GEOLOGICAL SURVEY CIRCULAR 910 

Evidence for 

Acid-Precipitation-Induced 

Trends in Stream Chemistry at 

Hydrologic Bench-Mark Stations 

Evidence for 

Acid-Precipitation-Induced 

Trends in Stream Chemistry at 

Hydrologic Bench-Mark Stations 

By Richard A. Smith and Richard B. Alexander 

GEOLOGICAL SURVEY CIRCULAR 910 

1983 
United States Department of the Interior 

JAMES G WATT, Secretary 

Geological Survey 

Dallas l. Peck, Director 

Free on application to Branch of Distribution, U.S. Geological Survey, 604 South Pickett Street, Alexandria, VA 22304 
FIGURE 1. 

2. 

Abstract .. 

Introduction 

Methods 

CONTENTS 

Atmospheric contributions to stream sulfate . 

Results and discussion . . ·. . 

Trends in stream sulfate . . 

Trends in S02 emissions . . 

Trends in stream alkalinity 

Trends in stream pH 

Summary . 

References . . . . . . . . 

ILLUSTRATIONS 

Page 

1 

1 

2 

4 

7 

7 

7 

8 

10 

11 

12 

First year of record for (a) sulfate, alkalinity, and cation concentrations, and (b) pH at Bench-Mark stations . 

Comparison of trends in stream sulfate concentrations at Bench-Mark stations for the period of record 

through 1981 with trends in S02 emissions to the atmosphere by State, 1965-1980 ..... . 

3. Trends in (a) alkalinity, and (b) the ratio of alkalinity to total major cation concentration at Bench-Mark 

stations for the period of record through 1981 . . . . . . . . . . . . . . . . 

4. Trends in pH at Bench-Mark stations for the period of record through 1981 

TABLES 

Page 

3 

5 

6 

9 

Page 

TABLE 1. Drainage area, mean discharge, and annual precipitation at Bench-Mark stations . . . . . . . . . . . . 2 

2. Summary statistics for sulfate concentrations at Bench-Mark stations, period of record through 1981 4 

3. Summary statistics for alkalinity at Bench-Mark stations, period of record through 1981 . 7 

4. Summary statistics for the ratio of alkalinity to total major cation concentrations at Bench-Mark 

stations, period of record through 1981 . . . . . . . . . . . . . . . . . . . . . . . 8 

5. Summary statistics for pH at Bench-Mark stations, period of record through 1981 10 

6. S02 emissions by State for the period of record 1965-1980 . . . . . . . . . . . . . . 11 

Evidence for Acid-Precipitation-Induced Trends in 

Stream Chemistry at Hydrologic Bench-Mark Stations 

By Richard A. Smith and Richard B. Alexander 

ABSTRACT 

Ten- to 15-year water-quality records from a network of 

headwater sampling stations show small declines in stream sulfate concentrations at stations in the northeastern quarter of 

the Nation and small increases in sulfate at most southeastern 

and western sites. The regional pattern of stream sulfate 

trends is similar to that reported for trends in 802 emissions 

to the atmosphere during the same period. Trends in the ratio 

of alkalinity to total major cation concentrations at the stations 

follow an inverse pattern of small increases in the Northeast 

and small, but widespread decreases elsewhere. The undeveloped nature of the sampled basins and the magnitude and 

direction of observed changes in relation to 802 emissions support the hypothesis that the observed patterns in water quality 

trends reflect regional changes in the rates of acid deposition. 

INTRODUCTION 

During the past decade evidence has accumulated suggesting that the phenomenon of acid precipitation may involve the transport of air pollutants over long distances and the deposition of 

acidic materials in basins with widely differing 

geochemical capacities for neutralizing acids (N ationa! Research Council, 1981; 1983). These two 

characteristics of the acid deposition problem give 

rise to the need for a more detailed geographic 

understanding of the phenomenon than presently 

exists for the Nation as a whole. A recent analysis 

of available data from eastern North America by 

the National Research Council (1983) links historical trends in atmospheric emissions of so2 and 

NOx to trends in precipitation chemistry at a 

single site, the Hubbard Brook Experimental 

Forest in New Hampshire. A major conclusion of 

that study is that the lack of long-term records 

1 

of precipitation chemistry at sites in other regions 

of the country greatly hinders efforts to associate 

specific source areas of acid-producing materials 

with the sensitive areas receiving those materials. 

In this report we describe a geographic pattern 

in recorded changes in water chemistry at a 

nationwide network of stream sampling stations. 

The nature of these stations, and the geographic 

pattern of atmospheric so2 emissions occurring 

during the period of sampling, suggest that the 

stream chemistry changes result from regional 

changes in the rates of acid deposition. There are 

difficulties inherent in the use of stream chemistry 

data to indicate changing rates of acid deposition. 

Because of the numerous natural and human 

sources of materials entering streams in general, 

it is difficult to separate atmospheric factors from 

other possible causes of chemical change in the 

absence of simultaneous records of precipitation 

chemistry. This problem is greatly alleviated in 

the pl"esent study, however, by virtue of the predominantly undeveloped nature of the drainage 

basins in which the sampling stations are located. 

The principal advantage to the use of stream 

chemistry records over precipitation data in discerning trends in acid deposition is the larger 

number and wider geographic distribution of sampling sites for which long-term(> 10 year) records 

are available. A further advantage of stream data 

is that streams tend to carry acidic material deposited in both wet and dry forms so that effects 

on stream chemistry tend to reflect the total deposition rate. To date, direct quantification of dry 

deposition rates at precipitation monitoring sites 
TABLE !.-Drainage area, nz.ean discharge, and annual precipitation at Bench-Mark stations 

STATION 

NUMBER 

10542.00 

13621.98 

14665.00 

15456.00 

20388.50 

21353.00 

21973.00 

22126.00 

23271.00 

24502.50 

24791.55 

32372.80 

32767.00 

34600.00 

3604 o. 00 

40010.00 

40637.00 

50649.00 

51244.30 

53760.00 

62882.00 

63325.15 

64090.00 

66238.00 

67759.00 

68979.50 

70607.10 

70830.00 

73112.00 

73357.00 

73730.00 

81039.00 

83779.00 

93529.00 

94306.00 

95083.00 

101722.00 

102449.50 

102493.00 

112645.00 

114755.60 

120393.00 

124160.00 

124473.90 

130183.00 

131695.00 

133315.00 

STATION NAME AND LOCATION 

WILD RIVER AT GILEAD, ME 

ESOPUS CREEK AT SHANDAKEN, NY 

MCDONALDS B IN LEBANON STATE FOREST, NJ 

YOUNG WOMANS CREEK NEAR RENOVO, PA. 

HOLIDAY CREEK NEAR ANDERSONVILLE, VA. 

SCAPE ORE SWAMP NEAR BISHOPVILLE, SC 

UPPER THREE RUNS NEAR NEW EllENTON, ~C 

FALLING CREEK NEAR JULIETTE, GA. 

SOPCH~PPY RIVER NR SOPCHOPPY, FLA. 

SIPSEY FORK NEAR GRAYSON, AL 

CYPRESS CREEK NR JANICE, MS. 

UPPER TWIN CREEK AT MCGAW, OH 

SOUTH HOGAN CREEK NEAR DILLSBORO, IND. 

CATALOOCHEE CREEK NEAR CATALOOCHEE, NC 

BUFFALO RIVER NEAR FLAT WOODS, TENN. 

WASHINGTON CREEK AT WINDIGO, MICH. 

