Spatial and Temporal Variation of Inorganic Nitrogen Wet Deposition to the Yangtze River Delta Region, China

Two-year (June 2003–May 2005) precipitation samples were collected from three monitoring sites with similar economy development level in the Yangtze River Delta Region of China to investigate the spatial–temporal variation of inorganic N wet deposition. The results showed that the Yangtze River Delta Region had higher inorganic N wet deposition than the northwestern, northern, or southern China. There was spatial variation of inorganic N wet deposition. The positive relationship between inorganic N deposition and precipitation suggested that rainfall amount might be an important factor influencing the wet deposition of inorganic N. Deposition of inorganic N occurred mainly in the spring and summer season (March–August; 70% of the annual total), which was in accord with seasonal distribution of precipitation. However, a negative logarithmic relation between rainfall and inorganic N concentration in rainwater indicated the dilution effect of rainwater on inorganic N concentration. Distinguished variation of NH4+/NO3− ratio in wet deposition existed in the different time scale. NH4+/NO3− ratio evidently decreased from 6 in 1980s to 1.2 in 2003/2005 and greatly varied between 0.3 and 9.9 within a year. NH4+/NO3− ratio peaked in accordance with nitrogen-fertilizing time during crop growing season. Annual alternate appearance of the 15N-enriched and 15N-depleted periods coincided with the temporal variation of NH4+/NO3− ratio, which was closely related to the timing of fertilization and seasonal climate changes, suggesting the effect of NH4+ sources in the wet deposition.