Effects of peat content,rainfall duration and aggregate size on soil crust strength

The effect of peat on crust strength was investigated using ten soils with organic matter levels ranging from 1-50 to 18-23 per cent. As peat content increased, the crust strength reduced. This occurred in spite of the inability of peat to increase the stability of soil aggregates. Peat reduced crust strength by acting as a mulch on the soil surface, thereby reducing breakdown of soil aggregates. Peat also formed a source of weakness on the soil, reducing crust formation. Using a factorial experiment involving a further seven soils with different levels of peat treatment, exposed to four rainfall durations and with two aggregate sizes, crust strength was described in terms of the direct effects and the interactions of these factors. Most of the crust strength values reduced with increasing peat content. For each soil, crust strength increased significantly with increasing rainfall duration. Crust strength was greater for the smaller aggregate size. The most significant interactions affecting crust strength were between soil and aggregate size, rainfall duration and aggregate size, and soil and rainfall duration in that order. These interactions were used to describe the effect of organic matter in form of peat on crust strength. For each soil and aggregate size, polynomial relationships were established to relate crust strength to total kinetic energy of rainfall.     

Establishing the role of pedogenesis in changing soil hydraulic properties

Chronosequences provide suitable sources for the study of changes in soil hydraulic behaviour as a result of long-term pedogenesis. For a podsol chronosequence in the Scottish Highlands, data are presented to indicate the changes that have occurred over 13000 years in the saturated hydraulic conductivity (K_sat) in each horizon. As the soil profile has evolved into a differentiated sequence of three horizons, the resulting hydrological changes can be both measured and quantified by relating K_sat to textural properties and bulk density. The results are significant for interpretation of changing runoff processes and slope stability.     

Run off-on-out method and models for soil infiltrability on hill-slope under rainfall conditions

Infiltration is the process of water penetrating into soil, generally referred to as the downward movement of water from the soil surface[1,2]. This process is af-fected by water supply and the soil infiltrability, de-termines the amounts of water entering into soil pro-file and the surface runoff. Infiltrability is defined as the infiltration flux of a unit area under atmospheric pressure and sufficient water supply. The actual infil-tration rate and/or the infiltrability is expressed in m/s …     

Occurrence,shape and movement of daily rainfall in the Huai Basin,China

The upper reaches of the Huai River in Central China are located in the East Asian monsoon region. Strong seasonality, as well as large interannual variability of rainfall, causes floods and an uneven supply of water. In order to conserve the water and mitigate the floods, dams and flood protection structures are constructed. Their design requires information about the rainfall. Daily observations from 1957 to 1986 from 78 rain gauges were used to study shape, orientation, movement and geographical and seasonal occurrence of storms in the 79 000 km² study area. The rainfall characteristics were described using graphical plots, cross‐ and autocorrelation. Storms larger than 50 mm/day were found to occur from February to November, whereas storms exceeding 350 mm/day were confined to the main rainfall season from late June to mid‐August. The southern part of the study area experienced a break in the rainfall season in late July, corresponding to the seasonal northward shift of the rain belt. A weekly periodicity of 7–8 days for rainfall was found during June–July, but not during August–September. During the whole period June–September, the spatial pattern of daily rainfall revealed an elongated shape, more pronounced during June–July than August–September. The rainfall area was orientated approximately from WSW to ENE during the whole period, and showed an anticlockwise rotation of about 16° per day during June–July. The cross‐correlation analysis revealed that the rainfall area moved about 100 km/day eastward. These results and an investigation of meteorological maps indicate that the spatial correlation pattern of daily rainfall is produced by cold fronts on the Mei‐Yu front. Suggestions are made as to how to use the results for the construction of design rainfalls in the study area. Copyright © 1999 John Wiley & Sons, Ltd.     

