Geochemical and geotechnical characterization of colluvium soils of Nanka Area, as indicators and control of gully erosion within Anambra Basin, Nigeria

Gully erosion is one of the geohazards considered to be of serious impact to our environment and capable of posing threats to human existence, properties, biodiversity, arable land and other sources of livelihood. Southeastern Nigeria is known to be vulnerable to gully erosion which has defied several interventions. Colluvial soils which contains soil organic carbon is a veritable tool for researching the intenseness of soil erosion. Therefore, the geochemical and geotechnical properties of colluvial soils from Nanka erosion sites in Anambra, Southeastern Nigeria, was used to determine parameters that influence the formation of gullies and how to mitigate it. Representative soil samples were collected from ten erosional sites. Geochemical analysis was done with an Atomic Absorption Spectrometer (AAS) to determine elemental composition and Exchangeable Base values. Physicochemical parameter tests include Bulk Density, Organic Matter Content (OMC), pH and Total Dissolve Solids (TDS). Geotechnical parameters such as Atterberg Limits, Plasticity Index were measured using appropriate laboratory procedures and apparatus. Trace elements concentration in mg/kg ranged Zn(0.02–0.10), Cu(0.02–0.07), Fe(33.24–74.49) and Mn(0.06–0.28). Effective Cation Exchangeable Capacity (cmol+/kg) ranged 2.65–15.85, while the concentration of (Ca, Mg, K and Na) ranged from 0.00% to 0.10%. pH ranged from 4.57 to 5.61, TDS ranged from 11.00ppm to 40.00ppm, and OMC ranged from 0.16% − 1.60%. Plasticity Index ranged from 15% to 22% while Bulk Density ranged from 1.35 g/cm3 to 1.75 g/cm3. The lithology comprising mainly of Sands, low Clay/Silt fractions and depleted OMC, suggest poor soil cohesion which is the bane of erosional control. Reforestation and the use of manure are recommended to mitigate adverse environmental impact.