Full text of DOI:10.1672/0277-5212(2001)021[0125:EIOPSC]2.0.CO;2

WETLANDS, Vol. 21, No. 1, March 2001, pp. 125–134
ꢀ
2001, The Society of Wetland Scientists
ENVIRONMENTAL INFLUENCES ON PLANT SPECIES COMPOSITION IN
GROUND-WATER SEEPS IN THE CATSKILL MOUNTAINS OF NEW YORK
1
Brian R. Hall , Dudley J. Raynal, and Donald J. Leopold
Faculty of Environmental and Forest Biology
College of Environmental Science and Forestry
State University of New York
Syracuse, New York, USA 13210
1
Present Address and Address for Correspondence
PO Box 68
Harvard Forest
Petersham, Massachusetts, USA 01366
E-mail: brhall@fas.harvard.edu
Abstract: Ground-water seeps in the Catskill Mountains are important water sources for streams and often
have different chemistry than nearby surface water. Many studies have shown correlations between water
chemistry and plant species composition in wetlands, but there are no such studies in the Catskill Mountain
ground-water seeps. The objective of this study was to identify the chemical and physical environmental
variables that most strongly influence plant species composition in seeps. Environmental variables and plant
species abundance were measured at 33 seeps. TWo-way INdicator SPecies ANalysis with analysis of var-
iance and Canonical Correspondence Analysis showed that plant species composition is determined primarily
by water depth and alkalinity/acidity complex gradients. Growing season changes in water chemistry were
not shown to influence the plant community.
Key Words: wetlands, wetland vegetation, seeps, springs, bryophytes, Catskill Mountains, indirect gradient
analysis
INTRODUCTION
velop when ground water reaches the surface through
faults or fractures in impermeable rock (de Blij and
Muller 1993). In the Catskill Mountains of New York
State, many seeps flow throughout the summer and
have well-developed channels approximately 0.5–5 m
wide. Channels with high velocity flow usually have
cobble substrates with very little sand, silt, or clay.
Often, these cobbles are covered with mat-forming
mosses such as Brachythecium rivulare BSG. and
Bryhnia novae-angliae (Sull. & Lesq. ex. Sull) Grout;
these moss mats are usually the most common sub-
strate for vascular plants in the seep. Channels with
low velocity flow often have muddy substrates with
less exposed cobble; these channels often have dense
populations of herbaceous species such as Impatiens
capensis Meerb., Laportea canadensis (L.) Wedd., or
Eupatorium rugosum Houttuyn.
Ground water is an important water source for
streams, especially during the summer when the quan-
tity of surface water diminishes (Williams and Pinder
1990, Likens and Bormann 1995, Rice and Bricker
1995). Ground-water hydrologic flowpaths differ from
surface waters and therefore differ in chemistry, even
on sites with relatively unreactive bedrock (Rice and
Bricker 1995). For example, hydrologic characteriza-
tion at Hubbard Brook Experimental Forest (HBEF)
models two types of waters, dilute surface water and
‘‘salty’’ ground water (Likens and Bormann 1995). In
the eastern United States, ground waters usually are
less acidic and have higher alkalinities than surface
waters due to ground-water/bedrock reactions, which
2ϩ
2ϩ
yield base cations such as Ca and Mg .
Ground-water discharge areas, or seeps, typically
occur at the bases of steep slopes where the ground
surface intersects the water table. Frequently, seeps are
caused by an aquiclude, an impermeable layer of rock
or clay in the hill. Aquicludes inhibit downward move-
ment of water to the water table but allow horizontal
movement to the ground surface. Seeps can also de-
Specific environmental conditions are known to af-
fect plant community characteristics in many types of
wetlands. For example, a strong relationship between
water chemistry and species composition has been
shown in peatlands (Jeglum 1971, Karlin and Bliss
1984, Johnson and Leopold 1994, Walbridge 1994,
Anderson et al. 1995, Anderson et al. 1996). Ionic con-
125

126
WETLANDS, Volume 21, No. 1, 2001
inceptisols (Tornes 1979) with low to moderate cation
exchange capacities (Murdoch and Stoddard 1993).
