Particle size-related vertical redistribution of phosphorus (P)-inactivating materials induced by resuspension shaped P immobilization in lake sediment profile

Abstract

Lake geoengineering with phosphorus (P)-inactivating materials to reduce sediment P loading is often used for eutrophication control. The redistribution of materials in sediment, especially those induced by resuspension, is reportedly a common phenomenon during practical applications, which may interfere with the pollution control. Notably, a recent study by the authors initially found that the heterogeneous properties of materials and sediments varied the P immobilization in different sized sediments which exhibited diverse movement characteristics. Therefore, this study hypothesizes a particle size-related vertical redistribution of materials in the sediment profile induced by resuspension, which shapes sediment P immobilization at different depths. Based on two differently sized materials, lanthanum (La)-modified bentonite clay (Phoslock) and drinking water treatment residue (DWTR), this study found a weakened reduction of mobile P and bioavailable P pool by both DWTR and Phoslock in surface sediment after resuspension. As the depth decreased from >12 to surface 0–1 cm, the remaining mobile P increased from 7.11%–10.8% to 11.0%–17.8% of the total P in the sediment with Phoslock and from 1.66%–4.73% to 9.70%–20.7% of the total P in the sediment with DWTR; meanwhile, bioavailable P pool reduction proportions decreased from 48.6%–72.3% to 3.23%–45.1% for Phoslock and from 51.5%–71.4% to 4.94%–25.2% for DWTR. Further analysis verified the hypothesis of this study; importantly, the redistributions of the potential target P (including mobile and bioavailable P) for immobilization were regulated by relatively small sediments (e.g., <8 μm fraction), which tended to become enriched in surface sediment after resuspension, while relatively large materials (e.g., >63 μm fraction) regulated their redistributions and were more likely to be buried at the bottom of the sediments. Accordingly, to design appropriate strategies for lake geoengineering, relatively small materials (e.g., <8 μm) targeting to immobilize both mobile and bioavailable P are typically recommended to be developed for restoration of lakes with frequent sediment resuspension.