Wet atmospheric deposition of nitrogen and phosphorus and estimation of their contributions to the lake in typical subtropical reservoir basins

To understand seasonal and spatial wet deposition characteristics of nutrients input to the Tangpu Reservior Basin, precipitation samples at four sites and stream water samples at three sites were collected from the basin during 2014-2015. The mass concentration of total nitrogen(TN), nitrate nitrogen (NO3--N), ammonia nitrogen and total phosphorus(TP) in the wet deposition were measured, and the precipitation characteristics of nitrogen and phosphorus nutrients, the deposition rates and their contributions compared with their counterparts from external loading of streams to the reservoir were studied. The results showed that the annual wet deposition concentration of TN was 1.02±0.58 mg/L, and the percentages of ammonium, nitrate and organic nitrogen contributed 60.65%, 34.07% and 5.28% of TN, respectively. The annual wet deposition concentration of TP was 0.033±0.028 mg/L. Seasonally, the concentrations of TN and TP in wet deposition were higher in winter and spring than in summer and autumn. Spatially, the concentrations of TN and TP were the highest at Wanghua site. The annual wet deposition rates of TN and TP were about 18.151 and 0.62 kg/(ha•a), and their average annual budgets reached 834.94 and 28.39 t, respectively. The wet depositions of water surface into Tangpu Reservoir were 24.14 and 0.82 t, and the direct contributions as 1.77% and 3.07% of the stream input. The indirect contributions of nitrogen and phosphorus from wet deposition sources accounted for 8.3% and 4.6% of the stream input. In summary, the nutrient load from the wet deposition plays a crucial role in the nutrient input of reservoirs. Understanding the nutrient load from the wet deposition will help us to better manage the reservoir basin and reduce the external nutrient loads to the basin. © 2020 by Journal of Lake Sciences.