partially considered because it is quite difficult to quantify. Likewise, wet or bulk
deposition of inorganic N (NH 4
+
-N+NO 3
À -N) has been systematically measured in
China, but organic N was seldom analyzed (Xu et al. 2015). Such omissions may
result in a considerable underestimation of N deposition directly to these waters.
Second, due to low concentrations of gaseous or particulate N, most measurements
applying passive samplers yield ambient exposures on a monthly interval (Xu et al.
2015). Although active samplers (e.g., denuder systems) can be deployed to determine concentrations of gaseous constituents and fine-fraction particulates at high
temporal-spatial resolution (Toya et al. 2007), they are unsuitable for long-term field
observations without a power supply (Xu et al. 2015). In addition, riverine N inputs
(i.e., N concentration  river discharge) in previous studies were generally determined by using process-based models or statistical model (runoff from agriculture,
urban areas and upland forests, point sources) (Castro and Driscoll 2002; Dolislager
et al. 2012; He et al. 2010). However, one of the major shortcomings in such models
is the large uncertainties arising from structure and parameter choices (Seitzinger
et al. 2005). Such uncertainties can be reduced by performing observations of N
concentrations and river discharge at high spatial and temporal resolutions.
In this study, we take Lake Dianchi, the sixth largest freshwater lake and one of
the three major eutrophic lakes in China, as an example. High-resolution (daily or
biweekly) observations of dry and wet deposition fluxes of all N species and riverine
N inputs were quantified. Based on these observations, we explore the contribution
of atmospheric N deposition to total N loads for eutrophic lake. Additionally, we
considered the importance of N deposition on lake eutrophication and implications
for lake ecosystem management.
12.2 Observations of N Depositions over Lake Surface
12.2.1 Study Area
Lake Dianchi, located in Southwest China (24
29
0
–25
28
0 N, 102
29
0
–103
01
0 E),
has a surface area of 310 km
2 at the elevation of 1887.5 m, a mean depth of 5.3 m, a
shoreline of 150 km, and water retention time of 3.5 years (Zhang et al. 2016)
(Fig. 12.1). Lake Dianchi watershed has a total area of approximately 2920 km
2 , of
which 1088.6 km
2 is controlled by ten large- to medium-sized reservoirs (Fig. 12.1).
The lake is divided in two by an artificial dam in the northeast. The smaller part
(12 km
2 ) is called Caohai surrounded by urban area of Kunming City. The larger part
(298 km
2 ), which forms the study area, is called Waihai, bordered by an intensively
managed farmland. Land use is primarily forest (47%) and cropland (20%), followed
by urban areas (16%), water (11%), grassland (2%), and bare land (4%). The
regional climate is subtropical (humid monsoon type), with an annual mean temperature of 14.7
C, an average precipitation of 797–1007 mm, and 227 frost-free days
per year. Nineteen rivers, accounting for 95% of lake’s inflow, were chosen for
measuring N concentration and discharge (Fig. 12.1). The total population of Lake
12 Impacts of Nitrogen Deposition on China’s Lake Ecosystems. . .
265
deposition of inorganic N (NH 4
+
-N+NO 3
À -N) has been systematically measured in
China, but organic N was seldom analyzed (Xu et al. 2015). Such omissions may
result in a considerable underestimation of N deposition directly to these waters.
Second, due to low concentrations of gaseous or particulate N, most measurements
applying passive samplers yield ambient exposures on a monthly interval (Xu et al.
2015). Although active samplers (e.g., denuder systems) can be deployed to determine concentrations of gaseous constituents and fine-fraction particulates at high
temporal-spatial resolution (Toya et al. 2007), they are unsuitable for long-term field
observations without a power supply (Xu et al. 2015). In addition, riverine N inputs
(i.e., N concentration  river discharge) in previous studies were generally determined by using process-based models or statistical model (runoff from agriculture,
urban areas and upland forests, point sources) (Castro and Driscoll 2002; Dolislager
et al. 2012; He et al. 2010). However, one of the major shortcomings in such models
is the large uncertainties arising from structure and parameter choices (Seitzinger
et al. 2005). Such uncertainties can be reduced by performing observations of N
concentrations and river discharge at high spatial and temporal resolutions.
In this study, we take Lake Dianchi, the sixth largest freshwater lake and one of
the three major eutrophic lakes in China, as an example. High-resolution (daily or
biweekly) observations of dry and wet deposition fluxes of all N species and riverine
N inputs were quantified. Based on these observations, we explore the contribution
of atmospheric N deposition to total N loads for eutrophic lake. Additionally, we
considered the importance of N deposition on lake eutrophication and implications
for lake ecosystem management.
12.2 Observations of N Depositions over Lake Surface
12.2.1 Study Area
Lake Dianchi, located in Southwest China (24
29
0
–25
28
0 N, 102
29
0
–103
01
0 E),
has a surface area of 310 km
2 at the elevation of 1887.5 m, a mean depth of 5.3 m, a
shoreline of 150 km, and water retention time of 3.5 years (Zhang et al. 2016)
(Fig. 12.1). Lake Dianchi watershed has a total area of approximately 2920 km
2 , of
which 1088.6 km
2 is controlled by ten large- to medium-sized reservoirs (Fig. 12.1).
The lake is divided in two by an artificial dam in the northeast. The smaller part
(12 km
2 ) is called Caohai surrounded by urban area of Kunming City. The larger part
(298 km
2 ), which forms the study area, is called Waihai, bordered by an intensively
managed farmland. Land use is primarily forest (47%) and cropland (20%), followed
by urban areas (16%), water (11%), grassland (2%), and bare land (4%). The
regional climate is subtropical (humid monsoon type), with an annual mean temperature of 14.7
C, an average precipitation of 797–1007 mm, and 227 frost-free days
per year. Nineteen rivers, accounting for 95% of lake’s inflow, were chosen for
measuring N concentration and discharge (Fig. 12.1). The total population of Lake
12 Impacts of Nitrogen Deposition on China’s Lake Ecosystems. . .
265