Distribution of soil organic carbon in Wadi Al-Thulaima, Saudi Arabia: A hyper-arid habitat altered by wastewater reuse

The carbon cycle is being altered as a result of human-induced changes in the Earth's system. Therefore, ecosystems such as wetlands, authentic CO2 sinks, are becoming especially important. Little information exits on the soil organic carbon (SOC) stock for the middle east-countries man-made wetlands making wadis permanent with the outflow of wastewater treatment plants. This paper presents the vertical distribution of SOC content, soil bulk density (SBD) and SOC density in soil of vegetated and bare sites in Wadi Al-Thulaima, one of the artificial wetlands in central Saudi Arabia. The mean distribution of SBD in the vegetated and bare sites increased significantly with depth. Inversely, the SOC content declined significantly with depth, from 17.1 g C kg−1 at 0-3 cm depth to 3.3 g C kg−1 at 15-18 cm depth in vegetated sites and from 4.7 g C kg−1 at 0-3 cm depth to 0.7 g C kg−1 at the 15-18 cm depth in bared sites. Vegetation significantly affected the SOC pool, the total mean SOC pool of the vegetated sites (2.0 kg C m−2) was higher than that of the bare sites (0.5 kg C m−2). Therefore, arid regions could contribute to carbon sequestration with appropriate management, which would result in the enhancement of soil quality.