Umnol. Oceanogr.. 33(3), 1988, 447-458
© 1988, by the American Society orLimnology and Oceanography, Inc.
Spatial patchiness in the lacustrine sedimentary environment1
lated with depth, cause heterogeneous sed
iment distribution: sediment distribution
patterns can be affected by the deposition
of lotic sediments in lentic waters (Hakanson 1982; Fabre and Patau-Albertini 1986;
Hilton et al. 1986); slumping, sliding, and
turbidity currents can generate heteroge
neous horizontal sediment displacement at
subordinate depths (Ludlam 1969, 1974;
Hakanson 1982; Hilton et al. 1986); reser
voir sediment patterns reflect the course of
the original riverbed (Fabre and Patau-Al
bertini 1986); currents redistribute sedi
ments in very large lakes (e.g. Lake Huron:
Wood 1964); finally, Hargrave and Nielsen
(1977) have suggested that irregularities in
original lake basins can lead to large-scale
spatial heterogeneity in deposited sedi
Abstract—Spatial patchiness of sediment char
acteristics in central, bathymetrically uniform sites
in eight lakes was examined by comparison of
within- and among-core variation in water, or
ganic matter, pigment, and phosphorus concen
trations. Sampling sites were chosen to avoid
known sources of sediment heterogeneity. Re
gression analysis of within-core and among-core
variance on mean sediment characteristics was
used to examine sampling exigencies. Compari
sons of microscale and analytical variation with
variation in sediment characteristics among core
samples, within sites, showed significant {P <
0.05) sediment heterogeneity in >62% of the
comparisons. AH sediment characteristics and all
sampling sites showed some significant hetero
geneity. The variance in sediment characteristics
among core samples, within sites, was from 2 to
320 times greater than analytical or microscale
variation. Spatial heterogeneity might result from
aggregated benthic animals, slow currents, or
small-scale variations in bottom profile.
ments.
It has long been observed that sediments
are not uniformly distributed in lakes. Many
studies have demonstrated that sediment
accumulation increases with depth (e.g.
Lehman 1975; Likens and Davis 1975; Sly
1977; Evans and Rigler 1980; Davis and
Ford 1982, and many others). Such sedi
ment focusing results from the resuspension
of sediments by wave action and by sea
sonal or continuous mixing, from slumping
and sliding on steep slopes, and from re
duced organic matter degradation at depth
(Hilton 1985). Sediments are therefore usu
ally less abundant and coarser in high-en
ergy, shallow environments and are usually
thick, fine, and flocculent in deeper waters.
Several other factors, not directly corre-
1 This is publication 319 of the Groupe d'Ecologie
des Eaux douces of l'Universite de Montreal. This work
was supported by the Natural Sciences and Engineering
Research Council of Canada, the Department of Ed
ucation of the Province of Quebec (F.C.A.R.), the
Sportsmen's Fund, and the Secretary of State.
In open, flat areas of sediments at uni
form water depth, where these mechanisms
do not operate, sediments should be uni
form in composition. This uniformity
should be assured by the random rain of
sedimentary material and by the lack of sed
iment redistribution mechanisms in such
areas. Current information on sediment dis
tribution mechanisms therefore suggests that
sediments ofuniform depth, far from deltas,
inputs, and steep slopes, should be homo
geneous in spatial distribution.
There is some indirect evidence that sed
iments in bathymetrically uniform areas are
patchily distributed. Several workers have
found that much of the variation in sedi
mentation rates (Kimmel 1978; Dillon and
Evans 1982; Hilton et al. 1986), sediment
lead burden (Evans and Rigler 1985), sed
iment particle size and organic matter con
tent (Keulder 1982) cannot be explained by
variation in water depth. Anderson et al.
(1982) found that the variance in numbers
of dinoflagellate cysts found in replicate
samples was always greater than the mean
447
448
Notes
number per cubic centimeter. Both sonar
(Miiller 1977) and visual observations
(Fabre and Patau-Albertini 1986; Sweerts
et al. 1986) reveal sediment patchiness.
Hargrave and Nielsen (1977) concluded that
the variation among replicate sediment
samples exceeds values expected from an
alytical error alone, although they present
no such analysis. Thus, sediments may be
highly variable, even within small, uniform
sampling sites.
In spite of the potential importance of
sediment assessment to lake management,
the possibility of sediment patchiness is sel
dom considered in experimental design.
Most paleolimnological and sediment de
position investigations are based on the
analysis of a single core sample per site
(Wentz and Lee 1969; Shapiro et al. 1971;
Lehman 1975; Kimmel 1978), even though
adjacent samples sometimes yield different
profiles (e.g. Whitehead et al. 1973). Esti
mates of sediment chemistry are usually
based on one sample taken at each arbi
trarily chosen station (e.g. Williams et al.
1971,1976; Hart et al. 1976; Premazzi and
Ravera 1977; Johnson et al. 1982). If sed
iments are patchy, extrapolation of single
core samples to entire sites or lakes could
yield greatly biased estimates of actual con
ditions. The magnitude of bias depends on
the degree of spatial heterogeneity of the
sediments and the relative size of analytical
error and spatial variation.
