كليدواژه :
فرسايش خندقي , ويژگي ها فيزيكي و شيميايي خاك , مقادير (SAR,EC,PH)
چكيده لاتين :
Introduction
Gully erosion is one of the erosive processes that mostly contributes to shape of the
earth surface. The development of gullies causes the loss of a great amount of
soil and can be considered as one of the principal causes of geoenvironmental
degradation in eastern shores of Urmia Lake. Soil erosion by water is
considered one of the major causes of land degradation in a wide range of
environments. There are three types of water induced soil erosion: Sheet, rill and
gully erosion. Gully erosion begins when runoff concentrates into channels, and
results in the development of rills that enlarge into deep trenches on land surface
over time. Gully erosion in one of the different types of soil erosion by water that
initiation and advancement of it can tend to the great changes on landscape, degrade
the lands and deteriorate the environment. Gullies occur when a geomorphologic
threshold is exceeded due to an increase in water flow erosivity and/or sediment
erodibility. According to the Hungarian classification gully erosion is one of the
processes of linear erosion. A gully is usually defined as a deep channel eroded by concentrated flow of water, removing upland soil and parent material, that is too big
to be obliterated by normal tillage operations. The greatest threat to the
environmental settings of east Urmia Lake plain is the gradual but constant dissection
of the landscape by soil erosion by water. The aim of this study was the analysis of
effective factors on creating and advancement of gully erosion.
Matherials and Methods
Study area is located in north west Iran within the East Azerbaijan Province and the
city of Osku, a very small area at coordinates 37 degrees 51 minutes 30 seconds
latitudes and 47 degrees 50 minutes 30 seconds longitudes on the size of 2 to 4 km.
Average height of area is 1282, an area without topography and very low slope
toward Urmia Lake.
In this research we used amounts of electrical conductivity (EC), sodium adsorption
ratio (SAR), PH of soil type for analysis of effective factors on creating gully erosion
and climatology index, humidity index in regional formations for analysis of creating
potential of gully. In order to measure soil chemical and physical parameters, 4
samples of combined soil separately were taken from 10 introducing gullies inside
gullies. Then selected samples were transmitted to Soil Mechanics Laboratory,
College of Agriculture (Soil Science) University of Urmia, and then parameters of soil
(clay, silt and sand) were measured through hydrometer method. Soil samples were
analyzed for Ca, Mg and Na and sodium absorption ratio (SAR). The electrical
conductivity (EC) of the samples was measured by Electro Conductometer Method
(Shahrivar et al, 2012). and soil reaction with PH meter.
Both EC and SAR are commonly used to classify salt-affected soils. Waskom et al.
(2006) classified all soils in 3 groups, In this classification, EC= 4.0 dS/m and SAR ~ 13
have been used as the threshold of EC and SARto define saline, sodic and saline-sodic
soils. Humidity coefficient was obtained using climate factors for identifying gully potential
of area. It is in this way that if the rate of existing humidity is decreased on surface
structures means reduction of absorbable humidity of plants' root. As a result plants
cannot use trivial sticking humidity to soil particles (hygroscope humidity) and are
withered. Alternate warm and dry seasons cause in warm seasons with land drought
and withering vegetation, some cracks are created in level of fine formations and
these cracks become the place for watercourses concentration and creation of gully
and rill erosion at the time of first sudden rainfalls. Human actions (Plow, fire, bushes,
overgrazing of the area) cause misbalancing of nature especially in warm seasons
(months which becomes Ws), therefore, reduction or negativism of Ws gets
importance when after one period of drought among rainfalls as well as misbalancing
of earth, the first raining starts.
Discussion and Conclusion
Based on values (EC, SAR) the type of area soil is sodium salty that sodium salty soils
have more destructive effects than salty soils and sodium salts. The risk of
desertification in area considering the desertification index of Christos et al (2010) is
very high, the value of electrical conductivity of area soils is very high that requires
serious attention and doing necessary actions. Area's soils have the necessary
threshold for linear erosion (piping, rill and gully} based on (EC= 0.1 and PH= 5.9}.
Therefore considering criteria and various scientists categorizing, area's soils have
high potential in order to expand gully erosion in case of providing other conditions.
The texture of study gullies soils are mainly silt loam being dominant in all gullies.
Based on this, one of the advancing factors longitudinal and cross of study gullies is
the presence of silt (because of high sensitivity to erosion) in layers and different
horizons of area's soils with increasing the rate of silt, the erosion intensively
increases because of the susceptibility of the clay particles (2 to 5 microns} (Rangavar, 2009}. The resistance of silt particles against erosion is relatively low in terms of
either measure or stickiness. Silt soils are usually seeded well but because of being
humid, aggregates are easily broken and silt particles are separated and transmitted.
As water content increases in soil, clay and silt become softer, shifting from a solid to
a plastic state, and eventually to a liquid state once the soil fails to retain its shape.
Analyzing the results of WS index shows that except month Jan, in the rest of year WS
index is negative. Months of the year which have negative humidity fluctuation are
prepared for gully erosion therefore based on the results of study area, in whole
year; humid fluctuation of soil is prepared for gully erosion; that is, it happens in case
of intense rainfall or showers in the area of soil erosion. Hence area's climate
conditions are very susceptible for creating gully erosion.
Conclusion
·The results of analyzing the texture of selected samples showed that consisting
components of geology structures being fine has provided very appropriate
conditions for vertical and horizontal leveling of gullies because of weak building of
aggregates in a way of monitoring. The results of climate indexes include existing
wetness in formations of area represent high potential of area for creating gullying in
area.
Analysis of texture selective samples indicated fine particles of geological formations
because of the weak structure of aggregates have provided suitable conditions for
Longitudinal and latitudinal development of gully. The high concentration of soluble
salts In particular, high levels {EC and SAR} have caused dissolution erosion and piping
erosion. Results indicated that creating of Gully erosion in area is impressed from two
factors: 1. Climatic factors that create runoff and change in permeability rate 2.
Physical and chemical characteristics of area soil.
