Cloud water from Loft Mt. (Shenandoah National Park), VA (990 m); ... automobile traffic, and agricultural areas) and availability of field .... VIRGINIA FIELD pH.
CHEMICAL CONCENTRATIONS IN CLOUD WATER FROM FOUR SITES IN THE EASTERN UNITED STATES
Kathleen C. Weathers 1 , Gene E. Likens 1 , F. Herbert Bormann 2 , John S. Eaton 1 , Kenneth D. Kimbal1 3 , James N. Galloway4, Thomas G. Siccama 2 and Daniel Smiley5. 1Institute of Ecosystem Studies, Millbrook, New York 12545, USA 2Yale University, New Haven, Connecticut 06511, USA 3Appalachian Mountain Club, Gorham, New Hampshire 03581, USA 4University of Virginia, Charlottesville, Virginia 22903, USA 5Mohonk Preserve, New Paltz, New York 12561, USA ABSTRACT. Event samples of cloud and fog water were collected in 1984 and 1985 as part of the Cloud Water Project, a large-scale network designed to chemically analyse cloud and rain water from ten sites in North America. The data presented here are from four sites in the eastern United States that ranged in elevation from 5 m to 1534 m, and in geographic location from Virginia to Maine. Cloud water from Loft Mt. (Shenandoah National Park), VA (990 m); Mohonk Mt., NY (467 m); Lakes-of-the-Clouds (Mt. Washington), NH (1,534 m); and Bar Harbor, ME (5 m) was found to be acidic (pH range 2.4-5.5) and dominated by H+, NH4+, S04=, and N03-. Sulphate:nitrate ratios in cloud water for all four sites were similar to sulphate: nitrate ratios in rain water, but varied considerably by event. Very acidic cloud water samples « pH 3.4) were common for all sites: Virginia (31% of all events)~Maine (31% of all events), Mohonk (28% of all events) and Mt. Washington (22% of all events). Although cloud water chemistry at these four sites was similar, deposition rates are likely to be quite different from site to site. For example, wind speeds vary typically from < 1 mls (Maine) to greater than 40 mls (Mt. Washington) and vegetation types range from lowgrowing coniferous (Mt. Washington), to broad-leaved tree species (Virginia and Mohonk) • 1.
INTRODUCTION
In a preliminary study, cloud water collections were made near the summit of Mt. Washington, New Hampshire (Lakes-of-the-Clouds [LC]) from 1981-1983. Average values for cloud water from LC were higher in dissolved substances and lower in pH than rain water collected from the Hubbard Brook Experimental Forest, approximately 80 km SW of the LC 345 M. H. Unsworth and D. Fowler (eds.), Acid Deposition at High Elevation Sites, 345-357. © 1988 by Kluwer Academic Publishers.
346
site (Bormann, 1983). These data, coupled with a few other studies suggesting the same phenomenon (Mrose, 1966; Okita, 1968; Falconer and Falconer, 1980) led us to initiate the Cloud Water Project (CWP) to evaluate the potential stress on terrestrial ecosystems subjected to cloud and fog. The project was designed to gather information on the chemical concentrations of selected elements in cloud, fog and rain water from several sites in North America. The CWP established ten coastal and montane sites that ranged in elevation from 5 m to 1534 m. General criteria for site selection included a high frequency of cloud or fog events, distance from local sources of pollution (e.g. power plants, automobile traffic, and agricultural areas) and availability of field technicians to initiate collections and maintain CWP equipment (Weathers et al., 1986; Weathers et al., in review). The data presented here-are from four CWP sites in the eastern United States. 2.
