Original Research
Predicting soil erosion hazard in Lattakia Governorate (W Syria)

https://doi.org/10.1016/j.ijsrc.2020.06.005Get rights and content

Abstract

The main objective of this study is to predict soil erosion in the Lattakia Governorate (W Syria) using the Water Erosion Prediction Project model (WEPP) and to compare the result with that of the RUSLE. Field survey and data collection were carried out, and 44 soil samples were analyzed. In addition, all the necessary input files were prepared for use in the WEPP model and RUSLE. Results show that more than of 80% of the locations studied experience slight to moderate erosion (less than 5 t/ha/y), whereas the rest of the locations experience severe soil erosion hazard. Moreover, the volume of runoff estimated by the WEPP model is in the range of 51–321 mm, and the R2 between the simulated soil erosion and the predicted runoff reached 0.68. Interestingly, the R2 between the WEPP model and RUSLE is 0.56, which indicates a good correlation between the two models.

Introduction

Soil erosion is a major environmental threat to sustainable land resources and crop production (de Oliveira et al., 2011; Jain & Das, 2010; Phinzi et al., 2020; Tamene et al., 2014; Tarolli & Sofia, 2016; Zhao et al., 2013). Different estimations of the impact of water soil erosion on the agricultural sector have been carried out in the past. The United Nations Environmental Program [UNEP] reported a production reduction in agricultural land of 20 million hectares to zero due to water soil erosion (UNEP, 1991). The Global Soil Partnership concluded that the amount of soil erosion by water is more than 75 billion tons per year (Borrelli et al., 2017); this significantly exceeds soil formation, which is estimated at approximately 1.5 million tons per year (Pimentel & Burgess, 2013). Moreover, Bernard and Iivari (2000) noted that the economic cost of water soil erosion with respect to agricultural land around the world is up to US$400 billion annually (Verheijen et al., 2009). Interestingly, the estimated amount of soil erosion in India is 16.4 tons per hectare annually, with an annual total loss of 5.334 billion tons, compared with 1.725 billion tons in the US. Therefore, controlling soil erosion is one of the most important environmental issues of the current millennium (Kumar et al., 2014; Pimentel & Burgess, 2013; Prasannakumar et al., 2011).

The impact of soil erosion ranges from on-site to off-site effects due to the dynamics and mechanism of the force of water, including splashing, flow detachment, deposition, and transportation of soil particles and nutrients, which affect the physical, chemical, and biological properties of the soil. Therefore, the soil depth, organic matter, and available water for crops and soil fertility will all be reduced, and pollution of natural water resources and groundwater can occur due to the use of fertilizers and herbicides (Duan et al., 2011; Lal, 1998; Lobo et al., 2005; Poesen, 2018).

In general, water soil erosion is the outcome of two basic processes. The first process involves splashing and detachment of soil aggregates by the kinetic energy of raindrops. The second process involves detachment and transportation of separate particles by surface runoff associated with other factors such as slope, vegetation cover, and soil physical properties, which cause different forms of erosion (e.g. gully, sheet, rill, inter-rill) (Lal, 2001; Poesen, 2018; Schwen et al., 2014).

Several mathematical models have been developed to simulate water soil erosion dynamics; these models are mostly based on the Universal Soil Loss Equation (Wischmeier & Smith, 1978), the Revised Soil Loss Equation (RUSLE), and the Modified Soil Loss Equation (MUSLE) (Williams, 1975). The models can be divided into the following three categories (Bhattarai & Dutta, 2007; Dutta, 2016; Singh et al., 2012):

  • 1

    Empirical models: these are based on statistical analysis of a huge amount of long-term field data. The USLE and RUSLE are examples of empirical models developed in the United States based on results of more than 10,000 plot years of data. Other examples of empirical models include the Soil Loss Estimation Model for Southern Africa (SLEMSA) (Elwell, 1981; Smith, 1999; Svorin, 2003) and the Agricultural Non-Point Source (AGNPS) model (Mtibaa et al., 2018; Young et al., 1989). However, although the RUSLE can easily be applied worldwide, some limitations have been identified such as lack of some necessary data for RUSLE calculation (Loch & Rosewell, 1992).

  • 2

    Physical-based models: these are based on knowledge of the basic processes within the laws of conservation of mass and energy, as well as on the physical understanding of the processes involved in the phenomenon. They rely on the use of differential equations, known as continuity equations, that preserve matter as it moves through space and time (inputs and outputs= loss or gain of soil). These include the Water Erosion Prediction Project model (WEPP) (Anache et al., 2018; Nearing et al., 1989), the European Soil Erosion Model (EUROSEM) (Liu et al., 2018; Morgan et al., 1998), and the Erosion/Productivity Impact Calculator (EPIC) (Williams et al., 1984)

  • 3

    Conceptual models/hybrid models: these are based on a combination of physical-based and empirical models. The Large-Scale Catchment Model (LASCAM) (Silberstein, 2006; Viney & Sivapalan, 1999) is an example of models developed to study the impact of land use and climate change on water soil erosion and water quality in the forests of southern Australia in large catchment scales.