POPPLE RIVER NEAR FENCE, WI 

BEAVER CREEK NR FINLEY, ND 

KAWISHIWI RIVER NEAR ELY, MN 

NORTH FORK WHITEWATER RIVER NEAR ELBA, MN 

BEAUVAIS CREEK NEAR ST. XAVlER, MT. 

BEAR DEN CREEK NR MANDAREE, ND 

CASTLE CR ABOVE DEERFIELD RES NEAR HILL CITY, SD 

ENCAMPMENT RIV AB HOG PARK CR NR ENCAMPMENT, WYO 

DISMAL RIVER NR THEDFORD, NEBR 

ELK CREEK NEAR DECATUR CITY, IOWA 

NORTH SYLAMORE CREEK NEAR FIFTY SIX, ARK. 

HALFMOON CREEK NEAR MALTA, CO. 

BLUE BEAVER CREEK NR CACHE, OK 

KIAMICHI RIVER NR BIG CEDAR, OK 

BIG CREEK AT POLlOCK, LA 

SOUTH FORK ROCKY CREEK NEAR BRIGGS, TEX. 

RIO MORA NEAR TERRERO, NM 

VALLECITO CREEK NEAR BAYFIElD, CO. 

MOGOLLON CREEK NEAR CLIFF, NM 

WET BOTTOM CREEK NR CHILDS, ARIZ. 

RED BUTTE CREEK AT FT. DOUGLAS NR. SLC, UTAH 

STEPTOE C NR ELY, NV 

S TWIN R NR ROUND MOUNTAIN, NV 

MERCED R AT HAPPY ISLES BRIDGE NR YOSEMITE,CALIF 

ELDER CREEK NEAR BRANSCOMB, CALIF 

NORTH FORK QUINAULT R NEAR AMANDA PARK, WASH. 

HAYDEN CK BELOW N FK, NR HAYDEN LAKE, IDAHO 

ANDREWS CREEK NEAR MAZAMA, WASH. 

CACHE CREEK NEAR JACKSON, WYO 

BIG JACKS CREEK NEAR BRUNEAU, ID 

MINAM RIVER AT MINAM,OREG. 

1 Estimates of annual precipitation are from Cobb and Biesecker, 1971. 

DRAINAGE 

AREA 

(km2) 

180 .o 1 54.1 

6.0 

119.7 

22.1 

24 8.6 

225.3 

187 .o 264.2 

233.4 

135.2 

31.6 

98.7 

1 27.4 

11 57.7 

34.2 

360.0 

414.4 

655.3 

261.6 

259.0 

1 91.7 

215.0 

188.3 

2486.4 

136.0 

1 50.5 

61. 1 

63.7 

103.9 

132.1 

86.2 

137.8 

186.7 

1 78.7 

94.3 

18.8 

213.7 

51.8 

468.8 

16.8 

1 91.9 

57.0 

57.2 

27.5 

655.3 

621.6 

MEAN ESTIMATED 

DISCHARGE ANNUAL 

PRECIPITATION1 

(m3 sec-1) (em yr 4 ) 

4.53 112 

3.79 107 

0.03 112 

2.01 97 

0.20 109 

2.78 114 

3.09 112 

1.50 112 

4.42 142 

4.39 132 

2.69 1 52 

0.34 109 

1.08 102 

3.1 4 1 24 

21 0 3 5 1 32 

o. 4 5 71 

3.40 74 

0.42 48 

6.00 71 

1. 1 6 76 

0.62 36 

0.20 38 

0.28 51 

3.03 76 

5.38 51 

0.6d 81 

1.19 114 

0.74 76 

0.25 74 

2. 0 7 1 42 

1.47 1 4 2 

0.37 76 

0 0 7 6 61 

3.85 102 

o. 76 33 

0.34 64 

0.08 64 

0.17 30 

0.14 20 

1 4. 7 5 140 

0.65 203 

23.87 SOB 

0.68 102 

0.91 89 

0.34 76 

o. 2 5 25 

1 2. 2 3 102 

has proved very problematic (Hicks, and others, 

1981). Moreover, stream chemistry data provide 

direct evidence of the geochemical sensitivity of 

an area to acid deposition and are thus, in a sense, 

a step closer to the problem. 

1979) for a 10-15-year period at each site, waterquality records from the network are particularly 

appropriate for investigating atmospheric influences on water quality during the past decade. 

Since 1964 the U.S. Geological Survey has operated the Hydrologic Bench-Mark Network of 47 

streamflow and water quality monitoring stations 

in small, predominantly undeveloped stream basins (table 1; Cobb and Biesecker, 1971). The network includes stations in 37 states and was originally established to help define baseline hydrologic 

conditions in a variety of natural environments. 

Because of little or no changes in land use in these 

basins and the application of consistent sampling 

and analytical methods (Skougstad and others, 

2 

METHODS 

In this report we present the results of applying 

the Seasonal Kendall test for trend (Hirsch and 

others, 1982) to monthly records of stream sulfate, 

pH, alkalinity, and the ratio of alkalinity to total 

major cation concentration at Bench-Mark stations. 

Records of sulfate, alkalinity, and major cation 

concentrations begin generally in the mid- to late 

1960's (fig. la), while pH records begin generally 
a SULFATE, ALKALINITY, CATIONS 

FIRST YEAR OF RECORD 

FIRST YEAR OF RECORD 

FIGURE 1.-First year of record for (a) sulfate concentration, alkalinity, and total major cation concentrations, and 

(b) pH at Bench-Mark stations. 

3 
TABLE 2.-Summa:ry statistics for sulfate concentrations at Bench-Mark stations, for the period of record through 1981 

STATION 

NUMBER 

STATION NAME AND LOCATION NUMBER MEAN 

ESTIMATED 

TREND SLOPE SIGNIFICANCE PRECIPITATION 

OF SAMPLES LEVEL CONCENTRATION1 

10542.00 

13621.9!! 

