نوع مقاله : پژوهشی
نویسندگان
1 استادیار بخش تحقیقات حفاظت خاک و آبخیزداری، مرکز تحقیقات و آموزش کشاورزی و منابع طبیعی استان فارس، سازمان تحقیقات، آموزش و ترویج کشاورزی، شیراز، ایران
2 دانشیار بخش تحقیقات حفاظت خاک و آبخیزداری، مرکز تحقیقات و آموزش کشاورزی و منابع طبیعی استان فارس، سازمان تحقیقات، آموزش و ترویج کشاورزی، شیراز، ایران
3 استادیار، بخش تحقیقات خاک و آب، مرکز تحقیقات و آموزش کشاورزی و منابع طبیعی فارس، سازمان تحقیقات، آموزش و ترویج کشاورزی، شیراز، ایران
4 دانشیار، بخش تحقیقات حفاظت خاک و فرسایش، پژوهشکده حفاظت خاک و آبخیزداری، سازمان تحقیقات، آموزش و ترویج کشاورزی، تهران، ایران
چکیده
کلیدواژه‌ها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
Introduction and Goal
Marl rocks are highly porous, with porosity ranging from 73% to 95%. These formations contribute significantly to sediment production, and their physical and chemical properties play a key role in determining the intensity and type of erosion. Variations in soil texture, such as sand, silt, and clay content, strongly influence the severity of water erosion. Studies show that the sand content is highly correlated with erosion intensity, and as the sand content increases relative to silt and clay, gully erosion becomes more prevalent. In contrast, the clay ratio index is a key factor in gully erosion, while the runoff volume index is vital for surface and rill erosion in marl formations.
Significant differences have been observed in the sodium, magnesium, organic carbon content, pH, and SAR (sodium adsorption ratio) levels between different forms of erosion in marl soils, including surface, rill, and badland erosion. Marl soils are evolving materials, and their inherent properties can be enhanced through additives for various uses. The establishment of vegetation on marls is challenging due to the relationship between clay and gypsum content and plant growth. Thus, marls present significant challenges regarding land use, stabilization, construction, erosion, and sedimentation. The Maharlu watershed in Fars Province is home to extensive marl formations, which have a high potential for erosion and sediment production. Understanding the characteristics of these marls is essential for developing effective soil conservation strategies.
Materials and Methods
The Tang-e Sorkh and Bordkal watersheds, located in the Maharlu watershed to the west of Shiraz, cover an area of 500 hectares. Nearly the entire surface area of these sub-basins is covered by the Gachsaran geological formation. Using geological, topographic, and slope maps, along with field observations of erosion features, 11 marl soil samples were collected from a depth of 0–30 cm across three slope classes: less than 5%, 5–10%, and 10–20%.
Soil parameters analyzed included the electrical conductivity of the saturation extract (ECe), pH of the soil saturation paste, and concentrations of calcium, magnesium, sodium, carbonate, chloride, bicarbonate, and organic carbon. Additionally, cation exchange capacity (CEC), gypsum content, and equivalent calcium carbonate content were measured. The physical and chemical properties were analyzed using methods from the Soil and Water Research Institute. Soil particle size was determined using the hydrometer method, and soil texture was classified according to the USDA system. Statistical analysis was performed using an independent-sample t-test, analysis of variance (ANOVA), principal component analysis, and Duncan’s test using SPSS statistical software.
Results and Discussion
The results revealed significant differences in various soil properties between the two regions. The equivalent calcium carbonate content was significantly higher in Tang-e Sorkh compared to Bordkal, with a 1% level of significance. The sand content was approximately 5% higher in Bordkal than in Tang-e Sorkh. The acidity (pH) of the marl soils also differed significantly between the two sub-basins, with Tang-e Sorkh having higher acidity. The sulfate content in Bordkal was significantly higher than in Tang-e Sorkh, while bicarbonate content was also higher in Bordkal, with the difference being significant at the 5% level.
The analysis of different erosion types showed significant variations in the equivalent calcium carbonate, gypsum, acidity, and calcium content at both the 5% and 1% significance levels. For gully erosion, Tang-e Sorkh marls exhibited higher acidity, calcium carbonate, sodium, and clay content, while other variables were higher in Bordkal marls.
The organic carbon content was highest in gully erosion and lowest in sheet erosion across both watersheds. Moisture content was highest in sheet erosion and lowest in gully erosion, while bicarbonate content was higher in gully erosion compared to other erosion types. Key variables such as bicarbonate, equivalent calcium carbonate, gypsum, acidity, calcium, sand content, and the sum of silt and clay were found to be helpful in predicting the occurrence of different erosion types.
The high sodium adsorption ratio (SAR) in the marls can lead to more prominent surface and rill erosion compared to gully erosion. Increased gypsum content in the Gachsaran marl formation likely reduces the role of salinity in exacerbating erosion. Furthermore, higher calcium carbonate content contributes to greater stability in the Bordkal watershed, helping control salinity and sodium effects. The water absorption capacity of Tang-e Sorkh marls was found to be higher than that of Bordkal, which suggests a greater potential for mass erosion in Tang-e Sorkh.
Conclusion and Suggestions
The study highlights the critical role of marl characteristics in the Maharlu watershed, especially regarding erosion and sedimentation processes. To manage erosion and sediment deposition effectively, understanding the physicochemical properties of marls—such as bicarbonate, calcium, sodium ions, salinity, and the percentage of sand and clay—is essential. The influence of gypsum content on mitigating salinity’s impact on erosion, along with the effect of acidity on different erosion types, should also be considered. Incorporating these properties into watershed management plans is crucial for the success of erosion control projects.
For sediment management in the Maharlu basin, recommendations include using vegetation cover and biodegradable mulches to stabilize soils and constructing sediment retention dams. Additionally, GIS and remote sensing technologies should be employed to identify critical areas for intervention and to develop comprehensive water and soil resource management plans.
کلیدواژه‌ها [English]
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