Despite the abundance of indirect evi
dence of small-scale spatial heterogeneity in
sediments and the importance of sediment
assessment to aquatic ecology, no one has
tested the hypothesis that the variation
among sediments in different core samples,
taken at the same sampling site, is greater
than either analytical error or microspatial
variation within core samples. In fact, many
believe that sediments are homogeneous at
a given depth (e.g. Twinch and Peters 1984)
or station (e.g. Reynoldson and Hamilton
1982). Although some researchers have
shown high coefficients of variation, C.V. =
100 (sVmean), among replicate cores taken
at the same site (Hargrave and Nielsen 1977;
Slater and Boag 1978; Anderson et al. 1982),
it is unclear whether this "heterogeneity"
results from spatial variation or analytical
error (cf. Eddington and Robbins 1976). The
purpose of our study was to estimate several
important sediment characteristics (organic
matter, water content, phosphorus, and pig
ments) in small, potentially uniform areas
of eight lakes, to determine the frequency
of significant spatial patchiness in the sed
imentary environment.
We thank M. Portier, Y. Rochon, and D.
Miron for technical assistance. R. D. Evans,
D. R. Lee, J. Hilton, J. Cornett, H. Cyr, S.
Lalonde, G. Niirnberg, C. Plante, and A.
Vezina provided criticisms. We also thank
the staff of the Station de Biologie of l'Universite de Montreal and the Limnology Re
search Group of McGill University for use
of their field stations.
The general experimental design was to
take a series of replicate core samples within
a zone that would normally be considered
homogeneous with respect to large-scale,
erosional-depositional processes. Each of
these sites was nearly uniform in depth, near
the center of the lake or bay, and far from
inputs and obvious sources of sediment het
erogeneity. Either microscale spatial vari
ation (within cores) or analytical error was
determined within each core sample, and
intercore vs. intracore variation in several
sediment characteristics was compared with
a Kruskal-Wallis one-way analysis (Conover 1971).
Twelve series of core samples were taken
at sites in eight lakes within a 150-km radius
of Montreal, Quebec. Sampled lakes were
morphometrically and trophically diverse
(Table 1). We took 6-28 core samples at
each site with a Kajak-Brinkhurst corer (Kajak et al. 1965; Brinkhurst et al. 1969)
equipped with a contractible, machined ny
lon flange to permit gentle removal ofsharp
ened acrylic core tubes (26 cm2). The sam
pler was lowered smoothly into the sediment
and no core sample was retained that showed
either sediment disruption or obvious com
paction (Hongve and Erlandsen 1979; Ev
ans et al. 1986). Samples were spaced as
evenly as possible over the sampling site
(100-1,000 m2) by anchoring the boat per
pendicular to the wind, taking samples at
the bow, center, and stern, reanchoring about
5 m downwind, and repeating the process
until all the samples were obtained. Core
Notes
449
Table 1. Average characteristics of the study lakes. Zm is the mean depth, Zmm is the maximum depth (in
m), area is measured in hectares, TP is average annual water column total phosphorus (in /ig liter"1), Secchi disk
transparency is growing season average (in m), Chi is seasonal average Chi a concentration of the water column
(in mg m~3) (<64 ftm), cond. is average conductivity (in fitnho cm"'), and alk. is average alkalinity (in mg liter"1).
Median values for conductivity and alkalinity are shown for Lac Hertel. Lake Memphremagog chlorophyll
analyses were performed on whole samples.
Lake
de PAchigan
Connelly
Cromwell
Hertel
Area
zm
12.3
7.7
3.0
3.8
26.8
20.1
8.0
8.0
527.8
129.4
9.2
4.7
TP
Secchi
Chl
Cond.
Alk.
9.5
9.2
11.5
10.0
5.0
5.1
2.4
3.4
1.0
1.5
8.6
3.0
56.5
95.5
35.1
104.0
15.2
21.7
9.8
28.5
Reference
Lafond 1985
Lafond 1985
Lafond 1985
Kalffl972;
Heath 1985;
R. H. Peters
pers. comm.;
J. Rasmussen
pers. comm.
Memphremagog,
7.0
9.1
5,607.0
12.6
2.9
5.4
130.0
46.0
8.7
14.0
2.5
4.0
14.8
5.3
10.7
3.1
1.6
2.7
70.6
12.1
1.7
9.8
2.9
5.6
3.5
42.3
33.6
17.5
8.3
8.0
south basin
Pin Rouge
Thibault
Triton
1.4
2.1
samples in Lake Memphremagog were tak
en randomly by divers to assure minimal
compaction. The water depth to sediment
surface (±1 cm), the pH (±0.01) and the
sediment temperature at 2-cm sediment
depth (±0.035°C) were recorded immedi
ately for each core sample. Samples were
kept cold and undisturbed during transport
to the laboratory.
