Meta-Analysis of Modified Clay Minerals for Phosphorus Removal in Eutrophic Waters: Efficacy, Mechanisms, and...

Eutrophication caused by excessive phosphorus loading remains one of the most pressing challenges in freshwater management. Modified clay minerals have been widely proposed as a geoengineering approach to reduce bioavailable phosphorus, but their overall effectiveness and long-term reliability remain unclear. To provide a comprehensive evaluation, we conducted a meta-analysis of 130 international studies published between 2005 and 2025. Literature was systematically searched in Web of Science, with inclusion restricted to studies that reported quantitative data on phosphorus removal efficiency and clearly described the type of clay mineral, the modification method (chemical or physical), and experimental conditions. Both laboratory, mesocosm, and field studies were included to ensure ecological representativeness. Our analysis shows that modified clay minerals significantly increased removal efficiency, with average improvements of 47% for total phosphorus and 48% for soluble reactive phosphorus compared with untreated controls. Diatomite and lanthanum-modified bentonite outperformed other materials because of their high porosity and enhanced ion-exchange capacity. However, the dataset exhibited very high heterogeneity (I² > 99%), largely driven by geographic bias and the scarcity of long-term field experiments, especially in China. Compliance with environmental standards was low: for lakes, only 17.76% of laboratory studies and 15.38% of field studies reduced phosphorus concentrations below the eutrophication threshold, while short-term river microcosm experiments achieved up to 70% compliance. These discrepancies highlight the gap between laboratory conditions and real-world applications, influenced by factors such as pH, temperature, hydrodynamics, and competing ions. Overall, modified clay minerals demonstrate clear short-term benefits for phosphorus control and provide a useful temporary measure to curb eutrophication. Nevertheless, their long-term performance and ecological risks remain uncertain, underscoring the need for large-scale, multiyear field trials and the integration of modified clays with complementary technologies such as bioremediation or constructed wetlands. This study establishes a global evidence base that can guide more rigorous, standardized, and ecologically safe applications of modified clay minerals in eutrophication management.