Spatial evolution of soil properties in near-natural constructed wetland after 15 years of operation

Abstract

Near-nature restoration is a key research focus in the field of ecological restoration. Near-natural constructed wetlands (NCWs) play an important role in water resource purification. During the long-term operation of NCWs without intervention, their purification ability gradually weakens and the soil structure and function change. In the present study, based on the operation of NCWs for 15 years, we measured the physicochemical properties (e.g., carbon, nitrogen, and phosphorus contents, water contents, and pH) and activities of enzymes (e.g., urease (URE), alkaline phosphatase (PHO), dehydrogenase, and sucrase (SUC)) at a soil depth of 0–20 cm; the levels of these parameters at different flow sections of, and different distances from, the NCW were assessed. The results showed no significant difference between the soil carbon and total nitrogen at different distances from the NCW. Further, the phosphorus and NH₄⁺-N contents increased with the increase in distance from the wetland and were the lowest in the wetland center; further, the NO₃^--N content was the highest in the wetland center (p < 0.01). The soil carbon, nitrogen, and phosphorus contents were the highest in the surface soil (0–5 cm) and were higher in the surface of the NCW than in the subsurface of the NCW. The activity of most enzymes decreased significantly with the increase in soil depth; the highest enzyme activities were observed on the bank of the NCW (p < 0.01). Redundancy analysis showed that soil carbon and nitrogen had a strong explanatory power for the soil enzyme activity. After long-term operation, the soil properties in the NCW showed spatial changes. The discovery of this rule is conducive to the ecological design of NCWs and will aid the protection and restoration of ecosystems subjected to the combined influence of natural and human activities.