Runoff generation in a degraded Andean ecosystem: Interaction of vegetation cover and land use

Tropical mountain regions are affected by rapid land use/-cover change, which may threaten their (eco-)hydrological functions. Although there is a growing interest in evaluating the effect of land use/-cover change on mountain hydrology, quantitative assessments of the impact of land use/-cover on hydrological processes are hampered by the lack of field measurements characterizing runoff generation processes. In this paper, we present results from field experiments of rainfall runoff mechanisms in the southern Ecuadorian Andes. A rainfall simulator was used to quantify the hydrological response of distinct land use/-cover types to intense rainfall (about 40 mm/h). The rainfall runoff experiments indicate that degraded and abandoned land generate surface runoff within a few minutes after the start of the rainfall event. These lands have a very rapid and sharp hillslope hydrological response, as Hortonian overland flow is the dominant runoff generation mechanism. In contrast, surface runoff on arable and rangelands is rare, as their soils are characterized by a high infiltration capacity (i.e. > 29 mm/h). Our experiments provide evidence that runoff generation in degraded Andean ecosystems is mainly controlled by the surface vegetation cover and land management. When reducing the surface vegetation cover, the soil is increasingly affected by rapid hillslope runoff as the presence of large amounts of smectites in the outcropping soft rocks makes the material very prone to sealing and crusting, thereby enhancing runoff generation.     

Heterogeneity in soil hydrological response from different land cover types in southern Spain

This paper reports results from the analysis of the soil hydrological response to simulated rainfall in a cork oak forest in Los Alcornocales Natural Park (SW Spain). Four different soil/vegetation units were selected for the field experiments: [1] cork oak woodland, [2] heathland, [3] grassland, and [4] cork oak/olive tree mixed forest. Rainfall simulations tests were performed on circular plots of 1256.6 cm² at an intensity of 56.5 mm h^− 1 for 30 min.Marked differences in the hydrological behavior of the studied vegetation types were observed after the rainfall simulations. The soils under woodland showed low runoff rates and coefficients. The highest runoff rates were measured on the heath and grass-covered parts of the hillslope. Water repellency of the soil, measured from water drop penetration tests, reduced infiltration (especially under the heathland), and seems to be the cause of fast ponding and runoff generation during the first stages of rainstorms.The mosaic of different patterns of hydrological response to rainfall, such as runoff generation or infiltration, is governed by the spatial distribution of vegetation and its influence on the soil surface.     

Controls of infiltration–runoff processes in Mediterranean karst rangelands in SE Spain

Semiarid karst landscapes represent an important ecosystem surrounding the Mediterranean Basin for which little is known on runoff generation. Knowledge of the sources and patterns of variation in infiltration–runoff processes and their controls is important for understanding and modelling the hydrological functions of such ecosystems. The objectives of this paper are to determine the infiltration rates and their controls in a representative mountain karst area (Sierra de Gádor, SE Spain) at micro-plots and to investigate the integrated response of rainfall on a typical hillslope. Rainfall simulations in micro-plots and natural rainfall-runoff monitoring on a hillslope were carried out complementarily. We investigated the role of soil surface components (vegetation, rock outcrop, fracture, and soil crust), topographic position, antecedent soil moisture, and rainfall characteristics in regulating infiltration–runoff processes. Results of rainfall simulation revealed the importance of vegetation cover and the presence of rock fractures in promoting the infiltration in the limestone karst landscape, while bare patches and rock outcrops acted as sources for runoff. All plots with > 50% vegetation cover had no runoff with up to 55 mm h^− 1 of simulated rain. In contrast, nearly all bare plots had runoff under the same simulated rain, with runoff coefficients ranging from 3.1 to 20.6% on dry soil surface conditions, and from 2.0 to 65.4% on wet soil surfaces. Runoff coefficients amounted to 59.0–79.5% for rock outcrops without cracks, but were drastically reduced by the presence of cracks. The surfaces with rock fragments resting on the soil (generally located in the middle of the slopes) prevented more effectively the runoff generation than those surfaces where rock fragments were embedded in the top soil. Antecedent soil moisture had significant impact on runoff generation, with wet soil having doubled runoff coefficient, shortened time to runoff, and increased runoff rate compared to the same but dry soil. Linear regressions indicated that the main controls for constant infiltration rate were the cover percentages of vegetation and litter, plus rainfall intensity; while the major controls for runoff coefficient were the bare soil and vegetation coverage, plus rainfall intensity. High infiltration rates measured at the micro-plots agreed with low intra-event runoff coefficients (mostly below 1%) observed under natural rainfalls at the hillslope. Runoff depth and coefficient at the hillslope was significantly correlated with rainfall depth, maximum hourly rainfall intensity and antecedent precipitation over 20 days (AP₂₀). During the 1.5-year monitoring period from Sep-2003 to Mar-2005, the overall infiltration was 41% of the total rainfall amount and the maximum infiltration rate was almost 94% of the largest single rainfall event. The results from this study contribute to improved understanding of the magnitude and controls of the surface runoff in semiarid karst mountain areas.     

