Atmospheric Nitrogen Deposition In a Watershed In Central South China.

Increasing atmospheric nitrogen deposition has caused a serial of ecological and environmental problems in the recent years all over the world. For example, nitrogen deposition can contribute a large quantity to diffuse pollution. However, it is rarely quantified in Central South China (CSC), where diffusion pollution is serious due to excess input of nitrogen and phosphorus to waters. Hear we report preliminary results of atmospheric nitrogen deposition in a watershed in CSC to evaluate the contribution of atmospheric deposition to diffuse pollution. Sampling was conducted at three sites, which were located in typical paddy, tea garden and forest ecosystems. The monthly volume-weighed means for ammonium, nitrate and dissoluble organic nitrogen in bulk deposition samplers were 0.26-0.39, 0.30-0.41 and 0.05-0.10 mg N L-1 respectively. The calculated corresponding wet deposition across the sites was 0.80-1.11 kg N ha-1 mo-1. For nitrogenous gases and particles, the monthly mean concentrations were 1.68-2.40, 4.09-7.06, 0.44-1.09, 3.19-8.55 and 0.66-2.32 ¦Ìg N m-3 for NH3, NO2, HNO3, particulate NH4+ and NO3-, respectively. Nitrogen dry deposition was estimated from the products of measured concentrations and literature-based mean dry deposition velocities, and was 1.2-1.6 kg N ha-1 mo-1. When extroplated to a year, the total nitrogen deposition in the watershed can be as high as 24-33 kg N ha-1 yr-1. This indicates that to reduce diffuse pollution in CSC, pollutants from atmospheric deposition can not be ignored, and thus decreasing atmospheric emissions of reactive nitrogen species from agricultural, industry and traffic sources in this region should be emphasized in the future.