Erodibility and loss of marly drived soils

Received : 02.03.2015 Accepted : 01.05.2015 Considering to high distribution of the marly lands in west Azerbaijan province and high sediment yield of such lands, in this research, the relation among the form and the rate of erosion on marls with their erodibility properties were studied. Therefore, marly regions of province with the special properties were recognized and the soils samples were taken from 15 points of the topsoil of this area. Soil erodibility indices were determined and analyzed by statistical methods considering the form and rate of erosion. Also portable rain simulator were used to study of the runoff and sediment yield potential of such soils. Finally the factors affected the soil erodibility were determined by variance analysis. Results showed erosion rate could be classified as moderate. Gully erosion had highest number in Gare-Agaj and Gare-tappe areas whereas rill erosion had high number in all area of marly lands. Surface runoff volume ranged between 255 to 577 cm3 in Shabanlu region and surface runoff coefficient varied from 0.23 to 0.53 in Gare-tappe. Maximum turbidity yield was determined 180 gr/lit in Gare-Agaj area. It was found that the clay ratio played the important role (P≤0.05) in creating the gully erosion and the volume of runoff in the surface and rill erosion.


Introduction
Marly soils are very sensitive to erosion and considered one of the most important sources of sedimentations in catchments (Bouma and Imeson, 2000;Jafari Ardekani, 2002).Marl is a mixture of clay and calcium carbonate.Its carbon content is between 35 to 65% and occurs during the weathering and erosion of other rocks.Marl also contains high amounts of the silt (Feiznia et al., 2007).The deposition of fine particles is become so dense by the erosion, and a new rock is created.The type of this new rock is depending on the material of eroded rock.The term of the Marl generally used to describe the marine sediments in North America (Schnurrenberger et al., 2003).One of the inhibitor factors of the environmental behavior of marl is its chemical properties (Abdi Nejad et al., 2011).Due to the great spread of the marl rock in many countries, the study of the characteristics of these formations is essential (Hooshmad et al., 2012).Feiznia et al. (2003) determined the resistance of different formations to erosion in semi-humid to humid and semi-arid to arid climates.They reported that the red upper and lower formations show the greatest sensitivity to erosion.The emergence of various forms of erosion is one of the characteristics of the marl areas (Ismail Nejad et al., 2007).The clay and the sand are effective parameters in determination of the sensitivity of the marly derived soils to erosion (Smaeilzadeh, 2002;Gadimi Aroose Mahaleh et al., 1999).Thoms et al., (2004) reported that marly lands with high erodibility, are the origin of sediment yield in arid areas.Cerda (2002) used a portable rainfall simulator and a double cylinder to determined runoff volume.He indicated that water runoff is occurred sooner on the marl with low permeability and high runoff coefficient.In the Clay and sandy soils, the start of the runoff is delayed and erosion and sediment yield will be in the lower than marl in such soils.Hamidzade (2000), determined sheet, rill and bad-land erosions as the erosion forms of marly soils of some areas of Iran.He repoted that the marly soils have high sodium adsorption ratio and the gully erosion has further development in such areas.According to Thoms et al. (2004), different forms of soil erosion, especially bad-land erosion is one of the outstanding features in the marly areas.Esteves et al. (2005) investigated the hydraulic properties of the gullies that were created on marly soils.He concluded that due to the structure and type of the clay minerals in the marl, the hydraulic conductivity coefficient is very low in such soils.In addition, when the marly soil is saturated with water the hydraulic conductivity coefficient will be negligible.The erodibility of marly soils is different and these factors can influence the form and intensity of the erosion.Therefore, the sensitivity to erosion and sediment yield from Miocene and Neogene marls of northern areas of west Azerbaijan province was investigated in this study.The runoff and sedimentation were determined by using portable rainfall simulator.The erosion rate was measured by the Bureau of Land Management (BLM) of US method.The sensitivity to erosion determined by using the clay ratio and the erodibility indexes.The survey was conducted for the first time in this area.

