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 NH 4 + /NO 3 − ratio in wet deposition existed in the different time scale. NH 4 + /NO 3 − 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. NH 4 + /NO 3 − ratio peaked in accordance with nitrogen-fertilizing time during crop growing season. Annual alternate appearance of the 15 N-enriched and 15 N-depleted periods coincided with the temporal variation of NH 4 + /NO 3 − ratio, which was closely related to the timing of fertilization and seasonal climate changes, suggesting the effect of NH 4 + sources in the wet deposition.

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