Seasonal impact of constructed wetlands on nitrogen and phosphorus in sediments of flood control lakes with pollution assessment

The primary drivers of eutrophication in lakes following the reduction of external nutrient inputs are the release of N and P from sediments. Constructed wetlands play a pivotal role in ameliorating N, P, and other biogenic element levels. However, the presence of large vegetation in these wetlands also substantially contributes to nutrient accumulation in sediments, a phenomenon influenced by seasonal variations. In this study, a typical constructed wetland was selected as the research site. The research aimed to analyze the forms of N and P in sediments during both summer and winter. Simultaneously, a comprehensive pollution assessment and analysis were conducted within the study area. The findings indicate that elevated summer temperatures, together with the presence of wetland vegetation, promote the release of N through the nitrification process. Additionally, seasonal variations exert a significant impact on the distribution of P storage. Furthermore, the role of constructed wetlands in the absorption and release of N and P is primarily controlled by the influence of organic matter on nitrate-nitrogen, nitrite-nitrogen, and available phosphorus, and is also subject to seasonal fluctuations. In summary, under the comprehensive influence of constructed wetlands, vegetation types, and seasons, sediments within the lake generally exhibit a state of mild or moderate pollution. Therefore, targeted measures should be adopted to optimally adjust vegetation types, and human intervention is necessary, involving timely sediment harvesting during the summer to reduce N and P loads, and enhancing sediment adsorption and retention capacity for N and P during the winter. High temperatures and wetland plants promote nitrification, thereby enhancing the release of N from the sediment. The uptake and release of N and P are controlled by the effects of organic matter (OM) on nitrate-nitrogen, nitrite-nitrogen, and available phosphorus. The control of OM by wetlands is subject to seasonal cycles. The primary drivers of eutrophication in constructed wetlands following the reduction of external nutrient inputs are release of N and P from sediments. A constructed wetland was selected to analyze the forms of N and P in sediments during summer and winter, and a pollution assessment was conducted. We find that elevated summer temperatures, together with vegetation, promote release of N through nitrification process. Furthermore, the role of constructed wetlands in absorption and release of N and P is primarily controlled by the influence of organic matter on nitrate-nitrogen, nitrite-nitrogen, and available phosphorus, and is also subject to seasonal fluctuations. Under the comprehensive influence of constructed wetlands, vegetation, and seasons, sediments exhibit mild or moderate pollution. Therefore, human intervention is necessary, involving timely sediment harvesting during the summer to reduce N and P loads, and enhancing sediment adsorption and retention capacity for N and P during the winter.