Decoupling effects of driving factors on sediment yield in the Chinese Loess Plateau

Investigations of runoff and sediment yield changes and their relationships with potential driving factors provide good insights for understanding the mechanisms of hydrological processes. This study attempted to present a comprehensive investigation on the spatiotemporal variations of sediment yield in the Loess Plateau using continuous observed data at 46 hydrological stations during 1961–2016, and its responses to changes of precipitation, land use/cover and vegetation cover were analyzed by using the Partial Least Squares-Structural Equation Model (PLS-SEM). The results indicated that sediment yield reduced pronouncedly during 1961–2016 in the Loess Plateau, and 77.9% of this variation was explained by the combined effects of precipitation, land-use change, vegetation dynamics and runoff reduction. Indirect effects of precipitation, land-use change, and vegetation cover on sediment yield were 0.242, ?0.528 and ?0.630 (P < 0.05), respectively, and direct effect of runoff on sediment yield was 0.833 (P < 0.05). According to the Pearson Correlation Coefficient, the strongest positive correlation existed between annual sediment yield and runoff (r = 0.88, P < 0.05), followed by vegetation cover (r = ?0.47, P < 0.05) and land-use change (i.e. forest land and grassland) suggesting their significant trapping effects on soil erosion. However, lower correlations were examined between sediment yield and precipitation indices (?0.14<r < 0.34), and a relatively higher relationship was examined between sediment yield and heavy rainfall (P₂₅) (r = 0.34). Overall, changes in runoff and land-use/vegetation cover well explained variations in sediment yield in the Loess Plateau. The findings are expected to provide scientific and technical support for future soil and water conservation planning in the Loess Plateau, and are valuable for sustainable water resources and sediment load management in the Yellow River Basin.     

Impact of afforestation on hydrological response and sediment production in a small Calabrian catchment

Extensive afforestation using Pinus and Eucalyptus has taken place in Calabria since the early 1960's to control expansion of calanchi and biancane. In 1978 three small catchments were established near Crotone to monitor the effect of afforestation on hydrological response and sediment yield. In 1992, rainfall simulation experiments were carried out on plots in these catchments to determine more precisely the effect of tree and ground vegetation on surface runoff and erosional response. Most experiments were carried out in a logged catchment with slopes ranging from 20 to 30° and aspects from SW to NE. Results showed complex runoff generation and sediment production, reflecting the effect of microclimate and subtle variations in vegetation on infiltration characteristics. On south-facing slopes with little ground vegetation runoff generation was rapid with runoff coefficients from 27 to 37% and peak sediment concentrations reaching 83.7 g · 1⁻¹. On north-facing slopes with good tree cover, little grass, but continuous leaf litter, runoff coefficients reached 21%, but peak sediment concentration was only 3.6 g · 1⁻¹, while on recently logged north-facing slopes with dense grass cover the highest runoff coefficient was only 5.5% runoff coefficient, and there was virtually no sediment production. Implications of results for forest management and soil conservation are discussed.     

