Spatial Variation in Surface Soil Total Carbon and Its Relationship with Soil Color in a River Floodplain Ecosystem of Northern Ghana

抄録

In this study, we aimed to identify the factors underlying the spatial variation of total carbon (TC) and its relationships with soil color parameters in the surface soil (0 to 15 cm in depth) of the White Volta River floodplain in northern Ghana. The 75 soil samples collected in 2014 from an area of about 3 km × 4 km in this floodplain showed a large variation in TC content (4.1-40.1 g kg⁻¹), and to cover this variation, 63 soil samples were additionally collected from two line transects (1419 and 1177 m long), across the same floodplain in 2015. TC content in these two transects ranged from 3.7 to 54.9 g kg⁻¹, and most of the carbon (> 75.9%) was in the heavy fraction (> 1.6 g cm⁻³) of the soil in 2014. Soil TC content was significantly correlated with clay content and soil moisture content (r = 0.87 and 0.84, respectively; P < 0.001 for each) in 2015. Soil TC content decreased exponentially with the increase in downward gradient (R² = 0.41; P < 0.001) in 2015. Sloped areas, where the downward gradient was larger than 0.3%, had low soil TC content (ranging from 3.7 to 20.2 g kg⁻¹ with a mean of 10.0 g kg⁻¹), while the other locations had high soil TC content (ranging from 5.5 to 54.9 g kg⁻¹ with a mean of 26.1 g kg⁻¹) in 2015. Soil moisture content and clay content decreased exponentially with the increase in downward gradient (R² = 0.39 and 0.43, respectively; P < 0.001 for each) in 2015. Chromaticity values of soil color such as a*, b*, and C* decreased exponentially with the increase in soil TC content (R² = 0.68, 0.63, and 0.65, respectively; P < 0.001 for each), and would be better indices for the estimation of TC than the lightness of soil color (L*, R² = 0.32; P < 0.001) in the studied floodplain.