EPA-600/D-84-216
June 1985
TOTAL ALKALINITY OF SURFACE WATERS: A MAP
OF THE NEW ENGLAND AND NEW YORK REGION
by
James M. Omernik
Corvallis Environmental Research Laboratory
U.S. Environmental Protection Agency
200 S.W. 35th Street
Corvallis, Oregon 97333
and
Andrew J. Kinney
Northrop Services, Inc.
200 S.W. 35th Street
Corvallis, Oregon 97333
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Abstract
This map illustrates the spatial patterns of mean annual alkalinity of
surface water in the New England and New York Region. As such, it affords a
qualitative graphic overview of the relative potential sensitivity of surface
waters to acidic input. The map is based on data from approximately 1,500
lakes and streams and the apparent spatial associations between these data and
macrowatershed characteristics, especially land use.
DISCLAIMER
The information in this document has been funded by the United States
Environmental Protection Agency. It has been subjected to Agency
review and approved for publication.
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A major goal specified in the National Acid Precipitation Assessment Plan
(Interagency Task Force on Acid Precipitation, 1982) is the quantification of
the extent of sensitivity of the nation's lakes and streams to acidification.
Most earlier efforts to determine patterns of surface water sensitivity to
acidic deposition have relied on interpretations of bedrock distribution and
chemistry (Galloway and Cowling, 1978; Likens et al., 1979; Hendrey et al.,
1980; National Atmospheric Deposition Program, 1982). However, one effort was
based on soil sensitivity (McFee, 1980) and another on surficial geology
(Shi Its, 1981). While each of these contributed to the general knowledge of
the extent of surface water sensitivity, they are in sharp disagreement for
many portions of the country. More importantly, there is a lack of spatial
correlation between the patterns drawn by these efforts and the observed
patterns of surface water alkalinity.
Although there is general agreement that surface water alkalinity is
directly related to mineral availability, it is apparent that maps of rock type
or soil type alone are inadequate to express patterns of mineral availability
that are meaningful in terms of surface water sensitivity. For instance,
results from several recent studies of patterns of surface water sensitivity in
different regions of the United States (Eilers et al., 1983; Haines and
Akielaszek, 1983; Twaroski et al., 1984) indicate that no single factor (e.g.,
bedrock geology) can explain observed patterns of surface water alkalinity.
Rather, these studies indicate that one must consider a variety of driving or
integrating spatial factors that affect alkalinity such as land use, physio-
graphy, and soil type (as well as geology), and that the relative importance of
any one, or a particular combination of those factors, may vary within or among
regions.
A recent report of the National Academy of Sciences (Environmental Studies
Board, 1984) defined several important geochemical and hydrological processes
of watersheds that determine whether waters will acidify and the rate at which
acidification would proceed. These processes are not yet defined on a regional
scale and, therefore, cannot presently be used in a definition of relative
sensitivity of regions to acidic deposition.
In light of the above, it is clear that caution must be used in any effort
to use a single measure such as alkalinity to assess the sensitivity of surface
waters to acidic deposition because the actual response of a given lake or
stream is determined by numerous biogeochemical and hydrological factors of the
watershed plus chemical processes within water bodies. Alkalinity is certainly
the most readily available measure of the acid-neutralizing capacity of surface
waters. Although alkalinity measurements do not completely incorporate the
influences of all factors into a definition of surface water sensitivity, they
do reflect the interactions of biogeochemical and hydrological processes that
ultimately influence sensitivity.
With this rationale, we approached the problem of depicting the likely
patterns of surface water sensitivity in the conterminous United States by
synoptically analyzing spatial patterns of surface water alkalinity as an
integrator of the various factors which determine sensitivity. We accomplished
this by: (1) assembling available alkalinity data on as many representative
surface waters as necessary and/or possible; (2) plotting these data on
1
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relatively large-scale maps; and (3) analyzing the patterns of the values of
the plotted data for spatial correlations with other characteristics such as
land use, geology, and physiography.