Rangeland restoration in Jordan: Restoring vegetation cover by water harvesting measures

Restoration of the degraded rangelands in Jordan using mechanized water harvesting and native species planting has become key to enhancing and maintaining the productivity and resilience of fragile ecosystems. A balanced interaction between the rangeland's hydrology and vegetation states is vital for achieving long-term sustainability. To gain a better insight into the impact of restoration on surface runoff and erosion and its role in recovering the ecosystem functions, we used the Rangeland Hydrological and Erosion Model (RHEM) to simulate various vegetation scenarios. Our research aims to understand the rangelands' water and sediment dynamics and the vegetation transition states of the ecosystem through evaluating the current (degraded) situation, assess the restoration approach on improving the degraded status (restored), and investigate the long-term sustainability of the restoration approach compared with historical rangeland conditions (baseline). Several scenarios were developed with rangeland experts, local community representatives, and measurements at protected and restored areas to represent the rangeland conditions. We found that restoration of the degraded Badia areas will decrease annual surface runoff from an average of 23.5 to 19.1 mm/year and soil erosion rate from 3.3 to 1.3 tons/ha. With time, restoration can bring back rangeland water and sediment dynamics closer towards the baseline conditions, which were 16.9 mm/year runoff rates and 0.85 ton/ha/year soil loss. The results indicate that restoration is a promising methodology to restore the degraded ecosystem and approximate the environment's historical hydrological regime.     

生态修复对采矿废弃地土壤性质的影响

以南京幕府山采矿废弃地生态修复为例,探讨生态修复如何影响采矿废弃地土壤的性质。研究结果表明:生态修复在先的废弃地土壤有机质含量相对高,因修复模式不同,同一时期修复的土壤有机质含量存在差异;土壤pH值与土壤容重主要取决于修复覆盖的土壤性质,且随修复时间增加,容重降低,而修复植被的生长也影响土壤pH值与土壤容重;土壤水文效应则主要取决于覆土厚度,其次是土壤孔隙度,而土壤孔隙度与土壤容重也与修复植被有关。     

Plant‐compositional effects on surface runoff and sediment yield in subalpine grassland

Soil erosion such as sheet erosion is frequently encountered in subalpine grassland in the Urseren Valley (Swiss Central Alps). Erosion damages have increased enormously in this region during the last 50 y, most likely due to changes in land‐use practices and due to the impact of climatic changes. In order to estimate the effect of vegetation characteristics on surface runoff and sediment loss, we irrigated 22 pasture plots of 1 m² during 1 h at an intense rain rate of 50 mm h^–1 in two field campaigns using a portable rain simulator. The rain‐simulation plots differed in plant composition (herb versus grass dominance) and land‐use intensity but not in plant cover (>90%) nor in soil conditions. Prior to the second rain‐simulation campaign, aboveground vegetation was clipped in order to simulate intense grazing. The generated surface runoffs, sediment loss, relative water retention in the aboveground vegetation, and changes in soil moisture were quantified. Runoff coefficient varied between 0.1% and 25%, and sediment loss ranged between 0 and 0.053 g m^–2. Thus, high infiltration rates and full vegetation cover resulted in very low erosion rates even under such extreme rain events. Surface runoff did not differ significantly between herb‐ and grass‐dominated plots. However, clipping had a notable effect on surface runoff in the test plots under different land‐use intensity. In plots without or with intensive use, surface runoff decreased after clipping whereas in extensively used plots, surface runoff increased after the clipping. This opposite effect was mainly explained by higher necromass and litter presence at the extensively used plots after the clipping treatment. The results obtained here contribute to a better understanding of the importance of vegetation characteristics on surface‐runoff formation, thus, on soil‐erosion control. Overall, we delineate vegetation parameters to be crucial in soil‐erosion control which are directly modified by the land‐use management.     

