EPA-600/D-82-333
Map and text
TOTAL ALKALINITY OF SURFACE
WATERS -- A NATIONAL MAP
by
James M. Omernik and Charles F. Powers
Con/all is Environmental Research Laboratory
U.S. Environmental Protection Agency
Con/all is, Oregon 97333
Abstract. This map illustrates the regional patterns of mean
annual alkalinity of surface water in the conterminous United
States. As such, it affords a qualitative graphic overview to the
sensitivity of surface waters to acidification. The map is based
on data from approximately 2500 streams and lakes and apparent
spatial correlations between these data and macro-watershed
characteristics, especially land-use.
Key Words: surface water alkalinity, sensitivity to acidifica-
tion, water quality.
Introduction
The accompanying map represents the first step in a comprehensive project
to identify general patterns of surface water sensitivity to acidification.
The map results from the growing demand for accurate identification of
acid-sensitive aquatic areas of the conterminous United States and is part of
a continuing program to (1) inventory and synthesize, state-by-state, the vast
quantities of relevant water quality data; (2) conduct general field surveys
to fill data gaps; (3) prepare detailed regional maps and update national
maps; and finally (4) conduct extensive field surveys (including biological
parameters) of critically sensitive areas.
The map was developed from mean annual total alkalinity values of
approximately 2,500 streams and lakes and from the apparent relationships of
these data with land use and other macro-watershed characteristics such as
soil type and geology. Total alkalinity is used as an index of sensitivity
because it expresses the acid neutralizing capacity of water bodies and thus
their relative sensitivity or tolerance to acid inputs. The ranges of our six
map units were chosen to illustrate patterns of relative sensitivity on a
national scale. Although there is general agreement that total alkalinity
expresses acid sensitivity of surface water, there is lack of agreement on
exactly where the breaking points exist between sensitive, moderately sens-
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Tl.S. Snv'froranontaT Protection
Begion 5, Library (5PL-16)
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itive, and insensitive waters. Hendrey et al. (1980) considered waters not
sensitive to acidification when alkalinities exceeded 500 ueq/1 and of high
sensitivity when alkalinities were less than 200 ueq/1. The Ontario Ministry
of the Environment (1981) proposed that alkalinities between 0 and 40 ueq/1
indicate extreme sensitivity and those between 40 and 200 ueq/1 moderate
sensitivity. Zimmerman and Harvey (1978-1979) have suggested a triad of
parameters to define acid sensitivity in surface waters: pH < 6.3-6.7,
conductivity < 30-40 umho/cm, and alkalinity < 300 (jeq/1.
General patterns of average sensitivities of surface waters to acid-
ification are depicted by this map, not worst-case or best-case conditions.
Our intent is to show what one might expect to find in most surface waters
most of the time. Subsequent larger-scale maps of the more sensitive areas
will address worst-case conditions, ranges of conditions, and significant
regional and (to the extent possible) local relationships between alkalinity
and geology; soils; and climatic, physiographic, and human use factors.
Confidence limits for areas of greatest sensitivity will also be provided.
These maps will be compiled as detailed information is gathered and analyzed.
For the present, however, there is an urgent need to understand the
relative sensitivity of surface waters in different parts of the country in
order to (1) provide a national perspective on the extent of the problem, (2)
provide logic and/or rationale for selecting geographic areas for more
detailed studies, and (3) allow more accurate regional economic assessments of
acid precipitation impacts on aquatic resources.
Map Development
The data used to compile this map were selected and mapped according to
several categories. Stream sites were listed separately from lakes, natural
lakes were distinguished from impoundments, and both stream sites and lakes
were separated into two groups -- those associated with watersheds of less
than 260 square kilometers (100 square miles) and those associated with
watershed areas of between 260 and 2600 square kilometers (100 and 1,000
square miles). Except in areas that were very similar in land use, physio-
graphy, and soils (e.g., the Great Plains), data associated with watersheds
larger than 2600 square kilometers (1,000 square miles) were excluded. As
might be expected, we found that the patterns of alkalinity values in streams
were quite similar to those of lakes in the same area. As the data were being
gathered and plotted, and geographical patterns of high and low alkalinities
developed, collection efforts tended to concentrate on these apparent areas of
greatest sensitivity.
Most of the data were obtained from the U.S. Geological Survey via
STORET, an EPA computer-based water quality data storage and retrieval system.
The remainder came from varied sources, principally the National Eutrophica-
tion Survey (U.S. Environmental Protection Agency, 1974, 1978a, 1978b, 1978c),
the Pennsylvania Cooperative Fishery Research Unit (Arnold, 1981), and the
Tennessee Valley Authority (Meinert and Miller, 1981). Although various
analytical procedures were used by the various agencies [U.S. Geological
Survey and the Tennessee Valley Authority, single endpoint titration to pH
4.5; National Eutrophication Survey, colorometric end point (methyl orange);
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and Pennsylvania Cooperative Fishery Research Unit, double endpoint titra-
tion], the alkalinity values obtained are reasonably equivalent and, we feel,
comparable for our scale of spatial analysis.