A national map compiled earlier (Omernik and Powers, 1983) described the
general patterns of surface water alkalinity in the conterminous United
States. By comparison, the regional map presented here is based on an order of
magnitude more data and depicts the spatial patterns of surface water alka-
linity at a greater resolution than was possible in the national map.
The alkalinity ranges of the five map units were chosen to reflect
potential sensitivity patterns on a regional scale, as compared with the
broader ranges used for the national map. Although it is impossible to define
exact break points between sensitive, moderately sensitive, and insensitive
waters, it is generally agreed that waters of total alkalinity > 200 ueq/1 are
relatively insensitive to acidic deposition.
As was the case with the national map, our purpose is to show what range
of alkalinity one might expect to find in most of the surface waters most of
the time. Relative to the national map, the regional map provides more
detailed ancillary information on ranges of conditions, significant apparent
regional and local relationships between alkalinity and macro-watershed
characteristics such as land use and physiography, seasonal variations, and
other factors. This information in turn provides a basis for understanding the
confidence with which predictions and estimations of potential surface water
sensitivity might be made for the region, or parts of the region. We emphasize,
however, that the map and the anci 11 ary information are not intended for making
precise predictions of sensitivity for individual water bodies or specific
locations. Rather, this map and the other regional maps are intended to help
fill the urgent need to understand the relative potential sensitivities~of
surface waters in different parts of the country in order to provide a "naFi ona 1
perspective of the potential problem, provide rationale for selecting geo-
graphic areas for more detailed studies, and allow more accurate regional
economic assessments of acidic deposition impacts on aquatic resources.
Map Development
The data used to compile this map were selected and mapped according to
several categories. Stream sites were distinguished from lakes, both were
categorized by their watershed size, and data were separated as to the number
of samples they represented. Data from one sample per site were plotted on one
l:2,500,000-scale map overlay, and mean values from two samples per site were
plotted on another so as to be distinguished from mean values of three or more
samples, which were plotted on a 1:2,500,000 scale base map.
Most of the data were acquired from cooperators who performed the Inven-
tory of Available Data Relevant to a National Assessment of the Extent of
Surface Water Sensitivity and Acidification — Project E 1-1, Task Group E
(Allum and Powers, 1983). The remainder were largely obtained from STORET, an
Environmental Protection Agency (EPA) computer-based water quality data storage
and retrieval system. More than 80 percent of the data were from dates no
earlier than 1977; no more than 5 percent were for dates earlier than 1973.
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Because the data were from a variety of sources and different years
(including that assembled by the inventory cooperators), the analytical proce-
dures also varied. Only about 3 percent of the data were determined using the
titration method of Gran (1952), about 18 percent by double endpoint titration
(potentiometric) (American Public Health Association, 1980), about 22 percent
by single endpoint titration (potentiometric), and about 38 percent by single
endpoint titration (colorimetric). For approximately 19 percent of the values,
the analytical methods are unknown. The state from which the greatest percent
of data (at least 40%) were determined using either a double endpoint procedure
or the method of Gran (1952) was Vermont. By contrast, at least 85 percent of
the data from Maine were determined using colorimetric methods.
For low alkalinity waters the most commonly used fixed endpoint procedures
(either potentiometric or colorimetric) often yield overestimates of alkalinity
(Dillon et al., 1978; Zimmerman and Harvey, 1979-1980; Jeffries and Zimmerman,
1980; National Research Council of Canada, 1981; Henriksen, 1982; Kramer and
Tessier, 1982; Church, 1983). Precision may also be significantly less with
colorimetnc procedures because of uncertainty as to the exact endpoint (Kramer
and Tessier, 1982; Church, 1983). In contrast, the double endpoint procedure
and the procedure of Gran (1952) are unbiased and probably more precise for low
alkalinity waters (Gran, 1952; American Public Health Association, 1980;
Church, 1983).