Impacts of soil tilth on the effectiveness of biological geotextiles in reducing runoff and interrill erosion

The effectiveness of a surface cover material (e.g. geotextiles, rock fragments, mulches, vegetation) in reducing runoff and soil erosion rates is often only assessed by the fraction of the soil surface covered. However, there are indications that soil structure has important effects on the runoff and erosion-reducing effectiveness of the cover materials. This study investigates the impact of soil pre-treatment (i.e. fine tilth versus sealed soil surface) on the effectiveness of biological geotextiles in increasing infiltration rates and in reducing runoff and interrill erosion rates on a medium and steep slope gradient. Rainfall was simulated during 60 min with an intensity of 67 mm h⁻¹ on an interrill erosion plot having two slope gradients (i.e. 15 and 45%) and filled with an erodible sandy loam. Five biological and three simulated geotextiles with different cover percentage were tested on two simulated initial soil conditions (i.e. fine tilth and sealed soil surface). Final infiltration rates on a sealed soil surface (7.5–18.5 mm h⁻¹) are observed after ca. 10 min of rainfall compared to ca. 50 min of rainfall on an initial seedbed (16.4–56.7 mm h⁻¹). On the two tested slope gradients, significantly (α = 0.05) smaller runoff coefficients (RC) are observed on an initial seedbed (8.2% < RC < 59.8%) compared to a sealed soil surface (75.7% < RC < 87.0%). On an initial seedbed, decreasing RC are observed with an increasing simulated geotextile cover. However, on an initial sealed soil surface no significant effect of simulated geotextile cover on RC is observed. On a 15% slope gradient, calculated b-values from the mulch factor equation equalled 0.054 for an initial fine tilth and 0.022 for a sealed soil surface, indicating a higher effectiveness of geotextiles in reducing interrill erosion on a fine tilth compared to a sealed soil surface. Therefore, this study demonstrates the importance of applying geotextiles on the soil surface before the surface tilth is sealed due to rainfall. The effect of soil structure on the effectiveness of a surface cover in reducing runoff and interrill erosion rates, as indicated by the results of this study, needs to be incorporated in soil erosion prediction models.     

坡地开垦的径流泥沙响应

Land use and land cover change is a key driver of environmental change. To investigate the runoff and erosion responses to frequent land use change on the steep lands in the Three Gorges area, China, a rainfall simulation experiment was conducted in plots randomly selected at a Sloping Land Conversion Program site with three soil surface conditions: existing vegetation cover, vegetation removal, and freshly hoed. Simulated rainfall was applied at intensities of 60 (low), 90 (medium), and 120 mm h 1 (high) in each plot. The results indicated that vegetation removal and hoeing significantly changed runoff generation. The proportion of subsurface runoff in the total runoff decreased from 30.3% to 6.2% after vegetation removal. In the hoed plots, the subsurface runoff comprised 29.1% of the total runoff under low-intensity rainfall simulation and the proportion rapidly decreased with increasing rainfall intensity. Vegetation removal and tillage also significantly increased soil erosion. The average soil erosion rates from the vegetation removal and hoed plots were 3.0 and 10.2 times larger than that in the existing vegetation cover plots, respectively. These identified that both the runoff generation mechanism and soil erosion changed as a consequence of altering land use on steep lands. Thus, conservation practices with maximum vegetation cover and minimum tillage should be used to reduce surface runoff and soil erosion on steep lands.     

Hydrological and sediment connectivity under freeze–thaw meltwater compound erosion conditions on a loessal slope

