The bioturbation effect of the snail Bellamya aeruginosa on phosphorus immobilisation by drinking water treatment residue in sediment: A long-term continuous flow test

Abstract

This study used a relatively long-term (350 d) continuous flow test to determine the bioturbation effect of a benthic macroinvertebrate (the snail Bellamya aeruginosa) on sediment internal phosphorus (P) pollution control by in-situ immobilisation using drinking water treatment residue (DWTR) as the inactivating agent. The results showed that DWTR substantially reduced P concentration in overlying water, had a limited effect on other overlying water properties, and tended to reduce nitrogen release from the sediment. Variations in overlying water properties induced by DWTR were generally not associated with snail activity or population density. However, the snails were found to promote DWTR burial and induce DWTR mixing within the sediment, indicating that bioturbation could change the distribution of P inactivating agents in sediment. The mobility of P was closely related to oxalate extractable aluminium, iron, and P (Alox, Feox, and Pox, respectively) in sediments at different depths. Typically, mobile P was stable at a relatively low level when the total content of Alox and Feox was >0.750 mmol g−1 or when the ratio of Pox to (Alox + Feox) was <0.05. Given these results, recommended practices include repeated dosing of the immobilising agents at intervals determined by the relationships among mobile P, Pox, Alox, and Feox in the sediment, especially for Al- and Fe-based agents such as DWTR. Overall, the effect of bioturbation on the stability of in-situ P immobilisation in sediment should be fully considered during long-term pollution control.