Mechanisms Underlying the Enhanced Removal of Nutrients at the Sediment-Water Interface Using Mixed Aeration Augmented with Limnodrilus hoffmeisteri

Abstract

The sediment–water interface (SWI) is a critical zone for material cycling in deep-water reservoirs but is highly vulnerable to organic pollution and eutrophication. Although mixed aeration can enhance oxygen availability at the SWI, this study further evaluated the synergistic remediation potential of combining mixed aeration with benthic organisms. Nutrient removal and its underlying mechanisms were investigated using mixed aeration combined with Limnodrilus hoffmeisteri, the dominant benthic species in Shibianyu Reservoir. Compared with L. hoffmeisteri alone (5.12%), the combined treatment achieved higher TN removal in overlying water (10.04%), with efficiency increasing with organism density. In sediments, maximum TN and TP removals reached 3.95% and 4.60%, respectively, with stable performance across density treatments. Overall, nutrient removal efficiency followed the order: combined treatment > L. hoffmeisteri alone > mixed aeration alone. Under combined treatment, L. hoffmeisteri was the primary contributor to sediment TN and TP removal, with contribution rates of 3.95% and 7.32%. The combined treatment maintained dissolved oxygen at 8.23 mg/L, increased bioturbation depth by 3-5 cm, and significantly enhanced aerobic microorganisms (e.g., Pseudomonas spp.). and nitrogen-cycling functional genes. Field data further confirmed the practical efficacy of this approach, achieving an annual TN removal of 8.04 tons. These results provide theoretical support for improving sediment water quality in lakes and reservoirs.