Effects of moss-dominated biocrusts on soil detachment by overland flow in the Three Gorges Reservoir Area of China

Biological soil crusts(biocrusts)are important landscape components that exist in various climates and habitats.The roles of biocrusts in numerous soil processes have been predominantly recognized in many dryland regions worldwide.However,little is known about their effects on soil detachment process by overland flow,especially in humid climates.This study quantified the effects of moss-dominated biocrusts on soil detachment capacity(Dc)and soil erosion resistance to flowing water in the Three Gorges Reservoir Area which holds a subtropical humid climate.Potential factors driving soil detachment variation and their influencing mechanism were analyzed and elucidated.We designed five levels of coverage treatments(1%–20%,20%–40%,40%–60%,60%–80%,and 80%–100%)and a nearby bare land as control in a mossdominated site.Undisturbed soil samples were taken and subjected to water flow scouring in a hydraulic flume under six shear stresses ranging from 4.89 to 17.99 Pa.The results indicated that mean Dc of mosscovered soil varied from 0.008 to 0.081 kg m^-2 s^-1,which was 1.9 to 21.0 times lower than that of bare soil(0.160 kg m^-2 s^-1).Rill erodibility(Kr)of mosscovered soil ranged from 0.0095 to 0.0009 s m^-1,which was 2 to 20 times lower than that of bare soil(0.0187 s m^-1).Both relative soil detachment rate and Kr showed an exponential decay with increasing moss coverage,whereas the critical shear stress(τc)for different moss coverage levels did not differ significantly.Moss coverage,soil cohesion,and sand content were key factors affecting Dc,while moss coverage and soil bulk density were key factors affecting Kr.A power function of flow shear stress,soil cohesion,and moss coverage fitted well to estimate Dc(NSE=0.947).Our findings implied that biocrusts prevented soil detachment directly by their physical cover and indirectly by soil properties modification.Biocrusts could be rehabilitated as a promising soil conservation measure during ecological recovery to enhance soil erosion resistance in the Three Gorges Reservoir Area.

Apportioning above-and below-ground effects of moss biocrusts on soil detachment by overland flow in a subtropical climate

Biocrusts affect soil detachment through above-ground(top crust’s surface covering)and below-ground(sub-crust’s binding and bonding,B&B)effects,which might vary with biocrust development or coverage.However,these effects in humid climates are still unclear.This study was conducted to apportion and quantify the surface covering and B&B effects of moss biocrusts with five coverage levels(1%–20%,20%–40%,40%–60%,60%–80%,and 80%–100%)on soil detachment by overland flow in a subtropical humid climate.Two treatments with one being intact moss crusts and one removing the aboveground moss tissues were designed for each coverage level,and bare soil was used as the baseline.The results indicated that soil detachment capacity(Dc)and rill erodibility(Kr)decreased with biocrust coverage.After removing the above-ground moss tissues,the impeding effect of biocrusts on soil detachment weakened,but still increasing soil erosion resistance relative to bare soil.For intact crust,Dc was reduced by 50%–95%compared with bare soil,wherein 36%–55%and 14%–40%were attributed to the surface covering and B&B,respectively.The top crust contributed more than sub-crust to the soil detachment reduction,which were related to but not linear with biocrust coverage.When biocrust coverage reached mid-to-higher level(40%–100%),both top crust and sub-crust steadily contributed to soil detachment reduction with 60%and 40%,respectively.The findings advance a better understanding of the influencing mechanism of biocrusts on soil erosion in humid climates and highlight the importance of saving biocrusts as ecosystem functions.

An evaluation on using soil aggregate stability as the indicator of interrill erodibility