Field measurements of rainfall drop-size distribution,and the relationships between rainfall parameters and soil movement by rainsplash

Rainfall drop-size distributions were measured at a site in northern England using the ‘oflour-pellet’ technique. A relationship between intensity and kinetic energy is presented. Even at the low rainfall intensities observed (< 5 mm h^?1 average over an hour) measureable amounts of rainsplash movement took place, and these movements have been related to rainfall parameters.     

Spatial variability of rainfall on a sub‐kilometre scale

The variability of rainfall in space and time is an essential driver of many processes in nature but little is known about its extent on the sub‐kilometre scale, despite many agricultural and environmental experiments on this scale. A network of 13 tipping‐bucket rain gauges was operated on a 1·4 km² test site in southern Germany for four years to quantify spatial trends in rainfall depth, intensity, erosivity, and predicted runoff. The random measuring error ranged from 10% to 0·1% in case of 1 mm and 100 mm rainfall, respectively. The wind effects could be well described by the mean slope of the horizon at the stations. Except for one station, which was excluded from further analysis, the relative differences due to wind were in maximum ±5%. Gradients in rainfall depth representing the 1‐km² scale derived by linear regressions were much larger and ranged from 1·0 to 15·7 mm km^?1 with a mean of 4·2 mm km^?1 (median 3·3 mm km^?1). They mainly developed during short bursts of rain and thus gradients were even larger for rain intensities and caused a variation in rain erosivity of up to 255% for an individual event. The trends did not have a single primary direction and thus level out on the long term, but for short‐time periods or for single events the assumption of spatially uniform rainfall is invalid on the sub‐kilometre scale. The strength of the spatial trend increased with rain intensity. This has important implications for any hydrological or geomorphologic process sensitive to maximum rain intensities, especially when focusing on large, rare events. These sub‐kilometre scale differences are hence highly relevant for environmental processes acting on short‐time scales like flooding or erosion. They should be considered during establishing, validating and application of any event‐based runoff or erosion model. Copyright © 2009 John Wiley & Sons, Ltd.     

An alternative method for density variation modeling of the crust based on 3-D gravity inversion

In this paper we are proposing an alternative method for determination of density variations of the crust from constrained inversion of the terrestrial gravity data. The main features of the method can be summarized as follows: (i) Constructing a band-pass filter to remove the long and short wavelength signals from the terrestrial gravity data. (ii) Using an iterative method for stabilization and solution of the inverse problem. The mentioned regularization method is first validated by simulated gravity data and next the methodology is used for development of a new regional density variation model of the crust in three layers based on real gravity data in geographical area of Iran. Application of the band-pass filter to the latter data resulted the residual gravitation variations in the range of − 300 to 50 (mGal) which next based on the iterative method resulted following ranges for residual densities: −120 to 40 (kg/m³) in first layer, −40 to 40 (kg/m³) in second layer, and − 40 to 40 (kg/m³) in third layer.     

Measurement and prediction of water movement in a field soil: The matrix-macropore dichotomy

The saturated and unsaturated flow properties of a field soil under two tillage treatments were obtained with ponded rings and disc permeameters of dissimilar radii. No difference was observed between tillage treatments but the flow properties displayed a distinct macropore-matrix dichotomy, with K changing by an order of magnitude as ψ₀ went from just - 30 mm to zero. Accurate prediction of time to incipient ponding was achieved using both numerical and analytical models calibrated with field hydraulic properties that were characteristic of the soil matrix. However, extension of the numerical model to the prediction of the wetting front development under non-ponded conditions was less accurate due to localized preferred wetting It is hypothesized that at this site, localized concentration of rainfall and hence, preferred wetting, May, occur by interception and stemflow associated with lines of standing stubble present in the original seeding slots.     