Soils at the study site are in the Arnot-Oquaga-Lack-
awanna association, which was derived from glacial
till consisting of fragments of regional bedrock (red-
dish sandstones, siltstones, and shale). The Arnot and
Oquaga soils are both moderately to excessively well
drained. The Arnot soil has a depth of 25 to 50 cm;
the Oquaga soil has a depth of 50 to 100 cm. The
Lackawanna soil is very bouldery and has a root-re-
strictive fragipan at a depth of 43 to 92 cm (Tornes
1979).
Mean annual precipitation is 119 cm. Mean January
temperature is
Ϫ4.2Њ C; mean July temperature is 21.5Њ
C (Tornes 1979). The elevation range for the study
site is approximately 550 m to 900 m.
The forests at the study sites include species typical
of the Catskill Mountains. The canopy is dominated
by Fagus grandifolia Ehrh., Betula alleghaniensis
Britton, and Acer saccharum Marsh.; associated tree
species include Tsuga canadensis (L.) Carr., Prunus
serotina Ehrh., Acer rubrum L., Fraxinus americana
L., and Tilia americana L. Subcanopy species include
saplings of the above tree species, and Acer pensyl-
vanicum L., Hamamelis virginiana L., Ilex montana
(T. & G.) A. Gray, Ostrya virginiana (Mill.) K. Koch,
and Viburnum alnifolium Marsh. Common herbs in-
clude: Dryopteris intermedia (Muhl.) A. Gray, Den-
nstaedtia punctilobula (Michx.) Moore, Lycopodium
lucidulum Michx., L. annotinum L., Laportea cana-
densis, Tiarella cordifolia L., Trillium erectum L.,
Trientalis borealis Raf., and Oxalis acetosella L. No-
menclature for mosses follows Crum (1983), for liv-
erworts follows Schuster (1974), and for vascular
plants follows Gleason and Cronquist (1991).
Figure 1. Locations of study areas (in boxes) and number
of seeps sampled in each area. Approximate location of
study region on inset map.
2ϩ
2ϩ
centrations, especially pH, Ca , and Mg , affect spe-
cies composition in moderately to strongly minero-
trophic peatlands (Karlin and Bliss 1984, Motzkin
1994). Because there have been few studies of vege-
tation/environment relationships in seeps and none in
the Catskill Mountains, we characterize the environ-
mental factors that are correlated with plant species
composition in Catskill ground-water seeps. Knowl-
edge of the effects of seep water on vegetation is im-
portant for a basic understanding of these systems; this
knowledge will also be useful to watershed managers
responsible for prioritizing sites for protection, espe-
cially if bioindicators of flow regimes or water chem-
istry can be found.
METHODS
Site Description
Vegetation Sampling
Seeps were selected for sampling based on the fol-
lowing criteria: 1) the presence of an extensive water
chemistry data set from ongoing hydrologic investi-
gations by the United States Geological Survey; 2)
high or low pH, relative to previously sampled seeps,
to include as large a range of site conditions as pos-
sible; and 3) a high abundance of plant species not
encountered in previously sampled seeps. Seeps with
continuous flow throughout most of the summer were
preferentially selected over similar ‘‘ephemeral’’
seeps.
This study was conducted at the Frost Valley
YMCA camp, Ulster County, New York, USA (41Њ59’
N, 74Њ31’ W) and at the headwaters of Biscuit Brook
(both branches) and High Falls Brook. All seeps are
at headwaters of brooks that flow into the West Branch
of the Neversink River (Figure 1).
The Catskill Mountain region has bedrock consist-
ing primarily of interbedded layers of shales, sand-
stones, and conglomerates. Quartz and metamorphic
rocks make up approximately 78% and 16% of the
mineral and rock fragments; therefore, the bedrock is
relatively unreactive (Murdoch and Stoddard 1993).
The study area has a ‘‘step-riser’’ topography that re-
sults from uneven weathering of the bedrock layers
(Kudish 1979).
Vegetation was sampled in 10
ϫ 20 m plots placed
so that the seep channel bisected the long axis of the
plot (the 20 m side). Initially, 2 or 3 plots were placed
along the seep channel, with the center of the first plot
placed 15 m downstream from where the seep first
discharged above ground and the centers of the down-
Soils are primarily silt loams and bouldery silt loam

Hall et al., PLANT SPECIES COMPOSITION IN GROUND-WATER SEEPS
127
stream plots 10–25 m apart from the previous plot,
depending on channel length. It became apparent that
the vegetation was homogenous along a given seep
channel, so only one plot was established on subse-
quently sampled seeps. Forty-five plots were estab-
lished on 33 seeps. Percent cover of herbaceous spe-
tember 1996 and in April 1997. Because all plots had
not been set up for the entire study period, some plot
sample data are missing. The number of samples per
month is as follows: May–18; June–20; July–34; Au-
gust–45; September–41 (4 seeps were dry); April
(1997)-43. In each quadrat, the typical substrate height
above or below the water table was measured and ex-
pressed as a plot mean height above water table
(MHAWT). Percent open water (%OW) was estimated
in each of the quadrats using the same cover classes
as for vegetation cover; a plot mean was calculated.