Two different measures of within-core
variation in sediment characteristics were
used. First, four tests of the relative size of
among-core and within-core spatial varia
tion were made by subsampling each core
sample with a 2.3-cm2 glass tube. The glass
tube was pushed into the sediment to a depth
of 10 cm while applying a controlled vac
uum to the subsampler such that no differ
ence between the level of sediment in the
subsampler and the core sample could be
detected visually. Each ofthese three or four
subsamples were homogenized indepen
dently, and sediment characteristics were
determined for each. Within-core variation
in these experiments represents the sum of
microscale and analytical variation. Be
cause this measure of within-core variation
was not significantly different (P > 0.05)
from analytical error alone (J. A. Downing
unpubl.), eight further analyses compared
Nakashima and
Leggett 1975;
Ross and Kalff
1975
Lafond 1985
Lafond 1985
Lafond 1985
analytical error with among-core variation.
Two 2.3-cm2 subsamples were extracted as
above, mixed together, and homogenized
by hand-stirring before sediment analyses
were performed on 2-4 subsamples of the
homogenate. Four 2.3-cm2 subsamples of
5-cm depth were taken in Lake Memphre
magog.
Sediment subsamples were analyzed for
several characteristics of limnological and
geochemical importance. The water content
was determined by massing (±0.0001 g)
fresh sediment samples of about 5 ml, then
drying to constant mass (60°C, 24-48 h).
Organic matter content was approximated
by loss on ignition (55O°C, 6 h). Organic
matter content was analyzed both per unit
of sediment fresh mass and per unit of dry
mass.
Sediment phosphorus content was mea
sured because of its importance to lake eutrophication studies. Total phosphorus
analysis of homogenate samples was per
formed with a modification of Andersen's
(1976) ignition method. Ashed sediment
samples from water content and organic
matter analyses were boiled in 50-ml beak
ers containing 25 ml of 1 N HC1. After re
duction of sample volume to 5 ml, deionized water was added to return sample
450
Notes
volume to ~25 ml. This procedure was re
peated three times. Samples were then
cooled, and the volume was made up to
about 50 ml and the exact dilution factor
determined gravimetrically (F. H. Rigler
pers. comm.). A further dilution, with a
Brinkmann Diluette (50:1; 500:1 in Lake
Memphremagog), was necessary to decrease
the acidity and to bring color development
into the detectable range. Internal phos
phorus standards were prepared in triplicate
with a sample chosen randomly from each
sample series. Reagents were added to all
samples (Murphy and Riley 1962), and
phosphorus concentration was determined
spectrophotometrically at 890 nm, 30 min
after reagent addition. Sediment phos
phorus content was analyzed per unit offresh
mass, of dry mass, and of organic matter.
Rudimentary sediment pigment analyses
were performed because ofthe potential use
of sediment pigments as indicators of eutrophication (e.g. Gorham 1960). Chloro
phyll a and pheopigment concentration of
the sediments were determined with a mod
ification of Lorenzen's (1967) method. A
known quantity of fresh sediment was ho
mogenized in 12 ml of 90% spectrograde
acetone. Tubes were covered with Parafilm,
and samples were digested in the dark (4°C,
6-12 h), then centrifuged in a clinical cen
trifuge until clear (~ 5 min). The superna
tant was decanted and 21 ml of 90% acetone
added to it. Chlorophyll a and pheopigments were determined (Strickland and
Parsons 1968) with a Bausch and Lomb
Spectronic 21 UDV spectrophotometer. The
sum of Chi a and pheopigments and the
ratio of Chi a to pheopigments were cal
culated because degradation of chlorophyll
may decrease under anaerobic conditions
(Staub 1977; Swain 1985), which may vary
in space.
Sediment characteristics are expressed per
unit of fresh mass, of dry mass, and of or
ganic matter, where possible, because units
ofsediment mass can influence the apparent
concentration (Shapiro et al. 1971; Hakanson and Jansson 1983; Swain 1985). In
addition, the expression ofconcentration per
unit of dry mass or of organic matter elim
inates variation due to sediment compac
tion caused by sampler penetration.
Analytical error and within-core microscale variation were quantified by calculat
ing the (n — l)-weighted variance among
subsamples withdrawn from the same core.
This variance was compared to the withincore average for each sediment character
istic (mw) with logarithmic transformation
and least-squares regression analysis, re
sulting in typical variance: mean relation
ships (cf. Downing and Anderson 1985). The
residuals from each of these equations were
calculated, and the hypothesis of amonglake homogeneity of analytical variation was
tested with Kruskal-Wallis one-way analy
sis (Conover 1971) of these residuals.
The hypothesis that sediment character
istics varied significantly among core sam
ples was tested at each site with KruskalWallis one-way analysis (Conover 1971),
considering within-core subsamples as rep
licates. This nonparametric test was used
because data were often heteroscedastic. The
Kruskal-Wallis analysis is more conserva
tive than normal ANOVA applied either to
the raw data or their ranks.
Variation in sediment characteristics
among core samples was quantified by cal
culating the (n — l)-weighted variance of
the within-core averages (mw) within each
sampling site. This variance was compared
to the average of within-core averages with
logarithmic transformation and leastsquares regression analysis. Approximate
calculation of the requisite number of sam
ples for a given precision follows Downing
and Anderson (1985).