Freeze-thaw processes can influence hydrology, soil erosion, and morphological development by altering the connectivity between active pathways of water and sediment transport. Concentrated flow experiments were conducted involving frozen, shallow thawed, and unfrozen soil slopes under 1, 2, and 4 L/min runoff rates at a temperature of approximately 5 °C. In this study, hydrological connectivity was analysed via the simplified hydrological curve and relative surface connection function. Sediment connectivity was analysed via the sediment structure connectivity and sediment functional connectivity. Results indicated that hydrological connectivity was greatest on frozen slopes (FS), followed by shallow thawed slopes (STS), and unfrozen slopes (UFS) given a constant flow rate. Hydrological connectivity increased with increasing runoff rate for each freeze-thaw condition. Freezing condition and runoff rate exhibited a positive response to the hydrological connectivity. Sediment structure connectivity increased with increasing runoff rate for each slope condition. The ordering of sediment structure connectivity across freeze-thaw condition was that FS was greater than STS while STS was greater than UFS independent of flow rate. Sediment functional connectivity included longitudinal, lateral, and vertical connectivity components. Sediment longitudinal and vertical connectivity indicated a trend of first increasing and then decreasing under the different runoff rates and freeze–thaw conditions. For a given runoff rate, the ordering of sediment longitudinal and vertical connectivity across freeze-thaw condition was that FS was greater than STS while STS was greater than UFS. Sediment lateral connectivity exhibited a trend of first decreasing and then stabilizing. The ordering of sediment lateral connectivity across freeze-thaw condition was that UFS was greater than STS while STS was greater than FS. FS could more easily reach longitudinal and vertical penetration. Sediment longitudinal and vertical connectivity rates demonstrated increasing trends with increasing runoff rate after runoff generation stabilization and gradually approached unity. This research further improves our understanding of the hydrological and erosional mechanisms of meltwater and the generation of flooding in frozen soil conditions.     

Surface runoff and soil erosion in a natural regeneration area of the Brazilian Cerrado

The Brazilian Cerrado has been converted to farmland, and there is little evidence that this expansion will decrease, mainly because agriculture is the country’s main economic sector. However, the impacts of intense modification of land use and land cover on surface runoff and soil erosion are still poorly understood in this region. Here, we assessed surface runoff and soil loss in a woodland Cerrado area under a former pasture area, which was abandoned and has undergone a natural regeneration process for 7 years (RC). Its results were compared with that found in an undisturbed area of woodland Cerrado (CE), 40-month-old eucalyptus (3.0 × 1.8 m) (EU), and pasture under rotational grazing (PA). The study was conducted on Red Acrisol located in the Brazilian Cerrado. We performed rainfall simulations on a plot of 0.7 m² and using three constant rainfall intensities of 60, 90, and 120 mm h⁻¹ for 1 h. For each rainfall intensity, we carried out four repetitions using different plots in each treatment, i.e. 12 plots per treatment studied and 48 plots in total. We noted that the soil physical properties were improved in RC and, consequently, water infiltration and soil erosion control; RC presented surface runoff and soil loss different from EU and PA (α = 0.05). The macroporosity and soil bulk density affected surface runoff in RC and PA because the RC was used as pasture and is currently regenerating back to the cerrado vegetation. As the rainfall intensity increased, EU became more similar to PA, which showed the highest surface runoff and soil loss. Our findings indicate that natural regeneration processes (pasture to the cerrado vegetation) tend to improve the soil ecosystem services, improving infiltration and reducing surface runoff and soil erosion.     

黄河中游地区生态恢复对流域水资源的影响

[目的] 研究黄河中游地区生态恢复对水资源的影响,为流域生态保护和高质量发展提供科学依据。[方法] 利用GIMMS NDVI、ET、土壤水分、地表径流等相关水文数据,基于趋势分析和双累积曲线等方法,探讨生态恢复前后黄河中游地区蒸散发、土壤水分、地表径流的时空变化特征。[结果] 1982-2018年,黄河中游地区植被覆盖度增加了29.72%;在黄河中游地区植被覆盖度增加1%,蒸散发量增加了3~4 mm;在生态恢复区土壤水分呈下降趋势,下降速率为0.001 3%/a;各站点的平均径流量在1961-2018年呈逐年下降趋势,以生态恢复为代表的人类活动对径流量下降起到重要作用。[结论] 由于生态恢复和暖干化的气候背景,黄河中游水资源严重短缺。建议后续黄河中游生态恢复综合考虑水资源,减少人为干扰,以自然植被恢复为主。     

基于SWAT模型的罗玉沟流域森林植被变化的水文生态响应研究

以甘肃天水罗玉沟流域为研究区,应用分布式水文模型（SWAT）对该流域的径流、泥沙和水质状况进行模拟研究,并重点探讨了降雨和森林植被变化对水文生态响应的影响。结果表明:降雨因子对径流的影响略大于对泥沙的影响;森林植被具有明显的减水减沙生态水文功能,尤其对泥沙的影响更大于对径流的影响。     

