Fog Studies at Kīlauea Hawai`i
Karin Schlappa, currently: HPI-CESU, NPS Inventory and Monitoring Program, PO Box 52, Hawaii National Park, HI 96718 schlappa@hawaii.edu
Barry Huebert, University of Hawaii, Oceanography Dept., 1000 Pope Rd., Honolulu, HI 96822
Study Site
Methods
The study period lasted from January 2001 to September 2003.
This study was carried out at Hawai`i Volcanoes National Park on the island of Hawai`i. The
site is located in the wet forest at 1200 m asl. Prevailing NE trade winds, a temperature
inversion and orographic uplift lead to frequent and persistent fog (cloud) immersion.
Pu`u O`O the
active vent of
Kīlauea Volcano is
located
approximately 16
km E of the study
site. Depending on
wind conditions,
volcanic emissions
may heavily
influence air quality
at this site.
Fog presence was defined as Liquid
water content (LWC) >0.02g/m3.
LWC was measured with a
particulate volume monitor (PVM100 Gerber Scientific Inc.).
PVM
Fog water collector
Fog samples were collected with
an automated collector system.
When the PVM indicated fog
presence, air was aspirated into an
acrylic housing where droplets
impacted on Teflon strings and
were funneled into bottles.
The instruments were located
on a 16 m tall tower in a
forest clearing.
Fan inside
Frames with Teflon
Strings inside
Air aspirated from below
Tubing to bottles
Fog interception was estimated using a canopy water
balance method where water inputs (Fog and Rain)
equal the different ways into which this water is
partitioned (canopy storage, throughfall, stemflow,
evaporation). Fog interception was then estimated as:
F = CS + TF+ SF + E – R
TF and SF were measured in the forest 900 m from
the clearing where the tower with the fog collector and
PVM was located.
Evaporation was estimated using the PenmanMonteith method.
A value of 3.9 mm (Heath 2001) was used for
maximum canopy storage.
Chemical analysis was
performed by ion
chromatography.
Results
Fog frequency
Fog chemical concentrations
3
Fog Presence (% time with LWC > 0.02g/m )
fog2001
fog2002
fog2003
35
30
25
solute
mean
median
min
max
NO3¯
NH4+
18.9
6.6
0.0
437.0
25.5
10.6
0.1
279.2
20
SO42¯
109.0
27.9
0.1
4812.1
15
Na+
189.8
68.5
0.1
3598.3
10
K+
7.1
3.5
0.1
120.3
5
0
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Nov
Oct
Dec
Only months for which at least 70% valid data were
collected are included in the data presented.
Mg2+
23.2
8.4
0.0
362.3
Ca2+
10.6
3.9
0.0
152.6
Cl¯
314.7
118.2
0.1
4262.1
F¯
13.3
5.4
0.1
232.3
The influence of
the nearby active
volcanic vent is
particularly
evident in the
extreme
variability of the
sulfate
concentrations,
for which
maximum values
were as much as
44 times the
mean.
Fog interception and N deposition estimates
Conclusions
Mean annual fog interception for the years 2001-2003 was estimated at 740
mm compared to 2766 mm or rain. However, the uncertainty in this estimate
was high due to uncertainties in the individual parameters of the water balance
equation.
Comparison of inorganic N deposition via different pathways:
This study provided new insight into
ranges and variability of nutrient
concentrations of fog at this site.
A comparison with deposition amounts
via wet and dry deposition shows that
fog contributes the most N to this Nlimited ecosystem, even when an
uncertainty as high as 50% is
assumed.
-1
4
3
Fog dep inorganic N
Wet dep inorganic N
Dry Dep HNO3¯
Dry Dep NO2 Vd = 0.36 cm/s
-1
Estimates of N deposition via fog were
based on average fog N concentrations
and annual interception amounts.
N kgha yr
% Time with Fog
40
2
1
0
Deposition Pathway
Given the high uncertainty in the fog
interception estimates it is clear that
more studies are needed to improve
this estimate and subsequent
deposition estimates.
Long term monitoring of fog frequency
and duration are also needed to
determine the effect of larger climate
patterns such as ENSO cycles.
The majority of the samples
(87%) had less than 1 mg N/L.
Samples with high N
concentrations were rare; only
1% of the samples had
concentrations above 6 mg N/L.
In previous studies of fog at this
site N concentrations were
dominated by N from NO3-. In
contrast, we found that fog
delivers equal amounts of
oxidized and reduced N
10
8
6
-1
50
45
Earlier studies (Heath 2001) at this site had shown
occasional samples with extremely high Nitrogen (N)
content. The origin of these high N samples was found to be
thermal fixation of atmospheric dinitrogen at the hot lava
surface flows (Huebert et al. 1999). One focus of the
intensive sampling in 2001-2003 was to determine the
frequency of such high N samples.
Below are the results for the major ions based on
analysis of >500 samples collected over a 14 months
period. As has been shown in other studies, fog chemical
concentrations were highly variable.
mg NL
Fog was present 23% of the time (mean) and varied
between 8 and 45% on a monthly basis. No seasonal
patterns were evident.
4
Sources of reduced N likely
include volcanic emissions,
biomass burning due to surface
lava flows, and the ocean.
2
0
7/1/2002
9/1/2002
11/1/2002
1/1/2003
Date
3/1/2003
5/1/2003
7/1/2003
Gray bars represent the sum of N from NO3and NH4+. Overlaid in red are concentrations of
N from NO3-. Results for over 500 samples are
included in the graph.
Future Studies
The NPS Inventory and Monitoring program is
initiating climate monitoring in Pacific island
national parks. If funding allows, this effort will
include monitoring of fog frequency & duration
at selected sites in Hawaii and American
Samoa.
References:
Heath, J. A. 2001. Atmospheric nutrient deposition in
Hawaii`i: methods, rates and sources. Ph. D. Dissertation.
University of Hawaii, Honolulu.
Huebert, B., P. Vitousek, J. Sutton, T. Elias, J. Heath, S.
Coeppicus, S. Howell, and B. Blomquist. 1999. Volcano
fixes nitrogen into plant-available forms. Biogeochemistry
47:111-118.
Acknowledgements
This study was funded by a Mellon
Foundation grant. The research was
supported by NPS and USGS staff at
Hawaii Volcanoes National Park.