Dredging is a common technique for managing eutrophication problems in waters, reducing the accumulation of pollutants by removing sediments from the bottom of water bodies. However, dredging can have complex impacts on lake ecosystems, and it is crucial to understand its benefits and mechanisms for the environment. In this paper, the dredged and undredged areas in the Caohai portion of Dianchi Lake were studied to analyze the effects of dredging on nitrogen–phosphorus transport and conversion and changes in nitrogen–phosphorus morphology content and its mechanisms by comparing the nitrogen–phosphorus morphology content and percentage, the nitrogen–phosphorus ratio, and the release contribution of the two areas. It was found that the ratio of stabilized nitrogen (SN) to stabilized phosphorus (SP) in the dredged area was lower than that in the undredged area and the BD-P and TOC content had a large turnaround at the 16–20 cm position of the sediment in the dredged area. The main conclusions were that the dredging would disrupt the internal equilibrium of the lake system for many years, with the greatest effect on the balance of the BD-P in the phosphorus forms of the sediment, and that the column cores of the dredged area at 0 to 16 cm might be newly accumulated sediments after the dredging project. However, with time, the distribution of nitrogen and phosphorus forms in the newly accumulated sediments will gradually reach a new equilibrium. In addition, dredging will also cause significant changes in the retention efficiency of nitrogen and phosphorus in the sediment, and the stable nitrogen and phosphorus forms will be released and transformed into unstable nitrogen and phosphorus forms.

Constructed wetlands can treat various types of sewage and have good nitrogen removal capacity. With the deterioration of the environment, nitrogen emission requirements have also increased; how to maximize the nitrogen removal function of constructed wetlands is particularly important. Therefore, this paper aims to summarize the measures to increase the nitrogen removal capability of constructed wetlands. New nitrogen removal methods such as simultaneous nitrification and denitrification, partial nitrification-denitrification, and anaerobic ammonium oxidation are efficient ways to remove TN. The effect of nitrogen removal in constructed wetlands can be strengthened by optimizing the configuration, such as improving the water intake mode, optimization of substrate combinations, optimization of plant species configuration, and novel constructed wetland coupling process, and improving the operating conditions, such as adding external carbon sources, improving redox conditions, microbial enhancement technology, and aeration. On this basis, the mechanisms of nitrogen removal by microorganisms, substrates, and plants as well as the coupling roles played by each other in the process of wastewater purification are illustrated. This paper provides a systematic idea for increased nitrogen removal in constructed wetlands, provides some references for research in this field, and finally provides prospects for future research.