Predicting runoff from semi-arid hillslopes as source areas for water harvesting in the Sierra de Gador, southeast Spain

The effectiveness of water harvesting systems collecting surface runoff form rangeland hillslopes in semi-arid regions is difficult to predict, since the hydrological response at the outlet depends on the heterogeneity of hydrological processes. The lack of continuous runoff pathways, due to the irregular spatial patterns of soil properties and the variety of antecedent soil moisture conditions directly influence runoff generation and control discharge into the water harvesting cisterns. The aim of this paper is to evaluate the effectiveness of semi-arid hillslopes in generating runoff for water harvesting systems. Runoff was estimated by the STREAM expert-based model which was applied to three semi-arid hillslopes (0.4 to 6 ha). On the one hand the STREAM model rules were adapted to the regional conditions i.e. an antecedent precipitation index was adjusted to local soil moisture conditions and the rainfall duration was defined as the total rainfall event quantity and the effective rainfall duration (P_tot/t_eff). On the other hand, the distribution of rock outcrop and vegetation cover along the slopes was used to define homogeneous hydrological units. Final infiltration capacities were attributed to these hydrological units based on values found in the literature. The prediction performances are acceptable for the three water harvesting systems with an RMSE of 13.9 m³. It was shown that the rainfall/runoff model was more sensitive to the duration of the storm than to the antecedent soil moisture conditions. The use of a unique set of hydrological parameters for the three water harvesting systems on representative hillslopes allows the runoff prediction from any rangeland hillslope within the same region. Furthermore, the spatial patterns of soil surface characteristics are crucial for collecting runoff at the outlet of the system. Model runs demonstrated that degradation of vegetation and sealing of very small areas within flow paths can lead to an increase of annual runoff by as much as a factor two.     

黄土高原典型地区不同植被覆盖下坡面土壤侵蚀阈值研究

为了分析植被覆盖对黄土高原坡面水土流失的影响，量化土壤侵蚀的植被覆盖阈值，基于模拟降雨数据分析了植被覆盖对土壤侵蚀的作用机制，利用绥德、西峰、天水等黄土高原高原典型地区的野外径流小区定位观测资料，探讨了不同覆被类型下植被覆盖控制径流和土壤侵蚀的有效性，确定了不同覆被类型下植被覆盖调控径流和防治土壤侵蚀的植被覆盖下限阈值和上限阈值。结果表明：(1)植被覆盖度的提高增加了土壤入渗、减少了径流量、延缓了径流流速、增加了土壤抵抗侵蚀的能力。(2)坡面径流量随植被覆盖度呈幂函数或指数函数下降，土壤侵蚀量随植被覆盖度呈指数函数、幂函数或者对数函数下降。(3)总体而言，不同地区植被控制土壤侵蚀的下限阈值在20%～30%,上限阈值在50%～70%。(4)土壤质地、植被类型、甚至植被的根系特征对植被控制径流和土壤侵蚀的效益有重要影响。研究结果为黄土高原水土保持工作提供研究依据。     

Effects of 30-year-old Aleppo pine plantations on runoff,soil erosion,and plant diversity in a semi-arid landscape in south eastern Spain

Forest management policies in Mediterranean areas have traditionally encouraged land cover changes, with the establishment of tree cover (Aleppo pine) in natural or degraded ecosystems for soil conservation purposes: to reduce soil erosion and to increase the vegetation structure. In order to evaluate the usefulness of these management policies on reduced erosion in semi-arid landscapes, we compared 5 vegetation cover types (bare soil, dry grassland, shrublands, afforested dry grasslands and afforested thorn shrublands), monitored in 15 hydrological plots (8 × 2 m), in the Ventós catchment (Alicante, SE Spain), over 4 years (1996 to 1999). Each cover type represented a different dominant patch of the vegetation mosaic on the north-facing slopes of this catchment. The results showed that runoff coefficients of vegetated plots were less than 1% of the precipitation volume; whereas runoff in denuded areas was nearly 4%. Soil losses in vegetation plots averaged 0.04 Mg ha^− 1 year^− 1 and increased 40-fold in open-land plots. The evaluation of these forest management policies, in contrast with the natural vegetation communities, suggests that: (1) thorn shrublands and dry grassland communities with vegetation cover could control runoff and sediment yield as effectively as Aleppo pine afforestation in these communities, and (2) afforestation with a pine stratum improved the stand's vertical structure resulting in pluri-stratified communities, but reduced the species richness and plant diversity in the understorey of the plantations.     

