The content and storage of phosphorus in fine-grained channel bed sediment in contrasting lowland agricultural catchments in the UK

Deposition and storage of fine sediment on channel beds can represent an important component of catchment sediment budgets and can therefore have implications for particulate phosphorus (PP) transfers. Accordingly, spatial and temporal variations in the phosphorus (P) content of fine (< 63 μm) bed sediment and associated P storage have been studied in three UK lowland permeable catchments, the Pang and Lambourn (Berkshire) and the Tern (Shropshire). These catchments were chosen because of their contrasting geologies. Fine bed sediment was sampled in representative reaches on a bi-monthly basis using a re-suspension technique, and analysed for total P, a range of P fractions and particle size. The results demonstrate significant spatial and temporal variability in PP concentrations and storage both between and within the study catchments, with concentrations and storage of PP higher in the Tern catchment than in the Pang and Lambourn, mainly due to the contrasting geologies and different land management practices in the catchments. Maximum and minimum PP concentrations and storage occurred in late summer and winter, respectively. It was concluded that geology played an important role in P storage associated with fine bed sediments.