METHODS
A CWP active collector was used to collect samples of cloud and fog water. A battery-driven fan at the rear of the collector pulls atmospheric droplets (50% efficiency for 5 ~m diameter droplets) through a ventral opening and across a cartridge of 0.78 rom diameter Teflon strands at a velocity of 7.6 m sec-I. The droplets impact on the strands, form larger droplets and drip into a polyethylene bottle below. The collector has been described elsewhere in detail by Daube et a1. (1987). ----Cloud collections were initiated when a prominent, stationary object one kilometer distant (e.g. tower, tree etc.) was obscured from view consistently for fifteen minutes. These conditions constituted an event. The sampling time for each cloud water event was set at five hours from initiation of collection, primarily because of the power limitations of the batteries (few of the CWP sites had AC power in close proximity). Sampling times varied, however, since (a) not all events lasted for five hours and (b) at the Maine site, fog events often occurred from late evening to early morning hours, hence collections were made for the duration of the night. If clouds lifted during the event and visibility improved for fifteen minutes or more, sampling was discontinued. Rain water was collected (wet only) using a standard Hubbard Brook-type rain collector (Likens et al., 1967). Both cloud and rain collectors were covered between eventS-to exclude dry deposition. Field operators used standardized protocol for sample and equipment handling, and for measuring pH. Shipping bottles were acid washed (50% HCl) , rinsed copiously with deionized water at the Institute of Ecosystem Studies (IES), and sent to the sites. Collectors, collection bottles, and tubing were cleaned initially at IES, and were rinsed copiously with deionized water after each collection at field laboratories. Samples of collection-equipment rinsewater and site deionized water were sent to IES for chemical analysis during the collection season.
347
Field operators completed a Sample Description Form for each event noting date; sample type; time collection began and ended; beginning and ending temperature, windspeed and wind direction (at sites where meteorological equipment was available); and general information, including whether the vegetation was wet as a result of the cloud-fog event. Samples were measured for pH (Thomas general purpose glass and Fisher calomel reference electrodes) in the field, usually within one hour of collection. Periodically, inter-laboratory precision was checked by sending reference samples to each of the field technicians for pH measurement. Intra-laboratory accuracy was determined by having the field operators measure pH on two separate aliquots of the same sample for each event they collected. If the two pH measurements differed by more than 0.05 pH units, the aliquots were discarded and two new aliquots of the sample were measured. Samples were stored in the dark and kept cool until they were shipped to IES in Millbrook, New York for chemical analyses. Where volume was sufficient (> 50 ml), samples were analysed for Ca++, Mg++, K+, Na+, NH4+, S04=, N03-, and CI- and measured for pH in the IES laboratory. Sulphate and nitrate were determined by ion exchange chromatography (Dionex 21 I and Dionex 14) (Small et al., 1975), chloride and ammonium using standard Technicon autoanalyser techiques (NH4+ = Indophenol method, CI- = Mecuric thiocyanate method), potassium and sodium by flame atomic absorption (Perkin Elmer 2380) (Slaven, 1968), and calcium and magnesium by inductively coupled plasma (PerkinElmer 6000) emission spectroscopy. pH was measured with a Fisher Accumet 610A pH meter. 3.
COLLECTION SITES
The four CWP sites considered here are: Loft Mt., Virginia (VA); Mohonk Mountain, New York (MK); Lakes-of-the-Clouds, New Hampshire (LC); and Bar Harbor, Maine (ME). The sites are described elsewhere (Weathers et al., in review, Dauble et al., 1987), but in general, vary in elevation from 5 m (ME) to 1534 m-rLC) , and in vegetation type from low-growing, spruce/fir krummholz (alpine vegetation) (LC) to northern hardwood (VA) (Table 1). Three of the sites were located in montane areas, including VA (Blue Ridge Mountains, central VA), MK (Shawangunk Mountains, eastern NY), and LC (White Mountains, northern NH). Sampling season varied somewhat between sites and was dependent primarily upon weather: rime ice collection using the CWP collector was not possible, therefore, since rime iCe is often the form of cloud precipitation from September until May at LC, sampling was conducted from June-September at LC. At sites where rime ice was not a problem, the sampling season was extended beyond June-September: at the ME site collections were made from June-November, from June-December at VA, and year-round at MK.
348
Table
Cloud Water Project.
