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Journal of Arid Land  2025, Vol. 17 Issue (11): 1576-1589    DOI: 10.1007/s40333-025-0031-9    
Research article     
Assessment of organic carbon stock and labile carbon in soils of the Gataaya Oasis, Tunisia
Noura BCHATNIA1, Manel ALLANI1,*(), Hatem IBRAHIM2, Ines BOUZRIBA1, Mohamed Amine MAAOUI1, Nadhem BRAHIM1
1University of Tunis El Manar, Faculty of Sciences of Tunis, Department of Geology, Plants Soils and Environment Laboratory, El Manar II 2092, Tunisia
2Faculty of Sciences of Bizerte, University of Carthage, Department of Earth Sciences, Plants Soils and Environment Laboratory, Jarzouna 7021, Tunisia
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Abstract  

Oasis soils in Tunisia are characterized by low soil organic carbon (SOC) stocks, primarily due to their coarse texture and intensive irrigation practices. In the Gataaya Oasis, soils receive 3.000 to 4.000 L/m2 annually through submersion irrigation, leading to a rapid decline in SOC stocks. Despite their sandy texture, which promotes good water infiltration, these soils are enriched with clay, dissolved materials, and fertilizers in deeper horizons. This study aimed to assess SOC content in the Gataaya Oasis soils, investigate the transport of labile carbon in drainage water, and clarify the destiny of this transported carbon. Soil samples were collected systematically at three depths (0-10, 10-20, and 20-30 cm), focusing on the top 30 cm depth, which is most affected by amendments. Two sampling points (P1 and P2) were selected, i.e., P1 profile near the trunk of date palms (with manure input) and P2 profile between two adjacent date palms (without manure input). Water samples were collected from drainage systems within the oasis (W1, W2, and W3) and outside the oasis (W4). A laboratory experiment simulating manure application and irrigation was conducted to complement field observations. Physical-chemical analyses revealed a significant decrease in SOC stocks with soil depths. In P1 profile, SOC stocks declined from 17.71 t/hm2 at the 0-10 cm depth to 7.80 t/hm2 at the 20-30 cm depth. In P2 profile, SOC stocks were lower, decreasing from 6.73 t/hm2 at the 0-10 cm depth to 3.57 t/hm2 at the 20-30 cm depth. Labile carbon content in drainage water increased outside the oasis, with chemical oxygen demand (COD) values rising from 73 mg/L in W1 water sample to 290 mg/L in W4 water sample, indicating cumulative leaching effects from surrounding oases. The laboratory experiment confirmed field observations, showing a decline in soil organic matter (SOM) content from 3.27% to 2.62% after 12 irrigations, highlighting the vulnerability of SOC stocks to intensive irrigation. This study underscores the low SOC stocks in the Gataaya Oasis soils and their rapid depletion under successive irrigations. The findings provide insights into the dynamics of labile carbon transport and its contribution to regional carbon cycling, offering valuable information for sustainable soil management and ecological protection in arid ecosystems.



Key wordsarid soil      carbon cycling      irrigation      leaching      soil physical-chemical characteristics     
Received: 24 March 2025      Published: 30 November 2025
Corresponding Authors: *Manel ALLANI (E-mail: manel.allani@fst.utm.tn)
Cite this article:

Noura BCHATNIA, Manel ALLANI, Hatem IBRAHIM, Ines BOUZRIBA, Mohamed Amine MAAOUI, Nadhem BRAHIM. Assessment of organic carbon stock and labile carbon in soils of the Gataaya Oasis, Tunisia. Journal of Arid Land, 2025, 17(11): 1576-1589.

URL:

http://jal.xjegi.com/10.1007/s40333-025-0031-9     OR     http://jal.xjegi.com/Y2025/V17/I11/1576

Fig. 1 Location of the study area and sampling sites. P1, profile near the trunk of date palms (with manure inputs); P2, profile between two adjacent date palms (without manure input); W1, W2, and W3 are water sample sites within the oasis; W4 is water sample site (a drainage station) outside the oasis.
Origin Type pH SOC (g/kg) TN (g/kg) TP (mg/kg) EC (mS/cm)
Goat and sheep Fresh manure 6.8 485 64.5 638.4 2.85
Table 1 Physical-chemical properties of fresh goat and sheep manure
Fig. 2 Experimental design of this study
Profile Depth (cm) Particle size (%)
Coarse sand Fine sand Coarse silt Fine silt Clay
P1 0-10 9.74±0.01c 56.89±0.03a 23.85±0.01a 8.34±0.02a 1.18±0.02a
10-20 26.20±0.01b 45.62±0.02b 20.94±0.02b 6.52±0.01b 0.74±0.01b
20-30 40.54±0.02a 44.57±0.00b 11.95±0.01c 2.61±0.01c 0.33±0.03c
P2 0-10 18.37±0.01c 61.51±0.01a 13.70±0.01a 5.60±0.01a 0.81±0.01a
10-20 29.22±0.02b 59.43±0.02a 8.34±0.03b 2.60±0.00b 0.41±0.01b
20-30 32.80±0.01a 52.30±0.00b 10.20±0.00b 4.03±0.01a 0.64±0.00a
Profile Depth (cm) CaCO3 (%) pH EC (mS/cm) BD (g/cm3)
P1 0-10 1.83±1.22a 7.21±0.08a 1.93±0.007b 0.70±0.00a
10-20 0.57±0.76b 7.21±0.06a 1.87±0.004b 0.75±0.01a
20-30 1.84±0.14a 7.16±0.08a 2.04±0.007a 0.61±0.01b
P2 0-10 0.00±0.00b 7.14±0.04a 2.78±0.013a 1.14±0.02a
10-20 0.58±0.78a 7.12±0.02a 2.49±0.004b 0.96±0.00b
20-30 0.00±0.00b 7.11±0.05a 2.26±0.011c 1.19±0.01a
Table 2 Soil physical-chemical characteristics
Profile Depth (cm) BD (g/cm3) SOM (%) SOC (%) SOC stock (t/hm2)

