Biological Management of Soil Erosion (Case Study: Gavoshan Watershed, Kermanshah Province, Iran)

One of the most important causes of land degradation and reduced fertility is soil erosion, a severe threat to human welfare and food security. With the intensification of erosion and sediment transport in the watershed, water quality is reduced, and sediment production and flood risks are increased. The consequences of soil impoverishment cause irreparable damage, including the abandonment of farms, increased migration, economic, social, and political problems. In this regard, paying attention to soil and water resources conservation is one of the most necessary measures to control erosion. So that the performance of natural ecosystems increases through conserving the soil and preventing the occurrence and intensification of erosion. Therefore, it is essential to know different stages of erosion and evaluation of the factors governing it in properly managing soil and water resources in a watershed. So far, various biological methods and structures are used to control soil and runoff loss in watersheds. Since biological methods are based on ecosystems' conditions, it is essential to control soil erosion in the early stages. In recent years, extensive methods for the conservation of soil and water resources have been introduced and used in practice. Therefore, one of the most important methods of protecting soil and water resources is the use of biological methods in terms of low use of tillage operations, limited intervention, and manipulation in nature, cost-effectiveness, and also better efficiency than structural measures. However, the biological management of soil erosion has not yet been welcomed by executive experts due to the lack of a proper implementation model.

The present study was conducted to investigate biological erosion management in the Gavoshan Watershed, Iran, due to distributed and manageable erosion and the available information. The Gavoshan Watershed, with an area of 7736 ha, the mean annual precipitation of 339 mm, the minimum and maximum elevations of 1635, and 2455 meters above sea level, is located in Kermanshah Province. After determining the erosion status, climatic characteristics, and plant growth conditions, the executive procedure of biological management of the region was proposed.

The results showed that surface erosion is predominant in the area, and therefore the suitability of the conditions for bio-management measures was confirmed. While reporting the prevalence of sheet erosion, the results emphasized the erosion status in the low and moderate classes and the ability to perform biological approaches in the watershed based on the climatic-agricultural map. The results further showed that according to the climatic-agricultural map, the whole study watershed was divided into five categories. In this regard, the second category with an area of 3421 ha had the highest, and the fifth category with 82 ha had the lowest areas. Finally, after determining the area of different land-uses and according to the maps of soil erosion and climatic-agricultural conditions as well as ombrothermic and hetherograph diagrams, suitable rangeland species were selected and suggested for each climatic-agricultural category based on the expected characteristics of elevation, precipitation, temperature, phenology and adequate role in soil conservation. Finally, the executive plan of biological management of soil erosion in the Gavoshan Watershed was presented based on phytosociology and relevant ecological expectations. Since bio-management measures are applicable in rangelands with moderate and poor vegetation conditions, the good rangelands were not prioritized for the planning. Accordingly, moderate and weak rangelands with an area of about 4219 ha, i.e.> 54%, of the watershed were considered for biological activities. It is expected that by taking biological measures, erosion control will be done in the early stages, and by increasing the vegetation level in 54.63% of the watershed, in addition to controlling soil erosion or at least stopping it in the early stages, carbon sequestration conditions, nitrogen fixation, and increase soil fertility. The use of endemic species in this watershed would facilitate ecological balance and at the same time protect the basic resources of water, soil, and vegetation by increasing the level of ground cover.

Biological management is a new approach in soil and water resource sustainable management that inhibits soil loss in the early stages of erosion and prevents the destruction of ecosystems. The results of the present study are anticipated to meet the expected needs in the protection of soil and water resources in similar watersheds in the west of the country. The results of the present study can be used in soil and water resources management in the western regions of the country with similar ecological conditions. Although the proposed approach can be used in most parts of the country rangelands, appropriate field studies and continuous monitoring of the proposed function will be necessary to provide comprehensive and integrated conclusions for soil and water resources management.