Site and Sampling Information
Sampling Period*
Site
Elevation
Vegetation Type
1984
1985
Loft Mt., VA
16 June-13 Aug
1 July-3D Nov
500
Northern Hardwood
Mohonk Mt.,
18 June-3 Dec
1 Jan-12 Nov
467
Mixed Hardwood, Conifer
18 June-12 Sept
16 June-6 Sept
8 June-29 Nov
5 June-13 Oct
(m)
NY
Lakes-ofthe-Clouds,
Spruce/Fir Krummholz Alpine Tundra
1534
NH
Bar Harbor,'
Conifer
5
ME
*Dates when first and last samples were collected. 4.
RESULTS AND DISCUSSION
Cloud water samples from these four CWP sites were acidic, with generally higher concentrations of ions relative to rain water from the same site. Sulphate, nitrate, ammonium and hydrogen ions constituted from 75 to 94% of the overall mean ionic composition for all four sites. The percent contribution of various ions was similar for all sites (Fig. 1). However, sodium and chloride from the Maine Site, AVERAGE PERCENT CONTRIBUTION of IONS for CLOUD WATER
I
NH4 504
catl
cat
I
504
I I
H
NH4
caq
N03
I
I
VIRGINIA
I
I
MOHONK MT , NY
N03
Cl
I
i
II
H
NH4 504
i
Cl
H
NO!
Cl [at,
0
Na, 504
NH4
(n= 20)
(n= 23)
LAKES, NH (n=35)
i
H
N03
(~eq/I)
MAINE
CI
(n= 16)
100%
Figure 1 Average percent contribution of ions for cloud water (unweighted) (lleq/1) • Cat = Ca++, Mg++, K+ , Na+. Cat* =Ca++, Mg++ , K+.
349
9 I/)
>
U Z
~ 7 IL
:I
5
0
'" 3
II:
0
III
:)
III LL
VIRGINIA FIELD pH CLOUDWATER
x= 3·5 MED
",3·7
I/)
LL
o 1
z
2·5 3·0 3·5 4·0 4·5 5·0 5·5 PH
MOHONK MOUNTAIN FIELD pH
9
CLOUDWATER
I/)
~ 7
> IL u :15 z
III
:)
0
III
II: LL
x",3·5 MED
'"
",3·5
1/)3 LL
0
o 1
z
2·5 3·0 3-5 4-0 4·5 5·0 5·5 PH
LAKES FIELD pH CLOUDWATER
X= 3·7 MED
",3·9
2·5 3·0 3-5 4-0 4·5 5·0 5·5 PH
9 I/)
~ 7
> IL U z :I 5
III
:)
0
III
II:
LL
MAINE FIELD pH FOG WATER
'"
1/)3 LL
0 o 1
z
2·5 3·0 3-5 40 4·5 5·0 5·5 PH
Figure 2
Field pH measurements of cloud water.
x=3·3 MED
",3·8
~
o
100
200
300
400
500
Figure 3.
u
o
Z
U
lI:I
~
= Z o ~
Cr lI:I
600
700
X
X I
~
X X X J
CLOUD
MK
v/////tj
~
RAIN
LC
V////J/fXXXl
Mean concentration for cloud and rain water (sulphate).
VA
veL/L/'] x
**
P~O.01.