Each data point was scrutinized to insure representativeness. To
accomplish this, it was necessary to keep the watershed size consistent with
the relative homogeneity of major watershed features such as physiography and
land use. In areas of relative heterogeneity, most of the data were associ-
ated with small watersheds (less than 260 square kilometers). Representative-
ness of the data was imperative for detection of spatial patterns of
alkalinity, possible correlations with patterns of other characteristics, and
ultimately, extrapolation of the data. To include data from sites having
large watersheds of widely differing characteristics (e.g., the Willamette
River at Salem, Oregon, the watershed of which includes vast contrasts in
soils, geology, climate, and land use), or data downstream from major
industrial or municipal waste discharges, would mask these spatial patterns.
The data were plotted on a 1:3,168,000 scale base map of the United
States. Each site was represented by a small circle color-coded to approx-
imate value. The exact value of the site was noted beside the circle,
together with a designation for lake or stream. The spatial patterns of
alkalinity were then compared with maps showing characteristics that are
believed to be driving or integrating factors affecting alkalinity; e.g.,
bedrock geology and soils, land use and vegetation. Driving factors, as used
in this paper, refer to those that directly affect alkalinity (e.g., geology
and soils). Integrating factors, on the other hand, are considered those that
reflect combinations of driving factors; for example, land use and potential
natural vegetation reflect regional combinations (or an integration) of
driving factors such as soils, land surface form, climate, and geology. We
believe that the importance of each of these driving factors, and the
hierarchy of importance relative to the combinations of factors varies from
one region to another. Clarifying these regionalities is a major goal of our
overall synoptic analyses; they will be addressed in the text accompanying the
subsequent larger scale maps.
It became apparent early in this study that land use generally correlated
with alkalinity throughout much of the United States, and particularly in the
West. In general, surface water alkalinity was low in areas of ungrazed
forest and high where cropland predominated. In-between types of land use
generally reflected alkalinity values that corresponded to the degree of
agricultural use. However, the apparent relationship between land use and
alkalinity varied considerably; in some areas, particularly in the Southeast,
the relationship was poorly defined or nonexistent.
Except for some localized situations, we were not able to relate geo-
graphical patterns of surface water alkalinity with geological sensitivity as
depicted by bedrock or soil types. Recent studies by Kaplan et aj. (1981),
McFee (1980), and Hendrey et aj. (1980), based on county-by-county average
values, have demonstrated such correlations. Since alkalinity, in large part,
is a function of the nature of the rock and soil makeup of a drainage basin
(Cole, 1975), it did not appear unreasonable to expect similar results in this
mapping study. The lack of correlation is probably in large part a function
of study scale. Had our focus not been on the nation, but rather on a small
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region or state, possible surface water alkalinity/geology and/or soil type
relationships may have been more perceptible. However, this lack of correla-
tion may be due to one or more of several other factors. First, inconsist-
encies and inaccuracies in rock and soil type maps are common between, and
even within, regions and between states. Second, the alkalinity in a lake or
stream reflects the characteristics of both rocks and soils in the watershed.
Even in small watersheds, large spatial variations in rock and soil types and
depths can be found. Another confounding factor is that surface and sub-
surface 'watersheds frequently are difficult or impossible to define, partic-
ularly in areas of karst or continental glacial topography (Hughes and
Omernik, 1981). Apparent surface watersheds of streams and lakes in such
areas often differ greatly in area from the even more difficult to define
ground watersheds.
Because of the general correlation of land use with alkalinity, the
1:3,168,000 scale base map with alkalinity values was overlayed onto a color
enlargement of Anderson's Major Land Uses map (U.S. Geological Survey, 1970).
When viewed on a light table, the general land use patterns and spatial
relationships of surface water alkalinity to land use could be visualized. By
studying these relationships and patterns, along with apparent local relation-
ships with geologic and soil characteristics, interpretations were made and
map units drawn to reflect these regional relationships.
Use of the Map
The development and usefulness of this map can best be illustrated by
comparison with a more familiar graphic -- an isometric map of mean annual
precipitation.1 One should not use a precipitation map to predict the
precipitation that will occur during a particular year at a given location.
Rather, the map illustrates patterns of long term conditions. Few parts of
the United States typically experience a truly "normal year" climatically.
Generally, precipitation totals are somewhat higher or somewhat lower than the
mean; occasionally, total deviation from the mean is extreme. Admittedly,
precipitation maps may provide a more accurate indicator of their subject than
the alkalinity map because of their more extensive data base (particularly
from the temporal standpoint). However, precipitation maps are compiled using
data from different geographical locations together with knowledge of apparent
associations of these data with physiographic characteristics, water bodies,
ocean currents, latitude, and other environmental factors. For example,
precipitation patterns in mountainous areas, where data are scarce or lacking,
are drawn to reflect the expected orographic effects of elevation and exposure
to weather systems. Much the same kind of qualitative analysis was used to
compile the alkalinity map. It is based on values from more than 2,500 stream
sites and lakes throughout the United States, as well as knowledge of the
apparent*associations between the alkalinity data and other spatial phenomena,
particularly land use.
