AI,,,o#& Euvimwmt Vol.2l.No.6.~. 1369-1374. 1987. PrinwdinGrutBriti.

ooM~1/87$3.00+0.00 Q I987 Rrpmcm Jourruls Ltd.

VARIATION OF WET DEPOSITION CHEMISTRY IN SEQUOIA NATIONAL PARK, CALIFORNIA

THOMAS J. STOHLGREN and DAVID J. PARSONS

Sequoia and Kings Canyon National Parks, Three Rivers, California 93271, U.S.A.

(Firsr received 25 July 1986 and injidjorm 5 Nooember 1986)

Abstract-Sequoia National Park has monitored wet deposition chemistry in conjunction with the National Atmospheric Deposition Program and National Trends Network (NADP/NTN). on a weekly basis since July, 1980. Annual deposition of H, NO, and SO4 (0.045,3.6, and 3.9 kg ha-’ a- r, respectively) is relatively low compared to that measured in the eastern United States, or in the urban Los Angeles and San Frannsco areas. Weekly ion concentrations are highly variable. Maximum concentrations of 324.162. and 156 pq C- ’ of H. NO, and SO. have been recorded for one low volume summer storm (1.4 mm). Summer concentrations of NO, and SO, average two and five times higher, respectively, than conantrations reported for remote areas in the world. There is considerable variability in the ionic concentration of low volume samples, and much less variability in moderate and high volume samples.

Key word index: Wet deposition, California, dry deposition, precipitation chemistry.

INTRODUCTION

Acidic deposition is widespread in California (Lawson and Wend& 1982). Its occurrence has been documented in the Los Angeles basin (Morgan and Liljestrand, 1980), the San Francisco Bay Area (McCall, 1980), the San Joaquin Valley (Rowe and Chestnut, 1985)and the Sierra Nevada (Melack et al., 1982).

Most of the early studies on precipitation chemistry in the Sierra Nevada were carried out in the N or central part of the range and were of relatively short duration (1 year or less). Many of these studies looked only at relatively clean winter precipitation. Brown and Skau (1975), McCall (1980) and Leonard et al. (1981) all reported volume weighted pH values between 5.1 and 5.7, NO, values beq d-l) between 2 and 8, and SO1 values @eq i- ‘) between 3.5 and 13.3. Laird et al.

(1986), in a one-time sampling of snowpack chemistry along the Sierra Nevada, commonly found nitrate and sulfate values of < 1 geq C - ’ and < 3 geq C- ‘, re- spectively. These data would suggest little or no anthropogenic influence on precipitation chemistry. In contrast, the first year (7/80-6/81) wet-only precipi- tation chemistry data from the Sequoia National Park NADP station (located at Giant Forest, elevation 1856m) in the S Sierra Nevada showed a volume weighted pH of 4.98 and mean volume weighted NO, and SO., concentrations of 10.6 peq d-’ and 12.9 cceq I-‘, respectively (Lawson and Wendt, 1982). In September 1981, a pH of 3.5 was recorded for a weekly NADP sample at Sequoia. In the E-central Sierra, Melack et al. (1982) found low NO1 and SO, concentrations ( < 3 keq d- ’ and < 7 peq t - ‘, re- spectively) in winter/spring precipitation as compared with summer/fall concentrations (17 peq d- ’ and 36peq d-l).

Concern has recently been expressed about the potential effects of acid deposition in the Sierra Nevada, which lies E and upwind of California’s major metropolitan areas (Roth et al., 1985). Recent studies found these mountainous areas to have shallow and poorly buffered, granitic soils (McCall, 1981), and extremely low alkalinity lakes (Melack et al., 1985). Under such conditions slight increases in deposition acidity may have pronounced ecological effects (Tonnessen and Harte, 1982). Careful monitoring of precipitation chemistry is important to fully under- stand the threat of anthropogenic pollution to such sensitive Sierran ecosystems as those found in Yosemite, Sequoia and Kings Canyon National Parks.

Although wet precipitation is responsible for only a part of an ecosystem’s total deposition, we have decided to monitor wet deposition until improved dry and/or bulk collectors become available (Hicks, 1985). This paper reviews the wet deposition chemistry recorded between 1980 and 1984 as part of the National Atmospheric Deposition Program (NADP) and National Trends Network (NTN) in Sequoia National Park.