ME
I(0C'ffAf'>C'C> MK & VA > ME) and assume comparable forest canopy capture efficiencies between all four of our sites, we would expect LC to have the greatest deposition rate by virtue of the fact that it has the highest overall windspeed. If we add an additional parameter--vegetation type (LC =
356
coniferous, MK & VA = deciduous and coniferous, and ME = coniferous)-and assume that coniferous vegetation is more efficient at scavenging cloud droplets than deciduous vegetation, we might still estimate highest deposition rates at LC, but, it becomes increasingly difficult to speculate about the relative deposition rates at the other three sites. Maine has the lowest average windspeeds, but is also characterised by coniferous vegetation while VA and MK have higher windspeeds and deciduous vegetation. The problem of quantifying and comparing deposition rates becomes very complex when comparing various sites with different characteristics. The challenge is clear relative to quantification of cloud and fog water deposition on natural landscapes. From the data we have presented for four CWP sites, it is clear that while chemical concentrations of cloud water are similar between the sites, deposition rates may vary considerably. To make estimates of the input of mineral acids and nutrients to specific ecosystem via cloud water deposition, future research should be directed toward making the measurements necessary to enable quantification of deposition of cloud water to forest canopies. ACKNOWLEDGEMENT This research was funded in part by grants from the Andrew W. Mellon Foundation, and through a cooperative agreement with the United Statdes Environmental Protection Agency (813-934010 as part of the Mountain Cloud chemistry programme, Dr Volker A. Mohnen, Principal Invesigator. We thank B. Daube, W. Malpass, J. Di Mauro, M. Keifer, R. Mannix, J. Coury, C. Wilson, D. Cass, J. Andersen, S. Eliassen and P. Huth for field assistance, and the Appalachian Mountain Club, Shenandoah National Park, and the College-of-the-Atlantic for use of their facilities. This is a contribution to the programme of the Institute of Ecosystem Studies, The New York Botanical Garden and the Hubbard Brook Ecosystem Study. REFERENCES Bormann, F.H. 1983. Factors confounding evaluation of air pollution stress on forests: Pollution input and ecosystem complexity. Proceedings of the symposium "Acid deposition a challenge for Europe". (Edited by H. Ott and H. Stangler, preliminary edition). Commission of the European Communities. XII/ENV/45/83. Brussels, Belgium. Daube, B.C. Jr., Kimball, K.D., Lamar, P.A. and Weathers, K.C. 1987. Two new cloud water collector designs that reduce rain contamination. Atmos. Environ. 21: 893-900. Falconer, R.E. and Falconer, P.D. 1980. Determination of cloud water acidity at a mountain observatory in the Adirondack Mountains of New York State. J. Geophys. Res. 85, 7465-7470.
357 Galloway, J.N., Likens, G.E. and Hawley, M. 1984. Acid precipitation: Natural versus anthropogenic components. Science 226, 829-831. Hori, T. (ed.) 1953. Studies on fogs in relation to fog preventing forests. Tanne Trading Co., Japan. Likens, G.E., Bormann, F.H., Johnson, N.M. and Pierce, R.S. 1967. The calcium, magnesium, potassium and sodium budgets for a small forested ecosystem. Ecology 48, 772-785. Lovett, G.M., Reiners, W.A. and Olson, R.K. 1982. Cloud droplet deposition in subalpine balsam fir forests: Hydrological and chemical inputs. Science 218, 1303-1304. Mrose, H. 1966. Measurements of pH, and chemical analyses of rain-, snow-, and fogwater. Tellus XVIII, 266-270. Okita, T. 1968. Concentration of sulphate and other inorganic materials in fog and cloud water and aerosol. J. Meteorol. Soc. of Japan 46, 120-127. Slavin, W. 1968. Atomic absorption spectroscopy. John Wiley Interscience,. New York. Small, H., Stevens, T.S. and Bauman, 1975. Novel ion exchange chromatographic method using conductimetric detection. Anal. Chern. 47, 1801-1809. Waldman, J.M., Munger, J.W., Jacob, D.J., Flagan, R.C., Morgan, J.J. and Hoffman, M.R. 1982. Chemical composition of acid fog. Science 218, 677-679. Waldman, J.M. 1985. Depositional aspects of pollution in fog. Ph.D. thesis, California Institute of Technology Report # AC-11-85. Weathers, K.C., Likens, G.E., Bormann, F.H., Eaton, J.S., Bowden, W.B., Andersen, J., Cass, D., Galloway, J.N., Keene, W.C., Kimball, K.D., Smiley, D. and Huth, P. 1986. A regional acidic cloud/fog event in the eastern United States. Nature 319, 657-658. Weathers, K.C., Likens, G.E., Bormann, F.H., Bicknell, S., Bormann, B.T., Daube, B.C. Jr., Eaton, J.S., Galloway, J.N., Kadlecek, J.A., Keene, W.C., Kimball, K.D., Lugo, A., McDowell, W.H., Siccama, T.G., Smiley, D. and Tarrant, R. Cloud water chemistry from ten sites in North America (in review).
