The decomposition of lake aquatic plant litter affects litter deposition and nutrient release into sediments and water. Consequently, the aquatic environment of the lake is affected. In the current article, the emergent aquatic plant lotus (Nelumbo nucifera) in the Beili Lake of the Hangzhou West Lake was chosen as the experimental material. The mesh bag method was used to study the decomposition rate and nutrient dynamics of lotus leaf litter. The effect of the decomposition of lotus leaf litter on the aquatic environment of the Beili Lake and even of the whole West Lake was also examined. The results revealed that the decomposition process of lotus leaf litter has alternating fast and slow stages. The peak of the decomposition rate constant occurred in June and fluctuated during other periods. For the lotus leaf, the average decomposition rate constant was 5.441 × 10^-3/d, and the annual residual rate was 13.72%. For the lotus petiole, the average decomposition rate constant was 4.477 × 10^-3/d, and the annual residual rate was 19.51%. Both nitrogen and phosphorus contents in the litter initially decreased, and then gradually increased until stabilizing. Although the nitrogen and phosphorus accumulation indices presented a release-accumulation-release trend, the overall variation characteristic was release. The initial decomposition stage featured the net release of nitrogen and phosphorus. In contrast, the net accumulation of the two elements occurred in April and May, and the net release continued after June. The nitrogen release rates were 78.98% (after 260 d) for leaves and 31.15% (after 180 d) for petioles. The phosphorus release rates were 57.01% (after 260 d) for leaves and 34.69% (after 180 d) for petioles. Changes in the residues as well as in the release amounts of nitrogen and phosphorus of lotus leaf litter in the Beili Lake within a decomposition cycle were quantified. The calculations were based on the variation characteristics of the litter decomposition rate constant, the nitrogen and phosphorus contents, as well as the lotus leaf biomass. Lotus leaf litter falling into the lake was calculated as 20% of the total amount of standing dead litter. The residues drastically increased from November to January of the following year, and reached the peak dry weight value of 6.541 t in late January. This peak value is equivalent to 118.93 kg m^-2 dry weight (calculated based on the area of the lotus pond). The dry weight of the residues continued to decrease to 1.675 t (30.45 kg m^-2) in late October, which was 74.39% less than the peak value. Litter decomposition led to the continued increase in nitrogen and phosphorus release from November to January of the following year. The release decreased in February and March. Net accumulation occurred in April and May, and net release continued from June to October. During the decomposition cycle in the Beili Lake, the nitrogen and phosphorus contents respectively increased by 0.143 and 0.010 mg L^-1. These values correspond to total nitrogen and phosphorus release amounts of 92.247 and 6.421 kg, respectively. Emergent aquatic plants absorb nitrogen and phosphorus salts from sediments throughout their growth. Therefore, lotus growth and decomposition play important roles in transferring nitrogen and phosphorus from sediments into water bodies. Consequently, aquatic nitrogen and phosphorus contents increase.