STUDY AREA

Sequoia National Park is located in the southern Sierra Nevada of California (Fig. 1). It is thought to receive airborne pollutants from as far as the San Francisco Bay area (Hansen et al., 1982). The Park encompasses an elevation gradient from 400 m in the foothills of the San Joaquin Valley to over 4408 m at the top of Mount Whitney. It includes foothill grass- land and chaparral landscapes, mixed conifer forests, extensive subalpine forests, granitic outcrops and over 2000 high elevation lakes.

1369

1370 THOMAS J. STOHLGREN and DAVID J. PARSONS

h CALIFORNIA

I L---w I

SEQUOIA NATIONAL

PARU

I I

Fig. 1. Location map of Giant Forest NADP site in Sequoia National Park, California.

Pr~ipitation varies along the elevation gradient from 680 mm a-’ (Ash Mountain, elevation 400 m) to 1170 mm a- ’ (Giant Forest, 1950 m). In California, the bulk of pollutant emissions are produced in three major areas: S California, the San Francisco Bay area, and the San Joaquin Valley. Pollutants from the San Francisco Bay area and the San Joaquin Valley likely travel on W winds into the S Sierra Nevada (Unger, 1978; Hansen et al., 1982).

Unlike climatic patterns in the NE United States where precipitation occurs at relatively regular inter- vals throughout the year, California experiences a M~iterranean climate with a predictable dry season in the summer months. Pollutant transport during wet season storms may be very different than transport during the dry season (Roth et ol., 1985). During the dry season when air masses stagnate over the San Joaquin Valley, air flow IO the S Sierra Nevada may originate from both the San Francisco Bay Area and the S end of the San Joaquin Valley near the Bakersfield oil refineries (Unger, 1978; Smith ef al.. 1981). This polluted air mass may be recirculated through the Central Valley via low ievel winds (the ‘Fresno Eddy’) between Bakersfield and Stockton prior to moving W and upslope into the S Sierra Nevada with the prevailing winds (Morgan and

Slusser, 1978). In contrast, it has been proposed that frequent winter wet-season storm tracks off the Pacific Ocean tend to transport pollutants N and NW from the San Francisco Bay area toward the Coast Range and N Sierra Nevada while San Joaquin Valley

pollutants move N and NW into the S Sierra Nevada and further N into the Central Valley (Hansen et ai.,

1982).

METHODS

The National Park Service, in conjunction with the National Atmospheric Deposition Program (NADP), began monitoring wet precipitation at Giant Forest (NADPsite057550;36:34’N Lat, 118:47’W Long)in July, 1980. This site is located on a west facing slope, at an elevation of 1856 m within a mixed conifer forest. Pr~ipi~tion samples are collected weekly in an Aerochem Metrics Model 201 device designed to expose a collection bucket only during periods of precipitation. Samples are analyzed according to stan- dard NADP procedures (National Atmospheric Deposition Program, 1984). If no precipitation occur- red during the week, the wet bucket is replaced by a cleaned one and no analyses are performed. Quality control and quality assurance procedures follow es- tablished NADP protocol (e.g. consistent use ofcheck- samples, and participation in NADP sample audit programs). Output tables are provided of weekly concentration (in mg 1c- ‘) and deposition (in mgm- *), and are available from the NADP Central Analytical Laboratory in Champaign, Illinois. Concentration data were converted to peq / - ’ to normalize data by ionic charge.

Dry bucket samples were collected several times during the study period in an effort to quantify dry deposition, Analysis showed that most dry bucket samples were contaminated with insects, bird feces, and an undetermined amount of dust and dirt. For such reasons, results are not considered to be reliable estimates ofdry deposition and are not presented here.

RESULTS

Annual pr~~pitation and ion deposition chemistry were found to vary (Table 1). In I981 and 1982, total precipitation was 44 % and 1440/, respectively, of the long term average for Giant Forest. Volume weighted concentrations of H, Ca. Mg, NH.+, NO3 and SO1 were nearly twice as great in 1981 as in 1982. Yet due to the higher total precipitation the deposition levels were actually greater for all ions in 1982. Annual wet deposition of NO3 and SO, increased from 1981 to 1983, then dropped in 1984. The relative contribution of the various ions does not appear to vary much from year to year. Anion abundance (mass/unit area) fol- lowed the general pattern SO, > NOa > Cl > PO4. Cation abundance followed the general pattern NH,

