracted by roots. As a result of errors in soil water measurements and uncertainties in the distinction between drainage and evaporation, estimates of soil water deficit and hence evaporation for a single profile are likely to have a precision of about ±5 mm. Larger variability is commonly found in soil water storage changes measured in replicate profiles partly because of uneven wetting of the soil during rain and partly because of non-uniform losses by drainage and root extraction. This variability requires careful attention to replication and location of access tubes when assessing the evaporation for a particular site.     

黄土高原水土保持措施强化降雨入渗分析及灰色预测

黄土高原水土流失综合治理是以强化降雨入渗,减少地表径流,阻止土壤侵蚀为目的。因此,治理区降雨入渗量的大小是衡量水土流失治理效果的关键指标之一。目前入渗量的计算多利用年总降雨量,由于在黄土地区小雨量或小强度的降雨具有与水土流失治理的零相关性,因而会导致对水土流失综合治理强化入渗作用估计的较大误差。提出用1a中产生径流的次降雨总量(产流降雨总量)计算入渗量。以西川河流域为例,采用1997—2001年的降雨径流资料,分别用年降雨总量与产流降雨总量推求降雨入渗系数,对比分析了入渗量随流域水土流失治理度的变化,结果表明:利用产流降雨总量能比较清晰地反映流域治理程度对降雨入渗的影响。在此基础上,采用GM(1,1)灰色动态模型预测西川河流域降雨入渗量随水土流失治理度的变化趋势。结果表明,GM(1,1)灰色模型能够合理地预测黄土高原水土保持措施对自然流域入渗量影响的变化趋势。     

黄土高原北部水蚀风蚀交错区产流条件及径流系数

为了揭示黄土高原北部水蚀风蚀交错区的产流机制并推求径流系数,为该地区地表水资源的深入研究提供基础数据,选取具有黄土高原北部水蚀风蚀交错区典型气象与水文特征的六道沟流域为研究区。通过分析实测水文数据,从机制上分别研究了试验流域在表层土壤（5—10 cm）达到饱和及不饱和条件下的产流过程,在长历时低强度降雨条件下,产流的必要条件是表层土壤达到饱和且雨强≥0.12 mm/min;在短历时高强度降雨条件下,表层土壤未达到饱和状态时,产流的必要条件是降雨强度≥0.52 mm/min;径流系数与平均降雨强度之间存在着显著的正相关关系;以运动波理论的基础方程式结合GIS技术开发了适用于试验流域的分布式降雨—径流数值模型,模型的误差<3%;基于2005—2009年（5 a）的降雨—径流数值计算,得到试验流域在这5 a的平均径流系数为0.11,从而推求出多年平均径流系数为0.10～0.15。     

Seasonal differences in the soil water balance under perennial and annual pastures on an acid Sodosol in southeastern Australia

Replacement of native deep‐rooted grasses by shallow‐rooted ones has resulted in greater losses of water and nitrogen by drainage. To counter this effect we have tested the hypothesis that liming, and the conversion of annual grass pastures to perennial grass pastures, could improve the sustainability of grazing systems in the high rainfall zone (> 600 mm per annum) in southeastern Australia, through better use of water and nitrogen. A field experiment consisting of sixteen 0.135 ha (30 m × 45 m) grazed paddocks representing four pasture combinations (annual pasture (mainly Lolium rigidum) without lime (AP–); annual pasture with lime (AP+); perennial pasture (mainly Phalaris aquatica) without lime (PP–), and perennial pasture with lime (PP+)) was carried out from 1994 to 1997 on an acid Sodosol (Aquic Hapludalf) in southern New South Wales, Australia. Measurements were made of surface runoff, subsurface flow (on top of the B horizon) and soil water content. The results showed that perennial grass pastures, especially PP+, extracted approximately 40 mm more soil water each year than the annual grass pastures. As a result, surface runoff, subsurface flow and deep drainage were at least 40 mm less from the perennial pastures. These measurements were further supported by a simulation of soil water deficit and deep drainage for AP– and PP+ paddocks, using 10 years' past meteorological records. Overall, the results suggested that well‐grown, phalaris‐based pastures could reduce recharge to groundwater and make pastoral systems more sustainable in the high rainfall zone.     

