Evaluating the Role of Land Use in the Provision of Soil Retention Ecosystem Service (Case Study: Semnan Province)

Abstract

Introduction: Soil resources play an important role in providing the necessary material goods for humans and other organisms and also deliver multiple ecosystem services that are essential for life on earth. They have also served for a long time as an important green infrastructure in protecting agricultural and forest landscapes by providing plants a foothold for their roots and holding the necessary nutrients for their growth. In addition, soils can provide various ecosystem services such as contaminant immobilization, rainwater control, carbon sequestration, and habitat provision that are directly beneficial for humans. Services provided by ecosystems for humans are called ecosystem services. Soil retention, which refers to the potential of ecosystems for controlling soil erosion and conserving soil, is classified in the class of regulating services. Materials and Methods: The InVEST Sediment Delivery Ratio (SDR) model was used in InVEST Software to quantify soil retention and erosion. The required inputs for implementing this model include land use maps, K-factor (soil erodibility), R-factor (rain erosivity), C-factor (land use and land cover or LU/LC), P-factor (support practices), DEM (digital elevation model), and the biophysical table. Results: Based on the results, the potential of soil loss and sediment transport in the study area ranged from zero to 248.18 t/pixel and from zero to 57.25 tons per pixel, respectively. Soil retention is also estimated in a range from zero to 124.85 tons per pixel in the studied area. The largest amount of soil loss happened in sub-basin number 14 with 13716400 t/year and the smallest in sub-basin number 4 with 416594 t/year. Most of the ecosystem service of soil retention belonged to sub-basin number 13 with 4304414 t/ha/ year and the least to sub-basin number 4 with 5645 tons/ha/year. Discussion: The dense forests in the northernmost part of Semnan Province provide the most part of the ecosystem service of soil retention with more than 36 t/ha and the desert areas, the salt lake, and the salt marsh the least. Based on this, the province's forests, including dense, semi-dense, sparse and thin forests, contribute to the maintenance of soil in the province by a total of 4269166 tons per year. Also, good pastures maintain more than 18 tons per hectare of the province's soil every year, and the total function of soil maintenance by all types of pastures in the province, including good, medium and poor pastures, is 9395160 tons per year. Since the area covered by the pastures is 18 times more than that by the forests, we can say that most of the ecosystem service of soil retention is provided by the pastures due to the geographical distribution of this service in the province, despite the fact that forests are more capable in soil conservation than pastures. The orchards and rainfed agricultural land rank third and fourth, respectively, in soil retention with 7.86 and 2.15 tons of soil/ha, respectively. However, man-made land uses such as urban areas decrease this ecosystem service because they are usually accompanied by removing or reducing the vegetation. The urban areas are located in the northern part of the study area, and they have negative impacts on this ecosystem service. Therefore, protection of the forest and rangeland covers in the province is vitally important for the continued conservation of the ecosystem service of soil retention.

Keywords

• ecosystem services
• soil retention
• land use
• semnan