64
L.O. Hedin and E.D. Hetherington
atmospheric inputs are dominated by sea-salt aerosols. Stream-water
Na+: Cl" ratios that are significantly elevated relative to sea salt would
mainly reflect weathering inputs of Na".
We found a strong overall relationship between Na" and Cl" for most
watershed streams considered in this study, as shown in Figure 4.2. Two
of the inland North American watersheds showed elevated Na+ relative
to Cl" (see the triangles in Figure 4.2), indicating contributions from
weathering to watershed outputs of Na+. When only coastal watersheds
were considered, we found an exceptionally strong correlation (r = 0.99;
P < 0.001) between Na+ and Cl- with a slope (0.58; n = 43; s.e. =
0.007) nearly identical to the ideal sea-salt ratio of 0.56.
These results indicate a strong link between hydrologic Na" and Cl"
losses from coastal temperate rainforest ecosystems and the atmospheric
input of marine aerosols. To further explore the biogeochemical constraints caused by this apparent link to atmospheric inputs, we subtracted
the contribution of sea-salt aerosols from the observed outputs of elements
from watersheds , as shown in Figure 4.3. The sea-salt corrected streamwater chemistry was calculated by using Cl" as a conservative tracer of
sea-salt aerosol inputs with the following element-to-Cl weight ratios:
Mg2+ = 0.067; sol- = 0.14; Ca
2
+ = 0.021; K+ = 0.021; and Na+
0.56 (Keene et al., 1986).
25
_(56,32~,~ _ (63,37)
20
10
15
Chloride (mg r
1
)
5
- / 6 -
/
-
/
/
/
o /
/
/
y"
~"
O+-----r---,---...,..----r------t
o
2 0 . , - - - - - - - - - - - - - - - - - - - ,
18
16
i: 14
00
6 12
- 6 10 s:
.S 8
"'0
o 6
rJ)
4
2
Figure 4.2. Concentrations of Na + as a function of Cl" in watershed streams that
drain coastal temperate forests at Cordillera de Piuchue, Chile (e); Cordillera
Pelada, Chile (0); and British Columbia, Canada (A) . 6. = Streams draining
inland watersheds in Alberta , Canada. Line indicates statistically significant regression at p < 0.05. Values from two coastal watersheds (indicated by the arrow)
were excluded from the correlation.
L.O. Hedin and E.D. Hetherington
atmospheric inputs are dominated by sea-salt aerosols. Stream-water
Na+: Cl" ratios that are significantly elevated relative to sea salt would
mainly reflect weathering inputs of Na".
We found a strong overall relationship between Na" and Cl" for most
watershed streams considered in this study, as shown in Figure 4.2. Two
of the inland North American watersheds showed elevated Na+ relative
to Cl" (see the triangles in Figure 4.2), indicating contributions from
weathering to watershed outputs of Na+. When only coastal watersheds
were considered, we found an exceptionally strong correlation (r = 0.99;
P < 0.001) between Na+ and Cl- with a slope (0.58; n = 43; s.e. =
0.007) nearly identical to the ideal sea-salt ratio of 0.56.
These results indicate a strong link between hydrologic Na" and Cl"
losses from coastal temperate rainforest ecosystems and the atmospheric
input of marine aerosols. To further explore the biogeochemical constraints caused by this apparent link to atmospheric inputs, we subtracted
the contribution of sea-salt aerosols from the observed outputs of elements
from watersheds , as shown in Figure 4.3. The sea-salt corrected streamwater chemistry was calculated by using Cl" as a conservative tracer of
sea-salt aerosol inputs with the following element-to-Cl weight ratios:
Mg2+ = 0.067; sol- = 0.14; Ca
2
+ = 0.021; K+ = 0.021; and Na+
0.56 (Keene et al., 1986).
25
_(56,32~,~ _ (63,37)
20
10
15
Chloride (mg r
1
)
5
- / 6 -
/
-
/
/
/
o /
/
/
y"
~"
O+-----r---,---...,..----r------t
o
2 0 . , - - - - - - - - - - - - - - - - - - - ,
18
16
i: 14
00
6 12
- 6 10 s:
.S 8
"'0
o 6
rJ)
4
2
Figure 4.2. Concentrations of Na + as a function of Cl" in watershed streams that
drain coastal temperate forests at Cordillera de Piuchue, Chile (e); Cordillera
Pelada, Chile (0); and British Columbia, Canada (A) . 6. = Streams draining
inland watersheds in Alberta , Canada. Line indicates statistically significant regression at p < 0.05. Values from two coastal watersheds (indicated by the arrow)
were excluded from the correlation.