天然降雨下川中丘陵区不同年限植物篱水土保持效用

通过对遂宁水土保持试验站内不同坡度(10°和15°)植物篱小区及对应对照小区为期7年的水土流失定位观测,探究了天然降雨条件下香根草植物篱和新银合欢植物篱在其生长年限增长过程中对紫色土坡耕地水土流失的影响。结果表明:(1)当植物篱开始发挥其水土保持作用时,减流率(年均)达10.5%～20.0%,减沙率(年均)达53.5%～54.5%,减流作用随年限增长波动较大,减沙作用逐渐趋稳;(2)10°香根草植物篱水土保持效果最优,其减流和减沙作用均在生长年限为1年时开始发挥,10°新银合欢植物篱次之,其减沙作用较减流作用提前约1年凸显,15°香根草植物篱最弱,其布设小区多数次降雨减流率均明显低于10°植物篱小区;(3)总体上植物篱能够降低坡度对坡耕地水土流失的加剧作用,其中径流流失减少28.9%,泥沙流失减少11.3%,并削弱降雨量与径流泥沙的相关程度;(4)平均径流系数和降雨引发泥沙量随植物篱年限增长逐渐趋稳,其中10°小区香根草植物篱和新银合欢植物篱对特大暴雨(12 h降水总量140.0 mm)和大暴雨(12 h降水总量为70～140 mm)下产生的径流系数消减明显,达15.0%～34.4%,各植物篱对所有降雨等级平均单位降雨所产生泥沙量均有明显消减作用,达34.1%～48.5%。     

Siltation and radiocesium pollution of small lakes in different catchment types far from the Fukushima Daiichi nuclear power plant accident site

The Fukushima Daiichi nuclear power plant accident caused radioactive pollution in northeastern Honshu Island, Japan. This study examined the influence of snowmelt and rainfall on soil erosion processes and siltation of small lakes in Miyagi Prefecture (150 km northwest of the power plant). Two sets of slopes and lakes, respectively in pasture and forest catchments, were examined. Snowpack thickness, soil infiltration, surface runoff volume, soil and sediment physicochemical properties, Cs concentration of precipitation, meltwater, and rainwater, and lake siltation rates were determined. The total radioactive Cs content in precipitation was 0.7–7.4 BqˑL⁻¹ and was below the Japanese standard (10 BqˑL⁻¹). Total radioactive Cs was at the allowable level in water flowing down the pasture catchment slope (0.1–9.2 BqˑL⁻¹) during snowmelt and rainfall, as well as in pasture (0.9–8.8 BqˑL⁻¹) and forest (0.7–5.2 BqˑL⁻¹) catchment lake water. There was no soil erosion (surface runoff) in the forest catchment. Soil losses in the pasture catchment were 23 due to rainfall and 9 kg ha⁻¹ yr⁻¹ following spring snowmelt. After snowmelt, a 0.5 and 0.2 mm thick layer of silt was deposited in pasture and forest catchment lakes, respectively, and 1.4 and 0.6 mm were deposited during the rainfall period. Average siltation rates were 1.9 and 0.8 mmˑyr⁻¹ for pasture and forest catchment lakes, respectively. The upper layer of lake bottom sediments is represented mainly by silt fractions (2–50 μm), with high organic matter (4.0–5.7%) and radiocesium (1100–1600 kgˑha⁻¹) contents.     

EFFECTS OF CULTIVATION ON SOIL WATER RETENTION AND WATER USE BY CEREALS IN CLAY SOILS

The effects are repotted of direct drilling and mouldboard ploughing on soil water retention and extraction in three soils over two to four years. In the years 1972–75 when winter rainfall was close to or greater than the long-term average the maximum soil water content of the upper 100 cm differed little between the cultivation treatments. In contrast, after the dry winter of 1975–76, about 10 per cent more water was stored in the direct-drilled soil, especially below 50 cm. In the following dry summer, winter wheat extracted up to 22 mm more water from uncultivated soil and this was associated with better growth of the crop than after ploughing. When simulated rain was applied, water infiltrated rapidly to a depth of 50–100 cm in direct-drilled soil, whereas on ploughed land its movement was retarded below the plough sole even when cultivation had been carried out under conditions which minimized smearing. Water storage at depth was consequently greater under dry conditions in the direct-drilled soil while excess water reached drain depth more rapidly in wet conditions.     

