Evaluation of water table dynamics for sustainable cultivation in wetlands

Sustainable management of wetlands for cultivation calls for a thorough knowledge of factors that influence wetlands hydrodynamics. The use of the geographical information system led to an accurate assessment and prediction of water dynamics in wetlands. Rainfall, evapotranspiration and field elevation are major factors of importance influencing water table changes and soil moisture in wetlands. A survey of a non-tidal wetland in south western Nigeria showed that the mean depth to water table ranged between 0 cm (ground surface) and 92 cm (maximum depth). A total of 686.0 and 852.6 mm of rainfall and potential evapotranspiration, respectively, were recorded with the period of low water table. The impacts of these factors on the depth to water table among the observation wells were found to be significant at p < 0.05. Sustainable cultivation of wetlands is feasible during the period with potential evapotranspiration > rainfall because there is movement of moisture from the saturated to the unsaturated soil zones. Variation in available moisture across the field was influenced by field elevation and groundwater fluxes from saturated to unsaturated zone. Even though there may be no water table recharge during the period of agricultural drought, the soil available moisture was found to be high (ranging between 0.20 and 0.50 m(3)m(-3)) and sufficient for crop water supply without supplemental irrigation in the non-tidal wetland.