Effectiveness of different geo-engineering materials in controlling internal nutrient loading in lakes

Eutrophication is a major global water issue. Geo-engineering materials offer a promising approach to reducing internal nutrient release. This study applied six materials to sediment cores to analyze changes in phosphorus (P) and nitrogen (N) concentrations in overlying water and sediment fractions. Natural zeolite (NZ) application reduced 76% NH 4 + -N flux compared to the control but did not affect P flux. Zeofixer®, a novel commercial lanthanum material reduced soluble reactive P (SRP) flux (-0.06 mg P m -2 d -1 ) compared to the control (4.72 mg P m -2 d -1 ) but did not affect N fluxes. Aluminum-modified zeolite (Aqual-P™), NZ combined with La-modified bentonite (NZ+Phoslock®) and NZ combined with poly-aluminum chloride (NZ+PAC) strongly reduced P and N fluxes, with Aqual-P™ showing the strongest NH 4 + -N flux reduction. Natural bentonite showed no significant change in total P and SRP fluxes compared to the control and slightly reduced NH 4 + -N flux. NZ, Aqual-P™, NZ+PAC, and bentonite had similar mobile P content in the top sediment layer. The two La-based P binders control P mainly through precipitation, forming rhabdophane, while the natural and modified zeolite control NH 4 + -N release primarily via ion exchange. In Zeofixer® and NZ+Phoslock® treatments, mobile P was reduced while the HCl-P fraction increased. NZ, Aqual-P™, NZ+Phoslock®, and NZ+PAC had a higher sediment exchangeable-NH 4 + -N content compared to other treatments. This study offers water managers strategies tailored to different conditions/aims, including both P-only and dual N+P control. Considering the cost-effectiveness and ecological feasibility, NZ combined with Phoslock®/ Zeofixer® seems a promising approach for simultaneous N and P mitigation. • Natural zeolite (NZ) only reduced N release, and Zeofixer ® only reduced P release. • Aqual-P TM , NZ+Phoslock ® and NZ+poly-aluminium chloride reduced N and P release. • La-based products transferred mobile P to non-mobile P in top sediment layer. • Natural/modified zeolite adsorbed NH 4 + -N in top 3 cm of sediment porewater. • Lake restoration efforts may benefit from dual control of sediment N and P.