14665.00 

15456.00 

20388.50 

21353.00 

21973.00 

22126.00 

23271.00 

24502.50 

24791.55 

32372.80 

32767.00 

34600.00 

36040.00 

40010.00 

40637.00 

50649.00 

51244.80 

53760.00 

62882.00 

63325.15 

64090.00 

66238.00 

67759.00 

63979.50 

70607.10 

70830.00 

73112.00 

73357.00 

73730.00 

81039.00 

83779.00 

93529.00 

94306.00 

95083.00 

101722.00 

102449.50 

102493.00 

112645.00 

114755.60 

120393.00 

124160.00 

124473.90 

130183.00 

131695.00 

133315.00 

WILD RIVER AT GILEAD, ME 87 

ESOPUS CREEK AT SHANDAKEN, NY 155 

MCDONALDS B IN LEBANON STATE FOREST, NJ 79 

YOUNG WOMANS CREEK NEAR RENOVO, PA. 143 

HOLIDAY CREEK NEAR ANDERSONVILLE, VA. 84 

SCAPE ORE SWAMP NEAR BISHOPVILLE, SC 124 

UPPER THREE RUNS NEAR NEW ELLENTON, SC 77 

FALLING CREEK NEAR JULIETTE, GA. 62 

SOPCHOPPY RIVER NR SOPCHOPPY, FLA. 172 

SIPSEY FORK NEAR GRAYSON, AL 73 

CYPRESS CREEK NR JANICE, MS. 68 

UPPER TWIN CREEK AT MCGAW, OH 167 

SOUTH HOGAN CREEK NEAR DILLSBORO, IND. 128 

CATALOOCHEE CREEK NEAR CATALOOCHEE, NC 76 

BUFFALO RIVER NEAR FLAT WOODS, TENN. 89 

WASHINGTJN CREEK AT WINDIGO, MICH. 71 

POPPLE RIVER NEAR FENCE, WI 146 

BEAVER CREEK NR FINLEY, ND 79 

KAWISHIWI RIVER NEAR ELY, MN 53 

NORTH FORK WHITEWATER RIVER NEAR ELBA, MN 134 

BEAUVAIS CREEK NEAR ST. XAVIER, MT. 125 

BEAR DeN CREEK NR MANDAREE, ND 141 

CASTLE CR ABOVE DEERFIELD RES NEAR HILL CITY, SD 167 

ENCAMPMENT RIV AB HOG PARK CR NR ENCAMPMENT, WYO 124 

DISMAL RIVER NR THEDFORD, NEBR 81 

ELK CREEK NEAR DECATUR CITY, IOWA 107 

NORTH SYLAMORE CREEK NEAR FIFTY SIX, ARK. 157 

HALFMOON CREEK NEAR MALTA, CO. 161 

BLUE BEAVER CREEK NR CACHE, OK 43 

KIAMICHI RIVER NR BIG CEDAR, OK 149 

BIG CREEK AT POLLOCK, LA 119 

SOUTH FORK RJCKY CREEK NEAR BRIGGS, TEX. 41 

RIO MORA NEAR TERRERO, NM 81 

VALLECITO CREEK NEAR BAYFIELD, CO. 123 

MOGOLLON CREEK NEAR CLIFF, NM 73 

WET BOTTOM CREEK NR CHILDS, ARIZ. 105 

RED BUTTE CREEK AT FT. DOUGLAS NR. SLC, UTAH 144 

STEPTOE C NR ELY, NV 120 

S TWIN R NR ROUND MOUNTAIN, NV 108 

MERCED R AT HAPPY ISLES BRIDGE NR YOSEMITE,CALIF 108 

ELDER CREEK NEAR BRANSCOMB, CALIF 130 

NORTH FORK QUINAULT R NEAR AMANDA PARK, WASH. 110 

HAYDEN CK BELOW N FK, NR HAYDEN LAKE, IDAHO 80 

ANDREWS CREEK NEAR MAZAMA, WASH. 87 

CACHE CREEK NEAR JACKSON, WYO 164 

BIG JACKS CREEK NEAR BRUNEAU, ID 62 

MINAM RIVER AT MINAM,OREG. 104 

(meq L"1) 

0.10 

0,16 

0.13 

0.16 

0.06 

0.06 

0.02 

0.08 

0.09 

0.08 

0.04 

0.54 

1.20 

0.02 

0.08 

0.12 

0.16 

6.02 

0.10 

0 • .32 

11. 7 2 

12 0 99 

0.16 

0.08 

0.15 

1.07 

0.12 

0.11 

0.31 

0.07 

0.04 

0.38 

0.18 

0.18 

0.33 

0.18 

1. 84 

0.18 

0.12 

0.03 

0.07 

0.19 

0.06 

0.05 

0.13 

0,14 

0.03 

(J.leq L-1 yr-1) (p) (j.leq L"1) 

-1.7 

-2.4 

-2.9 

-0.9 

-1.0 

2.9 

1.0 

0.6 

7.8 

1 • 1 

2.3 

11.6 

-4.3 

1. 0 

-0.7 

-1.3 

-2.1 

29.2 

-1.0 

2.0 

100.2 

167.9 

2.6 

4.0 

2.4 

-8.7 

2.1 

0.7 

-3.6 

0.6 

3.2 

11 .8 

2.0 

2.1 

-0.9 

-0.7 

22.0 

1 • 3 

-0.5 

0.3 

o.o 

1.8 

1.9 

0.2 

-2.7 

1.4 

2.8 

o.ooo 

o.ooo 

0.034 

0.088 

0.040 

o. 001 

0.007 

0.696 

o.ooo 

0.016 

0.002 

o.ooo 

0.239 

0.031 

0.048 

0.308 

0.034 

o. 51 3 

o. 118 

0.1 57 

0.032 

o. 001 

0.001 

o.ooo 

0.001 

0.541 

0.001 

0.351 

0.367 

0.391 

0.000 

0.044 

0.064 

0.051 

0.743 

0.661 

o.ooo 

0.086 

0.316 

0.954 

0,947 

0.024 

0.009 

0.778 

0.005 

0.225 

o.ooo 

50 

65 

60 

75 

55 

so 

so 

50 

46 

45 

3S 

80 

75 

60 

55 

40 

5{) 

30 

35 

50 

40 

30 

35 

40 

40 

50 

50 

40 

30 

30 

30 

30 

45 

45 

40 

50 

30 

25 

20 

20 

10 

20 

25 

20 

30 

20 

20 

1 Estimates of precipitation sulfate concentration are from 1981 N.A.D.P. data (Gibson and Baker, written communication, 1982). 

in the late 1960's to the early 1970's (fig. 1b). The 

pH of samples collected prior to dates given in 

figure 1b were measured in the laboratory and are 

not comparable to in-stream measurements. Records of stream nitrate concentrations are available only since the mid- to late 1970's and are considered too short for comparison with the other 

records. 

The Seasonal Kendall test is nonparametric and 

is intended for analysis of time trends in seasonally varying water-quality data from fixed, regularly sampled monitoring sites such as those which 

the Bench-Mark Network comprises (Hirsch and 

others, 1982; see also Smith and others, 1982). In 

addition to a test for trend, the statistical procedure includes an estimate of the median rate of 

4 

change of quality over the sampling period (trend 

slope) and a method for adjusting the data to correct for effects of changing stream flow on trend 

in the water-quality record. Trend is defined here 

simply as monotonic change with time, occurring 

either as an abrupt or gradual change in water 

quality. 

ATMOSPHERIC CONTRIBUTIONS 

TO STREAM SULFATE 

An important assumption of the present analysis 

is that stream sulfate concentrations at most 

Bench-Mark stations are low enough to be significantly influenced by changes in the rate of atmospheric deposition of sulfur. Annual average sulfate 
concentrations of precipitation in the United 

States, based on 1981 data from the National Atmospheric Deposition Program (table 2), range 

from approximately 20t.J.eq L-1 in the West to 

70t.J.eq L-1 or more over the Ohio Valley (J. H. 

Gibson and C. V. Baker, National Atmospheric 

Deposition Program, Fort Collins, Colorado, 1982, 

written communication). These data can be used 

to estimate the contribution of wet deposition to 

stream sulfate, provided that the tendency for 

evapotranspiration to increase the concentration of 

dissolved constituents in precipitation is taken into 

account. Correction factors for the effects of 

evapotranspiration are calculated as the ratio of 

annual precipitation to annual runoff (table 1; 

Cobb and Biesecker, 1971) and range from 10 or 

greater for much of the West to about 2 in New 

England and as low as 1.5 in the far Northwest. 

After adjusting for the effects of evapotranspiration, precipitation is estimated to contribute at 

least 90 percent of the mean sulfate concentration 

at half of the Bench-Mark stations and at least 

SIGNIFICANCE LEVEL 

• NO TREND p > 0.2 

' 0.01 <p < 0.1 

j 0.1 <p<0.2 

j p<0.01 

22 percent of the mean sulfate concentration at 

all but six stations. The Bench-Mark stations at 

which precipitation is estimated to contribute less 

than 22 percent of stream sulfate are: South 

Hogan Creek near Dillsboro, Indiana (19 percent); 

North Fork Quinault River near Amanda Park, 

Washington (11.5 percent); Beaver Creek near 

Finley, North Dakota (9.2 percent); Red Butte 

Creek at Ft. Douglas near Salt Lake City, Utah 

(6.5 percent); Bear Den Creek near Mandaree, 

North Dakota (2 percent); and Beauvais Creek 

near St. Xavier, Montana (1.5 percent). 