Aggregate stability is a very important predictor of soil structure and strength, which influences soil erodibility. Several aggregate stability indices were selected erodibility of four soil properties from temperate for estimating interrill types with contrasting and subtropical regions of China. This study was conducted to investigate how closely the soil interrill erodibility factor in the Water Erosion Prediction Project （WEPP） model relates to soil aggregate stability. The mass fractal dimension （FD）, geometric mean diameter （GMD）, mean weight diameter （MWD）, and aggregate stability index （ASI） of soil aggregates were calculated. A rainfall simulator with a drainable flume （3.0 m long × 1.0 m wide × 0.5 m deep） was used at four slope gradients （5°,10 °,15° and 20°）, and four rainfall intensities （0.6, 1.1, 1.7 and 2.5 mm/min）. Results indicated that the interriU erodibility （Ki） values were significantly correlated to the indices of ASI, MWD, GMD, and FD computed from the aggregate wet-sieve data. The Kihad a strong positive correlation with FD, as well as a strong negative correlation with ASI, GMD, and MWD. Soils with a higher aggregate stability and lower fractal dimension have smaller Ki values. Stable soils were characterized by a high percentage of large aggregates and the erodible soils by a high percentage of smaller aggregates. The correlation coefficients of Ki with ASI and GMD were greater than those with FD and MWD, implying that both the ASI and GMD may be better alternative parameters for empirically predicting the soil Ki factor. ASI and GMD are more reasonable in interrill soil erodibility estimation, compared with Ki calculation in original WEPP model equation. Results demonstrate the validation of soil aggregation characterization as an appropriate indicator of soil susceptibility to erosion in contrasting soil types in China.

Annual Discharge and Sediment Load Variation in Jialing River During the Past 50 Years

Annual discharge and annual suspended sediment loads of Beipei Hydrological Station of the Jialing River catchment were analyzed to describe the trend of Jialing River over the last five decades (1956-2006). These loads were also analyzed to ascertain the influential factors associated with its variation with the help of Kendall's Tau-b correlation analysis and regression analysis. The results indicated that the Jialing River annual discharge showed no significant trend at >95% confidence level while the annual sediment load appeared to have a significant decrease trend over the last 50 years. A decrease in the annual sediment load was particularly apparent after the year 1985, at which a substantial shift in the sediment level occurred. This shift is attributed to the construction of numerous dams in 1980s. However, after the year of 1985, two periodical stages (1986-1991 and 1992-2006) with distinct sediment load and sediment-runoff ratio were identified. The period 1992-2006 is characterised by low sediment load, which is most probably due to the impact of large scale of soil and water conservation, which took place at the end of the 1980s. Last, models describing the relationship between the discharge and the sediment load, discharge and sediment-runoff ratio as well as between the sediment load and sediment-runoff ratio were constructed.

Grey Relational Analysis on the Effects of Rainfall Factors on Runoff and Sediment in the Sloping Farmland with Different Plants in the Central South of Shandong Province

[Objective] The aim was to study the main rainfall factors influencing runoff and sediment in the sloping farmland with different plants in the central south of Shandong Province.[Method] Through grey relational analysis,the effects of different rainfall factors on runoff and sediment with different plants in the central south of Shandong were studied.[Result] In the sloping farmland with different plants,the effects of rainfall factors on runoff and sediment weren’t consistent.Rainfall was the dominant influencing factor of runoff,but PI30 had the greatest influence on runoff in natural grassland.Meanwhile,rainfall intensity was the main influencing factor of sediment,but PI had the greatest influence on sediment in Astragalus adsurgens Pall.plot.The compound factor had the minimal influence on runoff and sediment in Arachis hypogaea plot and natural grassland.In A.adsurgens Pall.plot,rainfall intensity had the minimal impact on runoff,but the compound factor had the least effect on sediment.[Conclusion] The study could provide theoretical references for the comprehensive control of slope soil erosion,the optimum utilization and sustainable development of land.

Using Automation Controller System and Simulation Program for Testing Closed Circuits of Mini-Sprinkler Irrigation System

The field experiments were conducted at the experimental farm of Faculty of agricultural, southern Illinois University SIUC, USA. The project makes the irrigation automated. With the use of low cost sensors and the simple circuitry makes currently project a low cost product, which can be bought even by a poor farmer. This research work is best suited for places where water is scares and has to be used in limited quantity and this proposal is a model to modernize the agriculture industries at a mass scale with optimum expenditure. In the field of agricultural engineering, use of sensor method of irrigation operation is important and it is well known that closed circuits of Mini-sprinkler irrigation system are very economical and efficient. Closed circuits are considered one of the modifications of Mini-sprinkler irrigation system, and added advantages to Mini-sprinkler irrigation system because it can relieve low operating pressures problem at the end of the lateral lines. In the conventional closed circuits of Mini-sprinkler irrigation system, the farmer has to keep watch on irrigation timetable, which is different for different crops. Using this system, one can save manpower, water to improve production and ultimately profit. The data could be summarized in following: Irrigation methods under study when using lateral length 60 mcould be ranked in the following ascending order according the values of the predicted and measured head losses CM1M-SIS CM2M-SIS.The correlation (Corr.) coefficients were used to compare the predicted and measured head losses along the lateral lines of all the closed circuits designs. Generally, the values of correlation analysis were (>0.90) were obtained with 0% field slope60 mlength (experimental conditions) for all closed circuits.The interaction between irrigation methods: at the start there are significant differences between CM2M-SIS and CM1M-SIS.

