Effects of light regime and oxygen profile on transformation of oxolinic acid in pond sediment

This study investigated the effects of light (visible light - 5800 lux, 24 h) or dark regime and aerobic or anaerobic condition on the decay of added oxolinic acid (OA) at 5, 10 and 20 mg L−1 in eel pond sediment. An asymptotic decaying exponential model Ct = Cmin + Co × exp (−k × t) was used to facilitate quantitative approach to OA transformation, where Ct is the concentration of OA after t days, Cmin the estimated level-off concentration of OA residue, Co the concentration of added OA and k the decaying coefficient. OA decayed faster under light (Cmin = 4.6 mg L−1) than under dark (Cmin = 7.8 mg L−1) and also decayed faster under aerobic (Cmin = 4.0 mg L−1) than under anaerobic condition (Cmin = 8.5 mg L−1). Cmin increased with Co. Sundrying and tilling eel pond bottom should be able to reduce OA residue significantly.