ali baliani; Ali Reza Vaezi
Abstract
IntroductionRainfall erosion results from the expenditure of the energy of falling raindrops and flowing water when these two agents act either singly or together. Soil erosion by rainfall is a serious ongoing worldwide environmental issue that contributes to soil and water quality degradation. Understanding ...
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IntroductionRainfall erosion results from the expenditure of the energy of falling raindrops and flowing water when these two agents act either singly or together. Soil erosion by rainfall is a serious ongoing worldwide environmental issue that contributes to soil and water quality degradation. Understanding raindrop-impact-induced erosion processes are key to design and apply soil management techniques that minimize and control soil erosion risk. Water erosion and especially raindrop-impact-induced erosion is the primary agents that cause soil erosion-induced degradation and has been identified as one of the major processes contributing to the soil and water quality degradation. Soil degradation caused by rainfall raindrops impacts the soil surface disperses and splashes the soil, and displaces particles from their original position. Raindrops striking the soil surface develop a raindrop-soil particle momentum before releasing their energy in the form of the splash. Other causes of soil degradation are including compaction and penetration resistance.
Materials and Methods: This study was conducted to investigate the raindrop-impact-induced erosion in relation to slope gradient (0, 10, 20, and 30%) and antecedent moisture content or AMC (air dried, quarter saturation, semi saturation, and saturation). Toward this, six soil texture classes were exposed to simulated rainfalls with 40 mm h-1 in intensity for 15-min in four slope gradients and four antecedent moisture contents. Rainfall was simulated using rainfall simulator from soil erosion laboratory of the University of zanjan with 3-meter height and surface of 2 m2. A total of 288 experimental soil boxes with 25 cm × 35 cm dimensions and 5-cm depth were investigated using the completely randomized block design with three replications. Data of soil erosion processes include splash erosion particles amount caused raindrop impact, soil resistance ratio after rainfall using penetrometer, and compaction percent using bulk density after and before rainfall was measured and then compared using Duncan's test among the slope steepness and antecedent moisture content
Results and Discussion: Significant relationships were found between the splash erosion rate, soil resistance ratio and soil compaction means (P<0.01. (The results showed that silt soil carried the highest mean value in splash erosion rate with 1574.93 gm-2 h-1, soil resistance ratio with 10.53 and soil compaction with 17.43 percent, while sand soil carried the lowest mean value in splash rate with 437.37 gm-2 h-1, soil resistance ratio with 2.66 and soil compaction with 0.25 percent. Soil erosion processes were significantly affected by slope gradient and AMC. Soil erosion processes showed a decreasing rate in 0 slope degree and increasing rate in 30 slope degree and also decreasing rate in air dried and increasing rate in semi saturation AMC. Significant correlations (P< 0.01 and 00.05) were found between soil erosion processes and sand, silt, geometric mean particle diameter, bulk density, saturated hydraulic conductivity, and calcium bicarbonate equivalent. among the physical properties of the studied soils, the sand percentage, bulk density, and Geometric mean diameter showed a negative significant correlation with splash erosion, soil compaction, and soil resistance, and the percentage of silt and calcium carbonate content with splash erosion, soil compaction, and soil resistance were positive significant correlated. The cause of this negative and positive correlation might be dependent on particles size and more percent of coarse particles, the transfer of particles from the soil mass is reduced due to raindrops and degradation processes occur with less intensity. In addition, destruction processes with more intensity occurred with increasing silt and lime percent.
Conclusion: Increasing the slope gradient has an incremental effect on the amount of rainfall erosion processes i.e. sediment load, penetration ratio, and soil compaction value. However, antecedent moisture content in various soil textures has the different effect on the amount of rainfall erosion processes. Among the soil chemical properties, only calcium carbonate equivalent with splash erosion, density, and soil surface resistance was positively correlated and chemical properties such as a percentage of organic matter and exchangeable sodium percent no significant correlated with soil erosion processes. In other words, the physical nature of soil-forming particles such as particle size, as well as some of the chemical properties of soil particles such as organic matter, have a more effect on soil degradation, density, and soil resistance ratio. also the role of soil physical properties such as sand percent and calcium carbonate equivalent on the rainfall processes were more than soil chemical properties. In general, increasing the percent of silt and lime in the soil, unlike sand, was increased the sensitivity of the soil to the rainfall erosion and as a result increasing the splash erosion leads to increased soil compaction and soil resistance ratio.
