Spatial Variability of Hydric Soil Properties to Delineate Khalong-la-Lithunya Wetlands

Spatial variability in wetland soils provide insight into underlying ecosystem processes and may itself give an indication of wetland condition. The study was conducted to characterise and delineate soil variability of wetlands of Khalong-la-Lithunya from hydric soil properties. Sampling was carried on three sub catchments within Khalong-la-Lithunya catchment. In each sub catchment, soil samples were dug at 100m interval along three transects that were 200m apart. Detailed soil profile description of 36 pits was done using USDA-NRCS (2010) manual. Field data included detailed description of redoximorphic features. Soil samples were collected at the depth of 0-15, 15-30, 30-45, 45-60, 60-75 and 75-90cm for determination of chemical and physical soil properties. Soil samples were analyzed for moisture content, soil organic carbon (SOC), soil organic matter (SOM), base cations (Ca2+, Mg2+, Na+, K+) and CEC, available P (Av-P), available Nitrogen (Av-N), and soil pH particle size analysis (sand, clay and silt). Mean soil properties were 3.5mg/kg Av-p, 3.0mg/kg Av-N, 28.3% SOC, pH 5.1, bulk density 0.7g/cm3 and the texture is sandy. The means base cations were 2.8, 1.8, 7.9 and 2.3cmol/kg for Na, K, Ca and Mg respectively with CEC 82.5cmol/kg included. Av-P was the most variable property with CV ranging from 115 and 162% in different soil depths while pH was the least variable with CV ranging from 6 and 12%. The Nugget/Sill ratios were less than 56%, indicating random heterogeneity. The semivariograms indicated moderate spatial dependence (25% < DSD ≤ 75%) for soil properties including SOC, Av-P, Av-N, pH in water and sand. Most properties indicate moderate spatial dependence and hence easily managed. The physical properties were least variable; however, silt and silt/clay ratio had weak spatial dependence and thus not easily managed. All soil properties were not significantly different between depths and showed inconsistent trends down the profile except for Av-N which was significantly higher at 45-60cm depth. Homogeneous profile and inconsistent trend of properties down the profile indicates the influence of biogeochemical processes that take place within the wetland. Amongst the identified hydric field indicators, Histosols (A1) and histic epipedon (A2) indicators were frequent in many profiles. The occurrence of these unique properties within the landscape is therefore used to delineate wetlands and can be used as indicators of wetland conditions. Soils were classified as Humic Dystrudepts, Typic Cryaqualfs, Histic Cryaquolls, Fibric Haplohemists, Cumilic Cryaquolls vii and Fluvaquentic Cryofibrists. There is a need for future research focusing on verifying and adding more soil indicators within the highland ecosystems to develop hydrologic criteria that will be used to further characterise soils of such highland wetlands. Facing the intensification of land-use conversion, wetlands soil management and careful land use planning are needed to take into account the spatial variability of soil properties, delineating management zones and conservation practices and other efforts to introduce conservative and protective measures to control soil erosion. Future research is needed to seek for appropriate approaches with regard to wetlands use management and more especially the grazing system of Lesotho in the highlands agro-ecological zone.