When making our final interpretations of spatial patterns of the data and
subsequent map unit delineations, we attempted to compensate for the probable
bias introduced by selected analytical procedures. If actual endpoint pH
values of the titrations are known, then quantitative procedures may be applied
to correct for bias (National Research Council of Canada, 1981; Henriksen,
1982; Kramer and Tessier, 1982; Church, 1983). Because of the lack of such
data, however, these calculations were outside the scope of this work. In
areas where representative sites had borderline or slightly above borderline
values between alkalinity classes (e.g., 50, 100, 200, and 400 ueq/1) and where
the analytical methods had been other than double endpoint or Gran's titration,
we assigned the respective areas to the lower alkalinity class and drew the map
units accordingly. However, in many cases the compensation may not have been
enough to account for the bias due to methodology as suggested in the sources
cited above. Hence, the areas shown to be in the lower alkalinity classes may
actually be larger. We believe this to be particularly true in Maine, because
the alkalinity data available for that state were largely determined by titra-
tion to a colorimetric endpoint. The areas illustrated by map unit #1 (< 50
ueq/1) may actually comprise some of the adjacent area illustrated by map unit
#2 (50 to 100 ueq/1), the areas illustrated by map unit #2 may comprise some of
the adjacent areas illustrated by map unit #3, and so on.
Each data point was scrutinized to insure representativeness. To accom-
plish 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 associated with
small watersheds (less than 50 square miles). Representativeness of the data
was imperative for detection of spatial patterns of alkalinity, possible
correlations with patterns of other characteristics, and ultimately, extrapola-
tion of the data. To include non-representative data from sites having large
watersheds of widely differing characteristics [e.g., the Hudson River in New
3
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York (just above the confluence with the Mohawk River), the watershed of which
includes vast contrasts in soils, geology, and land use], or data downstream
from major industrial or municipal waste discharges, would mask these spatial
patterns.
The data were plotted on a l:2,500,000-scale base map (or, for data refer-
encing fewer than three samples, on overlays registered to a base map) of the
United States. Each site was represented by a small circle color-coded to one
of the following alkalinity classes: < 50, 50 to 100, 100 to 200, 200 to 400,
and > 400 ueq/1. The exact value of the site was noted beside the circle,
together with a designation for lake or stream. The spatial patterns of alk-
alinity were then compared with maps showing characteristics that are believed
to be driving or integrating factors affecting alkalinity. Driving factors, as
used in this paper, refer to those that are generally believed to directly
affect alkalinity (e.g., geology and soils). Integrating factors, on the other
hand, are considered those that tend to 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 factors, and the hierarchy of importance relative to the combina-
tions of factors, varies from one region to another. Clarifying these regional
factors is a major goal of our overall synoptic analyses.
As with the national map,' the interpretations were made and map units
drawn based on the spatial patterns of the actual alkalinity values and the
apparent spatial associations of these values with areal characteristics in
land use, physiography (including land surface form and elevation), geology,
soils, and vegetation. The map unit alignments comprise isolines which are
more accurate representations in areas where there are dense concentrations of
data and where the values of these data exhibit significant regional patterns.
The apparent spatial associations of the alkalinity values with other areal
characteristics allowed extrapolation into areas where data were sparse or
lacking. Obviously, the accuracy of isolines in these areas is a function of
the strength of the spatial associations. Because so many more data points
(~ 1500 vs ~ 150) were used to construct this map of New England and New York
than were used to compile that portion of the national map, the spatial
patterns of the alkalinity values were much more clear.