Percent slope and aspect of each plot were estimated
with a clinometer and compass, respectively. Canopy
basal area (Can BA) and subcanopy density (Sub den)
data were collected as part of the vegetation sampling
(see above). Water samples were collected in August
1996, and the concentrations of major ions were mea-
cies, bryophytes, and woody seedlings
was estimated in eight 0.5 1 m quadrats placed in
a continuous line approximately in the center of the
seep channel and within the 10 20 m plot. The her-
Ͻ 0.5 m tall
ϫ
ϫ
baceous species on the banks of the seep channel were
not sampled because they were dry and occupied by
typical upland herbs as described in the site descrip-
tion. Plant cover was visually estimated and recorded
in a cover classification system ranging from 1 to 5
with the following values: 1
ϭ 1–5% cover, mean val-
ue
ϭ
2.5%; 2
ϭ
5–25% cover, mean value
ϭ
15%; 3
50–75%
75–100% cover,
ϩ
ϭ
25–50% cover, mean value
ϭ
35.5%; 4
ϭ
sured by the following methods: NH4 —Wescan Am-
-
-
2-
cover, mean value
mean value
cover, mean value
ϭ
62.5%; 5
ϭ
monia Analyzer; Cl , NO3 , SO4 —Dionex Ion Chro-
ϩ ϩ
2ϩ
2ϩ
ϭ
82.5%; p
ϭ
present but less than 1%
matograph; Ca , Mg , Na , K , Al—Spectro-Ana-
lytical Instruments Model FMA-07 Inductively Cou-
pled Plasma-Atomic Emission Spectrometer. Detailed
chemical analyses were conducted only once since pre-
liminary research showed high correlations between
pH and ions. The quantity of light (
ϭ
0.1% (Barbour et al. 1987). The
relative cover of each species was calculated as a per-
centage of the sum of all species’ cover in the plot;
thus, an individual species relative cover value ranged
from 0 to 100 with a sum of 100 for each plot. Esti-
mating cover of the mosses Brachythecium rivulare
and Bryhnia novae-angliae was difficult because they
have very similar appearances in the field and often
grow together in mixed mats on cobbles in the seep
channel. The cover of the two-species mixture was es-
timated as with other species. To estimate the relative
proportions of the two species in the mixture, the mats
2
␮
einsteins/m /sec)
was measured using a LI-COR model LI-185B Quan-
tum/Radiometer/Photometer. Measurements were
made at 0.5 m above the ground at four equally spaced
points in the seep channel, and the readings were ex-
pressed as percent full sun (PFS), which was measured
in nearby open fields. To minimize temporal variabil-
ity, all light measurements were taken between 1000
and 1400 hrs during two weeks of August 1996 on
sunny or uniformly cloudy days.
were removed from four 0.25
ϫ 0.25 m quadrats in
each 10 20 m plot and allowed to dry at room tem-
ϫ
perature. After drying, the appearance of the two spe-
cies became less similar, and they could be identified
macroscopically with confidence. The relative propor-
Data Analysis
tions of each species in the 0.25
ϫ 0.25 m quadrats
Plot Classification. The TWINSPAN program
(TWo-way INdicator SPecies Analysis; Hill 1979) was
used to divide the seep herb-layer data into a hierarchy
of vegetation community types, or classes, based on
presence/absence of species. All dichotomies through
the third division level were retained if the resulting
groups had greater than four sampling plots in them.
This classification facilitates descriptions of the seeps
based on their vegetation and allows the differences in
vegetation to be correlated to the measured environ-
mental variables as described below.
were then estimated and the mean proportion was cal-
culated for each plot. The mean relative proportions
were multiplied by the relative cover of the two-spe-
cies mixture to get an estimate of each species’ cover
in the 10
The diameter of all woody stems
20 m plot was measured at breast height (dbh)
and recorded by species. Canopy stems were defined
as having a dbh 5 cm; subcanopy stems were de-
fined as having a dbh 4.9 cm.