The 178 core samples showed fairly uni
form physical conditions within each site.
The coefficients ofvariation (C.V.) for depth
to sediment surface were usually <6 (Table
2). Water depth was therefore fairly con
stant except in Lac Cromwell and Lac Con
nelly where depth to sediment surface var
ied as much as 3 m without apparent
gradient. Sediment temperature was some
what more variable, with C.V. often > 12.
It was common for within-site sediment
temperature to vary >PC, and sediment
temperature in Lac Connelly, for example,
varied as much as 5°C within the same site.
Most variations in sediment temperature are
probably significant because measurement
error was <0.07°C. Sediment pH was vir-
Notes
451
Table 2. Average sampling depths (m), sediment temperatures (°C at 2-cm depth), and sediment pH and
their C.V. Averages were calculated among core samples within sampling sites.
Sampling depth
Lake, site
Connelly
Cromwell, site 1
site 2
de 1'Achigan, site 1
site 2
Hertel
Pin Rouge
Thibault
Triton, site 1
site 2
site 3
Memphremagog, south basin
A'
Mean
C.V.
20
10
12
12
20
10
12
6
12
24
12
28
7.62
10.14
7.05
4.57
5.44
17.53
2.75
2.20
6.94
4.09
5.36
5.57
4.33
2.15
9.42
9.08
6.72
7.38
2.18
3.48
3.38
3.69
6.00
tually invariant both within and among
sampling sites.
The composition of the sediments at our
sampling sites was similar to that reported
in other lakes. The median water content of
our samples was 90% (range: 28-97%), and
a median 35% (range: 8-98%) of the dry
matter was lost on ignition. Sediment total
phosphorus content varied from <200 to
>5,000 Mg g"' dry mass (>0.5%), which
nearly covers the range reported for lakes
in general (Williams et al. 1971; Sly 1977;
Graneli 1979), except perhaps warm, turbid
reservoirs (e.g. Keulder 1982). Many have
shown that Chi a and other photosynthetic
pigments are abundant in sediments (e.g.
Gorham 1960) and increase with eutrophication (Gorham 1961; Sangerand Gorham
1970). We found that the median concen
tration of Chi a and pheopigments (on a
fresh mass basis) in our sediment samples
was 1.8% (range: 0.7-5.3%), which is greater
than the average chlorophyll concentration
in fresh algal cells (Parsons and LeBrasseur
1970; Nicholls and Dillon 1978). Although
our sediment samples covered a range of
depths, only the sediments at Lac Triton,
site 1, stood out as being qualitatively dis
tinct. These samples were rich in undecomposed forest litter and thus were low in water
content (<35%), high in organic matter
(>96%), and poor in phosphorus. Compar
ative analysis of the sediment characteris
tics themselves is presented elsewhere
(Downing in prep.).
We found that within-core and analytical
—
Sediment temp
Sediment pH
C.V.
Mean
c.v.
9.02
17.20
6.56
3.03
4.84
6.47
7.31
8.13
14.82
Mean
7.54
14.90
5.18
22.98
19.21
21.22
10.64
10.27
3.55
5.25
12.60
13.24
1.61
1.84
0.75
1.88
16.35
—
—
6.39
5.40
—
—
—
—
6.58
6.75
6.30
2.67
2.27
1.86
_
_
6.55
1.35
variation could often be quite substantial.
Despite our best efforts, the standard de
viations of replicate determinations were
often as great as their means. Coefficients
of variation for sediment pigment analyses
were largest with median values between 10
and 35. Measures of organic matter and
water content were the least variable with
C.V. frequently <1. The variance attrib
utable to within-core and analytical varia
tion varied significantly with the mean mea
surement (e.g. Fig. 1A-B). Table 3 shows
that within-core variation rises significantly
with the average measurement in all vari
ables but water content (e.g. Fig. 1B). The
variance of water content decreases as av
erages approach 1.0 (Fig. 1 A) because water
content is constrained to the range of 0-1.
In all cases, however, analytical variance is
unstable, implying the necessity of data
transformation if parametric statistical
analyses are to be applied (Downing 1979).
More troublesome is the fact that analyt
ical error varied significantly among sam
pling sites. Nonparametric one-way analy
sis of the residuals from the variance: mean
relationships in Table 3 shows that different
sampling sites, although treated equally,
yielded different degrees of analytical vari
ation that were unexplained by differences
in the average of sediment determinations.
This result implies both that workers in oth
er lakes may not find the same level of error
predicted by Table 3, but also that it may
be misleading to infer spatial hetero- or ho
mogeneity simply by comparison ofamong-
452
Notes
0.56
□
□
12
1.5
1.7
1.9
2.1
2.3
2.5
2.7
14
16
18
SEDIMENT TEMPERATURE (°C)
log WITHIN-CORE AVERAGE
Fig. 1.