The Mediterranean region is considered a hotspot of soil erosion, with many studies emphasizing the accelerated water soil erosion experienced in different countries in this region, such as France, Italy, Spain, Greece, Lebanon, Al-Maghrabe, Algeria, Tunisia, and Syria. Climate change (particularly variations in rainfall intensity and duration) and dramatic changes in agricultural practices in the last decades have accelerated land degradation and increased the amount of soil erosion in the Mediterranean region (Benchettouh et al., 2017; Blavet et al., 2009; Cerdà et al., 2018; de Hipt et al., 2018; Lal, 1990, 1998; Zalidis et al., 2002). Syria is a Middle Eastern country that experiences different types of erosion. The eastern region (the Syrian Badia) has a semi-arid climate with many windy storms. Overgrazing in this area results in destruction of soil aggregates and disturbance of the topsoil layer, which can cause wind erosion. The estimated soil loss by wind erosion is in the range of 40 96 t/ha/y (Masri et al., 2003, 2015). On the other hand, water soil erosion dominates in the coastal region (i.e., the Mediterranean mountains) due to deterioration and burning of vegetation cover, deforestation, high rainfall intensity, and lack of land use management.

Many studies have been conducted to measure or predict soil erosion in the Syrian coastal region (Brakat, 2017; Kbibo et al., 2017; Kbibo & Nasafi, 1997; Mohammed et al., 2016a). Most of these studies used different approaches such as field plots, WEPP model, the Coordination of Information on the Environment CORINE model, and RUSLE-GIS approach. Within this context, Kbibo et al. (2017) studied soil erosion in the western Syria (Mediterranean part) and reported that measured soil water erosion ranges between 32 ton/h/year and 165 t/ha/y in the agricultural land, while it ranges between 9 and 56.9t/ha/y in burned forest, and between 1.4 and 15 t/ha/y in forest ecosystem. Mohammed et al. (2016b) predicted accelerated soil water erosion in the western Syria between 2016 and 2039 by using WEPP model, where the average predicted erosion (regardless slope) is 14 t/ha/y. Barneveld et al. (2009) Reported that the annual soil erosion in olive orchards (25%) equal to 8 kg m−2 in NW Syria.

Recently, accelerated steps have been taken to implement national soil conservation plans in the coastal region of Syria, particularly after severe deterioration of the vegetation cover. To prepare these plans, decision-makers need suitable scientific evidence. To the best of our knowledge, the WEPP model has only been employed in one study to predict soil erosion (Ali, 2009). The significance of this work is that it provides tools for decision makers and planners to simulate and predict the best practice for land use and soil conservation, which is particularly important because more than 77% of the forest in Syria has been burnt. This study aims to provide a comprehensive understanding of the soil erosion hazard in 15 different locations in the Lattakia Governorate using the WEPP model and the RUSLE for erosion hazard assessment in Syria.

Section snippets

Study area and data collection

The study area is located in the Lattakia Governorate in north western Syria between 35° 43′ and 6.43′ to 36° 00′ E and 35° 37′ 32.08″ to 35° 29′51.98″ N, with an area of 295.6 km2 and altitudes ranging from 0 to 276 m above sea level, as shown in Fig. 1. The area is classified as a first stabilization zone (A) with annual precipitation rate exceeding 600 mm, and more than 70% of the rainfall occurs in fall and winter months. The monthly average minimum temperature is 16 °C and the monthly

Predicted soil erosion and runoff by the WEPP model

Results show that the highest amount of predicted soil erosion was obtained in Mazar Katarieh (MZ), which is characterized as a clay loam soil with 22% slope and olive cultivation as its land use category. The lowest amount was obtained in Hanadi (HA), which is a sandy loam soil with 2% slope and citrus land use. The predicted runoff exceeded 239 mm in Samandiel (SM), and the lowest amount was predicted in Hanadi (HA), as shown in Fig. 4.

In this research, we attempted to simulate different

Conclusions

The present research was conducted in the coastal zone of Syria to simulate and predict soil erosion and runoff using the WEPP model and RUSLE. Results of WEPP model show that the highest amount of predicted soil erosion was in Mazar Katarieh (MZ) where the slope is 22% and the land use is olive cultivation, whereas the lowest amount was recorded in Hanadi (HA) with 2% slope and citrus as the land use. Most of the selected locations were considered to have moderate to severe erosion when using

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

The authors grateful for Tishreen (Faculty of Agriculture-Department of Soil and Water science) and Debrecen (Institution of Land Utilization, Technology and Regional Planning) Universities for their unlimited support. Authors also thank the staff members at the Administration of Natural Resources Management, General Commission for Scientific Agricultural Research, Damascus, Syria, (GCSAR), Damascus, Syria, for their help with sample analysis.

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