1 McDowell and Omernik (1979) used this comparison to clarify the utility of a
set of national maps of nutrient concentrations in streams from nonpoint
sources (Omernik, 1977). The total alkalinity map was compiled in a similar
fashion as the nutrient maps but with more than two and one-half times as many
data points.
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As with a precipitation map, caution should be exercised when using this
alkalinity map. In many parts of the nation, nearly all of the surface waters
have mean annual alkalinity values within the range illustrated in the map.
In other areas — particularly where there are complex variations in geology
and soil type, and other factors affecting acid sensitivity — there are wide
spatial and temporal variances in alkalinity. For these types of areas, at
this scale of mapping, we were only able to estimate the mean annual alka-
linity of most surface waters; many may reflect higher or lower values.
Acknowledgments
Many people contributed to the development of this map. Especially
deserving of recognition is Andrew J. Kinney for his help in gathering,
scrutinizing, and plotting the data.
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REFERENCES CITED
Arnold, D. E. 1981. Personal communication: preliminary unpublished data on
alkalinities of Pennsylvania waters. Pennsylvania Cooperative Fishery
Research Unit, Pennsylvania State University, University Park, Pennsyl-
vania.
Cole, G. E. 1975. Textbook of limnology. The C. V. Mosby Company, St.
Louis, Missouri. 283 pp.
Hendrey, G. R. , J. N. Galloway, S. A. Norton, C. L. Schofield, P. W. Shaffer,
and D. A. Burns. 1980. Geological and hydrochemical sensitivity of the
eastern United States to acid precipitation. EPA-600/3-80-024.
Corvallis Environmental Research Laboratory. U.S. Environmental Protec-
tion Agency, Corvallis, Oregon. 100 pp.
Hughes, R. M. , and J. M. Omernik. 1981. Use and misuse of the terms water-
shed and stream order. In: Proceedings of the Warmwater Streams
Symposium. Southern Division, American Fisheries Society, pp. 320-326.
Kaplan, E. , H. C. Thode, Jr., and A. Protas. 1981. Rocks, soils, and water
quality. Relationships and implications for effects of acidification on
surface water in the northeastern united states. Environmental Science
and Technology 15(5):534-544.
McDowell, T. R. , and J. M. Omernik. 1979. Non-Point source—stream nutrient
relationships: A nationwide study. Supplement 1: Nutrient map reli-
ability. EPA-600/3-79-103. Corvallis Environmental Research Laboratory,
U.S. Environmental Protection Agency, Corvallis, Oregon. 33 pp.
McFee, W. W. 1980. Sensitivity of soil regions to acid precipitation.
EPA-600/3-80-013. Corvallis Environmental Research Laboratory, U.S.
Environmental Protection Agency, Corvallis, Oregon. 179 pp.
Meinert, D. L. , and F. A. Miller III. 1981. A Review of water quality data
in acid sensitive watersheds within the Tennessee Valley — Volume 1.
Tennessee Valley Authority, prepared for the U.S. Environmental Protec-
tion Agency. Chattanooga, Tennessee.
Norton, S. A. 1981. Unpublished maps on acid sensitivity as suggested by
bedrock geology. Department of Geological Sciences, University of Maine,
Orono, Maine. 39 pp.
Omernik, J. M. 1977. Nonpoint source — stream nutrient level relationships:
A nationwide study. EPA-600/3-77-105. Corvallis Environmental Research
Laboratory, U.S. Environmental Protection Agency, Corvallis, Oregon. 151
pp.
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Ontario Ministry of the Environment. 1981. Acid sensitivity survey of lakes.
Acidic precipitation in Ontario study. (APIOS) Report No. API 002/81,
Toronto. 140 pp.
U.S. Environmental Protection Agency. 1974. A compendium of lake and
reservoir data collected by the aNtional Eutrophication Survey in the
northeast and northcentral United States. National Eutrophication Survey
Working Paper No. 474. Corvallis Environmental Research Laboratory, U.S.
Environmental Protection Agency, Corvallis, Oregon. 210 pp.
. 1978a. A compendium of lake and
reservoir data collected by the National Eutrophication Survey in the
eastern, northcentrals and southeastern United States. National Eutro-
phication Survey Working Paper No. 475. Corvallis Environmental Research
Laboratory, U.S. Environmental Protection Agency, Corvallis, Oregon. 266
pp.
. 1978b. A compendium of lake and
reservoir data collected by the National Eutrophication Survey in the
central United States. National Eutrophication Survey Working Paper No.
476. Corvallis Environmental Research Laboratory, U.S. Environmental
Protection Agency, Corvallis, Oregon. 199 pp.
. 1978c. A compendium of lake and
reservoir data collected by the National Eutrophication Survey in the
western United States. National Eutrophication Survey Working Paper No.
477. Corvallis Environmental Research Laboratory, U.S. Environmental
Protection Agency, Corvallis, Oregon. 168 pp.
U.S. Geological Survey. 1970. The national atlas of the United States. U.S.
Government Printing Office, Washington, D.C. 417 pp.
Zimmerman, A. P. , and H. H. Harvey. 1979-1980. Sensitivity to acidification
of waters of Ontario and neighboring states. Final Report for Ontario
Hydro. Univ. of Toronto. 136 pp.
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