2026 Volume 49 Pages 75-81
Magnesium ammonium phosphate (MAP) and sewage sludge compost, both derived from wastewater sludge, were applied to eelgrass seedlings to comparatively evaluate their effects on growth performance and nutrient release characteristics. In an indoor pot experiment, 1,000 mg of MAP or 2,000 mg of compost was added per 400 mL of sediment and incubated for 100 days. At the end of the incubation period, the germination rates were 22% in the unfertilized control, 20% in the MAP treatment, and 30% in the compost treatment. The mean shoot length was significantly greater in the MAP (64 mm) and compost (60 mm) treatments than in the control (43 mm) . In the MAP treatment, the ammonium concentration in sediment pore water remained high and reached up to 6.6 mg-N L-1 in the overlying seawater; however, phosphate release into seawater was suppressed by mixing the sediment with Andosol. In contrast, compost exhibited less phosphate release and smaller impacts on water quality. These findings suggest that fertilization strategies tailored to the characteristics of each material may contribute to eelgrass restoration and support the recovery of blue carbon ecosystems while promoting wastewater sludge resource recycling.
