Sediments act as phosphorus (P) reservoirs, where P binds to, or co-precipitates with metals, organic material and carbonates. Acid mine drainage (AMD) polluted systems experience an increase of metals and their associated precipitates, increasing the system’s capacity to immobilise P. However, the distribution of P between different adsorbent pools, and how this effect varies with distance from the pollution source remain poorly understood.
This study collected sediment and water samples from a section of the Molonglo River (New South Wales) impacted by AMD. All samples were analysed for P, and sediments were additionally analysed for P fractionation and metals.
Total P was elevated in sediments affected by AMD, suggesting that AMD conditions may influence P retention processes in sediments. Additionally, the bioavailable fraction of P in sediments and water at AMD affected sites were below the limit of detection (<0.005mg/L), despite the proximity of a water treatment facility, indicating that AMD pollutants may reduce the bioavailability of P. The distribution of P among fractional groups (according to Psenner's 1988 method), were varied, with the NaOH extractable fraction, which is primarily associated with Al3* and Fe2+ species, displaying the most variation. The P content of the NaOH fraction appeared to be dependent upon pH, with a pH<6 leading to decreased P content.
AMD polluted sediments act as a reservoir and buffer of P, however acidic conditions prevent the increasingly stable NaOH-P mineral fraction from forming, increasing the likelihood of P release and transport.