黄土高原水平梯田的蓄水保土效益分析

 在整理、分析黄土高原西峰等水土保持试验站径流、泥沙观测资料的基础上,研究了该地区水平梯田的蓄水保土效益。结果表明:其效益的平均值为867%和877%,但差异悬殊,主要是受暴雨、大暴雨质量的影响。次降雨综合参数PI、汛期降雨量和年产流降雨量分别小于200mm2/min、350mm和125mm时,蓄水保土效益均为100%,大于这些数值时,效益降低,两者呈负相关;同时,梯田的质量也影响蓄水保土效益。     

垄沟集雨对紫花苜蓿草地土壤水分、容重和孔隙度的影响

在旱作条件下, 将垄沟集雨措施应用于紫花苜蓿种植, 研究沟垄宽比和覆膜方式对2年龄紫花苜蓿草地土壤水分状况、土壤容重及孔隙度的影响。结果表明: 全越冬期, 膜垄和土垄处理0~120 cm土壤水分平均散失量分别低于CK(平作)28.43 mm和13.61 mm。膜垄处理整个集雨期的蓄墒增加率为59.03%~99.27%, 产流效率为53.43%~91.72%; 2009年集雨前期(4月上旬~6月上旬)土垄处理的蓄墒增加率、产流效率分别为1.92%~2.74%和1.71%~2.55%, 2009年集雨中后期(6月中旬~9月下旬)土垄处理的蓄墒增加率、产流效率较集雨前期显著升高, 分别为8.85%~36.77%和8.01%~35.82%; 膜垄和土垄处理的蓄墒增加率、产流效率均随垄面宽度增加而显著增加, 且膜垄的蓄墒增加率、产流效率显著高于土垄处理。垄沟集雨种植能够显著降低0~40 cm土壤层容重, 且0~20 cm土壤层容重降幅表现为膜垄大于土垄。垄沟集雨种植也能够显著增加0~40 cm土壤层孔隙度, 且0~20 cm土壤层孔隙度增幅表现为膜垄大于土垄。     

Differential hydrological response of biological topsoil crusts along a rainfall gradient in a sandy arid area: Northern Negev desert,Israel

Drylands are regarded as highly sensitive to climatic change. The putative positive relationship between average annual rainfall and runoff, assumed for areas between 100 and 300 mm ignores the fact that climatic change in drylands is not limited to climatic factors alone, but is often accompanied by a parallel change in surface properties. Data on rainfall, runoff and soil moisture regime were collected at five monitoring sites in a sandy area, along a rainfall gradient from 86 to 160 mm. Despite the uniform sandy substratum the frequency and magnitude of runoff declined with increasing annual rainfall. Under wetter conditions a thick topsoil biological crust develops. This crust is able to absorb and retain large rain amounts, limiting the depth to which water can penetrate, and therefore water availability for the perennial vegetation. In the drier area, the thin crust can absorb only limited rain amounts, resulting in surface runoff and deeper water infiltration at run-on areas. Our findings demonstrate the important role played by different types of biological soil crusts along the rainfall gradient considered, and question the generally held belief that higher rainfall necessarily leads to deeper water infiltration in sandy arid areas; and higher water availability for the perennial vegetation.     

Temporal Dynamics of Sediment Transport and Transient In‐channel Storage in a Highly Erodible Catchment

Elucidating the links between catchment and channel geomorphic processes helps the understanding of landscape evolution and the geomorphic development of river basins, and then the land degradation processes. In this study, we analyse suspended sediment dynamics and its relationship with rainfall, discharge and in‐channel sediment storage in a highly dynamic Mediterranean montane catchment (the River Isáben, Southern Pyrenees, NE Iberian Peninsula). The aim is to assess hydrological controls on and temporal patterns of the suspended sediment load. High loads in this basin occur as a consequence of intense erosion in badlands located in the middle of the catchment. This study focuses on a reach located downstream from the main badland areas, where rainfall, discharge (Q), sediment transport (SSC) and in‐channel sediment storage were monitored for a 1‐year period. Marked seasonality in water and sediment load was observed; whereas most of the discharge occurred in winter and spring, most of the sediment was transported during summer and autumn. Q‐SSC hysteretic loops revealed the importance of sediment availability (whether stored in the channel or originating from wider catchment source areas) in the river's sedimentary response. Clockwise loops dominated during winter and spring, whereas counter‐clockwise loops occurred mostly in summer and autumn, when in‐channel storage reached its maximum. There were significant correlations between rainfall intensity in the sediment source areas, in‐channel sediment storage and sediment yield. These correlations emphasize the importance of understanding sediment availability when analysing the temporal dynamics of sediment transport, especially in catchments where different source areas (slopes and riverbed) may contribute to the load to differing degrees and at different times of the year. Copyright © 2015 John Wiley & Sons, Ltd.     

