By synthesizing observed data from the 2000s, wet N deposition in China’s
coastal regions was found in the range from 7.6 to 61.3 kg N ha
À1 year
À1 with a
geometric mean of 17.5 (median ¼ 1.6) kg N ha
À1 year
À1 (Fig. 3.8). Metropolitan
regions of Shanghai and Guangzhou were two hotspots of wet N deposition, with
average rates of 61.3 and 40.5 kg N ha
À1 year
À1 , respectively. The measured wet N
deposition at coastlines was much higher than the modelling estimated wet N
deposition over China’s coastal seas (2–6 kg N ha
À1 year
À1 , Zhang et al. 2010;
3–8 kg N ha
À1 year
À1 , Zhao et al. 2015). A recent report based on monitoring data
across six coastal sites indicated that wet N deposition ranged from 14 to
25 kg N ha
À1 year
À1 in 2011 (Luo et al. 2014). A synthesis of the data indicated
that wet ammonium deposition ranged from 4.6 to 27.9 kg N ha
À1 year
À1 (geometric
mean 9.4, median 8.3 kg N ha
À1 year
À1 ) during the 2000s, while wet nitrate
deposition ranged from 3.0 to 33.4 kg N ha
À1 year
À1 (geometric mean 7.7, median
5.7 kg N ha
À1 year
À1 ) (Fig. 3.8). Overall, the ratio of NH 4
+
-N/NO 3
À -N averaged
1.34 Æ 0.54 (ranging from 0.36 to 2.45) during the 2000s, indicating a higher
contribution of ammonium than nitrate. However, the average NH 4
+
-N/NO 3
À -N
ratio decreased to 0.92 Æ 0.11 in 2011, implying an increasing contribution of nitrate
to N deposition (Luo et al. 2014).
3.5.2 Dry Deposition to Coastal Regions of China
Compared with wet deposition, less effort has been made to monitor dry N deposition at coastal sites in China. Based on limited measurements near the Yellow Sea
and East China Sea during the 2000s, dry deposition was much higher at shoreside
sites (21.1 kg N ha
À1 year
À1 , FLS) (Zhang et al. 2007) than at island sites (2.0–3.1 kg N ha
À1 year
À1 , ZS and SS) (Bi 2006; Zhang et al. 2007). The measured dry N
deposition at the island sites was generally in the same range as that from modelling
estimated dry N deposition over the eastern China seas during the 2000s (0.5–5.0 kg N ha
À1 year
À1 , Zhang et al. 2010; 1.6–4.1 kg N ha
À1 year
À1 , Zhao et al.
2015). By multiplying monitored concentrations of atmospheric N species by the
inferential deposition velocity, Luo et al. (2014) estimated that dry N deposition
ranged from 7.8–23.1 kg N ha
À1 year
À1 across six coastal sites.
There have been very few estimates of total N deposition based on monitoring
datasets. Recently, Luo et al. (2014) estimated that total N deposition ranged from
22 to 45 kg N ha
À1 year
À1 across six Chinese coastal sites, which was much higher
than modelling estimates of N deposition over China’s seas (Zhang et al. 2010; Zhao
et al. 2015). Overall, both observational and modelling results indicate that total N
deposition is dominated by wet deposition at coastlines (55–80%), whereas dry N
deposition only contributes approximately 20–45% (Zhang et al. 2010; Chen et al.
2011; Qi et al. 2013; Luo et al. 2014). As discussed above, the unavailability of
observed data limits more precise estimate of atmospheric N inputs to China’s
coastal regions. Further efforts are needed to establish a long-term monitoring
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