ϫ 20 m plot.
Ն
1.5 m tall in the
10
ϫ
Ͼ
Յ
Analysis of Variance (ANOVA). ANOVA was per-
formed between environmental variables of the two
resulting groups at each retained TWINSPAN dichot-
omy to show which variables differed between the two
groups (Jongman et al. 1987, Anderson et al. 1995).
ANOVA was also used to compare means of environ-
Environmental Sampling
Surface-water pH and conductivity (Cond) were an-
alyzed in a laboratory from seep-water samples col-
lected from the center of each vegetation plot. Samples
were collected monthly between May 1996 and Sep-

128
WETLANDS, Volume 21, No. 1, 2001
Figure 2. Dominant species, mean relative cover, and significantly different environmental variables between TWINSPAN
groups. Significantly different environmental variables (mean (standard deviation)), F, and P values are listed at each dichot-
omy. Dominant species had mean relative cover greater than or equal to 5.0.
mental variables for the final TWINSPAN groups. For
variables with significant differences as shown by the
ANOVA, Tukey’s Tests were used to identify the
groups with significantly different means (p
(Jongman et al. 1987, Suren 1996).
(Figure 2). The first dichotomy had one group, labeled
group A, which was dominated by (i.e., high mean
relative cover) Impatiens capensis, Bryhnia novae-an-
gliae, Brachythecium rivulare, and Eupatorium rugo-
sum. Group B was dominated by Laportea canadensis,
Dryopteris intermedia, Acer saccharum seedlings, Vi-
ola spp. (mostly V. cucullata Aiton and V. macloskeyi
F. Lloyd), and Bryhnia novae-angliae. The ANOVA
of environmental data of the two groups identified four
variables that differed significantly, including mean
height above water table, percent open water, canopy
Յ
0.05)
Canonical Correspondence Analysis. Investigations
of species’ responses to environmental variables were
conducted using canonical correspondence analysis
(CCA) with the program CANOCO 3.1 (ter Braak
1987–1992). The forward selection option for environ-
mental variables was used. Forward selection is useful
in identifying a few environmental gradients that are
associated with differences in species composition and
in reducing multicollinearity in the environmental data
set (Palmer 1993). All environmental variables, except
pH, were log-transformed prior to CCA to reduce
skewness in frequency distributions (Palmer 1993) and
to reduce variance dependence on the mean (Jongman
et al. 1987).
-
basal area, and NO3 . Group B was further divided into
a group dominated by Laportea canadensis, Bryhnia
novae-angliae, and Dryopteris intermedia (group B1)
and a group dominated by Acer saccharum seedlings,
Dryopteris intermedia, and Viola spp. (group B2).
There were no significant differences in environmental
data at P
table was significantly different at P
was different at P 0.075.
Յ
0.05, but the mean height above water
ϭ
0.06, and pH
ϭ
Group A was separated into a group (A1) with four
plots dominated by prostrate plants Chrysosplenium
americanum Schwein, the liverworts Scapania undu-
lata (L.) Dumort and S. nemorosa (L.) Dumort, and
the mosses Hygrohypnum ochraceum (Turn. ex Wils.),
RESULTS
Plot Classification
The TWINSPAN resulted in four retained divisions,
with five final groups of seep herbaceous communities

Hall et al., PLANT SPECIES COMPOSITION IN GROUND-WATER SEEPS
129
-
Figure 3. Environmental variables (mean height above water table, % open water, canopy basal area, pH, NO3 , and total
Al) with significant difference between the five final herb layer TWINSPAN groups (columns). Significance determined by
Tukey’s Studentized Range (HSD) Test with confidence limit differenced (CLDIFF), P
are significantly different. Error bars denote 1 SD.
Ͻ 0.05. Groups with different letters
and Plagiothecium denticulatum (Hedw.) BSG.; and a
group (A2) of 30 plots dominated by taller vascular
herbaceous plants Impatiens capensis and Eupatorium
rugosum and the mosses Brachythecium rivulare and
Bryhnia novae-angliae. Group A2 had a higher pH,
ation in the species data. The selected variables were
2ϩ
percent open water, pH, Mg , conductivity, mean
ϩ
height above water table, NH4 , and percent full sun.