The above estimates of the precipitation contribution to stream sulfate at Bench-Mark stations 

are conservative estimates of the total atmospheric contribution because dry deposition is not 

included. Dry deposition has proved difficult to 

quantify (Hicks and others, 1981) but, depending 

on climatic and other factors, has been estimated 

to contribute anywhere from a few percent to 60 

or 70 percent of the total sulfate deposition 

(Niemann, 1983). 

-25 

-70 

-71 

-49 

-8 

-37 

-30 

SCALE OF MILES 

0 200 400 600 800 1000 

FIGURE 2.-Comparison of trends in stream sulfate concentrations at Bench-Mark stations for the period of record through 

1981 with trends in S02 emissions to the atmosphere by State, 1965-1980. Triangles indicate direction and significance 

level of trends in stream sulfate. Numbers give percentage change in S02 emissions from 1965 to 1980 for each State. 

States showing increasing levels of S02 emissions are shaded; States showing decreasing levels of S02 emissions are 

unshaded. Source of emission data: G. Gschwandtner and K. Gschwandtner, written communication (1983). 

5 
a ALKALINITY 

b RATIO 

SIGNIFICANCE LEVEL 

• NO TREND p > 0.2 

'0.01 <p < 0.1 

' 0.1 <p< 0.2 

'p<0.01 

FIGURE 3.-Trends in (a) alkalinity, and (b) the ratio of alkalinity to total major cation concentration at Bench-Mark stations 

for the period of record through 1981. Symbols indicate direction and significance level of trends. Dark symbols indicate 

stations with mean alkalinity less than 1 meq L-1

• 

6 
TABLE 3.-Summary statistics for alkalinity at Bench-Mark stations, for the period of record through 1981 

STATION 

NUMBER 

10542.00 

13621.98 

14665.00 

15456.00 

20388.50 

21353.00 

21973.00 

22126.00 

23271.00 

24502.50 

24791.55 

32372.80 

32767.00 

34600.00 

36040.00 

40010.00 

40637.00 

50649.00 

51244.80 

53760.00 

62882.00 

63325.15 

64090.00 

66238.00 

67759.00 

68979.50 

70607.10 

70830.00 

73112.00 

73357.00 

73730.00 

81039.00 

83779.00 

93529.00 

94306.00 

95083.00 

101722.00 

102449.50 

102493.00 

112645.00 

114755.60 

120393.00 

124160.00 

124473.90 

130183.00 

13169 5. 00 

133315.00 

STATION NAME AND LOCATION NUMBER MEAN 

OF SAMPLES 

WILD RIVER AT GILEAD, ME 77 

ESOPUS CREEK AT SHANDAKEN, NY 148 

MCDONALOS B IN LEBANON STATE FOREST, NJ 48 

YOUNG WOMANS CREEK NEAR RENOVO, PA. 134 

HOLIDAY CREEK NEAR ANDERSONVILLE, VA. 80 

SCAPE ORE SWAMP NEAR BISHOPVILLE, SC 101 

UPPER THREE RUNS NEAR NEW ELLENTON, SC 72 

FALLING CREEK NEAR JULIETTE, GA. 61 

SOPCHOPPY RIVER NR SOPCHOPPY, FLA. 124 

SIPSEY FORK NEAR GRAYSON, AL 66 

CYPRESS CREEK NR JANICE, MS. 65 

UPPER TWIN CREEK AT MCGAW, OH 155 

SOUTH HOGAN CREEK NEAR DILLSBORO, INO. 118 

CATALOOCHEE CREEK NEAR CATALOOCHEE, NC 77 

BUFFALO RIVER NEAR FLAT WOODS, TENN. 76 

WASHINGTON CREEK AT WINOIGO, MICH. 70 

POPPLE RIVER NEAR FENCE, WI 147 

BEAVER CREEK NR FINLEY, NO 74 

KAWISHIWI RIVER NEAR ELY, MN 49 

NORTH FORK WHITEWATER RIVER NEAR ELBA, MN 131 

BEAUVAIS CREEK NEAR ST. XAVIER, MT. 125 

BEAR DEN CREEK NR MANDAREE, NO 132 

CASTLE CR ABOVE DEERFIELD RES NEAR HILL CITY, SO 151 

ENCAMPMENT RIV AB HOG PARK CR NR ENCAMPMENT, WYO 120 

DISMAL RIVER NR THEDFORD, NEBR 80 

ELK CREEK NEAR DECATUR CITY, IOWA 99 

NORTH SYLAMORE CREEK NEAR FIFTY SIX, ARK. 150 

HALFMOON CREEK NEAR MALTA, CO. 159 

BLUE BEAVER CREEK NR CACHE, OK 40 

KIAMICHI RIVER NR BIG CEDAR, OK 132 

BIG CREEK AT POLLOCK, LA 123 

SOUTH FORK ROCKY CREEK NEAR BRIGGS, TEX. 42 

RI~ MORA NEAR TERRERO, NM 77 

VALLECITO CREEK NEAR BAYFIELD, CO. 128 

MOGOLLON CREEK NEAR CLIFF, NM 71 

WET BOTTOM CREEK NR CHILDS, ARIZ. 97 

RED BUTTE CREEK AT FT. DOU~LAS NR. SLC, UTAH 131 

STEPTOE C NR ELY, NV 117 

S TWIN R NR ROUND MOUNTAIN, NV 109 

MERCED R AT HAPPY ISLES BRIDGE NR YOSEMITE,CALIF 107 

ELDER CREEK NEAR BRANSCOMB, CALIF 125 

NORTH FORK QUINAULT R NEAR AMANDA PARK, WASH. 110 

HAYDEN CK BELOW N FK, NR HAYDEN LAKE, IDAHO 76 

ANDREWS CREEK NEAR MAZAMA, WASH. 85 

CACHE CREEK NEAR JACKSON, WYO 152 

BIG JACKS CREEK NEAR BRUNEAU, 10 62 

MlNAM RIVER AT MINAM,OREG. 99 

(meq L-1) 

0.12 

0.23 

0.01 

0.17 

0.26 

0.07 

0.06 

1. 03 

0.60 

0.74 

0.07 

0.27 

3.53 

0.11 

0.74 

1. 25 

1. 61 

4.74 

0.22 

5.08 

3.67 

13.69 

5.07 

0.53 

1. 71 

4.42 

2.79 

o. 73 

1.22 

0.13 

0.23 

4.53 

0.86 

0.54 

0.76 

2.36 

4.75 

3.40 

1. 1 2 

0.13 

1.07 

0.54 

0.66 

0.48 

3.55 

1 • 1 5 

0.48 

TREND SLOPE SIGNIFICANCE 

LEVEL 

(~eq L -1 yr-1) (p) 