THE WATER BALANCE OF AN AGRICULTURAL CATCHMENT II. CROP EVAPORATION : SEASONAL AND SOIL FACTORS

Rates of evaporation, soil water deficits and extraction depths for spring cereals and grass were estimated from soil water measurements for a four year period. Estimates of evaporation were also compared with evaporation formulae and evaporimeter values. Evaporation and soil water deficit were highly dependent upon weather, particularly rainfall. Evaporation from grass was noticeably restricted whenever deficits exceed 50 millimeters. Cereals extracted water from a slightly greater depth of soil but developed deficits, up to harvest, very similar to those under grass. Deficits developed in sand and clay soils were also very similar, because water held in large dense clay aggregates is not readily accessible to roots. Although soil type had only minor influence on rates of evaporation, deficits and depths of drying, because of movement of water through fissures, slow drainage and delayed swelling effects soil type has a strong influence on stream behaviour.     

黄土旱塬区麦田休闲期降水与土壤贮水的变化特征

为提高休闲期降水资源利用效率和确保区域粮食安全,利用1981—2020年陇东黄土高原旱作麦田定位土壤水分和气象观测资料,分析了冬小麦田休闲期间降水与土壤水分的变化特征及其影响因素。结果表明:(1)近40年陇东黄土高原休闲期降水以14 mm/10 a的速率增加,降雨总日数和小雨日数呈减少趋势,中雨、大雨日数呈弱增加趋势;(2)近40年休闲期1 m土层平均以9.5 mm/10 d的速率充水,贮水量平均增加97 mm,21世纪以来贮水量增加明显;(3)休闲期降水与1 m土层贮水增量符合二次函数关系,1 m土层开始贮存水分的降水阈值为175 mm,贮水增量与中、大雨总日数相关性最高,前期降水主要以土壤蒸发消耗为主,后期降水则大部贮存于土壤中;(4)休闲期1 m土层平均贮水效率为0.27,贮水效率随着麦收时的土壤墒情增加而线性递减,当麦收时1 m土层贮水量小于田间持水量的45%～48%时,贮水效率较高,1 m土层水分得到充分补充的降水阈值为388 mm。该研究成果揭示了近40年陇东黄土高原休闲期降水和土壤贮水的转化规律,同时为指导区域水资源高效利用提供科学依据。     

太行山小流域降雨—径流关系及其过程的研究

观测了水源区的太行山小流域径流及降雨过程 ,分析了径流与降雨的关系。结果表明 ,流域降雨季节性变化很大 ,主要集中于 6～ 9月 ,总量达 3 89.2 mm ,占 86.5 % ,11月到翌年 5月仅 60 .75 mm。在旱季 ,流域径流量逐渐下降 ,11月到翌年 5月底减少 0 .0 0 2 3 m3/ s,此期降雨次数和量较少 ,径流量持续下降 ,11月至翌年 3月由于植物叶片枯落 ,浅层土壤水经长时间蒸发后对深层裂隙水无明显影响 ,径流量较稳定 ,进入生长季后 ,流量近至枯竭。雨季降雨是流域径流的主要来源 ,当降雨量小于 5 0 mm时 ,降雨对径流的影响很小。连续暴雨使径流迅速形成洪峰 ,在平均雨强达到 2 8.91mm / h后 ,4 h径流量达最大值 0 .90 5 m3/ s,此期径流量与累积降雨量呈极显著的线性正相关。但洪峰仅持续 1～ 2 h,后期 5 7.3 m m的降雨量并未再次引起洪峰。     

不同土地利用方式下赤红壤坡面土壤侵蚀特征

为探究降雨和土地利用对南方赤红壤坡面侵蚀特征的影响,通过天然降雨观测试验,定量分析不同土地利用方式(坡耕地、果园、人工草地和撂荒地)下坡面径流和侵蚀泥沙特征,探讨降雨类型及土地利用对坡面侵蚀产沙的影响以及降雨特征参数与坡面水沙指标间的关系。结果表明:(1)2018年研究区降雨主要集中在5—9月,且每月降雨量主要由一场或几场暴雨及大暴雨组成;(2)坡耕地坡面年径流量和年侵蚀量均最大,分别是果园、人工草地以及撂荒地处理下的3.4,8.0,6.0倍和340.5,1605.3,1720.3倍;(2)次降雨下,坡面径流量在年内表现为前期平稳,后期波动增加,侵蚀量表现为前期波动较大,后期变化相对平稳,且侵蚀产沙主要集中在前期;(3)不同土地利用方式下,暴雨及大暴雨产生的径流量均占年径流量的75%以上,坡耕地、果园、人工草地以及撂荒地处理下由暴雨和大暴雨产生的侵蚀量分别占年侵蚀量的99.1%,71.8%,52.3%和51.6%;(4)降雨量和最大30min降雨强度是影响赤红壤坡面侵蚀最重要的降雨特征参数,降雨历时和植被覆盖度均显著影响果园、人工草地及撂荒地坡面径流量。研究结果有助于明晰南方赤红壤区不同土地利用现状土壤侵蚀特征,为区域水土保持提供参考依据。     

