Transport of phosphorus in an alluvial gravel aquifer

Abstract

The transport of phosphorus (P) and bromide (Br) in an alluvial gravel aquifer was investigated in two tracing experiments: (1) injecting pulses of orthophosphate and (2) 10% diluted municipal effluent spiked with orthophosphate designed to simulate the leaching of P via preferential flow after the application of fertiliser or effluent on to shallow stony soils. Results indicated that compared with Br, filtered reactive P (FRP) transport was retarded, and its mass recovery relative to Br was only 6%–28%. Attenuation was probably a result of P sorption on iron (Fe) and manganese (Mn) oxides present in the aquifer media and filtration of colloidal-P. As a result, FRP could not be distinguished from background concentrations in the aquifer system when sampled 38 m from the injection site. At the concentrations/loadings used, surface water recharged from groundwater at this study site may receive P loading via the preferential flow of P into groundwater if the distance between source and recharge point is less than 38 m, and possibly at greater distances under higher loadings from intensive land use.

Keywords:

• attenuation
• groundwater
• phosphorus
• surface water
• transport

Acknowledgements

Thanks to Phil Abraham and Bronwyn Humphries ESR Ltd for expertise and assistance in the trial set up and sampling, and Nick Reed (AgResearch) and ECAN staff for sampling.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

Funding for this work was provided by Ministry of Business Innovation and Employment AgResearch Core funding contract number A20560.