1. 6 

1 • 5 

0.7 

3.3 

0.9 

3.1 

1.9 

-15.5 

2.0 

-11 .8 

2.8 

3.9 

-4.9 

0.7 

-7.1 

-7.5 

-5.2 

-37.5 

-2.8 

24.2 

51.1 

51 • 6 

1. 5 

-6.0 

-9.6 

-19.2 

-9.6 

-9.3 

22.2 

-3.0 

-1.2 

28.6 

-6.7 

-9.3 

-14.5 

1 5. 2 

-1.7 

21.6 

10.3 

-1.0 

1. 9 

-4.5 

-3.5 

-8.7 

-11.8 

9.0 

-5.3 

0.153 

0.079 

0.006 

0.010 

o. 390 

o. 001 

0.009 

0.030 

o. 458 

0.042 

0.008 

0.002 

o. 735 

0.278 

o.ooo 

a. 013 

0.203 

0.294 

0.040 

0.021 

0.006 

0.256 

0.825 

o.ooo 

o.ooo 

0.219 

0.019 

o.ooo 

0.183 

0.007 

o. 211 

0.684 

0.025 

0.000 

o.oos 

0.320 

o. 875 

o.ooo 

o.ooo 

0.192 

o. 421 

0.002 

0.270 

o. 011 

o.ooo 

0.149 

0.003 

RESULTS AND DISCUSSION 

TRENDS IN STREAM SULFATE 

The significance levels 1 and directions of apparent trends in sulfate concentration for the period 

of record at Bench-Mark stations are shown in figure 2. Sulfate concentrations have tended to increase during the 10-15-year period over a broad 

area of the continental United States extending 

from the Southeast to the mountain States and 

the Northwest. By contrast, stations in the northeastern quarter of the Nation have tended to show 

either no trend or declines in sulfate concentrations. This geographic pattern occurs more or less 

independently of the significance criteria used in 

mapping the trend test results (see table 2 for test 

results at all stations). Although the statistical significance of trends at many of the stations is high 

(p < .01), the magnitude of change has been small 

in most cases (table 2). The median slope of 2~.~-eq 

L-1 yr-1 among stations showing trend in sulfate 

concentration corresponds to a median relative 

change in stream sulfate of 1. 7 percent per year 

or about 25 percent over the period of record. 

'Significance level (p) is the probability of incorrectly rejecting the null hypothesis 

that there is no trend in the data. The significance level provides a measure of 

the confidence to be placed in the validity of an observed trend. For example, 

if p is greater than 0.1 but less than 0.2 (0.1 < p < 0.2), there is an 80 to 90 

percent likelihood that the observed trend is real and does not occur through chance 

alone. 

7 

TRENDS IN S02 EMISSIONS 

There is evidence (G. Gschwandtner and K. 

Gschwandtner, 1983, Pacific Environmental Services, Durham, North Carolina, written communi-
TABLE 4.-Summary statistics for the ratio of alkalinity to total major cation concentrations at Bench-Mark stations, for 

the period of record through 1981 

STATION 

NUMBER 

10542.00 

13621.93 

14665.00 

15456.00 

20388.50 

21353.00 

21973.00 

22126.00 

23271.00 

24502.50 

24791.55 

32372.80 

32767.00 

34oOO.OO 

36040.00 

40010.00 

40637.00 

5064 9.00 

51244.80 

53760.00 

62882.00 

63325.15 

64090.00 

66238.00 

67759.00 

68979.50 

70607.10 

70830.00 

73112.00 

73357.00 

73730.00 

81039.00 

83779.00 

93529.00 

94306.00 

95083.00 

101722.00 

102449.50 

102493.00 

112645.00 

114755.60 

120393.00 

124160.00 

124473.90 

130183.00 

131695.00 

133315.00 

STATION NAME AND LOCATION NUMBER MEAN 

OF SAMPLES 

WILD RIVER AT GILEAD, ME 76 

ESOPUS CREEK AT SHANDAKEN, NY 146 

MCOONALDS B IN LEBANON STATE FOREST, NJ 45 

YOUNG WOMANS CREEK NEAR RENOVO, PA. 134 

HOLIDAY CREEK NEAR ANDERSONVILLE, VA. 80 

SCAPE ORE SWAMP NEAR BISHOPVILLE, SC 99 

UPPER THREE RUNS NEAR NEW ELLENTON, SC 70 

FALLING CREEK NEAR JULIETTE, GA. 60 

SOPCHOPPY RIVER NR SOPCHOPPY, tLA. 89 

SIPSEY FORK NEAR GRAYSON, AL 63 

CYPRESS CREEK NR JANICE, MS. 59 

UPPER TWIN CREEK AT MCGAW, OH 154 

SOUTH HOGAN CREEK NEAR DILLSBORO, IND. 118 

CATALOOCHEE CREEK NEAR CATALOOCHEE, NC 75 

BUFFALO RIVER NEAR FLAT WOODS, TENN. 72 

WASHINGTON CREEK AT WINDIGO, MICH. 69 

POPPLE RIVER NEAR FENCE, WI 146 

BEAVER CREEK NR FINLEY, NO 74 

KAWISHIWI RIVER NEAR ELY, MN 52 

NORTH FORK WHITEWATER RIVER NEAR ELSA, MN 131 

BEAUVAIS CREEK NEAR ST. XAVIER, MT. 125 

BEAR DEN CREEK NR MANDAREE, NO 131 

CASTLE CR ABOVE DEERFIELD RES NEAR HILL CITY, SO 150 

ENCAMPMENT RIV AB HOG PARK CR NR ENCAMPMENT, WYO 119 

DISMAL RIVER NR THEDFORD, NEBR 76 

ELK CREEK NEAR DECATUR CITY, IOWA 97 

NORTH SYLAMORE CREEK NEAR FIFTY SIX, ARK. 148 

HALF~OON CREEK NEAR MALTA, CO. 153 

BLUE BEAVER CREEK NR CACHE, OK 38 

KIAMICHI RIVER NR BIG CEDAR, OK 127 

BIG CREEK AT POLLOCK, LA 118 

SOUTH FORK ROCKY CREEK NEAR BRIGGS, TEX. 39 

RIO MORA NEAR TERRERO, NM 77 

VALLECITO CREEK NEAR BAYFIELD, CO. 113 

MOGOLLON CREEK NEAR CLIFF, NM 71 

WET BDTTOM CREEK NR CHILDS, ARIZ. 97 

REO BUTTE CREEK AT FT. DOUGLAS NR. SLC, UTAH 131 

STEPTOE C NR ELY, NV 108 

S TWIN R NR ROUND MOUNTAIN, NV 104 

MERCED R AT HAPPY ISLES BRIDGE NR YOSEMITE,CALif 90 

ELDER CREEK NEAR BRANSCOMB, CALif 124 

NORTH FORK QUINAULT R NEAR AMANDA PARK, WASH. 103 

HAYDEN CK BELOW N FK, NR HAYDEN LAKE, IDAHO 75 

ANDREWS CREEK NEAR MAZAMA, WASH. 82 

CACHE CREEK NEAR JACKSON, WYO 152 

BIG JACKS CREEK NEAR BRUNEAU, ID 61 

MINAM RIVER AT MINAM,OREG. 100 

o. 51 

0.47 

0.04 

0.46 

0.71 

0.27 

0.49 

0.80 

0.53 

0.81 

0.38 

0.29 

0.65 

0.74 

0.82 

0.79 

0.82 

0.41 

0.58 

0.88 

0.23 

0.49 

0.93 

0.83 

0.87 

o. 73 

0.93 

0.82 

0.66 

0.49 

0.56 

0.85 

0.79 

0.70 

0.62 

0.76 

0.67 

o. 92 

0.87 

0.62 

0.86 

0.71 

0.89 

o. 91 

0.95 

0.81 

0.89 

TREND SLOPE SIGNIFICANCE 

LEVEL 

(yr-1) (p) 

