Table 9.15. Ion deposition in bulk precipitation (BP) at tropical premontane and montane forest sites in
Central and northern South America.
Ion Deposition (kg/ha/yr)Location
Siguartepeque, Honduras^3
Turrialba, Costa Ricab
El Verde, Puerto Ricoc
Pico del Este, Puerto Ricod
Monteverde, Costa Rica^6San Eusebio Venezuelaf
Santa Rosa de Cabal, Colombia^H+
n.d.
0.090
0.25
0.32
0.49
0.32
0.81
0.84
0.59N0 3 --N
0.4
0.5
2.0
5.3
3.4
1.6
n.d.
n.d.
n.d.NH 4 +-N
n.d.
1.2
1.5
6.9
3.4
1.6
n.d.
11.2
18.3P0 43 -P
0.10
0.09
n.d.
n.d.
0.06
0.04
n.d.
0.72
0.48K+
3.0
2.5
3.3
27
5.2
3.0
2.6
7.9
6.9Ca2+
18.3
1.4
11.4
47
8.7
5.8
5.6
10.1
7.3Mg2+
18.5
1.1
7.7
30
5.6
2.4
5.2
3.2
2.5Na+
4.4
5.9
55.4
247
43.8
19.5
3.3
24.1
15.9
n.d.a = not determined.
bKellman et al. 1982.
cHendry et al. 1984.
dMcDowell et al.^1990 (NO^3 '-N and NH^4 +-N for wet-only deposition).
eAsbury et al. 1994.
fThis chapter (estimates for deposition to the canopy and BP).
Steinhardt and Fassbender 1979.
sVeneklaas 1990 (sites at 3370 m and 2550 m elevation).the three wet seasons monitored, as reported for other
tropical sites (Lewis 1981, Kellman et al. 1982). De-
creases in ion concentrations are presumably due to
the washout of haze layers and reduced agricultural
burning as the wet season progresses (Crutzen and
Andreae 1990).
Compared to sites in North America (Johnson and
Lindberg 1992), Monteverde experienced relatively
low H+ and inorganic nitrogen deposition. This pat-
tern can be explained because no major urban areas
or point sources of H+, NOX, or NH 3 + exist in the vi-
cinity, and because dry deposition of HNO 3 ~ and NH 3 +
was likely underestimated in Monteverde. Although
relatively long dry periods occurred infrequently,
they were concentrated toward the end of the dry
season, when regional biomass burning activities were
greatest. Because NO 3 ~ and NH 4 + concentrations were
highest in cloud water and precipitation during this
period (Clark 1994), it follows that atmospheric con-
centrations of HNO 3 ~, NH 3 + and other gases and par-
ticles containing inorganic nitrogen were also rela-
tively high during the end of the dry season.
Net retention of H+ and inorganic nitrogen by the
canopy at Monteverde was within the range reported
from the 12 sites in the Integrated Forest Study (IPS;
Johnson and Lindberg 1992). Percentage net canopy
retention of inorganic nitrogen was greater at Monte-
verde compared with most IFS sites, but was closer
to the values reported from the four sites where cano-
pies had a substantial coverage of nonvascular epi-
phytes. Net retention of NO 3 ~ by the canopy was
greater than that of NH 4 + at this site (80% vs. 61%),
and NO 3 - flux in TF was only 47% of that of NH 4 +.
The lower net retention rate of NH 4 + may be partially
due to the leaching of NH 4 + mineralized from litter
and humus in the canopy (Vance and Nadkarni 1990,
Coxson 1991, Clark 1994). Net retention of NO 3 ~
averaged 57% of inorganic nitrogen deposition for the
four canopies in the IFS that had a substantial cover-
age of epiphytic vegetation (Clark 1994).
Deposition of inorganic nitrogen was low compared
to estimates from other sites. The majority of H+ and
inorganic nitrogen was retained by the canopy. Results
from other work suggest that epiphytic bryophytes and
assemblages of epiphytic bryophytes, vascular epi-
phytes, litter, and humus retained roughly 80% of the
inorganic nitrogen retained by the canopy (Clark 1994).
These abundant epiphytes may initially retain inor-
ganic nitrogen as a function of nitrogen deposition from
the atmosphere, and apparently buffer "pulses" of in-
organic nitrogen before they reach the forest floor.
Epiphytic bryophytes are only moderately productive,
but bryophyte-derived litter decomposes very slowly
(Clark 1994). Retained nitrogen is added to the rela-
tively large pools of nitrogen in litter and humus in the
canopy, and eventually to the very large pool of nitro-
gen in soil organic matter (Edwards and Grubb 1977,
Bruijnzeel and Proctor 1995).
There is little information on leaching of NO 3 ~ from
tropical montane forests. They may be more resistant
to increases in nitrogen deposition than many tem-
perate montane forests, because increased nitrogen
inputs may stimulate the production of both epiphytes
and their host trees and then get stored in soil organic
matter. However, the effects of chronic increase nitro-
gen deposition are unknown.328 Ecosystem Ecology and Forest Dynamics