Abstract: To effectively eliminate pollutants including nitrogen, phosphorus, and organic substances from eutrophic water bodies, layered double hydroxides (LDHs) with a Mg:Al molar ratio of 1:2 were immobilized on the surfaces of sponge iron and shale ceramsite via a hydrothermal coprecipitation method. Subsequently, a series of comprehensive characterization tests were implemented to thoroughly investigate the surface micromorphology, crystal structure, and surface functional groups of the modified composites. To evaluate the pollutant removal performance of these composites, both static and dynamic adsorption experiments were systematically conducted, while in-depth discussions were carried out to clarify the adsorption characteristics and the underlying mechanisms for the differences in adsorption behaviors. The results demonstrated that MgAl-LDHs were successfully loaded onto the surfaces of the two substrates. Both composites exhibited favorable phosphate adsorption capacities, with the LDHs-modified sponge iron showing a higher phosphate uptake and thus better application potential for phosphate removal. In contrast, an opposite trend was observed for ammonium nitrogen adsorption: the ammonium nitrogen adsorption capacity of the modified sponge iron was merely 70.14 mg/kg, indicating a relatively low adsorption affinity for this pollutant. Mechanistic analysis revealed that the adsorption of both nitrogen and phosphorus by the two composites were dominated by chemical adsorption. Additionally, desorption experiments verified that both modified materials presented a low desorption risk, implying that the adsorbed pollutants were not prone to being released back into the water environment. In dynamic vertical flow experiments, the two LDHs-modified composites initially displayed remarkable adsorption capabilities for nitrogen, phosphorus, and organic substances, but their removal performances declined to varying degrees as the experiments Three-dimensional excitation-emission matrix fluorescence spectroscopy analysis indicated that both modified composites could effectively improve the composition of dissolved organic matter (DOM) in the influent, in which aromatic protein-like substances served as the dominant component.