Variation of wet deposition chemistry in Sequoia National Park, California 1371

Table 1. Mean annual volume weighted pH, ~nduc~ivity and ion concentration and annual deposition of wet precipitation at Giant Forest, Sequoia National Park, ~liforn~

Conductivity Mean volume weighted concentration beq r- ‘) Year PH j&cm-’ H Ca Mg K Na NH, NO, Cl SO, PO4 Cations Anions

1981 4.98 7.2 10.5 4.69 2.55 0.59 4.00 9.4 8.4 4.5 12.3 0.09 31.7 25.3 1982 5.19 4.6 6.5 2.00 1.32 0.41 3.09 3.9 3.9 5.6 7.0 0.09 17.2 16.6 1983 5.26 4.4 5.5 2.65 1.81 0.95 5.00 7.2 6.1 5.6 7.9 0.13 23.1 19.7 1984 5.21 4.4 5.4 11.48 2.88 0.87 4.09 14.4 7.7 11.3 8.5 0.09 39.1 27.5 All samples 5.19 4.9 6.5 3.99 1.89 0.69 4.00 7.3 5.8 6.3 8.3 0.09 23.4 20.5

Precipitation amount Deposition (mg m-*)

Year (cm) H Ca Mg K Na NH4 NO3 Cl SO, PO4

1981 1982 1983 1984 Annual arithmetic mean S.E.

51.1 3.3 61.8 21.0 l5.0 60.5 111.0 341.5 104.0 388.1 2.2 168.9 7.2 63.0 25.9 24.4 114.9 102.3 378.6 322.8 441.8 4.5 136.7 4.8 71.6 30.7 54.4 162.0 182.1 531.4 279.2 531.1 5.8 58.4 2.8 41.6 19.9 47.3 48.0 44.3 202.6 80.0 201.5 2.2

103.8 4.5 59.5 24.4 35.3 96.4 109.9 363.5 196.5 390.6 3.7 29.1 1.0 3.2 2.5 9.3 26.3 28.2 67.6 61.2 69.6 0.9

Data are from 1981 to 1984. Sampler was inoperable from 17 February to 7 March 1981.

= Na > Ca > K = Mg > H. The ~tion/anion ratio beq L- ‘) for most precipilation samples, and thus for annual means, was slightly greater than 1 .O. The annual mean NO,/SO,, ratio (derived from concentrations, Table 1) ranged between 0.56 and 0.91. The mean ratio for all samples analyzed over the 4 years was 0.70.

Monthly variability of wet deposition chemistry is

much greater than annual variability (Table 2). There

is a strong relationship between sample vofume (gener- ally governed by climate and rainfall patterns) and precipitation chemistry. In general, specific conduct- ance and ion concentrations increase as sample volume decreases. Lower sample volumes generally occur during the drier summer months. The ions most often associated with acidic deposition (H, NO, and SOJaIl peak during summer months when sample volume

Table 2. Monthly volume weighted ion concentrations for wet deposition at Giant Forest, Sequoia National Park, California

Mean Volume sample weighted Volume weighted ion concentration

volume ml conductivity Month n (1 S.E.) WScm-‘) H Ca Mg K Cl so. PO,

January 10

February IO

March 13

April 10

May 10

June 5

July 4

August 7

Scptcmbcr 5

October II

November 15

Daxmher IS

3200 (1440) 3700 (830)

4110 (760) 2330 (950) 980 t.510)

f?Z)

(Z,

(21 2090

(1630) 1830 (620)

4830 (1050) 2920 (870)

3.2 9.2 t .50 0.82 0.51 3.04 2.8 1.9 10.4 3.3 0.09

3.7 4.8 8.48 1.65 0.26 3.04 3.8 3.2 4.2 5.6 0.09

4.9 6.4 2.00 1.65 0.26 3.92 50 5.0 10.2 5.6 0.09

5.9 10.8 3.49 1.65 0.51 2.61 8.9 6.5 2.8 12.7 0.09

11.7 14.5 13.97 7.41 1.28 12.18 20.5 13.9 10.4 30.8 0.09

15.7 44.1 12.97 4.11 1.53 5.22 30.5 28.4 4.8 39.3 0.09

23.1 37.0 16.70 6.58 8.44 11.74 27.7 49.5 8.2 35.6 0.13

19.1 18.9 17.50 5.76 5.63 5.66 63.8 59.2 7.3 40.0 0.09

5.1 11.4 3.99 1.65 0.77 1.74 5.5 7.6 2.0 9.2 0.09

6.8 11.2 3.99 2.41 0.77 3.92 11.1 13.7 3.9 II.9 0.09

3.9 6.7 2.99 1.65 0.51 2.61 9.4 3.7 3.3 6.2 0.09

4.0 5.2 2.50 2.47 1.02 6.52 2.8 2.7 8.2 7.3 0.16

Data are from July 1980 to Dwcmbcr 1984.

