Response of Soil Microbial Diversity to Physical and Chemical Changes Caused by Water Erosion: A Case Study of Cheheltan Forest Site, Bam County

Document Type : Research Paper

Authors

1 Rangeland and Watershed Management Department, Faculty of Water and Soil, University of Zabol

2 M.Sc. in Watershed Management, Faculty of Water and Soil, University of Zabol

10.22059/ijswr.2025.403696.670019

Abstract

Water erosion is a major factor in decreasing soil quality and fertility in arid and semi-arid ecosystems. This study examined how different levels of water erosion affect the physical, chemical, and microbial properties of soil at Cheheltan Forest Site, Bam County. Soil samples were collected at four erosion levels: no erosion, low, moderate, and severe erosion. Measurements included soil texture, bulk density, moisture, pH, organic and inorganic carbon and nitrogen, organic carbon, total nitrogen, available phosphorus and potassium, ammonium, and nitrate. Biological indicators such as catalase enzyme activity, microbial carbon and nitrogen stocks, basal microbial respiration, microbial populations, and overall soil microbial contribution were also evaluated. Results showed that as erosion severity increased, organic carbon decreased from 6.6 to 4 g kg⁻¹, total nitrogen from 0.6 to 0.3 g kg⁻¹, and available potassium from 156.3 to 83.28 mg kg⁻¹. Enzyme activity, microbial stocks, respiration, and microbial populations also declined significantly, with soil microbial contribution reaching 0.65 in severely eroded plots. Correlation analysis revealed that biological indices had positive and significant relationships with organic matter, total nitrogen, available phosphorus and potassium, and soil moisture. Conversely, sand percentage was negatively related, while clay and silt percentages showed positive relationships with microbial activity. These findings highlight that water erosion severely compromises the biological stability and function of soil ecosystems by reducing organic matter and nutrients and altering soil texture. Sustainable soil management is crucial to preserve soil fertility and ecological functions in these regions.

Keywords

Main Subjects

Introduction

Water erosion is particularly severe in arid and semi-arid regions, such as the Chehelton area in Bam city, due to irregular rainfall, steep slopes, and limited vegetation cover. This process significantly alters the physical and chemical properties of the soil by reducing soil depth, decreasing fertility, and transporting nutrients downstream. These changes include a reduction in organic matter, an increase in bulk density, and diminished nutrient availability. Given the high susceptibility of the Chehelton region to water erosion and the scarcity of studies on its natural soils, it is essential to investigate the effects of varying erosion intensities on the soil's physical, chemical, and biological properties. This study aims to analyze changes in soil aggregate stability, organic matter content, nutrient levels, and microbial communities resulting from erosion, in order to elucidate the relationships between soil properties and microbial responses. The findings will provide a scientific foundation for sustainable soil management and the enhancement of ecosystem function in arid and semi-arid areas. The primary hypothesis is that increasing erosion intensity will lead to reduced soil stability, loss of organic carbon, and decreased microbial diversity and activity.

Method

The study was conducted in the Dehbakari watershed, southeast of Bam city, with a semi-arid climate and an altitude of 1951 to 3168 m. The Chehelton forest site was selected as the focus of water erosion, and two working units with similar vegetation cover and a northern slope were identified using digital elevation model and GIS. Random sampling was carried out in two 100-m transects and four erosion intensities (no erosion, low, medium, severe) were investigated in each transect, so that a total of 24 plots and three soil samples were collected from a depth of 0 to 30 cm. The samples were stored for microbial analysis while maintaining the initial moisture content and were prepared for the evaluation of physical and chemical properties after drying. Physicochemical properties included texture, bulk density, moisture, pH, total and inorganic carbon and nitrogen, available phosphorus and potassium, ammonium and nitrate. Microbial indices included catalase enzyme activity, microbial biomass carbon and nitrogen, basal respiration, microbial population and soil microbial fraction were measured. Data were analyzed by one-way analysis of variance and Duncan test at 95% confidence level to investigate the effect of water erosion intensity on soil physical, chemical and microbial properties.

Results

Data analysis showed that water erosion intensity has a significant effect on soil physical, chemical and microbial properties. With increasing erosion intensity, the percentage of sand increased and the amounts of silt and clay decreased, indicating a decrease in soil cohesion and an increase in its sensitivity to movement and erosion. The results showed that with increasing erosion intensity, organic carbon decreased from 6.6 to 4 g kg⁻¹, total nitrogen from 0.6 to 0.3 g kg⁻¹, and available potassium from 156.3 to 28.83 mg kg⁻¹. Enzyme activity, microbial stocks, respiration, and microbial population also decreased significantly, and the soil microbial contribution in severe erosion plots reached 0.65. This indicates a decrease in nutrients and soil capacity to support biological activity. Correlation and PCA analysis showed that organic matter, nutrients, and soil texture are the main factors of biological stability, and the first two components explained more than 98% of the changes caused by erosion. These findings emphasize that water erosion significantly reduces soil biological capacity and fertility by destroying structure, reducing nutrients, and changing environmental conditions.

Conclusions

The present study demonstrates that soil erosion has extensive and multidimensional effects on the physical, chemical, and microbial properties of soil. Increasing erosion intensity alters soil texture by increasing the sand fraction while decreasing silt and clay content, reducing moisture levels, and increasing bulk density, all of which severely degrade the soil's physical quality. Concurrently, the selective removal of topsoil—rich in organic matter and nutrients—leads to declines in organic carbon, total nitrogen, available phosphorus, and potassium, thereby diminishing the soil's capacity to support biological activity and nutrient cycling. Soil biological indicators, including enzyme activity, microbial biomass, basal microbial respiration, and microbial population, are significantly impacted by erosion. The reduction of food resources and organic matter decreases microbial diversity and functionality, limiting the soil's ability to sequester carbon and sustain ecosystem functions. These findings suggest that soil erosion is a multifaceted, cyclical process that simultaneously disrupts the physical, chemical, and biological properties of the soil, ultimately reducing the performance of ecosystems. Therefore, implementing conservation and management strategies, identifying high-risk areas, and restoring degraded soils are essential to maintaining long-term soil quality and ecosystem performance. Future research should focus on the role of microbial species in response to erosion and their contributions to carbon and nutrient sequestration to inform optimal, science-based conservation strategies.

Author Contributions

Conceptualization, Morteza Saberi; methodology, Morteza Saberi and Mostafa Nori; Software and validation, Morteza Saberi; Investigation and resources, Mostafa Nori; data curation, Morteza Saberi; writing- original draft preparation, Morteza Saberi and Mostafa Nori; writing-review and editing, Morteza Saberi; visualization Mostafa Nori; supervision, project administration and funding acquisition, Morteza Saberi. All authors have read and agreed to the published version of the manuscript. All authors contributed equally to the conceptualization of the article and writing of the original and subsequent drafts.

Data Availability Statement

Data available on request from the authors.

Acknowledgements

The authors gratefully acknowledge the financial support of the University of Zabol (Grant code: IR-UOZ-GR-8721) for conducting this research.

Ethical considerations

The authors avoided data fabrication, falsification, plagiarism, and misconduct. The study involved only soil sampling and laboratory analysis, without any interaction with humans or animals; hence, ethical approval was not applicable

Conflict of interest

The author declares no conflict of interest. 

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Iranian Journal of Soil and Water Research
Volume 56, Issue 11
January 2026
Pages 3027-3046

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