Sediments serve as an important carrier during the migration and transformation of pollutants in surface-flow constructed wetlands. Exploring the accumulation characteristics and release patterns of nutrients is of great significance for assessing the purification functions of constructed wetlands after long-term operation. The contents of total organic carbon (TOC), total nitrogen (TN), and total phosphorus (TP) in sediments at various locations of the 5-year-old Yanlong Lake surface-flow constructed wetland were analyzed and static release experiments with cylindrical core samples were carried out. The results showed that after five years, sediments at this site have become moderately polluted and the nutrient accumulation level is mainly being affected by the influent flow, water depth, and plant effects. Additionally, ① nutrients in sediments were found to increase along the flow direction; ② they also increase as the depth of overlying water increases and are relatively affected by the carbon; ③ healthier growth of the wetland plants could lead to more nutrients being accumulated in sediments. The release trend of nutrients fell after a rise and basically reached equilibrium after 20 days, and the release rate was mainly affected by the accumulation level of nutrients, which is similar to the trend in light nutrient containing reservoirs. Plant residues contained in the sediments were associated with the stronger release of nutrients. These results can provide a scientific basis for solutions aimed at maintaining the purification capacity of long-running surface-flow constructed wetlands.
Keywords: accumulation; long-term; nutrient; release; sediment; surface-flow constructed wetland.