D. Baharlooi; S. Ghorbani Dashtaki; B. Khalil Moghadam; Mahdi Naderi; P. Tahmasebi
Abstract
Introduction: The detachment process can be conceptually divided in two sub-processes included aggregate breakdown (Le Bissonnais, 1996) and movement initiation of breakdown products(Kinnell, 2005). soil detachment depends on raindrop size and mass(Elison, 1944; Bisal, 1960), drop velocity(Elison, 1944; ...
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Introduction: The detachment process can be conceptually divided in two sub-processes included aggregate breakdown (Le Bissonnais, 1996) and movement initiation of breakdown products(Kinnell, 2005). soil detachment depends on raindrop size and mass(Elison, 1944; Bisal, 1960), drop velocity(Elison, 1944; Bisal, 1960), intensity rainfall (Ting et al, 2008), kinetic energy (Kinnell, 2003; Fernandez- Raga et al, 2010), runoff depth(Torri et al, 1987; Kinnell,1991 and 2005), crop covers(Bancy, 1994; Ghahremani et al, 2011), wind speed( Erpul et al, 2000) and experimental area (cup size) (Leguedois et al, 2005; Luk, 1979; Torri and poesen, 1988). Many of studies have been conducted to evaluate the relationship between splash and slope (Bryan, 1979; Torri and Poesen, 1992; Wan et al, 1996).Torri and Poesen (1992) expressed that in steep slope the gravity force adds to the drop detaching force and decreases of soil resistance, consequently increases splash erosion rate with increasing slope. Soil splash erosion is also strongly influenced by soil properties including soil particles size distribution (Mazurak and Mosher, 1968; Legout et al, 2005; fan and li, 1993), soil shear strength(Cruse and Larson, 1977; Al-Durrah and Bradford,1981; Ekwue and ohi; 1990 ), soil cohesion(Torri et al, 1987), soil organic matter content and aggregate size (Ekwue and Maiduguri, 1991; Qinjuan et al, 2008), soil aggregates stability(Qinjuan et al, 2008), surface crust (Qinjuan et al, 2008).
Fire, play an important role in splash erosion. The absence of vegetation cover in disturbed lands accelerates splash erosion rates by as much as several folds compared to undisturbed sites (Lal, 2001; Thomaz and luiz, 2012).The detachment of soil particles by splash depends on several raindrop characteristics, including raindrop size and mass, drop velocity, kinetic energy, and water drop impact angle (Sharma et al., 1993; Singer and Le Bissonnais, 1998; Cruse et al., 2000, Bhattacharyya et al., 2010). Detachment rate is strongly influenced by soil properties, including soil texture and thickness of the water layer at the soil surface (De Ploey and Savat, 1968; Moss and Green, 1983; Sharma et al., 1991; Kinnell, 1991, Jomaa et al., 2010), soil strength, bulk density, cohesion, soil organic matter content, moisture content, infiltration capacity (Nearing et al., 1988; Owoputi, 1994; Morgan et al., 1998, Planchon et al., 2000, Ghahramani et al., 2011), soil initial water content, surface compaction and roughness (Planchon et al., 2000), the nature of soil aggregates and crust, porosity, capacity of ionic interchange, and clay content (Poesen and Torri, 1988). Several studies have shown that splash detachment rate is mainly related to surface rock fragments in soils with sparse vegetation cover (Jomaa et al., 2012). The present study was conducted to investigate the effects of fire on splash erosion and some erosion depended properties in semi-steppe rangeland of Karsanak region in Chaharmahal and Bakhtiari province which affected by man-made fire during 2008, 2009, 2010 and 2011.
Materials and Methods: Soil samples were obtained on 2012 from the mentioned regions (8 samplesfrom the burned area and 8 samples as a control (unburned) in the adjacent burned area) from 0-7 cm depth. Splash erosion under simulated rainfall intensity of 2 mm per minute was measured using multivariate splash cup apparatus considering the slope of 5 and 25 degree. Soil pH, soil electrical conductivity, equivalent calcium carbonate, soil organic matter, sand size fraction particulate organic matter (SSF POM), mean weight diameter and, geometric mean diameter of aggregates, percent of macro and micro-aggregates, percent of clay, silt, sand, water dispersible clay and soil bulk density were measured. Statistical data analysis was performed by t-test at 5% level.