It should be noted that, as the regional maps were being compiled, our
methods of data analyses and interpretation underwent considerable modification
as the patterns of the complexity of the data, association between the data and
other spatial characteristics, and data quality became apparent. The New
England and New York map of surface water alkalinity was the first of the
regional maps to be compiled. It is now apparent that the map might be more
accurate if: (1) each of the data points were adjusted for bias in laboratory
analytical procedure; (2) greater consideration were given to values repre-
sented by only one sample; (3) the values were plotted on, and the interpret-
ations made at, 1:500,000- or 1:250,000-scale topographic maps; and (4) data
collected during 1983 and 1984 were utilized. The other regional maps have
been, or are being, compiled with greater utilization of one sample per site-
data and larger scale maps for interpretations of patterns and associations.
We intend to recompile this map of the Northeast in a similar fashion after the
data have been re-sorted by laboratory analytical procedures and agreement has
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been reached on methods for compensating for relative biases. However, the map
in its present form meets an urgent need to illustrate the regional patterns of
surface water alkalinity in the Northeast in greater detail and more compre-
hensively than was previously available.
It is also noteworthy that the synoptic geographic analysis used to
compile this map does not lend itself to the standard quality assurance (QA)
and quality control (QC) procedures required by EPA. Unlike typical research
or surveys, our work used available data, and employed subjective and quali-
tative processes to identify significant spatial patterns and associations.
These processes, by their very nature, have no standard methods and lack clear
precedents. However, as noted earlier, each value was screened for represen-
tativeness, and the cooperators who submitted data to ERL-Corvallis screened
the data for adequacy. Additionally, ERL-Corvallis conducted random spot
checks for "outliers" or questionable values (Allum and Powers, 1983).
Regional Patterns of Surface Water Alkalinity in New England and New York
In the Northeast, the surface waters of concern to the acid precipitation
issue are primarily the continental glacial lakes, but also many of the smaller
streams (relative to watersheds of generally less than 100 square miles) and,
to some extent, reservoirs. Compared to the Upper Midwest -- the other region
of the U.S. with a large concentration of continental glacial lakes -- the New
England and New York region has a far greater proportion of surface waters in
lakes and streams that are relatively low in alkalinity (Table I).
We have divided the New England and New York Region into five subregions,
based on significant regional patterns of homogeneity of general characteris-
tics and spatial associations that are important to an understanding of sensi-
tivity of surface waters to acidification in the areas of lowest alkalinity
waters within the Region (Figure 1). Subregion IA is centered on the
Adirondack Mountains. The portion of this subregion that contains the lowest
alkalinity surface waters is hilly or mountainous, forested, relatively
uninhabited, and has a high percent of surface area in lakes — characteristics
distinctly different from the surrounding more populated, less rugged area,
where cropland and pasture dominate. This area is so unique physiographical ly
that much of it has been set aside as a park.
Subregion IB is part of a larger area of generally small continental
glacial lakes, centered on the Catskill Mountains of southeastern New York but
extending into some of the hilly portions of northeastern Pennsylvania and
northwestern New Jersey. In New York, the areas of lowest alkalinity lakes and
streams are generally in the higher forested portions of the Catskills.
Subregion 1C comprises all of New Hampshire, most of Vermont, part of
western Maine, and small portions of Massachusetts and New York. Compared to
adjacent subregions in Maine and the Adirondacks, this area is characterized by
a relatively low percent of area in lakes. However, this subregion has fairly
extensive areas of streams and medium to small lakes of low alkalinity, partic-
ularly in the more rugged forested portions.
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NEW ENGLAND *
& NEW YORK
Total Area in Lakes (Hectares)*** 1,101,135
Lake Hectares by Alkalinity Class
< 50
50-100
100-200
< 200
117.691 (11%)
191,920 (17%)
286.844 (26%)
596.455 (54%)
UPPER
MIDWEST
1,868,799
8.086 (0.4%)
21,003 (1.1%)
95.214 (5.1%)
124.303 (6.6%)
• Includes Lake Chnrnplnin.