1372 THOMAS J. STOWLGREN and DAVID .I. PARSONS

(Table 2) is low. Although sample volume and sample volume variability are great in the winter months, ion concentrations remain relatively low.

There is great variability in the NO1 and SO, ion concentration of low volume samples, and much less variability in moderate and high volume samples (Fig. 2). All ions show similar patterns with respect to sample volume. Sample pH tends to be lower for lower volume samples. This was, however, not always the case. In fact, the highest pH values recorded (though few in number) were from low volume samples.

PRECIPITATION VOLUME ,,,,s.,L,

DISCUSSIOK 200

The use of Aerochem Metrics type samplers is a common technique for collecting wet deposition for chemical analysis. Prior to interpreting the data, however, it is important to discuss the inherent problems associated with these collectors. First, weekly samples may be an admixture of several precipitation events or a partial event (i.e. if the sample is collected during an event). Secondly, the chemistry of a pr~ipitation event that occurred early in the collec- tion period may be quite different from a chemically similar event occurring closer to the sample collection and analysis date. That is, storage of the former sample at ambient temperatures may alter chemistry. Thirdly, it has been demonstrated that weekly samples may yield different ion con~ntration and deposition values than those obtained from analyzing individual events (Pena et al., 1985; Sisterson et al., 1985; Reddy et nl., 1985). Finally, as mentioned earlier, wet precipitation data do not include dry deposition and thus cannot be used to describe total atmospheric deposition. This is particularly important in drier climate areas, such as California, where dry deposition may be a substantial component of total acid deposition (Lawson and Wendt, 1982; Hansen et al., 1982).

PRECIPITATION VOLUME IlilerSl

2604

- 1

- 200 7

zf 150 L 1

The variation in annual wet deposition chemistry found in Sequoia correlates well with total precipi- tation (Table I). The 2 years with the lowest total precipitation, 1981 and i984, had lower wet deposition rates for most ions relative to the wetter years, 1982 and 1983, which is expected as deposition is partly a function of precipitation volume. What is not known is whether dry deposition was corr~pondingly higher during the drier years, resulting in similar or even greater total deposition. It will be impossible to determine trends in deposition chemistry until ac- curate long term data sets are available for both wet and dry deposition (Hicks, 1985; Lawson and Wend& 1982).

Fig. 2. Distribution of pH, NO3 and SO, concentra- tions to precipitation (sample) volume in wet deposition at Giant Forest, Sequoia National Park, California.

Hampshire, is 0.44 (Likens et af., 1984). At Sequoia National Park, NOa may be a sig~i~cantly more important anion than sulfate (NOJSO* ratios may be as high as 1.48) during the summer months (Table 2). NOI/SO,, ratios at Hubbard Brook are highest (up to 0.77) during the winter months, but as in other areas in the East, strong acid ions in precipitation are suifate- dominated (Likens et al., 1977).

The mean N03/S04 ratio for wet deposition during Annual summaries of precipitation chemistry the 4 years of available data at the study site is 0.70 (Tabie 1) may underestimate the impact of anthropo- (Table 1). McCall et al. (1982) reported NOJ/SO~ gcnic pollutants to Sequoia. Table 3 shows that mean ratios greater than 1.0 in N California as did Morgan annual volume-weighted concentrations of H, SO, and Liljestrand (1980) in S California. In contrast, the and NOa are at or near levels found for precipitation in long term bulk precipitation NO,/SG, ratio at remote (un~~lut~~ areas of the world (Galloway er Hubbard Brook Experimental Forest, New al., 1984). Upon closer examination, however, summer

Variation of wet deposition chemistry in Sequoia National Park, California 1373

concentration of SO, is twice as high and NO, levels live times as high as pr~pitation in remote areas. And although Sequoia National Park receives just 4.7a/ 18.9% and 10.3% of the H, NO, and SO, bulk deposition that falls at Hubbard Brook (Likens et al., 19841, the high summer (and maximum) values re- corded at the Park (Table 3) may we!1 be cause for ecological concern, To complicate matters, the dry summer period is the time when the great bulk of dry deposition probably occurs in this area (Lawson and Wendt, 1982). Pulses of highly acidic precipitation or other pollutant loaded events are suspected to be potentially more damaging to certain ecosystems than higher total levels spread evenly through the year (Hooper and Shoemaker, 1985). This may be particu- larly important in the Sierra Nevada where low alkalinity lakes that characterize the area appear to be especially susceptible to pulse events of acidic input (Tonnessen and Harte, 1982 Melack er oL, l985).