Results Discussion: The results showed that soil splashing increased significantly in treatment 1 year after the fire in both slope 5 and 25 degree and in treatment 2 year after the fire in slope 25 degree. The amounts of increase in soil splashing compared to control treatment were 22, 24 and 15 percent in treatment 1 year after fire in slope 5 and 25 degree and in treatment 2 years after the fire in slope of 25 degree respectively. Comparison of the total soil splash on slopes of 25 degree at 1, 2, 3 and 4 years after the fire, showed a significant increase in the level of five percent relative to the slope of 5 degree at 1, 2, 3 and 4 years after the fire. The other measured soil properties (except equivalent calcium carbonate) was affected by fire. Also, the differences between many of the mentioned properties in the first 2 years after the fire was significant compared with the control area, but they have been reached to the initial values in the third and fourth years after the fire.
Conclusion: Time was shown to be effective factor inrecovering soil propertiesin Karsanak region of Chaharmahal and Bakhtiari province which affected by man-made fire during 2008, 2009, 2010 and 2011. Fire accelerates splash erosion rates by as much as several folds compared to control in this area.
S.H.R. Sadeghi; M.B. Raisi; Z. Hazbavi
Abstract
Introduction: The capability of a soil to resist erosion depends on soil-particle size and distribution, soil structure and structural stability, soil permeability, water content, organic matter content, and mineral and chemical constituents. Among many affecting factors on aforesaid characteristics, ...
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Introduction: The capability of a soil to resist erosion depends on soil-particle size and distribution, soil structure and structural stability, soil permeability, water content, organic matter content, and mineral and chemical constituents. Among many affecting factors on aforesaid characteristics, the freezing-thawing processes may considerably affects. Freeze–thaw fluctuation is a natural phenomenon that is frequently encountered by soils in the higher latitude and altitude regions in late autumn and early spring. Effects of freezing and freezing-thawing phenomena on soil erosion and sediment yield are important. Nevertheless, soil conservation under these phenomena by using different methods as well as soil amendments has not been yet considered. Surface application of anionic polyacrylamide (PAM) in solution has been found to be very effective in decreasing seal formation, runoff, and erosion.PAM stabilizes soil structure due to the ability of the polymer chains to adsorb onto clay particles and bridge them together forming stable domains. This adsorption can be a result of interactions between the negatively-charged functional groups of the PAM molecules and the positively-charged edges of clay minerals, orexchangeable polycations (mainly Ca2+) acting as ‘bridges’ between the negative charges of the PAM's functional groups and the negatively- charged planar surfaces of the clay. The PAM is adsorbed on the external surfaces of the aggregates and binds soil particles far apart together, thereby were shorter and evidently less effective in enhancing increasing their resistance to splash by raindrop impact and detachment by runoff. A lot of research work focused on freezing effects in soils on aggregation or increase aggregate stability and emphasis corresponding effects. But the effects of application of soil amendments on soil induced freeze and thaw cycle have not been studied yet.
Materials and Methods: The present study evaluated the performance of PAM in controlling freeze-thaw cycle effects on splash erosion from a silty loam soil. A freeze-thaw cycle was simulated in Soil Erosion and Rainfall Simulation Laboratory of TarbiatModares University. The present study was conducted under controlled laboratory conditions with a simulated rainfall. The maximum efforts were made to mimic natural conditions to get access to results with high level of fidelity. Towards this attempt, air and different soil depth temperatures were analyzed in natural condition and 10 cm soil depth was targeted for the soil laboratory experiments. The rainfall storm with 72 mm h-1 and 30 min duration was simulated and conducted for the study treatments. The soil was poured in small erosion box with 0.25 m2 surface area in three replicates. A thick filter, draining the lower 20 cm of the soil profile was generated using mineral pumices.The prepared soil sample was evenly packed into the soil plots at a bulk density of 1.3 Mg m−3 similar to that measured under natural conditions. The plots were then placed in saturated pool for 24 h and then left to be drained to achieve an average moisture content of 35% similar to that recorded for the realities in the study area. So, splash erosion rates were measured using splash cups in two control treatments without PAM subjected to freezing and freezing-thawing processes, and two other plots treated by freezing and freezing-thawing processesplus application of 20 kg ha-1 of PAM. After securing thenormality ofdata, the average net splash erosionand the average upward and downward rates of splash erosion in allexperimental treatmentswere comparedby paired sampled T-test.
Results and Discussion: According to the results of statistical analyses, the PAM application had a significant effect (p