•• Wiihin colored area on drall nlk.ilinily man ol Uooer Midwest (Omernik and Grillilh, 1985)
*** Lakes >6 hectares (15 acres).
Table I. Total hectares in lakes, by alkalinity class, in the New England and
New York Region and the Upper Midwest Region
Figure 1. Subregions of the New England and New York Region
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Subregion ID covers Connecticut, Rhode Island, most of Massachusetts, and
small portions of New York. Relative to the other subregions, this one is more
densely populated and is characterized by sandier soils and a higher percentage
of impoundments. Moreover, the areas of lowest alkalinity generally do not
correspond to the most rugged, highest elevations; in fact, one is largely a
wetland.
The remaining subregion, IE, comprises all but the western 15 percent of
Maine. The areas of lowest alkalinity waters within this subregion are charac-
terized by a high percent of area in lakes of all sizes and relatively low
elevations (with the exception of some hills and mountains in the central and
western portions of the subregion).
As previously explained, our interpretations of regional surface water
alkalinity and subsequent map unit delineations were based on the spatial
patterns of the actual alkalinity values and apparent spatial associations of
these values with macro-watershed characteristics such as land use and physio-
graphy. Although the patterns of the alkalinity values constituted the primary
information base, it was the apparent spatial associations between patterns of
the values themselves and the other characteristics that provided the basis for
extrapolation into areas without representative alkalinity values. These
spatial associations served as the fine tuning mechanisms for guiding the final
map unit delineations.
The most universally apparent of these associations was that between alka-
linity and land use (USDI Geological Survey, 1970). In general, surface water
alkalinity was low in areas of ungrazed forest and high where cropland predom-
inated. Intermediate types of land use generally reflected alkalinity values
that corresponded to the degree of agricultural use. Streams draining areas
with high agricultural potential tend to have higher alkalinity values than
those with little or no agricultural potential because of the natural composi-
tion of the soils. In most cases, such areas are put to agricultural uses.
Although the land use/alkalinity association was apparent in a general way for
the New England and New York Region as a whole, it was particularly distinct in
certain areas within the region, especially in eastern New York, southcentral
Maine, most of New Hampshire and Vermont, southeastern Massachusetts, and Rhode
Island.
Where alkalinity values varied within an area categorized entirely by
ungrazed forest, physiographic characteristics such as elevation or land
surface form could in some cases be used as guides in the interpolation or
extension of mapped alkalinity values. Such was the case in parts of the
Catskill Mountains of southeastern New York, in Rhode Island, and in portions
of Massachusetts. In only a few localized situations were we able to relate
geographic patterns of surface water alkalinity with geological sensitivity as
depicted by bedrock or soil types.
In other parts of the nation, particularly in much of the Upper Midwest,
there are striking differences in alkalinity between lakes and streams and
between seepage and non-seepage lake types (Eilers et al., 1983; Omernik and
Griffith, 1985; Scott et al., 1983; Heiskary and Thornton, 1983; Various
Authors, 1960-1980). However, like Haines and Akielaszek (1983), who conducted
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a survey of 226 headwater lakes and small streams in the six New England
States, we noticed no appreciable differences between these surface water types
in the larger New England and New York region.
The information in Table II provides a more detailed understanding of the
variability of surface water alkalinity within and between subregions. It also
provides a rough measure of confidence with which one might make predictions of
surface water alkalinity for the New England and New York Region, particularly
the more sensitive portions. For brevity, only the characteristics of those
values from the lowest alkalinity class areas are shown. The table should not
be used for assessing the extent of alkalinity or sensitivity of surface waters
without a clear understanding of the necessarily qualitative way in which the
map units were drawn. The actual extent of each unit is based not only on the
value of the alkalinity data points, but also on the patterns of representative
values of adjacent areas and apparent associations of these values with macro-
watershed characteristics as explained previously. It is also pertinent to
this understanding that the approximately 1500 values used in making these
determinations were thoroughly screened to ensure their relative representa-
tiveness.