It is uncertain at this time what minimum concen- trations of acid may cause direct or indirect foliar damage to most plant species, but it is important to note that concentrations are highest during the prim- ary growing season and the period of maximum drought stress, both of which occur during the summer (Table 2). The 96.6 ml sample collected following a low-volume (1.4 mm)storm on 15 September 1981, for example, had NO1 and SO, concentrations of 162 and 156 geq i - ‘, respectively, and a pH of 3.49. For areas in the W United States, it may be more important to monitor and evaluate dry-season acid deposition events such as these, than to attempt to evaluate subtle changes in annual precipitation chemistry. Additional plant physiological stresses (i.e. summer drought stress) may further effect plant growth and reproduc- tion by reacting synergisti~lly with stresses caused by ozone and acid deposition (Miller, 1985).

The inverse relationship between sample volume and ion concentration suggested earlier by Lawson and Wendt (1982) based on 1 year of data is only partially confirmed by this study. The extremely high variability of ion concentrations when sample volumes are low makes statistical interpretation of the distri-

bution problematic (Fig. 2). We attempted to fit the data to exponential and log normal curves with poor success (i.e. r2 values <0.25). Thus, sample volume alone does not explain much of the variability in the distributions. Some of the variability may be due, in part, to the length of the dry period between storm events (McCall et al., 1982) and/or collecting samples in the middle of events. If large volume winter storms with low ion concentrations are bisected by scheduled sampling, it artificially creates two low volume, low concentration samples. Sampling wet deposition on an event basis would eliminate this problem but would be more expensive and data would not be comparable to other NADP sites.

Acknowledgements-We thank John Melack. Jill Baron, Kathy Tonnessen, David Graber and others for critical reviews of earlier versions of the manuscript. Tom Nichols, Patti Haggerty, Anne Esperanza and Amy Workinger pro- vided valuable field and laboratory assistance. This work was jointly sponsored by the National Park Service and the National Atmospheric Deposition Program.

REFERENCES

Brown J. C. and Skau C. M. (1975) Chemical composition of snow in the east central Sierra Nevada. Cooperative Report Series Publ. No AG-1, Renewable Natural Resources Division, Univ. of Nevada, Reno. Nevada.

Galloway J. N, Likens G. E. and Hawley M. E. (1984) Acid precipitation: natural versus anthropogenic components, Science 226, 829-83 1.

Hansen D. A., Young J. R. and Hidy G. M. (1982) Review of acid deposition research in California. Environmental Research and Technology. Inc. ERT Document NO. P- ..- BSOi-000, Westlake Village, California.

Hicks B. B. (1985) Measuring dry deposition: a re-assessment of the state of the art. Proceedings of Symposium on Acid Precipifation. 15-20 Sept., 1985, Ontario, Canada.

Hooper R. P. and Shoemaker C. A. (1985) Aluminum mobilization in an acidic headwater stream: temporal variation and mineral dissolution disequilibria. Science 229,463-465.

Laud L, B., Taylor H. E. and Kennedy V. C. (1986) Snow chemistry of the Cascade-Sierra Nevada Mountains. Enoit. Sci. Technol. 20, 275-290.

Table 3. Comparison of major ion concentrations (req /- ‘) for Hubbard Brook Experimental Forest, New Hampshire (bulk precipitation for 1963-1982) and Sequoia National Park, California (wet pr~ip~tation for 7/80-12/84) to suggested background wet precipitation concentrations in remote areas (see Galloway et al.,

1984)

Hubbard Brookt Sequoia Sequoia: Experimental

Sequoia4 National Park National Park, National Park

Remote areas* Forest 1981-1984 summer only (a = 23) maximum

H lo-20 69.3 6.5 18.0 324 so, 3-10 54.0 8.3 19.4 156 NO, 2-5 23.5 5.8 24.1 162

l Remote sites are San Carlos, Venezuela; Poker Flat. Alaska; Amsterdam island, Indian Ocean; Bermuda, Atlantic Ocean.

t From Likens ef at., 1984. $ Summer samples include JuntSeptember samples, $From sample collected 15 September 1981 (pH = 3.49, sample volume = 96.9 ml).