0.010 

o. 001 

0.003 

0.009 

0.007 

0.009 

0.019 

-0.008 

0.002 

-0.006 

0.015 

o. 001 

o.ooo 

0.003 

-0.006 

-o. oo1 

-0.002 

-0.005 

-0.008 

-0.003 

o.ooo 

-0.002 

-0.004 

-0.009 

-0.005 

-0.004 

-0.002 

-0.006 

0.004 

-0.020 

-0.010 

-0.001 

-0.008 

-0.020 

-0.006 

-0.001 

-0.002 

o. 001 

0.002 

-0.013 

-0.003 

-0.009 

-0.008 

-0.025 

0.0.01 

0.005 

-0.016 

0.087 

0 .. 543 

o. 024 

0.002 

0 .. 172 

0.022 

0.002 

0.315 

0.555 

o. 009 

o. 006 

0.603 

0.855 

0.434 

0.002 

0.524 

0.091 

0.074 

0.027 

o. 001 

0.942 

0.1 58 

o.ooo 

0.002 

o.ooo 

0.021 

0.010 

o.ooo 

0.422 

o.ooo 

o.ooo 

0.475 

o.ooo 

o. 000 

0.004 

o. 770 

0.251 

0.801 

0.045 

0.008 

0.188 

o.ooo 

0.010 

o.ooo 

o. 138 

0.239 

o.ooo 

cation) that trends in S02 emissions to the atmosphere from 1965 to 1980 followed a similar geographical pattern to that described above for trends 

in sulfate at Bench-Mark stations (fig. 2; see also 

table 6). Substantial declines in emissions occurred 

from 1965 to 1980 in the Northeast and northern 

Midwest while increases occurred in the Southeast 

and in most States west of the Mississippi. Based 

on previous literature, it is difficult to construct 

a comparable nationwide picture of trends in 

stream and precipitation sulfate concentrations 

due to the limited number and uneven distribution 

of sampling sites with adequate record lengths 

(Bubenick and others, 1983). For the Northeast, 

however, there are other recent reports of declining stream and precipitation sulfate concentrations 

from scattered locations (National Research Council, 1983; Peters and others, 1982; Ritter and 

Brown, 1981; Likens and others, 1980). 

8 

TRENDS IN STREAM ALKALINITY 

Trends in alkalinity at Bench-Mark stations (fig. 

3a) display a geographic pattern that is the approximate inverse of that of sulfate trends: over 

a broad area from the Southeast to the Northwest, 

down trends in alkalinity greatly outnumber up 

trends, while in the Northeast, alkalinity trends 

are consistently up. The inverse relation with sulfate trends is somewhat stronger among stations 

with low average alkalinity (dark symbols in fig. 

3a) although a number of important exceptions to 

the pattern exist (for example, stations in South 
Carolina and Minnesota). On average, alkalinity 

trend slopes are of the same order of magnitude 

as sulfate trend slopes (see tables 2 and 3), but 

may differ considerably in magnitude from sulfate 

trends in a station-by-station comparison. 

An inverse relationship between sulfate and alkalinity is expected if the sulfate represents the 

introduction of sulfuric acid to the stream system 

and if that acid acts to reduce stream alkalinity 

rather than to dissolve minerals in the stream 

basin (Burns and others, 1981; Kramer and Tessier, 1982). To the extent the acid reacts with rock 

and soil, however, it is not available to reduce 

stream alkalinity. Also, because alkalinity itself 

occurs as a result of mineral dissolution, it follows 

that an inverse relationship between trends in sulfate and alkalinity will be strongest in low alkalinity waters. In fact, in basins characterized by carbonate weathering (and very high alkalinity) the 

introduction of strong acid may result in an increase in alkalinity (Kilham, 1982). 

pH 

SIGNIFICANCE LEVEL 

• NO TREND p > 0.2 

'0.01 <p < 0.1 

' 0.1 <p<0.2 

'p< 0.01 

Several investigators (Burns and others, 1981; 

Kramer and Tessier, 1982) have suggested using 

the ratio of alkalinity to major cation concentrations as an index of acidification of surface waters 

in order to overcome the confounding alternative 

effects of acidification in different basins (that is, 

a loss of alkalinity versus an increase in mineral 

dissolution). The ratio can only decrease (slowly 

in the presence of carbonate minerals in the drainage basin, more rapidly in their absence) as a result of an increased acid input to the system. 

In accordance with the above theory, trends in 

the ratio of alkalinity to total major cation concentration (sum of sodium, potassium, calcium, and 

magnesium) at Bench-Mark stations (fig. 3b; see 

also table 4) follow a more consistent inverse relation to sulfate trends than do alkalinity trends: 

declining values have occurred over a broad region 

extending from the Mississippi Valley westward, 

while rising values have occurred at most eastern 

stations as far south as South Carolina. 

FIGURE 4.-Trends in pH at Bench-Mark stations for the period of record through 1981. Symbols indicate direction 

and significance level of trends. Dark symbols indicate stations with mean alkalinity less than 1 meq L-1. 