The first axis (eigenvalue
ϭ 0.51) was most strongly
correlated with percent open water (negatively), pH
(negatively), and mean height above water table (pos-
2ϩ
2ϩ
higher Ca , higher Mg , and lower total Al than
group A1.
itively) (Figure 4). The second axis (eigenvalue
ϭ
The fourth dichotomy separated group A2 into two
groups of approximately equal numbers of plots (Fig-
ure 2). These two groups shared many dominant spe-
cies, including Impatiens capensis, Bryhnia novae-an-
gliae, Brachythecium rivulare, and Laportea canaden-
sis, although group A2a had higher values for Brach-
ythecium rivulare, Impatiens capensis, Eupatorium
rugosum, and Chrysosplenium americanum, while
group A2b had more Viola spp. For the environmental
0.40) was most strongly correlated with pH and mean
height above water table (both negatively), suggesting
that the second axis is related to the first, a common
problem with reciprocal averaging-based ordination
techniques. The third axis (not shown) (eigenvalue
ϭ
2ϩ
0.24) was negatively correlated with Mg and posi-
tively with conductivity, representing an ionic gradi-
ent. The fourth axis (not shown) (eigenvalue
ϭ 0.18)
ϩ
was most strongly correlated with NH4 .
-
data, group A2a had higher pH and higher NO3 .
The only ions entered into forward selection were
ϩ
2ϩ
NH4 and Mg . Other ions may not have been se-
ϩ
-
2-
Environmental Relationships Between the Five Final
Groups
lected because all, except NH4 , Cl , and SO4 , were
correlated with pH (not shown), and thus, variation in
vegetation associated with ions may be adequately
ANOVA of the five retained TWINSPAN groups
indicated six variables with significant differences be-
tween the groups: mean height above water table, per-
2ϩ
ϩ
summarized by pH and/or Mg . NH4 was the sixth
variable entered into forward selection; it may be re-
quired to summarize the variation in the data because
it was not correlated with any of the entered ion-re-
-
cent open water, canopy basal area, pH, NO3 , and total
Al (Figure 3).
2ϩ
lated variables (pH, Mg , and conductivity).
The position of species on the first two axes of the
CCA diagram was most strongly correlated with per-
cent open water, mean height above water table, and
pH. A species optimum for an environmental variable,
Canonical Correspondence Analysis
Forward selection of environmental variables in
CCA showed that seven variables described the vari-

130
WETLANDS, Volume 21, No. 1, 2001
Figure 4. Canonical Correspondence Analysis of all species with forward selection of environmental variables. The approx-
imate locations of the four major plot groups are shown in rings. Groups A2a and A2b are not shown for clarity. Eigenvalues
are as follows: axis 1, 0.51; axis 2, 0.40; axis 3, 0.24; axis 4, 0.18.
relative to other species, can be estimated by visual-
izing a perpendicular line from that species label to
the environmental vector, with values of the environ-
mental variable increasing towards the variable label
or the vector’s arrow-head.
pina L. in the region of mid- to low percent open wa-
ter, mean height above water table, and high pH.
DISCUSSION
The seedlings of the upland tree species, Acer pen-
sylvanicum, A. saccharum, and Fraxinus americana
were found in the area of lowest percent open water,
mid-range pH, and highest mean height above water
table. The bryophytes Scapania undulata, Hygrohyp-
num ochraceum, Plagiothecium denticulatum and the
grass Glyceria striata (Lam.) A. Hitchc. were found
in the area of medium percent open water, lowest pH,
and lowest mean height above water table. Oxalis ace-
tosella, Dicranum fulvum Hook., Laportea canadensis,
Acer rubrum, and Galium triflorum Michx. were in the
area of low percent open water, high mean height
above water table, and mid-range pH. There was a
cluster of the species Cinna latifolia (Trevir.) Griseb.,
Thuidium delicatulum (Hedw.) BSG., Dicranum sco-
parium Hedw., Impatiens capensis, Tiarella cordifolia,
Rorippa nasturtium-aquaticum (L.) Hayek, Brachythe-
cium rivulare, Bryhnia novae-angliae, and Circaea al-
Plant Species Distributions
Hydrologic characteristics, including percent open
water and substrate height above the water table, as
well as chemical characteristics including pH and con-
2ϩ
2ϩ
-
centrations of ions such as Ca , Mg , and NO3 are
correlated with plant species composition in Catskill
Mountain ground-water seeps. Other less strongly cor-
related variables that are significantly different among
the groups of the TWINSPAN dichotomies are canopy
basal areas and Al concentrations. Additional variables
that entered into the CCA equation include conductiv-
ϩ
ity, NH4 , and percent full sun.