Material and Methods
The study area is located in the northern part of West Azerbaijan province extends from the 38° 58' -39° 47' north latitudes to the eastern 44° 14' -46° 16' longitudes (Figure 1).Most of the area is mountainous at an altitude ranging from 800 to 4000 meters above the sea level.The marly lands within rock type were identified by using a digital geological map at 1: 100000 scale.After sampling the surface soil (0-30 cm) in 15 areas, the analysis consisted of determining the percentage of sand, silt, clay and very fine sand, organic matter, soil structure and permeability were conducted by the conventional methods of Soil and Water Research Institute (NSSH, 2006).The analyses were repeated in 3 replications and in total, 45 experiments were conducted on the rill, gully and surface erosion.The erosion rate of the selected marly soils was measured by the BLM method.The erosion class was determined by PSIAC method.Then the erodibility indexes (K) were determined by the global erosion formula (Wischmeier and Smith, 1978).The clay ratio was measured by Islami et al. (2007) method.The surface runoff, sediment and turbidity yield was measured by using the rainfall simulator.The rainfall simulator was made up of rain sprayer, body and metal frame (Figure 2).The capacity of the rainfall simulator tank was 1.2 liters with 49 pores.Its dimensions were 25 × 25 cm.The bottom of the body of the rainfall simulator had 20% vertical slope.This device sprayed 18 mm/3 min of water in on the plot.The rainfall intensity was 6 mm/min by this machine (Islam et al., 2007).The relationships between erodibility indices, the clay ratio, intensity and forms of erosion, runoff, and sedimentation yield of marly derived soils were determined by a correlation matrix of measured data.Then the erodibility index and clay ratio of marly soils were analyzed based on Duncan's method.According to the results of field studies, three types of marls were identified in study area.They are the Oligomiocene marls with conglomerate, sandstone, marl and shale, Neogene marls with red sandstone and red marl with conglomerate layers, and sandstones alternating with red to gray marls known as Upper Red Formation.The distribution of marls in study area is given in Figure 3.Some of the physical, chemical and geological properties of the soils are given in Table 1.According to the results of the soil analyzes, the texture of the most of the soils was silty clay loam that contain relatively high amounts of silt.However, the clay content of the samples was high (19 to 41 %).The Lime and salinity contents of the soils were determined ranging 3-23% and 0.3-4.3dS/m, respectively (Table 1).

Erosion
The erosion rate in field experiments was estimated according to BLM method.The results are given in Table 2.The results showed that the erosion rates are between 31 and 54 and classified in moderate level.The gully erosion has higher rate in GT and GA.However, the surface erosion also has higher rate in GA and SL2 areas.High rates of rill erosion were observed in all areas.According to Table 2, all forms of soil erosion with different intensity are obvious in study area.The surface erosion with moderate intensity, the rill erosion with linear shape and generally high intensity and the gully erosion frequently occurred in claw form (Figure 4).The rill and gully erosion were the dominant erosion forms of the Oligomiocene and Upper Red Formation marls, respectively.All forms of erosions were observed on Neogene marls (Table 2).

Sandstones alternating with red to gray marls known as Upper Red Formation
The Soil Loss The runoff volume, sediment and runoff coefficient of each treatment and replicates and the mean of these values are given in Table 3 Table 4, respectively.The surface runoff volume values varied from 255 to 577 cm 3 by using the rainfall simulator, in Shabanlu (SL) and Gare Tappe (GT), respectively (Table 3).The runoff coefficient was calculated by subtracting the volume of water in the tank of the rainfall simulator and the volume of water by surface runoff.These values were rated between 0.23 and 0.53 in the same areas, respectively (Table 3).The highest and lowest tubidity yield values were determined 180 and 10 gr/lit in the GA and GT regions respectively (Table 3).The Clay Ratio and Erodibility Index The clay ratio was calculated by the division of the sum of the percentages of silt and sand values to clay in soil texture class.These values varied between 9.6 and 26.3 in the GT and CL, respectively (Table 5).The mean of the clay ratio of these soils was determined 15.4.Wischmeier erodibility index were determined with the silt plus very fine sand, organic matter, sand percent, soil structure and permeability factors by using Wischmeier nemograph.Wischmeier erodibility index varied between 0.33 and 0.54.These values were obtained in CL, GA and SL, respectively (Table 5).