P1
0-10 0.70±0.00a 4.37±0.05a 2.53±0.03a 17.72±0.01a
10-20 0.75±0.01a 3.25±0.06b 1.88±0.03b 14.10±0.06b
20-30 0.61±0.01b 2.21±0.06c 1.28±0.03c 7.81±0.05c

P2
0-10 1.14±0.02a 1.02±0.02a 0.59±0.01a 6.73±0.02a
10-20 0.96±0.00b 0.66±0.02b 0.38±0.01b 3.65±0.02b
20-30 1.19±0.01a 0.52±0.03c 0.30±0.02c 3.57±0.01b
Table 3 Variations of BD, soil organic matter (SOM), soil organic carbon (SOC), and SOC stock
Fig. 3 Correlation between BD and SOC
Water sample site pH EC (mS/cm) SAR COD (mg/L) BOD (mg/L) COD:BOD ratio
W1 7.79±0.05a 8.58±0.02d 1.72±0.05c 73.0±0.04b 32.5±0.01b 2.25±0.01b
W2 7.58±0.04a 67.33±0.05b 9.77±0.03a 74.0±0.01b 26.4±0.05d 2.80±0.01b
W3 7.85±0.03a 38.18±0.02c 7.50±0.01b 83.0±0.03b 37.0±0.06c 2.24±0.01b
W4 7.58±0.03a 75.23±0.05a 1.14±0.02c 290.0±0.04a 64.5±0.02a 4.50±0.04a
Table 4 Chemical analysis of drainage water
No. SOC (%) SOM (%) EC (mS/cm) pH SAR COD (mg/L) BOD (mg/L) COD:BOD
ratio
1 1.90±0.005a 3.27±0.008a 9.79±0.834c 7.34±0.021a 1.43±0.06a 61,767±0.16a 17,800±0.06a 3.47±0.06a
2 1.79±0.027b 3.09±0.047b 4.03±0.064b 7.65±0.019a 2.14±0.10b 9167±0.11b 2070±0.05b 4.43±0.08b
3 1.79±0.011b 3.08±0.020b 3.60±0.010a 7.65±0.069a 2.09±0.07b 7033±0.17c 1808±0.06c 3.89±0.07c
4 1.75±0.021c 3.01±0.035c 3.55±0.027a 7.57±0.004a 2.14±0.07b 277±0.10d 114±0.03d 2.43±0.08d
5 1.70±0.005d 2.93±0.008d 3.59±0.090a 7.74±0.036a 2.18±0.15b 207±0.16e 111±0.05d 1.86±0.16e
6 1.63±0.005e 2.81±0.008e 3.35±0.030a 7.62±0.016a 1.98±0.32c 213±0.10e 100±0.01e 2.12±0.11f
7 1.72±0.005d 2.96±0.008d 3.23±0.062a 7.61±0.042a 1.82±0.18c 223±0.13e 88±0.01f 2.53±0.06d
8 1.65±0.009e 2.83±0.016e 3.20±0.033a 7.66±0.025a 1.50±0.04d 170±0.12f 73±0.06g 2.33±0.01d
9 1.68±0.005d 2.89±0.008d 3.30±0.004a 7.70±0.026a 1.71±0.05c 159±0.12f 64±0.01h 2.50±0.12d
10 1.71±0.005d 2.94±0.008d 3.31±0.002a 7.65±0.014a 1.70±0.13c 157±0.11f 67±0.06h 2.33±0.04d
11 1.65±0.005e 2.83±0.008e 3.35±0.016a 7.60±0.041a 1.84±0.08c 119±0.12g 58±0.02i 2.05±0.07f
12 1.52±0.005f 2.62±0.008f 3.33±0.035a 7.64±0.008a 1.82±0.05c 66±0.17h 38±0.01j 1.76±0.03e
Table 5 Chemical analysis of soil solution with the times of irrigation
Fig. 4 Correlations between chemical parameters and irrigation times
Fig. 5 Dynamics of dissolved nutrients and soluble minerals from the Gataaya Oasis to the Chott El Jerid Basin
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