Percent open water and mean height above water
table may be viewed as components of a complex gra-
dient of water quantity or depth. A complex gradient
is a series of environmental variables that change to-
gether along some primary gradient (Whittaker 1966).

Hall et al., PLANT SPECIES COMPOSITION IN GROUND-WATER SEEPS
131
Percent open water is an estimate of the amount of
submerged substrate unavailable for occupation by ter-
restrial plants (only two submerged plant species were
encountered in the study, Fontinalis antipyretica
Hedw., which occurred in only one plot and was there-
fore not in the data analysis, and Hygrohypnum ochra-
ceum). The mean height above water table is an esti-
mate of the water level relative to the rooting zone of
the vascular plants and the ramets of the bryophytes.
This measurement is analogous to floodplain elevation
used in many riparian vegetation studies, although on
a much smaller spatial scale. Several studies in many
types of wetlands have shown a significant vegetation-
water quantity or depth relationship, where water
quantity has been measured as percent standing water,
peat moisture, degree of soil saturation, floodplain el-
evation, depth of water, height above water table, or
microtopography. These studies include peatlands
(Glaser et al. 1990, Vitt et al. 1990, Anderson et al.
1995, Anderson et al. 1996), fens (Bernard et al. 1983,
Motzkin 1994, Walbridge 1994), riparian wetlands
(Bell 1974, Bell and del Morel 1977, Barnes 1978,
Bell 1980, Harris 1986, Menges 1986), and swamps
(Parsons and Ware 1982, Paratley and Fahey 1986).
Because there have been very few studies of seep
vegetation in the United States, riparian studies must
be used for comparisons. This comparison is valid be-
cause streams often have hydrologic regimes and veg-
etation similar to the seeps. Riparian vegetation com-
position is correlated primarily with floodplain eleva-
tion or height above the water table, which is a com-
plex gradient determining flood frequency, flood
duration, and water-table depth (Menges 1986). The
grade, or slope, of a stream can influence the stream
width, water depth, and velocity. Higher velocity
streams have increased sediment transport, which can
directly affect vegetation through physical disturbance
and can indirectly affect vegetation by determining soil
texture (Hupp 1982). Hupp (1982) found that a higher
stream gradient caused an increase in channel width,
a decrease in water depth, and the formation of a braid-
ed channel. At the Catskill study sites, the higher slope
channels were usually narrower, had deeper channels,
and were less braided than lower slope channels. The
water velocities were greater, which resulted in less
cobble and soil substrate and more exposed bedrock
in the channel.
cavifolium (Brid.) Iwats., Chrysosplenium american-
um, and Rorippa nasturtium-aquaticum (Figure 4)).
Channels with gentle slopes had lower water veloci-
ties, which resulted in less soil removal and fewer ex-
posed cobbles in the channel. These gentle-sloped
channels also had the only submerged aquatic plants
in the study, Hygrohypnum ochraceum and Fontinalis
antipyretica. Circaea alpina, a small upright plant,
also grows at lower levels on moss covered cobbles
(Haber 1977); perhaps the moss mats provide a firm
and erosion resistant substrate for the plants rhizomes.
Robach et al. (1996) found that Rorippa nasturtium-
aquaticum grew best in water that did not freeze dur-
ing the winter, such as ground-water streams; this spe-
cies also occurs in Catskill Mountain seeps that flowed
throughout the winter.
Several studies have shown that bryophytes are dis-
tributed in vertical zonation patterns along a stream
elevation (relative to water level) gradient, from aquat-
ic species to upland species. This patterning is related
to species tolerance to decreasing humidity away from
the water (Glime 1970, Craw 1976, Vitt et al. 1986,
Muotka and Virtanen 1995, Virtanen 1995, Suren
1996), physical damage from flowing water and sedi-
ments (Craw 1976, Kimmerer and Allen 1982, Suren
1996), and light intensity (Glime 1970).