A, B. Relationship between the average and variance of replicate determinations of sediment char
acteristics made within core samples. Data represent either the combination of analytical and within-core spatial
variability or analytical variation alone for (A) water content (g g"1, fresh mass) and (B) total phosphorus
concentration (pg g"1, fresh mass). C, D. Relationship between sediment temperature and sediment organic
matter (g g-', dry mass) for individual core samples taken from (Q Lac Cromwell, site 2, and (D) Lac Hertel.
core variation with analytical variation ob
served elsewhere. The only valid test for
sediment patchiness is a direct comparison
of within- and among-core sediment vari
ation.
Although our sampling sites were chosen
to avoid known sources of sediment het
erogeneity, all sampling sites showed sig
nificant sediment patchiness. Fifty-nine
percent of comparisons showed significant
ly (P < 0.05) more variation among core
samples than can be explained by analytical
variation, and 67% of comparisons showed
significantly (P < 0.05) more variation
among core samples than can be explained
by microscale and analytical variation (Ta
ble 4). Significant patchiness was more
readily demonstrated in organic matter and
water content because analytical variation
was lower for these sediment characteris
tics. Sediment total phosphorus and organic
matter concentrations varied significantly
among core samples whether expressed per
unit of fresh mass or dry mass, indicating
that sediment compaction was not respon
sible for variations in sediment quality
among core samples. Sediment pigments
were also significantly patchy, but chloro
phyll: pheopigment ratios varied little in
space, echoing the spatial uniformity of re-
Notes
t
44
Jg
40-
0
E
3
0 £
UJ t
0.
licate samples of the same core. Thus, single
a
36
32
D
O> 28
D
1
20
CO
16
UJ
D
D
0.91
DC -P
uj E
d
< Ta)0.90
a
D
□
Z Z0.89
UJ
1 P
S 00.88
a
□
in
a
D
CO O
0.87
1.40
CO
□
o
□
□
1.35
D
Q.
CO
o
I
IUJ
30
o>
□
1.25
5
UJ
CO
1.20
□
6.2
6.6
7.0
453
7.4
DEPTH TO SEDIMENT SURFACE (m)
Fig. 1. E-G. Relationship between the water depth
overlying each sediment core sample in Lac Hertel and
the sediment pheopigment concentration, sediment
water content, and sediment phosphorus concentration
in each sample.
dox potential suggested by sediment pH
measurements (Table 2). /^-statistics for
normal ANOVA (parametric equivalent of
Table 4) show that the variance in sediment
characteristics among core samples, within
sites, is from 2 to 320 times (median = 5)
greater than the variance found among rep
core samples cannot even characterize small
sampling sites without a level of bias that
is much greater than analytical error. Sed
iment heterogeneity was found at all sam
pling sites (Table 4), regardless of the sam
pling depth, size of lake, or trophic status
(Table 1).
The number of sediment samples needed
within each sampling site depends on the
sediment characteristic examined, the mag
nitude of the characteristic in the site ex
amined, and the required level of precision.
Table 5 shows that the among-core .y2 values
of sediment water, organic matter, pig
ments, and phosphorus concentrations vary
as power functions ofthe among-core mean.
Data on chlorophyll and pheopigments and
data on total phosphorus expressed with all
denominators (fresh, dry, and organic mass)
are pooled in common equations because
ANCOVA showed no partial effect of these
categories. Although these equations were
derived from limited data, they can be ana
lyzed with the protocol of Downing and An
derson (1985) to calculate the approximate
number of core samples that must be taken
within a similar 100-1,000-m2 area to ob
tain a requisite level ofprecision. For a stan
dard error of 5% of the mean, for example,
sediment phosphorus content can be esti
mated with 2-3 core samples, independent
of concentration. This finding is in basic
agreement with Reynoldson and Hamilton
(1982). Most other sediment characteristics
require greater sampling effort near the min
imum concentrations that we encountered:
300 samples for pigments, 80 samples for
organic matter (dry mass), 20 samples for
water content. Organic matter content ex
pressed per unit of sediment fresh mass re
quires little replication at minimum con
centrations (i.e. 2-3 samples) but up to 70
samples at the highest concentrations. More
samples would be required from larger sam
pling sites or sampling strata (i.e. > 1,000
m2) because larger areas probably include
more variability in sediment types. Hakanson and Jansson (1983) attempt to com
pute requisite sample number without such
information on spatial and analytical vari
ation, but it cannot be done with accuracy.
It is also apparent that analysis of a given
454
Notes
Table 3.
Coefficients for the equation s2 = amwh where s2 and mw are the variance and mean of sediment
characteristics calculated among the two to four replicate samples taken from each of the N core samples, r2 is
the coefficient of determination for the least-squares regression relationship, P is the probability of obtaining
such a relationship by chance alone, and F is the probability level associated with the Kruskal-Wallis test for
homogeneity of the residuals among sampling sites (asterisks: *—P < 0.05; **—P < 0.01). Sediment unitsfresh mass (fm), dry mass (dm), and organic mass (om), loss on ignition. Chi—sediment chlorophyll concentration.
