Phosphorus Storage in Fine Channel Bed Sediments

Deposition and storage of fine sediment on channel beds represents an important component of a catchment's sediment budget and can have important implications for sediment-associated P fluxes, due to storage and remobilisation, and for P concentrations through water-sediment interactions. Spatial and temporal variations in P content and storage in fine bed sediment have been studied in two UK lowland catchments, the Rivers Frome and Piddle in Dorset. Fine bed sediment was sampled in representative reaches on a bi-monthly basis using a re-suspension cylinder, and the resulting samples were 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, with maximum and minimum P concentrations and storage occurring in late summer and winter, respectively. Temporal variations in concentrations reflect residence times of the sediment and ambient P concentrations, while variations in storage are mainly due to hydrological regimes. Spatial variations reflect catchment characteristics, the location of inputs and local variations in hydrological and channel bed conditions.