Assessment of soil physical properties and shallow groundwater recharge in the Ashanti region of Ghana

Sammanfattning

This study projected shallow groundwater recharge processes in the sub-humid, agroforestry dominated Mankran watershed based on assessment of soil physical properties and application of the Chloride Mass Balance (CMB) and Water Table Fluctuation (WTF) methods. The objective was to enhance understanding of groundwater recharge in a tropical, cocoa forest dominated landscape with diverse land use and soil properties. Soil samples from 0 – 40 cm were analysed for texture, pH, organic matter content and bulk density. Additionally, topsoil field-saturated hydraulic conductivity (Kfs) was measured with single ring infiltrometers. The results revealed significant spatial variability with high sand contents ranging from ca. 60 – 80 % and near-neutral pH associated with higher infiltration rates, particularly in cocoa fields (120 – 200 mm h-1). During the study period of June 2023 – July 2024, shallow groundwater recharge rates estimated by the CMB method ranged from ca. 12 – 34 % (144 – 408 mm) of about 1200 mm rainfall, whereas the WTF method often produced higher and potentially overestimated rates. The findings pointed out the complexity of groundwater recharge processes and the necessity of applying multiple estimation methods for accurate assessment. Despite limitations in soil sampling and method applicability, the study provided valuable data enlarging sparse soil data basis while simultaneously giving insights into the hydrological dynamics of the Mankran watershed. These insights promote more informed, sustainable land use and agricultural management practices in the region, highlighting the importance of comprehensive soil and water data collection.