deposition, reaching 56–83% from late spring to summer. Progress toward mitigating eutrophication in part of lakes will be difficult without reductions in ammonia
emissions and subsequent N deposition.
12.1 Introduction
Intensive industry and agricultural activities have significantly increased emissions
of reactive nitrogen (N, including reduced and oxidized forms) to the atmosphere
and hence their deposition (Duce et al. 2008; Peñuelas et al. 2013). Atmospheric
deposition of N has been increasing by approximately threefold since the
pre-industrial period, especially over the East and South Asia (Wang et al. 2015).
For oligotrophic lakes and oceanic waters, the ecological effects of elevated atmospheric N deposition have been observed or modeled, showing that such N inputs
can stimulate phytoplankton growth (Elser et al. 2009; Paerl 1985, 1997; Bergström
and Jansson 2006). This also shows that N of human origin has caused an increase in
the stoichiometric N/phosphorus (P) ratio and hence a shift from N limitation to P
limitation of phytoplankton growth (Elser et al. 2009; Wang et al. 2015). However,
in comparison to the remote watershed, the contributions of atmospheric N deposition on eutrophic lakes have been rarely receiving attention (Liu et al. 2011; Luo
et al. 2007). Because that contributions are commonly considered to be much less
than N inputs from watersheds to these lakes (Yan et al. 2016).
But recent evidence from the field observations demonstrated that the contribution of N deposition is likely to increase with strict control of lateral inflows from
surrounding river for eutrophic lakes. For instance, in mesotrophic Lake Taihu
which is the third largest freshwater lake in China, wet N deposition accounted for
approximately 14% of total N inputs (Luo et al. 2007). For another mesotrophic lake
(Lake Maracaibo) in Venezuela, the percentage was reported for 19% (Morales et al.
2001). Furthermore, the percentage increased considerably when both dry (i.e.,
gaseous, particulate N) and wet deposition was included (Xu et al. 2015). With
long-term and strict controls of point and nonpoint sources from surrounding rivers
taking place in developed countries, atmospheric N deposition is becoming an
increasingly dominant N source to these waters. For instance, 15–42% of the total
N inputs to ten estuaries in the northeastern and mid-Atlantic regions of the United
States was contributed by atmospheric N deposition (Castro and Driscoll 2002).
Yet, the contribution made by atmospheric N deposition to the total inputs
remains elusive at annual or seasonal scale. There are several reasons for these
uncertainties, especially in quantifying dry deposition and N exports from watersheds to the waters. First, by current observation networks globally (e.g., EANET
(2000), CASTNET (Li et al. 2016), AMoN (Li et al. 2016), IMPROVE NHx
(Li et al. 2016), EMEP (2014)) and in previous regional assessments (Xu et al.
2015), gaseous N (i.e., ammonia [NH 3 ], nitrogen dioxide [NO 2 ], nitric acid, and
nitrous acid [HNO 2 /HNO 3 ]) deposition has generally been ignored or is only
264
F. Zhou et al.
emissions and subsequent N deposition.
12.1 Introduction
Intensive industry and agricultural activities have significantly increased emissions
of reactive nitrogen (N, including reduced and oxidized forms) to the atmosphere
and hence their deposition (Duce et al. 2008; Peñuelas et al. 2013). Atmospheric
deposition of N has been increasing by approximately threefold since the
pre-industrial period, especially over the East and South Asia (Wang et al. 2015).
For oligotrophic lakes and oceanic waters, the ecological effects of elevated atmospheric N deposition have been observed or modeled, showing that such N inputs
can stimulate phytoplankton growth (Elser et al. 2009; Paerl 1985, 1997; Bergström
and Jansson 2006). This also shows that N of human origin has caused an increase in
the stoichiometric N/phosphorus (P) ratio and hence a shift from N limitation to P
limitation of phytoplankton growth (Elser et al. 2009; Wang et al. 2015). However,
in comparison to the remote watershed, the contributions of atmospheric N deposition on eutrophic lakes have been rarely receiving attention (Liu et al. 2011; Luo
et al. 2007). Because that contributions are commonly considered to be much less
than N inputs from watersheds to these lakes (Yan et al. 2016).
But recent evidence from the field observations demonstrated that the contribution of N deposition is likely to increase with strict control of lateral inflows from
surrounding river for eutrophic lakes. For instance, in mesotrophic Lake Taihu
which is the third largest freshwater lake in China, wet N deposition accounted for
approximately 14% of total N inputs (Luo et al. 2007). For another mesotrophic lake
(Lake Maracaibo) in Venezuela, the percentage was reported for 19% (Morales et al.
2001). Furthermore, the percentage increased considerably when both dry (i.e.,
gaseous, particulate N) and wet deposition was included (Xu et al. 2015). With
long-term and strict controls of point and nonpoint sources from surrounding rivers
taking place in developed countries, atmospheric N deposition is becoming an
increasingly dominant N source to these waters. For instance, 15–42% of the total
N inputs to ten estuaries in the northeastern and mid-Atlantic regions of the United
States was contributed by atmospheric N deposition (Castro and Driscoll 2002).
Yet, the contribution made by atmospheric N deposition to the total inputs
remains elusive at annual or seasonal scale. There are several reasons for these
uncertainties, especially in quantifying dry deposition and N exports from watersheds to the waters. First, by current observation networks globally (e.g., EANET
(2000), CASTNET (Li et al. 2016), AMoN (Li et al. 2016), IMPROVE NHx
(Li et al. 2016), EMEP (2014)) and in previous regional assessments (Xu et al.
2015), gaseous N (i.e., ammonia [NH 3 ], nitrogen dioxide [NO 2 ], nitric acid, and
nitrous acid [HNO 2 /HNO 3 ]) deposition has generally been ignored or is only
264
F. Zhou et al.