A microcosm experiment to determine the consequences of magnetic microparticles application on water quality and...

This study used microcosms to evaluate the effects of adding iron (Fe) magnetic microparticles (MPs) on water quality, focusing on P concentrations in the water column and sediment. Two treatments were considered for a constant 85:1 MP:P_Mobile molar ratio: T-W, applying MPs on the surface water layer; and T-S, applying MPs on the sediment. MP addition reduced P concentrations in lake water and sediment, with both treatments producing a mean reduction of 68±6% in dissolved inorganic P concentration (DIP) over a 70-day oxic period and reductions of 80±8% (T-W) and 80±4% (T-S) over a 5-day anoxic period. MPs also decreased reactive silicate (Si) concentrations by around 50% in both periods, but dissolved organic carbon (DOC) was reduced by only 15% at 24h after MP addition. Despite the marked decrease in DIP concentration due to MP addition, there was no reduction in chlorophyll a (Chla), because post-treatment total P concentrations (>200μgL^-1vs. >700μgL^-1 before treatments) remained higher than required for changes in the biological community (0.05-0.1mgL^-1). With T-S treatment, there was a reduction of 15% in P bound to Al oxides, clay minerals, and humic substances (P_→NaOH) and of 12% in labile organic P (Org-P_Labile) versus controls. P bound to humic substances (P_{→NaOH, Humic}) was reduced by 11-22% in both treatments. Finally, T-W rather than T-S treatments are recommended for future whole-lake applications to achieve more effective P removal from water and sediment and a higher percentage MP recovery.