Changes in hydrologic components from a mid-sized plots induced by rill erosion due to cyanobacterization

Runoff components are the most important factors in explaining the hydrological behaviour of a system. So that the proper understanding of the runoff processes may effectively help managers and decision-makers adopt appropriate measures. In this regard, there are variety of approaches to handle runoff generation, but the application of environmentally friendly, biologic-based and cost-effective approaches such as soil microorganisms has been seldom reported. The study has therefore tried to investigate the role of inoculation of cyanobacteria on runoff components under rain simulation conditions at the mid-sized (i.e., 6×1m) plots installed at ≈ 30 % slope steepness. The treated plots were subjected to a simulated rainfall with an intensity of 50 mm h^-1 and an initial duration of 30 min with three replications. A simulated runoff of 2.18 ± 0.32 Lmin^-1 was also performed simultaneously on the onset of starting surface runoff. The results showed significant differences (P<0.021) in hydrological behaviours in control and treated plots. So that no surface runoff was produced in treated plots up to the end of the initial duration of 30 min of simulated rainfall. The results revealed that cyanobacterization by secretion of exopolysaccharides not only postponed runoff generation but also effectively inhibited runoff components even if the rainfall incident extended for longer periods. The positive effect of cyanobacterization on increasing infiltration and potential storage of water beneath the soil was also verified in the present study, which suggests the profitable application of cyanobacteria for regulating hydrologic components.     

The impact of vegetation and soil on runoff regulation in headwater streams on the east Qinghai–Tibet Plateau,China

Vegetation type is one of many factors that affect watershed hydrology and is an especially important influence on surface hydrological processes. Canopy and ground cover vegetation provide a natural cushion against the impact energy of rainfall in headwater portions of a stream basin, increasing water filtration into the soil and reducing surface runoff, but effects of different vegetation types are not fully understood. We sought to evaluate the capacity of different vegetation communities to regulate surface runoff in an alpine landscape. We collected water samples for stable hydrogen and oxygen isotopic analyses from precipitation, throughfall, soils, streams, and rivers and compared their isotopic signatures. Results indicated that different vegetation types had different capacities for water conservation. Forested vegetation types were best able to regulate surface runoff. Land use changes have dramatically affected water conservation in the study area in the past several decades; if forested land cover existed at the levels present in 1986 or 1974, the ability of the watershed to intercept surface runoff would increase by about 7% and 3%, respectively, over its capacity in 2000.     

Vegetation strategies for soil water consumption along a pluviometric gradient in southern Spain

Changes in vegetation and soil hydrological resources occur in southern Spain because of the presence of a pluviometric gradient from west (1100 mm year^?1) to east (240 mm year^?1). Five hillslopes under different rainfall regimes were selected along this gradient and studied over a 4-year period. The objectives of the work were to analyze variation in soil moisture, water availability for plants, and drying processes on the hillslopes, and relationships between these factors and the annual variability of vegetation cover. The results show that clay content is a key factor defining the limit of water availability in the soil (the wilting point). Significant differences between soil moisture/available water and vegetation cover were observed, defining a positive feedback process that varied in nature along the pluviometric gradient. The more arid the climatic conditions the weaker the feedback between water content and vegetation cover. These observations can be explained by the greater water requirements of plant species growing on the more humid hillslopes, resulting in a rapid uptake of available water and higher water stress. However, at the driest sites the vegetation species were better adapted to the lack of water and more independent of rainfall. Available water at these sites did not decrease, because the lower number of days with a water deficit resulted in water availability for plants over a longer period of time.