1374 THOMAS J. STOHLGREN and DAVID J. PARSONS

Lawson D. R. and Wendt J. G. (1982) Acid deposition in Tahoe, California, 19-21 June 1978, pp. 55-60. California. Society of Automotive Engineers, Inc. ISSN Morgan J. J. and Liljestrand H. M. (1980) Measurement and 0148-7191. interpretation of acid rainfall in the Los Angeles basin.

Leonard R. L., Goldman C. R. and Likens G. E. (1981) Some Final Report. California Air Resources Board, Sacramento. measurements of the pH and chemistry of precipitation at National Atmospheric Deposition Program (1984) NADP Davis and Lake Tahoe, California. Worer Air Soil Pollur. Quality assurance plan: deposition monitoring. 15. 153167.

Likens G. E., Bormann F. H., Pierce R. S., Eaton J. S. and Johnson N. M. (1977) Biogeochemisrry o/ a Forested Ecosystem. Springer, New York. _

Likens G. E.. Bormann F. H.. Pierce R. S.. Eaton J. S. and Munn R. ‘E. (1984) LongIterm trends’in precipitation chemistry at Hubbard Brook, New Hampshire. Atmospheric Environment 18, 2641-2647.

McCall J. G. (1980) A survey of acid precipitation in northern California. Final Report of Calif. Air Resources Board, Contract A7-139-30.

McCall J. G. (1981) ElTects ofacid rain on plants and soils in California. California Air Resources Board, Contract A8-13631, p. 111.

McCall J. G., Monette L. K. and Bush D. S. (1982) Chemical characteristics of wet and dry atmospheric fallout in northern California. J. Enuir. Quality 11, 585-590.

Melack J. M., Stoddard J. L. and Dawson D. R. (1982) Acid precipitation and buffer capacity of lakes in the Sierra Nevada, California. Proceedings of Inrernafional Symposium on Hydromereorology, American Water Resources Association, pp. 35-41.

Melack J. M., Stoddard J. L. and Ochs C. A. (1985) Major ion chemistry and sensitivity at acid precipitation of Sierra Nevada lakes. Water Resources Res. 21, 27-32.

Miller P. (1985) The impacts of air pollution on forest resources. USDA Forest Service, Forest Research West, August, 1985, pp. l-5.

Morgan D. L. and Slusser W. F. (1978) A pilot study of upslope winds in the Sierra Nevada. Paper presented at Conference on Sierra Nevada Meteorology, South Lake

Pena R. G., Walker K: C., Lebowitz L. and Micks-J. G. (1985) Wet deposition monitoring-effect of sampling period. Armospheric Enuironmenr 19, 151-156.

Reddy M. M., Lieberman T. D., Jelinski J. C. and Caine N. (1985) Variation in pH during summer storms near the continental divide in Central Colorado. U.S.A. Arctic A/pine Res. 17, 79-88.

Roth P., Blanchard C., Harte J., Michaels H. and El-Ashry M. T. (1985) The American West’s acid rain test. World Resources Institute Report No. 1.

Rowe R. D. and Chestnut L. G. (1985) Economic assessment of the effects of air pollution on agricultural crops in the San Joaquin Valley. j. Air Polk C&o/ Ass. 35,728-734.

Sisterson D. L.. Wurfel B. E. and Lenht B. M. (1985)Chemical differences between event and weikly precipitation samples in northeastern Illinois. Armospheric Environment 19, 145331469.

Smith T. B., Lehrman D. E., Reible D. D. and Shair F. H. (198 I) The oriein and fate of airborne nollutants within the San Joaquin talley Report to California Air Resources Board. Contract No. MRI-1838, pp. l-15.

Tonnessen K. A. and Harte J. (1982) Potential for acid precipitation damage to lakes of the Sierra Nevada. California. In Proceedings of lnrernarional Symposium on Hydromereorology, American Water Resources Association, pp. 75-78.

Unger C. D. (1978) The transport of photochemical smog in the Central Valley and the Sierra Nevada mountains of California. Paper presented at Conference on Sierra Nevada Meteorology, South Lake Tahoe, California, 19-21 July 1978, pp. 3841.