The bryophyte floodplain elevational pattern in the
Catskill Mountain seeps is similar to that shown in
other studies. Muotka and Virtanen (1995) found that
Hygrohypnum ochraceum and Scapania spp. were in
the lowest elevations above the water surface. Scapan-
ia undulata was at lower mean heights above the water
table than Scapania nemorosa (Figure 4), as shown by
Glime (1970) and described by Schuster (1974).
Brachythecium rivulare was most abundant at low-mid
heights above the water table and is classified as an
emergent (Vitt et al. 1986) and as a facultative aquatic
(Virtanen 1995). Virtanen (1995) considered Mnium
punctatum Hedw. to be a ‘‘terrestrial species of moist
and wet habitats’’ and Mnium affine Bland. ex Funck.
to be a ‘‘herb rich forest species.’’ In the study area,
M. punctatum appeared to occur in wetter areas than
M. affine, but M. affine was usually only found in seep
areas, not in the surrounding forest as described by
Virtanen. Many of the bryophyte species included in
the analysis are often found in upland forests on moist
decaying wood (Thuidium delicatulum, Hypnum im-
ponens Hedw.), tree roots (Hypnum pallescens
(Hedw.) P.-Beauv.), or rocks (Dicranum fulvum)
(Crum 1983). These species were usually on the moss-
covered cobbles close to the water, but occasionally
high local abundance may have been due to the pres-
ence of the preferred substrate in sampling quadrats
rather than to any of the variables measured in the
study.
Many riparian studies have shown the influence of
floodplain elevation on vegetation. In the present
study, the lower mean height-above-water-table ranges
were occupied by plants with adaptations to tolerate
flowing water such as being small statured, prostrate,
and/or being firmly attached to the rock substrates (Hy-
grohypnum ochraceum, Scapania undulata, Scapania
nemorosa, Plagiothecium denticulatum, Plagiothecium

132
The grasses, Cinna latifolia, Glyceria striata, and
Poa spp., had their greatest importance at the low- to
mid- mean height above water table, as in Menges and
Waller (1983) and Menges (1986). Apical meristems
of perennial forbs may be damaged by moving water
at the lower floodplain elevations, while the basal mer-
istems and overall morphology of grasses make them
more tolerant of flowing water (Menges and Waller
1983).
WETLANDS, Volume 21, No. 1, 2001
This complex gradient includes variables such as pH,
alkalinity, acidity, hardness, and base cation concen-
trations (Vitt and Chee 1990, Motzkin 1994, Anderson
et al. 1995), but in this study, additional ions such as
-
ϩ
ϩ
NO3 , K , and Na were positively correlated with pH
while total Al was negatively correlated. Alkalinity/
acidity complex gradients have been correlated with
plant species composition and abundances in many
types of wetlands, including near-ombrotrophic peat-
lands (Vitt and Slack 1975, Karlin and Bliss 1984,
Glaser et al. 1990, Vitt et al. 1990, Anderson et al.
1995, Anderson et al. 1996), minerotrophic fens (Vitt
and Chee 1990 (for bryophytes), Motzkin 1994, Wal-
bridge 1994), riparian wetlands (Dunn and Stearns
1987 (for trees)), and swamps (Parsons and Ware
1982).
In the low- to mid-range of mean height above the
water table, three tall herbs had large relative cover
values: Impatiens capensis, Laportea canadensis, and
Eupatorium rugosum. Barnes (1978) found that L.
canadensis had its greatest frequency at lower flood-
plain elevations, I. capensis at higher elevations, and
E. rugosum at mid- to high elevations, while Menges
and Waller (1983) found that I. capensis was more
frequent at lower floodplain elevations and L. cana-
densis at higher elevations. The results from this study
are sililar to those of Menges and Waller (1983); I.