9 
TABLE 5.-Summary statistics for pH at Bench-Mark stations, for the period of record through 1981 

STATION 

NUMBER 

STATION NAME AND LOCATION NUMBER MEAN TREND SLOPE SIGNIFICANCE 

OF SAMPLES LEVEL 

10542.00 WILD RIVER AT GILEAD, ME 60 

13621.98 ESOPUS CREEK AT SHANDAKEN, NY 86 

14665.00 MCDONALDS B IN LEBANON STATE FORESTr NJ 43 

15456.00 YOUNG WOMANS CREEK NEAR RENOVO, PA. 119 

20388.50 HOLIDAY CREEK NEAR ANDERSONVILLE, VA. 57 

21353.00 SCAPE ORE SWAMP NEAR BISHOPVILL£, SC 129 

21973.00 UPPER THREE RUNS NEAR NEW EllENTON, SC 81 

22126.00 FALLING CREEK NEAR JULIETTE, GA. 104 

23271.00 SOPCHOPPY RIVER NR SOPC~OPPYr FLA. 112 

24502.50 SIPSEY FORK NEAR GRAYSON, Al 65 

24791.55 CYPRESS CREEK NR JANICE, MS. 42 

32372.80 UPPER TWIN CREEK AT MCGAW, OH 109 

32767.00 SOUTH HOGAN CREEK NEAR DILLSBORO, IND. 84 

34600.00 CATAlOOCHEE CREEK NEAR CATALOOCHEE, NC 78 

36040.00 BUFFALO RIVER NEAR FlAT WOODS, TENN. 50 

40010.00 WASHINGTON CREEK AT WINDIGOr MICH. 47 

40637.00 POPPLE RIVER NEAR FENCE, WI 120 

50649.00 BEAVER CREEK NR FINLEY, NO 63 

51244.80 KAWISHIWI RIVER NEAR ELY, MN 28 

53760.00 NORTH FORK WHITEWATER RIVER NEAR ELBA, MN 106 

62882.00 BEAUVAIS CREEK NEAR ST. XAVIER, MT. 74 

63325.15 BEAR DEN CREEK NR MANDAREE, NO 115 

64090.00 CASTLE CR ABOVE DE!RfiElD RES NEAR HILL CITY, SO 134 

66238.00 ENCAMPMENT RIV AB HOG PARK CR NR ENCAMPMENT, WYO 95 

67759.00 DISMAL RIVER NR THEDFORD, NEBR 78 

68979.50 ELK CREEK NEAR DECATUR CITY, IOWA 105 

70607.10 NORTH SYlAMORE CREEK NEAR FIFTY SIX, ARK. 123 

70830.00 HALFMOON CREEK NEAR MALTA, CO. 109 

73112.00 BLUE BEAVER CREEK NR CACHE, OK 20 

73357.00 KIAMICHI RIVER NR BIG CEDAR, OK 93 

73730.00 BIG CREEK AT POLLOCK, LA 78 

81039.00 SOUTH FORK ROCKY CREEK NEAR BRIGGS, TEX. 37 

83779.00 RIO MORA NEAR TERRERO, NM 77 

93529.00 VALLECITO CREEK NEAR BAYFIELD, CO. 101 

94306.00 MOGOlLON CREEK NEAR CLIFF, NM 67 

95083.00 WET BOTTOM CREEK NR CHILDS, ARIZ. 74 

101722.00 REO BUTTE CREEK AT FT. DOUGLAS NR. SLC, UTAH 101 

102449.50 STEPTOE C NR ELY, NV 77 

102493.00 S TWIN R NR ROUND MOUNTAIN, NV 87 

112645.00 MERCED R AT HAPPY ISLES BRIDGE NR YOSEMITErCALIF 75 

114755.60 ELDER CREEK NEAR BRANSCOMB, CALIF 106 

120393.00 NORTH FORK QUINAULT R NtAR AMANDA PARK, WASH. 72 

124160.00 HAYDEN CK BELOW N FK, NR HAYDEN LAKEr IDAHO 52 

124473.90 ANDREWS CREEK NEAR MAZAMA, WASH. 80 

130183.00 CACHE CREEK NEAR JACKSON, WYO 137 

131695.00 BIG JACKS CREEK NEAR BRUNEAU, ID 30 

133315.00 MINAM RIVER AT MINAM,OREG. 60 

(std. units) (std. units yr-1) (p) 

6.5 

6.8 

4.2 

6.8 

6.8 

5.6 

6.0 

7.0 

5. 2 

7.2 

6.1 

6.8 

7.9 

7.0 

7.2 

7.4 

7.4 

8.1 

7.2 

8.1 

8.0 

8.4 

8.3 

7.4 

7.7 

8.0 

8.0 

7.4 

7.2 

7.1 

6.4 

7.7 

7.9 

7.7 

7.8 

7.8 

8.2 

8.4 

8.0 

6.7 

7.7 

7.2 

7.2 

7.6 

8.3 

8.1 

7.3 

-0.03 

-0.08 

-0.02 

-o. 01 

0.03 

-0.01 

-o. 01 

o. 01 

-0.04 

-o. 02 

0.04 

0.04 

o. 01 

-0.04 

-0.01 

0.03 

0.01 

o.oo 

-0.00 

-o.oo 

0.04 

o. 01 

-IJ. 00 

o. 01 

-0.04 

-0.03 

0.02 

-0.06 

-o. 01 

0.01 

-0.07 

0.02 

-o.oo 

-0.05 

-0.03 

0.11 

0.01 

0.03 

o. 01 

-0.05 

0.03 

0.03 

o. 01 

-0.02 

0.01 

0.03 

-0.06 

o. 011 

o. 001 

0.320 

0.217 

0.034 

0.116 

0.480 

0.500 

0.003 

0.187 

0.274 

0.002 

0.360 

0.059 

o. 778 

0.060 

0.398 

1.000 

1. 000 

0.598 

0.028 

0.053 

o. 573 

0.696 

o.ooo 

0.003 

0.015 

o.ooo 

0.837 

0.307 

0.033 

o. 623 

o. 597 

o. 041 

0.149 

o.ooo 

0.234 

o.ooo 

0.178 

0.102 

0.008 

0.153 

0.502 

o. 314 

0.027 

o. 681 

0.008 

TRENDS IN STREAM pH 

Trends in pH at Bench-Mark stations (fig. 4; 

see also table 5) do not follow a clear regional pattern and are only partly consistent with trends 

in sulfate and alkalinity. Approximately equal 

numbers of increasing and decreasing trends in pH 

have occurred nationally with down trends occurring much more frequently than up trends at low 

alkalinity stations (shaded symbols). An important 

divergence from the geographical pattern evident 

in figures 2 and 3 is that stations in New York 

and Maine show down trends in pH despite the 

fact that sulfate and alkalinity trends in those 

states suggest a slight lessening of acidification. 

Several possible explanations for the apparent 

inconsistencies between trends in pH and the 

other major ions are worth noting. First, pH records at Bench-Mark stations are somewhat shorter than records for the other major ions (compare 

figs. la and 1 b) and in some basins do not not 

cover periods when significant changes occurred 

in the other constituents. Second, alkalinities at 

most Bench-Mark stations (fig. 3a) are high 

enough to provide considerable resistance to 

changes in pH; the sulfate changes reported here 

are mostly small (see above) and would not be expected to cause significant changes in pH at the 

prevailing alkalinities of many stations. Third, the 

lack of comparable nitrate records makes it difficult to evaluate the role of atmospheric nitrogen 

in acid deposition at these stations. Precipitation 

data from Hubbard Brook, New Hampshire (Likens and others, 1980) show an increase in nitrate 

from 1964 until the early 1970's, followed .by a 

leveling off or slight decline since that time. Pre10 
TABLE 6.-SO~ emissions by state for period of record 1965-

1980. Data are recent revisions of SO~ emissions presented 

in Rivers and Riegal, 1982 (G. Gschwandtner and K. 

Gschwandtner, Pacific Environmental Services, Durham, 

NC, written communicatin, 1983). 

STATE 

Alabama 

Arizona 

Arkansas 

Ca 1 iforni a Colorado 

Connecticut 

Delaware 

D.C. 

Florida 

Georgia 

Idaho 

Illinois 

Indiana 

Iowa 

Kansas 

Kentucky 

Louisiana 

Maine 

Maryland 

Massachusetts 

Michigan 

Minnesota 

Mississippi 

Missouri 

Monatana 

Nebraska 

Nevada 

New Hampshire 

New Jersey 

New Mexico 

New York 

North Carolina 

North Dakota 

Ohio 

Oklahoma 

Oregon 

Pennsylvannia 

Rhode Island 

South Carolina 

South Dakota 

Tennessee 

Texas 

Utah 

Vermont 

Virginia 

Washington 

West Virginia Wisconsin 

Wyoming 

YEAR ( 1000 tons) 

1965 1970 1975 1978 1980 

897 

1829 

13 

293 

95 

300 

104 

50 

358 

295 

24 

2567 

2115 

408 

75 

894 

29 

54 

532 

452 

1678 

307 

8 

595 

270 

72 

204 

40 

607 

218 

1584 

331 

36 

3173 

35 

40 

2514 

43 

128 

20 

768 

144 

308 

10 

409 

64 

882 

680 

64 

869 1055 

2211 1393 

22 57 

485 314 

69 95 

281 94 

73 51 

124 33 

500 655 

381 637 

12 18 

2520 2135 

1985 2026 

368 303 

113 276 

1325 1356 

41 102 

72 62 

440 281 

552 267 

1595 1465 

383 284 

51 139 

796 1229 

264 199 

74 48 

304 263 

94 80 

532 275 

412 379 

1378 1039 

539 532 

48 62 

3182 3180 

19 24 

49 40 

2319 2020 

59 24 

197 199 

62 40 

1024 1453 

113 342 

237 222 

12 6 

463 345 

78 105 

955 1440 

879 665 

56 102 

718 

869 

113 

343 

128 

108 

57 

17 

651 

676 

20 

1625 

1807 

386 

283 

1375 

194 

59 

303 

392 

1078 

239 

250 

1224 

232 

75 

54 

67 

271 

403 

983 

555 

98 

2882 

54 

42 

1926 

21 

293 

56 

1176 

580 

343 

9 

335 

171 

1219 

969 

161 

738 

779 

79 

404 

144 

87 

96 

7 

832 

792 

16 

1625 

2135 

328 

345 

1328 

288 

50 

337 

338 

884 

221 

205 

1265 

168 

65 

62 

94 

307 

501 

900 

551 

137 

2878 

103 

53 

2259 

13 

309 

47 

1173 

765 

316 

6 

288 

173 

1173 

640 

229 

cipitation pH at the same site has varied considerably since 1964 but has shown no clear trend over 

the period. 