Runoff and Soil Erosion on Slope Cropland: A Review

Soil erosion has become a serious environmental problem worldwide,and slope land is the main source of soil erosion. As a primary cover of slope land,crops have an important influence on the occurrence and development of runoff and soil erosion on slope land. This paper reviews the current understanding of runoff and soil erosion on slope cropland. Crops mainly impact splash detachment,slope runoff,and sediment yield. In this review paper,the effects of crop growth and rainfall on the splash detachment rate and the spatial distribution of splash detachment are summarized. Crop growth has a significant impact on runoff and sediment yield. Rainfall intensity and slope gradient can influence the level of erosive energy that causes soil erosion. Furthermore,other factors such as antecedent soil water content,soil properties,soil surface physical crust,and soil surface roughness can affect soil anti-erodibility. The varying effects of different crops and with different influence mechanisms on runoff and soil erosion,as well as changes in their ability to influence erosion under different external conditions should all remain focal points of future research. The effect of crop vegetation on runoff and soil erosion on slope land is a very important factor in understanding large-scale soil erosion systems,and in-depth study of this topic is highly significant for both theory and practice.

陕西商南县栓皮栎林分评价与管理(英文)

The present study was conducted within the frame of the Sino-German project "Rehabilitation of degraded land ecosystems in the mountainous area of the Southern Shaanxi Province,China".The study deals with the assessment of the potential of oak coppices as well as the evaluation of the socioeconomic conditions in the Shangnan County.The ultimate objective of the study is to provide recommendations on the sustainable management of forest resources,which does not only aim to improve the environmental situation but also to satisfy the demands of the local rural residents.The study was based on 30 samples of oak coppices stands,which were randomly selected within an area of a size of 20 km × 20 km.In each selected stand,the mature stand and understory regeneration were investigated in depth.For the socio-economic survey,175 households from 11 villages were randomly selected.Results revealed that the stocking capacity of the cork oak coppices reaches 120 m3/ha in average at the older age classes(≥25 years) even after frequent timber harvest.High potential for productivity was indicated by the availability of sufficient vigorous individuals at different age classes.In addition,the understory regeneration was sufficient in density(19,000±133 individual/ha) and consisted of diverse valuable native-species(17 species within a survey area of 400 m2).The results of the assessment of the oak coppices provided possibilities for some practices that can be recommended towards sustainable management of such stands.On the other hand,results of the socioeconomic study showed a high degree of acceptance among the local inhabitants(79% of the total households) to change traditional land use,providing an enhancement of their economic situation.

Effects of patchy distributed Artemisia capillaris on overland flow hydrodynamic characteristics

Laboratory-simulated rainfall experiments were conducted to quantify the effects of patchy distributed Artemisia capillaris on overland flow hydrodynamics.Rainfall intensities of 60,90,120,and 150 mm h-1 were applied on a bare plot (CK) and four different patched patterns:a checkerboard pattern (CP),a banded pattern perpendicular to slope direction (BP),a single long strip parallel to slope direction (LP),and a pattern with small patches distributed like the letter'X'(XP).Each patterned plot underwent two sets of experiments,intact plant and root (the above-ground parts were removed),respectively.Results showed that flow velocity increased with rainfall intensity,and the lower slope velocity was higher than the upper slope.The removal of grass shoots significantly increased flow velocity.The contributions of grass shoots and roots to the reductions in flow velocity under different rainfall intensities were different.The shoots made greater contribution of 53-97% at 60 and 90 mm h-1,and the roots contributed more (51-81%) at 120 and 150 mm h-1.Mean flow depth increased with rainfall intensity and it declined after the aboveground parts were cleared.Reynold numbers (Re) in this study were 25-80,indicating a laminar flow in the study.Froude numbers (Fr) were ≥ 1 for CK and < 1 for patterned treatments.Fr of the lower slope was higher than the upper ones.Darcy-weisbach (f) and Manning (n) friction coefficient ranked in the order of CK < LP < BP/CP/XP with values of grass sections being higher than the bare sections and upper slope higher than the lower slope,and both decreased after removing the grass shoots.BP,CP,and XP performed more effectively than LP in retarding flow velocity and increasing hydraulic roughness.