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TABLE II. CHARACTERISTICS OF DATA POINTS IN AREAS ILLUSTRATED BY THE < 50 ueq/1 ALKALINITY CLASS IN EACH SUBREGION
Total Alkalinity (ueq/1 )
Subregions
IA
Adi rondacks
IB
SE. New York
1C
Vermont, New
Hampshi re ,
and W. Maine
No. of Sample
Points in Area
Classified
< 50 ueq/1 Mean Median Range
40 13 2 -57
to
157
7 54 38 17
to
95
73 28 24 -9
to
94
Seasonality
Range of
1 Standard
Error Frequency Distribution
7 10
" illS I
Lakes (N - 30)
-- Low in spring (April and May);
high in summer and early winter
(August /February)
-100-50 0 60 100150^200 <- J"a"'"" '• «"•«•"« "•"">. * iu \ieni I
-- Generally low year-round
41 6
0 60 10
?<, JO
32 is . ; lli"-
In -
10 : I-T::
These data have insufficient
year-round values to detect
seasonality. Data from nearby
areas indicate a winter-spring
(December through March) low and
a summer (July through September)
high.
These data have insufficient
:: year-round values to detect
areas indicate a spring (March
(July through September) high.
i
Major Factors and/or
Apparent Spatial Associations
Responsible for Delineation
of Map Units
-- Spatial pattern of values of
the data points.
-- Spatial associations between
alkalinity values and land
use patterns
-- Spatial pattern of values of
the data points.
-- Spatial associations between
alkalinity values with land
use and physiographic
characteristics.
-- Spatial pattern of values of
the data points.
-- Spatial associations between
alkalinity values and land
use patterns.
Comments
•- Watershed sizes for stream data points
were small (x = 12 mi2; range 2 to 25
mi2); watershed sizes for lake data
points were slightly larger but
generally < 30 mi2.
-- Seventy percent of the stream data are
from sites relative to small (< S mi2)
relatively high elevation (> 2,000 ft)
watersheds; hence, this may introduce a
bias toward lower values than are
generally typical of this portion of the
Adi rondacks .
-- All sample sites are from high gradient
streams with small (< 5 mi2) forested
watersheds, at high (> 1700 ft)
elevations. Sites from nearby areas of
lower elevations and/or pasture land or
cropland had considerably higher
alkalinity values.
-- Land use (forested vs. any agricultural
activity) and elevation are reflecting
factors.
10
Connecticut,
Rhode Island,
and
Massachusetts
17
24
12
-46
to
160
10
to
37
These data have insufficient
year-round values to detect
seasonalily. Data from nearby
60 100 150200 areas indicate a spring (March
through May) low and a summer
(July through September) high.
Spatial pattern of values of
the data points.
Spatial associations between
alkalinity values with land
use, physiographic character-
istics, geology, and vegeta-
tion types.
Watershed sizes were generally small (x =
Ib mi2) and drained ridges, except in
Massachusetts where the data were from
low lying wetlands categorized as being
high in geologic sensitivity (National
Atmospheric Deposition Program, 1982).
IE
Maine (except
for W.
porti ons)
64
53
40
-40
to
170
44
to
0 50 .00 150 200
Note: Majority of the
data have been
converted from »ig/l to
ueq/1 , hence the
20 yeq/1 intervals.
These data have insufficient
year-round values to detect
seasonalily. Data from nearby
areas indicate a spring (March
through May) low and summer (July
through September) and winter
(December through February) highs.
Spatial pattern of values of
the data points.
Spatial associations between
alkalinity values with land
use and geology.
Reported geologic sensitivity (National
Atmospheric Deposition Program, 1982)
appeared to correlate with alkalinity
values in the Mount Katahdin area and
along the Coastal Plain in Washington and
Hancock counties.
Most of the values obtained for subregion
were determined by laboratory analytical
procedures that tend to overestimate
alkalinity. Although efforts were made
to compensate for these biases, the areas
illustrated by lower alkalinity classes
may be slightly larger and extend into
the area illustrated by the next higher
akalinity class.
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