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Fig. 1.
The land use types in the Wujiang watershed and sampling points in the study area. The capital letters represent different regions:
“
BJ
”
for Bijie,
“
ZY
”
for Zunyi,
“
GY
”
for Guiyang,
“
TR
”
for Tongren,
“
YY
”
for Youyang,
“
PS
”
for Pengshui,
“
QJ
”
for Qianjiang,
“
WL
”
for Wulong,
“
FL
”
for Fuling, and
“
NC
”
for Nanchuan.Population density and fertilizer usage are indicated for specific areas.
Fig. 2.
Longitudinal variations of NO
3 -
-N, HN4
+-N, NO
2 -
-N, TN, PO
4 3
+-P, TP, and SiO
2
concentrations of surface waters along the Wujiang River. Winter (a, e), spring (b,f), summer (c, g), and autumn (d, h). The x-coordinate represents the surface water samples at sampling points from W1 to W29.
Fig. 3.
Variations of (a) DCO
2
concentrations, (b)
δ
13
C
DIC
, and (c)
δ
15
N-NO
3 -
of surface waters across the Wujiang cascade reservoirs.
Fig. 4.
Depth profiles of NO
3 -
-N, HN 4
+-N, TN, PO
4 3
+-P, TP, and SiO
2
of seven reservoirs in the wet season (spring and summer) and the dry season (autumn and winter). E, epilimnion (0.5, 5 m); T, thermocline (10, 15, 20 m); H, hypolimnion (30, 45, 60 m).
Fig. 5.
(a) Relationship between
Δδ
13
C
DIC
and
Δδ
15
N-NO 3
−in depth profiles from seven reservoirs. The four quadrants represent different processes influencing
Δδ
13C
DIC
and
Δδ
15
N-NO3
−. The outline color of the circles denotes different reservoirs, while the fill color indicates the values of DSi:HCO
3 -
. The stoichiometric limitation analysis of P (b) and CO
2
(c) in the Wujiang cascade reservoirs, DIN:DIP
>
20, DCO
2
:DIP
>
166 for P limitation; DIN:DCO
2
>
0.12, DIP:DCO
2
>
0.006 for CO
2limitation, and the ratios are mole ratios (
Sterner et al., 2008
).
Fig. 6.
The variation of NO
3 -
-N, HN4
+-N, TN, PO
4 3
+-P, TP, and SiO
2
concentrations in seven reservoirs across different seasons.
Fig. 7.
The variation of
Δ
TN,
Δ
TP, dN, and dP in different seasons in seven reservoirs, with units in
µ
mol/L. Each group exhibits a non-significant difference from the t
-test.
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