SUMMARY 

Water-quality records collected over a 10--15-

year period from the Hydrologic Bench-Mark Network, a nationwide network of sampling stations 

in predominantly undeveloped stream basins, 

11 

show small declines in stream sulfate at stations 

in the northeastern quarter of the Nation and 

small increases in sulfate at a number of southeastern and western sites. Stream sulfate concentrations at most Bench-Mark stations are low 

enough to be significantly influenced by changes 

in the rate of atmospheric deposition of sulfur. The 

geographic pattern of trends in atmospheric S02 

emissions from 1965 to 1980 approximately coincides with the pattern of sulfate trends at BenchMark stations, and tends to support the 

hypothesis that the stream sulfate trends reflect 

regional trends in sulfur deposition rates. 

Trends in stream alkalinity at Bench-Mark stations follow a regional pattern that is the approximate inverse of that of the sulfate trends: small 

increases have occurred at most stations in the 

Northeast and small decreases have occurred at 

many stations in the South and West. The inverse 

relationship is strongest at stations with relatively 

low mean alkalinity ( < 1 meq L-1). 

The ratio of stream alkalinity to the total major 

cation concentration can be used as an index of 

the geochemical effects of acidification in a stream 

basin because of the tendency of that ratio to decrease in response to increased acid inputs even 

in cases where the acid acts to dissolve minerals 

in the basin rather than reduce stream alkalinity. 

Accordingly, trends in the ratio of alkalinity to 

total major cation concentration at Bench-Mark 

stations follow a more consistent inverse relation 

to sulfate trends than do alkalinity trends: declining values have occurred over a broad region extending from the Mississippi Valley westward, 

while rising values have occurred at most eastern 

stations as far south as South Carolina. 

Trends in pH at Bench-Mark stations do not follow a clear regional pattern and are only partly 

consistent with trends in sulfate and alkalinity. 

Several factors make a strong relationship between pH trends and sulfate trends unlikely, however. These include shorter record lengths for pH 

data, possible conflicting effects of the nitrogen 

component of acid deposition, and sufficient alkalinity in many basins to resist significant changes 

in pH. 

Despite inconsistencies at individual stations, on 

a broad regional basis the data presented in this 

report show a consistent relationship between 

trends in S02 emissions and trends in stream sulfate, alkalinity, and the ratio of alkalinity to the 

total major cation concentration. 
In the northeastern quarter of the country, 802 

emissions have decreased over the past 15 years 

and the trends in the cited chemical characteristics 

of Bench-Mark streams are consistent with a 

hypothesis of decreased acid deposition in that region. Throughout much of the remainder of the 

country, 802 emissions have increased and trends 

in stream sulfate, alkalinity, and alkalinity/total 

cation ratios are consistent with a hypothesis of 

increased acid deposition. 

REFERENCES 

Biesecker, J. E., and Leifeste, D. K., 1975, Water quality of 

hydrolocyc bench marks: U.S. Geological Survey Circular 

460-E, 21 p. 

Bubenick, D. V., Record, F. A., and Kindya, R. J., 1983, Acid 

rain-an overview of the problem: Environmental Progress, v. 2, no. 1, p. 15-31. 

Burns, D. A., Galloway, J. N., and Hendrey, G. R., 1981, 

Acidification of surface waters in two areas of the eastern 

United States: Water, Air, and Soil Pollution, v. 16, p. 

277--285. 

Cobb, E. D., and Biesecker, J. E., 1971, The national hydrologic Bench-Mark network: U.S. Geological Survey Circular, 460-D, 38 p. 

Hicks, B. B., Wesely, M. L., and Durham, J. L., 1981, 

Critique of methods to measure dry deposition; concise 

summary of workshop: in Energy and Environmental 

Chemistry, v. 2, Acid Rain; chapter 12, p. 205-223, Ann 

Arbor Science Publishers, Ann Arbor, Michigan 

Hirsch, R. M., Slack, J. R., and Smith, R. A., 1982, Techniques of trend analysis for monthly water quality data: 

Water Resources Research, v. 18, no. 1, p. 107-121. 

Kilham, P., 1982, Acid precipitation: its role in the alkalization 

of a lake in Michigan: Limnology and Oceanography, v. 

27, no. 5, p. 856--867. 

Kramer, J., and Tessier, A., 1982, Acidification of aquatic systems: A critique of chemical approaches: Environmental 

12 

Science and Technology, v. 16, no. 11, p. 606A-614A. 

Likens, G. E., Bormann, F. H., and Eaton, J. S., 1980, Variations in precipitation and streamwater chemistry at the 

Hubbard Brook Experimental Forest during 1964 to 1977: 

in Hutchinson, T. C. and Havas, M., eds., Effects of acid 

precipitation on terrestrial acosystems, Plenum Press, 

New York, N.Y., p. 443--464. 

National Research Council, 1981, Atmosphere-biosphere interactions: Toward a better understanding of the ecological 

consequences of fossil fuel combustion: Washington, D.C., 

National Academy Press. 

--, 1983, Acid deposition: atmospheric processes in eastern 

North America: National Academy Press, Washington, 

D.C., 375 p. 

Niemann, B. L., 1983, Sulfur, nitrogen, and ammonia emissions and depositions (wet and dry) on a state/province 

basis for current emissions and proposed reductions: Report to the Office of Technology Assessment, Congress 

of the United States, Washington, D.C. 

Peters, N. E, Schroeder, R. A., and Troutman, D. E., 1982, 

Temporal trends in the acidity of precipitation and surface 

waters of New York: U.S. Geological Survey Water-Supply Paper 2188, 35 p. 

Ritter, J. R., and Brown, A. E., 1981, An evaluation of the 

effects of acid rain on low conductivity headwater ljltreams 

in Pennsylvania: U.S. Geological Survey Open-File Report 

81-1025, 53 p. 

Rivers, M. E., and Riegal, K. W., 1982, Report no. 3B final, 

prepared in fulfillment of Memorandum of Intent on Transboundary Air Pollution signed by Canada and the United 

States, August 5, 1980. 

Skougstad, M. W., Fishman, M. J., Friedman, L. C., 

Erdmann, D. E., and Duncan, S. S., eds, 1979, Methods 

for determination of inorganic substances in water and fluvial sediments: Techniques of Water-Resources Investigations of the United States Geological Survey, Book 5, 

Chapter Al. 

Smith, R. A., Hirsch, R. M., Slack, J. R., 1982, A study of 

trendsin total phosphorus measurements at NASQAN stations: U.S. Geological Survey Water-Supply Paper 2190, 

34p. 

t:r U.S. GOVERNMENT PRINTING OFFICE: 1983-676-041/35