capensis was most abundant at the lowest MHAWT,
L. canadensis was most abundant at the highest
MHAWT, and E. rugosum was most abundant in the
middle. Several additional factors may be associated
with the relative abundances of I. capensis and L can-
adensis. For example light, may be a determining fac-
tor; Menges and Waller (1983) consider L. canadensis
a ‘‘light generalist,’’ meaning it can exist in varied
light conditions, while I. capensis is a ‘‘high light spe-
cialist.’’ In field observations, it was noted that I. ca-
pensis was usually less than 30 cm tall on sites with
a denser tree canopy, but it was approximately 1 m
tall on open-canopy sites. Simpson et al. (1985) also
found that it had greater height and biomass on full-
sun sites. Differences in competitive abilities and site-
colonization strategies may also influence the abun-
dances of I. capensis relative to L. canadensis. Impa-
tiens capensis is an annual ‘‘competitive ruderal’’
(Menges and Waller 1983), and each year the popu-
lation must be reestablished by seeds, thus it is sus-
ceptible to local extinction. It may be poor at site col-
onization because the large seeds may depend on water
for dispersal (Winsor 1983). Laportea canadensis is a
competitive species that can reproduce either by seed
or by clonal growth (Menges and Waller 1983). Im-
patiens capensis was most often growing on moss-
covered cobbles, while L. canadensis was more often
on soil. Laportea canadensis may not survive on the
moss-covered cobbles because it needs deeper sub-
strate for its larger root system. If it is able to survive
on the cobbles, clonal expansion would be inhibited
by the small size of the cobbles and the flowing water
between them.
Most studies of environment-vascular plant species
composition relations in riparian wetlands have not fo-
cused on water chemistry but rather on components of
the floodplain elevation complex gradient, light, and
soil characteristics (Bell 1974, Bell and del Morel
1977, Barnes 1978, Bell 1980, Menges and Waller
1983, Harris 1986, Menges 1986, Dunn and Stearns
1987). In contrast, there are many water chemistry-
bryophyte species composition studies. Water chem-
istry may be more important for riparian bryophytes
that obtain most of their nutrients from water than for
terrestrial vascular plants that use soil nutrients. In
headwater streams, such as the study seeps, bryophytes
are often closer to the water and may be the only
streamside vegetation (Vitt et al. 1986). In streams of
western Canada, Vitt et al. (1986) found that the first
axis of a detrended correspondence analysis ordination
was correlated with Ca, Mg, and soil texture and the
second axis was correlated with soil texture and height
relative to the water surface. Brachythecium rivulare
was considered a calciphile; it also occurred in the
2ϩ
high Ca and pH seeps in our study (Figure 4). Muot-
ka and Virtanen (1995) also found Brachythecium ri-
vulare in streams with high pH and Scapania spp. and
Hygrohypnum ochraceum in the streams with low pH,
as in our study seeps.
Seep Biogeochemistry
-
NO3 and pH were positively correlated, although
-
they were expected to be negatively related since NO3
is often associated with episodic decreases in pH and
acid neutralizing capacity (e.g., Murdoch and Stoddard
-
1993). NO3 is positively correlated with all ions ex-
ϩ
-
cept NH4 and total Al; thus, sites with a high NO3
often have even higher concentrations of the base cat-
ions Ca and Mg , which results in an increase in
pH. The positive correlations between pH and con-
2ϩ
2ϩ
Water pH and ion concentrations may be viewed as
components of a complex alkalinity/acidity gradient.
-
ductivity and also between conductivity and NO3 are

Hall et al., PLANT SPECIES COMPOSITION IN GROUND-WATER SEEPS
133
further evidence for this high ion concentration/high
plants die each year and nutrients are re-released to the
water. The effects of seep vegetation on nitrogen re-
tention and transformation are complex and require
further investigation.
-
2-
pH relationship. Acidic anions, such as NO3 and SO4
, may increase the decomposition rate of rocks, which
would cause an increase in base cation concentrations
(Rice and Bricker 1995, van Dam and Mertens 1995).
-
The high NO3 /high pH relationship may be caused by
ACKNOWLEDGMENTS
the temporal aspects of ground-water recharge. It has
been shown that there are two separate ground-water
systems in the area of the Frost Valley site, one shal-
low and one deep (Burns et al. 1998). The shallow
system may be dry during the summer, except for
shortly after storms, while the deeper system flows
throughout the year. The deeper system has a residence
time of 6 to 22 months and is recharged during the
early spring (late February–March) and autumn (Au-
gust–November) seasons (Burns et al. 1998). Since the
vegetation is dormant during most of the recharge pe-
This project was supported by a contract from the
New York City Department of Environmental Protec-
tion. We thank R. W. Kimmerer, P. S. Murdoch, and
J. H. Porter for their assistance and helpful comments
on the manuscript. D. A. Burns assisted in site selec-
tion, and T. E. Yorks provided valuable field assis-
tance. We are grateful to M. J. Mitchell for providing
analytical facilities for water chemistry analysis.
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Manuscript received 24 June 1999; revisions received 3 August
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