Variable
Organic matter, fm
dm
Water content, fm
Chi, fm
Pheopigments, fm
a
b
-1.781
-4.780
-6.240
-0.433
3.138
0.973
-7.901
5.195
0.929
1.486
0.982
-0.551
-1.401
-1.721
-2.739
2.028
-1.152
Chi + pheopigment
Chl/pheopigment
Total phosphorus, fm
dm
om
p
p
178
0.62
0.06
0.52
**
**
0.06
0.09
0.19
0.17
177
167
133
141
141
134
149
149
148
1.999
0.484
1.569
number of samples will not yield equal precision for all variables of interest.
This research demonstrates for the first
time that sediments are spatially heterogeneous in ways that are unrelated to depth
gradients, sediment focusing, or other largescale redistribution processes. Unfortunately, we can make but little progress toward finding a cause for this patchiness.
There are at least five possibilities: sediments accumulate in the sediment shadows
of macrophytes or outcrops (de March
s
**
*
*•
**
*•
**
*•
♦*
*«
♦*
**
•*
0.30
**
**
0.02
*
**
0.32
**
**
1978), littoral materials are ice-rafted into
deeper waters (Pelletier 1968), local temperature differences due to groundwaterdiscontinuities (Lee 1985) cause differential
sediment decomposition (Nikaido 1978;
Kelderman and van de Repe 1982), patchily
distributed benthic invertebrates (Downing
1979) either accumulate materials around
them (Luckenbach 1986) or lead to patchy
aeration and release of sediment components (e.g. Petr 1977; Graneli 1979; Rippey
and Jewson 1982), and slow, deep currents
Table 4. Kruskal-Wallis one-way tests for heterogeneity among core samples within each of the 12 sampling
sites. The first four tests examined the hypothesis that variation among cores was greater than the combination
of within-core microscale and analytical variation, while the final eight tests examined the hypothesis that
among-core variation was greater than analytical variation within core samples (asterisks: *—differences at P <
0.05; ♦*—at P < 0.01; ns—no significant difference was found). Abbreviations: om—organic matter; Chi—
chlorophyll; Pheo—pheopigment; sum—chlorophyll + pheopigments; ratio—chlorophyll: pheopigments; TP—
total phosphorus; other abbreviations and units as in Table 3.
Sampling site
Water
om/fm
om/dm
*
**
Lacde PAchigan (1)
Lac Triton (1)
Lac Triton (2)
**
*
**
ns
ns
ns
**
♦*
**
Lac Connelly
Lac Cromwell (2)
Lac de l'Achigan (2)
**
•*
**
**
**
•*
**
**
**
Lac Hertel
Lac Pin Rouge
**
**
**
**
**
**
Lac Thibault
Lac Triton (3)
Lake Memphremagog
**
Chi
Pheo
Sum
Ratio
TP/fm
TP/dm
**
**
**
ns
ns
ns
ns
**
**
TP/om
Microscale vs. among-core
Lac Cromwell (1)
ns
*
ns
*
•
**
ns
ns
ns
*«
**
**
**
—
—
—
—
*
*
**
Analytical vs. among-core
ns
**
♦
**
**
♦
**
**
**
**
—
—
—
*
**
•*
ns
ns
ns
ns
ns
ns
*
ns
ns
ns
ns
ns
ns
*
ns
**
ns
ns
**
ns
—
ns
**
ns
**
ns
**
—
—
—
**
*
**
ns
ns
ns
ns
ns
ns
—
—
—
ns
ns
ns
*
*
Notes
455
Table 5. Coefficients for the equation s2 = amb where s2 and m are the variance and mean of sediment
characteristics among the replicate core samples taken at each of the 12 sampling sites, r2 is the coefficient of
determination for the least-squares regression relationship, and P is the probability of obtaining such a rela
tionship by chance alone (asterisks: **—P < 0.01). Data from Lac Triton, site 1, were not included in the analysis
because they were qualitatively different due to the large amount of undecomposed forest litter in these samples.
n—Number of sites for which data were available; other variables and units as in Table 3.
Variable
om/fm
om/dm
Water content/fm
Chi or pheopigments
Phosphorus (all forms)
a
b
n
4.299
-4.753
-5.520
-0.161
-2.065
6.226
-2.021
-18.907
0.904
1.939
11
(Lemmin and Imboden 1987) winnow and
redistribute sediments (Hakanson and Jansson 1983).
For our sites, the first two possibilities can
be tentatively eliminated because only the
sites in Lac Triton were near macrophytes
or outcrops, and no coarse, littoral materials
were ever observed in our core samples.
Temperature might play a role because sed-'
iment temperature is sometimes negatively
correlated with sediment organic matter
content within sites (e.g. Fig. 1C). The role
of temperature seems minor, however, be
cause out of 105 possible site-specific cor
relations between sediment characteristics
and sediment temperature, only 17 were
statistically significant (P < 0.05: Downing
unpubl.). In addition, three of these corre
lations are significantly positive (e.g. Fig.
ID).