Occurrence of water ponding on soil surfaces depending on infiltration rates on Mongolian rangeland

The occurrence of water ponding on soil surfaces during and after heavy rainfall produces surface run‐off or surface water accumulation in low‐lying areas, which might reduce the water supply to soils and result in a reduction of the soil water that plants can use, especially in arid climates. On Mongolian rangeland, we observed ponded water on the surface of a specific soil condition subjected to a heavy rainfall of 30 mm/hr. By contrast, ponded water was not observed for the same type of soil where livestock grazing had been removed for 6–8 years via a fence or for nearby soil containing less clay. We measured the infiltration rate (the saturated hydraulic conductivity of the surface soil, K_s) of the three sites by applying ponded water on the soil surface (an intake rate test). The results showed that K_s in the rangeland was lower than the rainfall intensity in the site where water ponded on the soil surface; however, K_s of the soil inside of the fence has recovered to 3 times that of the soil outside of the fence to exceed the rainfall intensity. Heavy rainfall that exceeds the infiltration rate occurs several times a year at the livestock grazing site where we observed ponded water. Slight water repellency of the soil reduces rain infiltration to increase the possibility of surface ponding for the soil.     

High-frequency monitoring of the occurrence of preferential flow on hillslopes and its relationship with rainfall features,soil moisture and landscape

ABSTRACT

High-frequency monitoring was conducted to quantify the frequency and controlling factors of preferential flow (PF) in a monsoon-influenced sub-humid mountainous catchment (6.48 km²) of Northern China. Rainfall was measured using nine bucket raingauges. Soil moisture probes were set up at 12 sites to observe the PF. Overall, 129 rainfall events were identified during the years 2014–2016. The average PF occurrence was 41%, which increased to 71% during heavy rainfall events (>20 mm) revealing a strong influence of the amount and intensity of rainfall. The study also revealed that the PF increased with antecedent soil moisture. Soil moisture was much higher on flat sites compared to sloping sites, providing evidence that the topography has a strong influence on rainfall infiltration and runoff which, subsequently, influence soil moisture variation and the occurrence of PF. Our findings provide valuable insights into the hydrological processes for studies in regions with similar environmental conditions.     

On estimating the hydraulic properties of soil,Part 1. Comparison between forms to estimate the soil-water characteristic function

The hydraulic properties of soil include the soil-water characteristic function [h(θ), in which θ is water content and h is pressure head (suction)], and the hydraulic conductivity function [K(θ) or K(h)]. These functions are essential to the solution of unsaturated groundwater flow problems. A number of empirical and semiempirical forms have been proposed in the literature to estimate these functions. The present paper employs a nonlinear least-square analysis for comparison between some of the available forms, using a large number of experimental measurements of h(θ) for different classes of soil. Suitability of the forms for predicting the hydraulic conductivity function is examined. In the absence of accurate measurements, the paper facilitates modeling by providing estimates for the parameters of the soil-water characteristic function.     

Impact of the water salinity on the hydraulic conductivity of fen peat

Coastal peatlands represent an interface between marine and terrestrial ecosystems; their hydrology is affected by salt and fresh water inflow alike. Previous studies on bog peat have shown that pore water salinity can have an impact on the saturated hydraulic conductivity (K_s) of peat because of chemical pore dilation effects. In this study, we aimed at quantifying the impact of higher salinities (up to 3.5% NaCl) on K_s of fen peat. Two experiments employing a constant‐head upward‐flow permeameter and differing in measurement and salinity change duration were conducted. Additionally, a third experiment to determine the impact of water salinity on the release of dissolved organic carbon (DOC) of the studied peat type was carried out. The results show a decrease of K_s with time, which does not depend on the water salinity but is differently shaped for different peat types. We assume pore clogging due to a conglomerate of physical, chemical, and biological processes, which rather depend on water movement rate and time than on water salinity. However, an increased water salinity did increase the DOC release. We conclude that salinity‐dependent behaviour of K_s is a function of peat chemistry and that for some peat types, salinity may only affect the DOC release without having a pronounced impact on water flow.     

