Comparative study of physico-chemical characteristics of some on-farm research ponds, Ethiopia
Changes in nutrient composition of four on farm research fish ponds measuring 100m2 in area and 1.5m depth and located on the North Eastern range of the Ethiopian highlands were studied in the wet season of 2008. The ponds stocked with Oreochromis niloticus were categorized according to their sources of water; subsurface and surface waters and the study was aimed at investigating differences in physico-chemical characteristics and nutrient composition of the ponds. Results showed that conductivity, total hardness, nitrate and ammonium were remarkably high in the subsurface water sourced ponds while temperature, turbidity, chloride, dissolved oxygen concentration and nitrite were high in the surface water sourced ponds. Higher turbidity in the ponds with water replenishment from surface water did not result in higher ionic concentrations and highly significant correlation between two nitrogen species (nitrate and ammonium) and dissolved oxygen in subsurface water ponds reinforced the overriding effect of management practices adopted by the farmers (which may include use of organic fertilizers and animal dung) rather than water source related factors in influencing the nutrient composition and material budget of the pond.
Key words: Physico-chemical properties, surface and subsurface water, fish ponds