The Relationship between the K (Erosion Index) and Clay Ratio with the Erosion Forms
According to the correlation matrix results, the relationship between K (erosion index) and silt and clay, and the relationship between clay ratio and sand and silt, values was significant (P≤ 0.05).On the other hand, The significant difference (P≤ 0.05) were observed between sand, silt, runoff volume and the clay ratio with erosion forms.But there were no significant difference between surface and gully erosion and between rill and gully erosion forms.The results of the correlation matrix also showed the significant difference between the clay ratio and erosion forms (P≤ 0.05).There was no significant difference between K (erosion index) and erosion forms.This might be related to the functional nature of the rainfall simulator that is designed primarily for surface erosion size but it can be used in the calculation of runoff and sediment yield.

The Relationships between the Erodibility Index, Soil Loss and Clay Ratio
Comparing the results of the assessment of soil loss by BLM (Table 2) with K (the erodibility index) and clay ratio indicated that, there was the significant difference (P≤ 0.05), between the clay content and K (the erodibility index) with soil loss.According to Table (3) there was a significant relationship (with correlation coefficient: 0.97 and SE: 0.028) between the clay ratio and the runoff volume (Equation 1).
(Equation 1) Where Wv= The runoff volume CR= The clay ratio Based on the results, according to erodibility index, the marls can be classified in the three groups with significantly different between them.
The first group was appointed to the Neogene marl soils, includes the erosion values to 41 points, by BLM method.The Second and third groups are belongs to the Oligomiocene marl soils and the Upper Red Formation with the erosion values points to 50 and more than 54, respectively (Table 3).The erosion rates significantly increased with increasing erodibility index (listed in columns 1, 2 and 3 of Table 6).Likewise, according to clay ratio the marls can be classified in the two main groups (Table 4).The first group includes the erosion values to 50 points and the second includes the erosion values more than 50 points by BLM method.The erosion rates significantly increased with increasing the clay ratio (listed in columns 1, 2 and 3 of Table 6).

Conclusion
In this study, the mean of the sediment yield of the marly soils was 4.96 ton/ha, by using the rainfall simulator.This result corresponded to the results of the investigation of Feiznia et al. (2003), Ismailnajad et al. (2007), Creda (2002) and Hamidzade (2002) on the erosion intensity and forms of the marly soils.The runoff coefficient (to 0.53) in this research showed that the runoff intensity is high in the study area.These outcomes are expectable according to the results of the investigation of Creda (2002) and Hassanzadeh et al. (2008) reported that the same results in runoff coefficient of the marly soils.In this investigation, the Wischmeier erodibility indices and the clay ratio varied from 0.33-0.54and 0.09-0.26,respectively.These result showed that the erosion intensity of the marly soils is moderate to high in study area.Meanwhile, in this study the marly soils were studied in relation to the type of geological formation and erodibilty which were not studied in previous researches.The Upper Red Formation marly soils had the highest erosion rate and Oligomiocene and Neogene formations, were in the later stages in the erodobility.

Figure1.
Figure1.The geographic location of the study area in West Azerbaijan province Figure 2. Vertical sections of the rainfall simulator

Figure 3 .
Figure 3.The distribution of marls in the study area

Figure 4 -
Figure 4-The erosion forms of the SL area with the Neogene marls with red sandstone and red marl with conglomerate layers lithology

Table 1 .
Some of the physical, chemical and geological properties of the marley soils in study area

Table 2 .
The determination of the erosion rate by BLM method

Table 3
. The Results of the runoff volume, sediment and runoff coefficient of each treatments and replicates by using the rainfall simulator

Table 4 .
The Mean values of the coefficient and volume of the runoff and sediment yield with the rainfall simulator in different places of the study area

Table 5 .
The erosion forms and intensity by modified MPSIAC method and erodibility index of the studied soils

Table 6 -
The Classification of the homogenous groups of the marl soils according to the index k by Duncan