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Phosphorus sorption in soils and sediments: implications for phosphate supply to a subtropical river in southeast Queensland, Australia

Kerr, Jason G., Burford, Michele, Olley, Jon, Udy, James
Biogeochemistry 2011 v.102 no.1-3 pp. 73-85
algal blooms, aquatic food webs, base flow, biogeochemistry, energy, freshwater, phosphates, phosphorus, rain, rivers, runoff, sediments, soil, sorption, stream channels, terrestrial ecosystems, watersheds, Queensland
Phosphorus (P) is often a key limiting nutrient in freshwater systems, and excessive P can result in algal blooms, with flow-on effects to aquatic food webs. P sorption is an important process in aquatic and terrestrial ecosystems whereby phosphate (PO₄ ³⁻) is exchanged between liquid and solid phases. This study shows that differences in the concentration of PO₄ ³⁻ in a subtropical river system during high and low flow can be attributed to differences in P sorption characterises of its catchment soils and sediments. The sediments have lower Equilibrium Phosphate Concentrations (EPC₀) and higher binding energy (Kd); the surface soils have higher EPC₀ and higher easily desorbed P (NH₄Cl-P). A comparison of filterable reactive phosphorus (frP) in water samples collected at high and low flows, with soil and sediment EPC₀, suggested that during event flows, the high EPC₀ and NH₄Cl-P of surface soils is producing a net movement of PO₄ ³⁻ from the soil/sediment system into runoff and stream flow. At baseflow, there is more likely a net movement of PO₄ ³⁻ into the riverbed sediments. This has important implications for management actions aimed at reducing P loads to river systems and downstream water storages, namely the need to increase the infiltration of rainfall to decrease the amount of PO₄ ³⁻ being flushed from the surface soil.