It is tempting to suggest that the activities
of invertebrates are responsible for sedi
ment patchiness, especially given their
striking heterogeneity (Elliott 1977; Down
ing 1979). Invertebrates may physically
transport sediments, ingest and degrade
them, or alter them by increasing the ex
change rates ofwater and oxygen (Petr 1977).
Such an explanation is even more plausible
considering that invertebrates and habitat
patches are sometimes correlated in fresh
water (e.g. Alley and Anderson 1968; Vodopich and Cowell 1984) and marine (e.g.
Gray 1974; Rhoads 1974) benthic environ
ments. This correlation is also found in the
lakes we examined (Rath 1986).
Whatever mechanism is ultimately re
sponsible for the patchiness of lake sedi
ments, this structure is expressed and per
12
11
20
30
P
0.51
0.59
**
0.53
0.44
0.92
**
**
♦*
♦*
haps maintained by physical variation in
the bottom profile. We found that the actual
depth to the sediment surface was more
variable than would be expected from
bathymetric maps or sonar scans (Table 2).
A typical 20° sonar transducer integrates
bottom depth over a circular surface with a
radius of Z tan(2072) (where Z is depth);
thus at 10-m depth, sediment details of a
diameter of < 3.5 m could not be discerned.
Visual inspection often reveals a rolling pro
file, with hummocks separated by small
depressions—a structure reminiscent of
moguls. The distance from water surface to
sediments was significantly (P < 0.05) cor
related with sediment characteristics in 25%
of the possible site-specific correlations.
Pigment concentrations, water content, and
phosphorus concentrations were often pos
itively correlated with depth to sediment
surface (Fig. 1E-G), suggesting that the sed
iments between the moguls are less compact
and accumulate pigments and phosphorus.
This accumulation could be mediated by
the winnowing effect of slow, deep-water
currents (Lemmin and Imboden 1987).
In addition to the depth gradients created
by sediment focusing, sediment deposition
is highly patchy, even at a relatively small
spatial scale within relatively uniform sites.
Heterogeneity among "replicate" sediment
samples is many times greater than microscale or analytical error, necessitating care
in sampling design. Sediment patchiness
may result from the activities of aggregated
animals, sediment transport by deep cur
rents, and small-scale variations in bottom
profile. Reynoldson and Hamilton (1982)
studied the spatial variation of phosphorus
Notes
456
in the sediments of one lake and concluded
that homogeneity is the most apparent fea
ture of the spatial pattern of the sediments.
Our research shows that sediment hetero
geneity necessitates careful sampling design,
even within bathymetrically uniform sam
pling sites.
John A. Downing
Departement de Sciences Biologiques
Universite de Montreal
C.P. 6128, Succursale 4A'
Montreal, Quebec H3C 3J7
Laurel C. Rath
Box 1591
Deep River, Ontario KOJ IPO
References
Alley, W. P., and R.F.Anderson. 1968. Small scale
patterns of spatial distribution of the Lake Mich
igan macrobenthos, p. 1-10. In Proc. 11th Conf.
Great Lakes Res., Univ. Mich. Great Lakes Res.
Div. Publ. 95.
Andersen, J. M. 1976. An ignition method for de
termination of total phosphorus in lake sediments.
Water Res. 10:329-331.
Anderson, D. M., D. G. Aubrey, M. A. Tyler, and
D. W. Coats. 1982. Vertical and horizontal dis
tributions of dinoflagellate cysts in sediments.
Limnol. Oceanogr. 27: 757-765.
Brinkhurst, R. O., K. E. Chua, and E. Batoosingh.
1969. Modifications in sampling procedures as
applied to studies on the bacteria and tubificid
oligochaetes inhabiting aquatic sediments. J. Fish.
Res. Bd. Can. 26: 2581-2593.
Conover, W. J. 1971. Practical non-parametric sta
tistics. Wiley.
Davis, M. B., and M. S. Ford. 1982. Sediment fo
cusing in Mirror Lake, New Hampshire. Limnol.
Oceanogr. 27: 137-150.
de March, L. 1978. Permanent sedimentation of
nitrogen, phosphorus and organic carbon in a high
arctic lake. J. Fish. Res. Bd. Can. 35: 1089-1094.
Dillon, P. J., and R. D. Evans. 1982. Whole-lake
lead burdens in sediments of lakes in southern
Ontario, Canada. Hydrobiologia 91: 121-130.
Downing, J. A. 1979. Aggregation, transformation
and the design of benthos sampling programs. J.
Fish. Res. Bd. Can. 36: 1454-1463.
, and M. R. Anderson. 1985. Estimating the
standing biomass of aquatic macrophytes. Can. J.
Fish. Aquat. Sci. 42: 1860-1869.
Eddington,D.N.,andJ.A. Robbins. 1976. Records
of lead deposition in Lake Michigan sediments
since 1800. Environ. Sci. Technol. 10: 266-27'4.
Elliott, J. M. 1977. Some methods for the statistical
analysis of samples of benthic invertebrates, 2nd
ed. Freshwater Biol. Assoc. Sci. Publ. 25.
Evans, H. E., D. C. Lasenby, and P. J. Dillon. 1986.