人工毛竹林生态水文过程对气候变化的响应

为揭示生态水文过程与气候变化的关系,以广西猫儿山典型流域人工毛竹林为研究对象,利用Hydrus-1D模型模拟了毛竹林土壤水分及其他水文要素,在此基础上,针对设定的不同气候变化情景,分析了人工毛竹林对气候变化的响应。结果表明:Hydrus-1D模型可满足人工毛竹林生态水文分析,人工毛竹林蒸散发量占总降水量的28.40%,径流以基流为主。在不同气候变化情景下,气温升幅控制蒸发和蒸腾的增幅,且冬季增幅大于夏季增幅。径流对降水变化更敏感,降水变化会更多地影响夏季径流,而气温则更易影响冬季径流。降水对夏季土壤储水量影响大于冬季,气温则更多地影响冬季土壤储水量。气温降水耦合情况下,土壤储水量对降水减少气温升高时敏感性最明显,总体表现为冬季土壤储水量更易受影响。研究结果可为区域生态规划、水资源开发利用等提供参考依据。     

人工集水面降雨径流观测实验研究

野外降雨径流观测实验研究表明 :土质集水面 (自然黄土坡面、清除杂草自然黄土坡面和夯实集水面 )的降雨产流方式为超渗产流 ,受降雨强度的影响大 ,径流的产生主要是由几次高强度的暴雨引起。此类集水面的年平均集水效率在 7.4%～ 35 .5 %之间 ,因此 ,增大集水区面积是保证土质集水面收集到更多雨水的基本途径。油毡、沥青和混凝土处理集水面的产流过程受降雨量和降雨强度的影响小 ,年平均集水效率在 5 0 %～ 80 %之间 ,但投资成本较高 ,其雨水利用方向是和设施农业相结合 ,修建固定集水面 ,发展高投入高产出农业。塑料膜集水面一次性投入低且平均集水效率较高 ,但寿命较短 ,建议利用简单临时性的移动塑料集水面收集雨水以供大田作物缺水期补灌。     

定量分解气候变化与人类活动对季节径流变异的贡献率

变化环境下径流序列可能发生变异。当前径流变异的贡献率分解研究多集中于年尺度,而对季节尺度的关注不足。以黄土高原典型流域——泾河流域为研究对象,应用小波分析方法揭示其季尺度径流序列的演变规律,采用有序聚类法和累积距平法对其径流序列进行变异诊断,最后采用累计斜率变化率比较法定量分解气候变化和人类活动对其四季径流变异的贡献率。结果表明:(1)泾河流域夏季和冬季径流的周期变化均在20世纪90年代左右有发生转变,均由小尺度周期变化转变为较大尺度周期变化;(2)春、夏、秋和冬季径流分别在1969年、1996年、1985年和1990年发生变异;(3)人类活动对春、夏、秋和冬季径流变异的贡献率分别为50.40%,89.69%,39.14%和84.59%,在夏季和冬季人类活动(主要是水土保持措施的不断深入)对泾河径流变异的贡献占主导地位,且干扰影响了径流的周期变化。     

淮北平原黄潮土多雨强变坡度产流产沙规律试验模拟

针对淮北平原黄潮土水土流失严重的问题,为揭示其产流产沙规律,利用五道沟水文实验站大型人工模拟降雨径流试验场,开展了40,60,80mm/h 3个雨强及5°,10°,15°3个坡度产流产沙规律试验模拟。结果表明:坡面初始产流时间随坡度、雨强的增大而缩短,雨强、坡度越大缩短越不明显;单位时间产流、产沙量随降雨时间变化的转折点在产流后6～15min,单位时间产流量随降雨时间变化表现为前期快速增加,中期缓慢增加,后期平稳,其中40,60mm/h雨强单位时间产流量随坡度增加而减小,80mm/h雨强随坡度的增加而增加;单位时间产沙量随雨强、坡度的增大而增大;不同坡度累计产沙量及产流量随降雨时间变化呈幂函数或线性函数关系(R20.99);坡度及雨强与坡面产流、产沙总量分别呈多元线性和多元幂函数关系。