The collector was kept completely closed and was opened only at the beginning of a
rainfall event, referring to the technical manual for wet deposition monitoring in East
Asia (EANET 2000). To prevent biological utilization of deposited N, thymol
(C 10 H 14 O) was used as a biocide in the wet bottle. A cap covered the “wet” bottle
which, in combination with the inherently low rainwater pH of 4 to 5, minimized the
potential for ammonia volatilization. Collectors were cleaned for each event with 1%
HCl and nanopure water. All samples were preserved with chloroform and stored
frozen in acid-washed HDPE bottles, which had been prerinsed with the sample,
until analysis.
TN concentrations were monitored in the outlet of 20 rivers on a biweekly
interval. Although river discharges were not recorded in the past except for
Panlongjiang (No. 8) and Baoxiang (No. 10) Rivers, the other 19 rivers that
contribute most (95%, Wang et al. 2014) of lake’s inflow were chosen to continuously measure water levels (Fig. 12.1). Water level was further converted into daily
discharge based on the rating curves for each river. The rating curves were developed by simultaneously measuring water levels and the current velocities for a cross
section of the river following the USGS guideline of the current-meter method
(Buchanan and Somers 1969). The sizes of cross section (i.e., width, depth, area)
were measured for each river (Table 12.1). To ensure rating curves over a wide range
of flow rates, enhanced observations were conducted for three stormwater events
(precipitation >30 mm day
À1 ), for which sampling duration lasted more than 48 h
per event. For each tributary, the 10-min water levels were continuously observed by
HOBO™ data logger (U20–001-01, Onset Computer Corporation, MA, USA), and
the current velocities were measured by the Global Water™ flow probe (FP201) in
each subsection of a channel cross section. All water samples were rapidly
transported to the KEMC for analysis.
All N species were analyzed following the standard methods for the examination
of water and wastewater (State Environmental Protection Administration. Standard
methods for the examination of water and wastewater (version 4) 2002) in China.
Ammonium nitrogen [NH 4
+
-N], nitrate nitrogen [NO 3
À -N], Kjeldahl nitrogen
(KTN), and total nitrogen (TN) were measured by Nessler’s reagent colorimetric
method, ultraviolet spectrophotometric method, semimicro-Kjeldahl method, and
K 2 S 2 O 8 oxidation-ultraviolet spectrophotometric method, respectively. Organic N
was determined by the difference between KTN and NH 4
+ -N. Additionally, blank
filter and reagent were also analyzed, for which N values were consistently below the
method detection limit.
12.2.2 Estimation of Deposition Fluxes
Biweekly flux of dry deposition (mg km
À2 s
À1 ) was calculated as a product of N
concentration (determined as described above) and deposition velocity (V d , m s
À1 ) at
each site. And the flux of wet deposition was calculated as a product of N
268
F. Zhou et al.
rainfall event, referring to the technical manual for wet deposition monitoring in East
Asia (EANET 2000). To prevent biological utilization of deposited N, thymol
(C 10 H 14 O) was used as a biocide in the wet bottle. A cap covered the “wet” bottle
which, in combination with the inherently low rainwater pH of 4 to 5, minimized the
potential for ammonia volatilization. Collectors were cleaned for each event with 1%
HCl and nanopure water. All samples were preserved with chloroform and stored
frozen in acid-washed HDPE bottles, which had been prerinsed with the sample,
until analysis.
TN concentrations were monitored in the outlet of 20 rivers on a biweekly
interval. Although river discharges were not recorded in the past except for
Panlongjiang (No. 8) and Baoxiang (No. 10) Rivers, the other 19 rivers that
contribute most (95%, Wang et al. 2014) of lake’s inflow were chosen to continuously measure water levels (Fig. 12.1). Water level was further converted into daily
discharge based on the rating curves for each river. The rating curves were developed by simultaneously measuring water levels and the current velocities for a cross
section of the river following the USGS guideline of the current-meter method
(Buchanan and Somers 1969). The sizes of cross section (i.e., width, depth, area)
were measured for each river (Table 12.1). To ensure rating curves over a wide range
of flow rates, enhanced observations were conducted for three stormwater events
(precipitation >30 mm day
À1 ), for which sampling duration lasted more than 48 h
per event. For each tributary, the 10-min water levels were continuously observed by
HOBO™ data logger (U20–001-01, Onset Computer Corporation, MA, USA), and
the current velocities were measured by the Global Water™ flow probe (FP201) in
each subsection of a channel cross section. All water samples were rapidly
transported to the KEMC for analysis.
All N species were analyzed following the standard methods for the examination
of water and wastewater (State Environmental Protection Administration. Standard
methods for the examination of water and wastewater (version 4) 2002) in China.
Ammonium nitrogen [NH 4
+
-N], nitrate nitrogen [NO 3
À -N], Kjeldahl nitrogen
(KTN), and total nitrogen (TN) were measured by Nessler’s reagent colorimetric
method, ultraviolet spectrophotometric method, semimicro-Kjeldahl method, and
K 2 S 2 O 8 oxidation-ultraviolet spectrophotometric method, respectively. Organic N
was determined by the difference between KTN and NH 4
+ -N. Additionally, blank
filter and reagent were also analyzed, for which N values were consistently below the
method detection limit.
12.2.2 Estimation of Deposition Fluxes
Biweekly flux of dry deposition (mg km
À2 s
À1 ) was calculated as a product of N
concentration (determined as described above) and deposition velocity (V d , m s
À1 ) at
each site. And the flux of wet deposition was calculated as a product of N
268
F. Zhou et al.