Phosphorus algal availability and release potential in suspended and streambed sediments in relation to sediment and catchment characteristics

Both suspended and streambed sediments from two pairs of streams (intervention outlet and control outlet, and Branch 14 and Branch 15) in livestock intensive catchments were analyzed for total phosphorus (TP), algal available P (AAP), P fractions and P saturation index (PSI). The variations in sediment P characteristics associated with sediment type and study sites were investigated; and the key variables controlling the variations were explored. Relative to streambed sediments, suspended sediments had significantly higher storage of TP and AAP and greater potential to continue adsorbing P from the water column. The differences between the two groups of sediments mainly resulted from differences in sediment particle size. For both suspended and streambed sediments, concentrations of TP, AAP, organic P (Po) and inorganic P (Pi) were not significantly different between the two catchment outlets, but were significantly higher in Branch 15 than in Branch 14; PSI values were considerably higher in the control outlet than at any of the study sites within the intervention micro-catchment. Sediment properties (e.g., calcium (Ca), aluminum (Al) and organic matter (OM)) and catchment characteristics (e.g., soil M3P status and drainage area) explained 62-87% of the variations in log-transformed TP, AAP, Po, Pi and PSI in suspended sediments, with sediment properties being the main contributor. For streambed sediments, variations in P concentrations and PSI were less well explained (13-56%), and sediment OM was the most importance predictor. Forest area percentage in landscape explained limited (3%) proportion of the variations in streambed sediment P concentrations and PSI.