Enrichment of bioavailable phosphorus in fine particles when sediment resuspension hinders the ecological restoration of shallow eutrophic lakes.

Sediment resuspension is one of the main factors impacting the ecological restoration of shallow eutrophic lakes, but the mechanisms connecting suspended particles and algal growth have not been clarified. Our research presents an innovative approach based on P reallocation among particles with various sizes, considering the changes in redox and pH conditions from the sediments to the overlying water during resuspension. A lab-scale experiment was conducted to simulate P reallocation in particles during sediment resuspension by periodically dosing the system with P and/or organic carbon. The sediments were sampled and sieved into five particle size groups, namely, 50-150 μm, 30-50 μm, 10-30 μm, 5-10 μm and <5 μm, and their P fractions during the operation were analyzed. The bioavailable P associated with aluminum (Al) and iron (Fe) (hydr)oxides showed exponential enrichment as the median grain size of particles decreased, with 54% of the added P adsorbed by fine particles of <10 μm (5-10 μm and <5 μm). Furthermore, a bioassay of algae growth potential (Microcystis aeruginosa sp.), along with P adsorption isotherms, was conducted to test the ability of the different size-resolved particles to supply P for algae growth. The fine particles of <10 μm supplied more P to algae under elevated pH values than did the coarse particles (>10 μm). The restoration of shallow eutrophic lakes faces great challenges due to the connection mechanisms between sediments and algae, as revealed by this research.