The possible influence of solar activity on Indian summer monsoon rainfall

The Indian summer monsoon rainfall （ISMR） plays an important role in the climate system of South Asia. Recently, studies about ISMR variations have been going into more depth. In this present paper, we mainly use the Scargle periodogram and wavelet transform methods to study the periodicity of ISMR changes between 1871 and 2004 and review the possible influence of solar activity on the rainfall. Analysis results show complicated ISMR variations have periodicities with remarkable time-variable characteristics. Investigating a possible connection between the rainfall and solar variations, we believe that solar activity affects the ISMR variations to some extent.     

On estimating the hydraulic properties of soil,Part 2. A new empirical equation for estimating hydraulic conductivity for sands

A new empirical equation to estimate hydraulic conductivity is proposed, based on a large set of measured data for hydraulic properties of soil. The equation is simpler and more accurate than the series-parallel model. Under conditions of insufficient data, the new equation provides a good estimation of hydraulic conductivity for sands. For the same class of soils, another empirical equation is proposed to estimate the power N in the Averjanov-Irmay function.     

Impact of spatial rainfall resolution on point-source solute transport modelling

Numerical simulations of unsaturated solute transport from point sources were carried out using HYDRUS-1D. Three different soil types cropped with spring wheat were considered at three different locations in Sweden: Malmö, Norrköping and Petisträsk. Two types of rainfall data were used, point-scale raingauge measurements and a gauge-adjusted weather radar product at four spatial resolutions, 2 × 2, 6 × 6, 10 × 10 and 14 × 14 km². The results showed that differences in the mean solute transport depths were small and not significant, with the exception of Petisträsk. Maximum transport depths were in most cases significantly larger using raingauge data compared to radar data. The results showed that using areal-averaged rainfall input will give solute transport estimations close to those using point-measured data. This shows the great potential in using radar-measured rainfall data in small-scale hydrological applications.     

降雨对土层标与基岩标影响的差异性分析

通过对南京地震台短水准测量中的基岩标志和土层标石的抗干扰分析,发现:温度、气压的影响可以通过改变观测时间段来尽量减小,使其对两类观测点观测资料没有明显影响;降雨量大小对基岩点的影响很弱,对土石点影响较大,则没办法消除.表明,在选择好的观测场地的同时,也要根据观测资料的需要埋设合理的测点标志类型.     

安徽琴溪地区土壤硒元素有效性及开发研究

富硒土壤资源日益引起重视,但如何界定富硒土壤没有统一标准.本文选取安徽琴溪地区作为研究对象,利用安徽省富硒土壤分级标准,系统研究琴溪地区农业可耕地土壤及其植物中硒含量,这为琴溪地区富硒产品开发的定位提供了一定的理论依据,并对当地富硒产品的开发提出可行性建议.     

Physical-hydraulic properties of tropical sandy-loam soil in response to rice-husk dust and cattle dung amendments and surface mulching

ABSTRACT

The effects of topsoil addition of rice-husk dust (RHD) and cattle dung (CD), alongside surface mulching with dry grasses/legume, on the infiltration characteristics and intrinsic structural properties of a deep, well-drained soil in southeastern Nigeria are assessed. Treatments are RHD-amended, CD-amended and “unamended”, each plot being either surface-mulched or left bare, with the unamended-bare plots as control. Amendments and mulch were applied at 20 t/ha equivalents. Their effects on the soil’s infiltration characteristics 7 months later were not evident; however, there was a tendency for differences: CD-amended ≥ RHD-amended ≥ unamended and surface-mulched ≥ bare-surface. By contrast, saturated hydraulic conductivity (K_s ) differed thus: CD-mulched ≥ unamended-mulched > the rest. Similar values were recorded for K_s (50.89 cm/h) and final infiltration rate (50.74 cm/h) only under CD-amended plots, which also showed the highest values (43.50 cm/h) for transmissivity of the soil. Soil penetrometer resistance was lowest in CD-amended plots (113.44 kPa) and highest in unamended plots (166.78 kPa). Topsoil addition of cattle dung and surface mulching could increase infiltration, though marginally, and permeability of coarse-textured tropical soils beyond the season of their application when their effects on soil structure have almost waned.