The effect of core compression on the measure
ment of zinc concentrations and anthropogenic
burdens in lake sediments. Hydrobiologia 132:
185-192.
Evans, R. D., and F. H. Rigler. 1980. Measurement
of whole lake sediment accumulation and phos
phorus retention using lead-210 dating. Can. J.
Fish. Aquat. Sci. 37: 817-822.
, and
. 1985. Long distance transport
of anthropogenic lead as measured by lake sedi
ments. Water Air Soil Pollut. 24: 141-151.
Fabre, A., and M. F. Patau-Albertini. 1986. Sed
iment heterogeneity in a reservoir subject to heavy
draw-down. Hydrobiologia 137: 89-94.
Gorham, E. 1960. Chlorophyll derivatives in surface
muds from the English Lakes. Limnol. Oceanogr.
5: 29-33.
. 1961. Chlorophyll derivatives, sulphur and
carbon in sediment cores from two English lakes.
Can. J. Bot. 39: 333-338.
Graneli.W. 1979. The influence of Chironomusplumosus larvae on the exchange of dissolved sub
stances between sediment and water. Hydrobio
logia 66: 149-159.
Gray, J. S.
1974.
Animal-sediment relationships.
Oceanogr. Mar. Biol. Annu. Rev. 12: 223-261.
HAkanson, L. 1982. Bottom dynamics in lakes. Hy
drobiologia 91: 9-22.
, and M. Jansson. 1983. Principles of lake
sedimentology. Springer.
Hargrave, B. T., and L. K. Nielsen. 1977. Accu
mulation ofsedimentary organic matter at the base
of steep bottom gradients, p. 168-173. In H. L.
Golterman [ed.], Interactions between sediments
and fresh water. Junk.
Hart, B. T., R. J. McGregor, and W. S. Perriman.
1976. Nutrient status of the sediments in Lake
Mulwala. 1. Total phosphorus. Aust. J. Mar.
Freshwater Res. 27: 129-135.
Heath, D. 1985. An experimental and theoretical
investigation of stunting in freshwater fish. M.S.
thesis, McGill Univ. 198 p.
Hilton, J. 1985. A conceptual framework for pre
dicting the occurrence of sediment focusing and
sediment redistribution in small lakes. Limnol.
Oceanogr. 30: 1131-1143.
, J. P. Lishman, and P. V. Allen. 1986. The
dominant processes of sediment distribution and
focusing in a small, eutrophic, monomictic lake.
Limnol. Oceanogr. 31: 125-133.
Hongve, D., and A. H. Erlandsen. 1979. Short
ening of surface sediment cores during sampling.
Hydrobiologia 65: 283-287.
Johnson, T. C, J. E. Evans, and S. J. Eisenreich.
1982. Total organic carbon in Lake Superior sed
iments: Comparisons with hemipelagic and pelag
ic marine environments. Limnol. Oceanogr. 27:
481-491.
Kajak, Z., K. Kacprzak, and R. Polkowski. 1965.
The tubular bottom sampler [in Polish]. Ekol. Pol.
Ser. B 11: 159-165.
Kalff.J.
1972. Net plankton and nanoplankton pro
duction and biomass in a north temperate lake.
Limnol. Oceanogr. 17: 712-720.
Notes
Kelderman, P., and A. M.vandbRepe. 1982. Tem
perature dependence of sediment-water exchange
in Lake Grevelingen, SW Netherlands. Hydrobiologia 92: 489-490.
Keulder, P. C. 1982. Particle size distribution and
chemical parameters of the sediments of a shallow
turbid impoundment. Hydrobiologia 91: 341-353.
Kimmel, B. L. 1978. An evaluation of recent sedi
ment focusing in Castle Lake (California) using a
volcanic ash layer as a stratigraphic marker. Int.
Ver. Theor. Angew. Limnol. Verh. 20: 393-400.
Lafond, M. 1985. Biomasse et production du nannoplancton par classes de taille dans dix lacs du
Bouclier Canadien: Relations avec la transparence
de Feau. M.S. thesis, Univ. Montreal. 99 p.
Lee, D. R. 1985. Method for locating sediment
anomalies in lakebeds that can be caused by
groundwatcr flow. J. Hydrol. 79: 187-193.
Lehman, J. T. 1975. Reconstructing the rate of ac
cumulation of lake sediment: The effect of sedi
ment focusing. Quat. Res. 5: 541-550.
Lemmin, U., and D. M. Imboden. 1987. Dynamics
ofbottom currents in a small lake. Limnol. Oceanogr. 32: 62-75.
Likens, G. E., and M. B. Davis. 1975. Post-glacial
history of Mirror Lake and its watershed in New
Hampshire, U.S.A.: An initial report. Int. Ver.
Theor. Angew. Limnol. Verh. 19: 982-993.
Lorenzen, C. J. 1967. Determination of chlorophyll
and pheopigments: Spectrophotometric equa
tions. Limnol. Oceanogr. 12: 343-346.
Luckenbach, M. W. 1986. Sediment stability around
animal tubes: The roles of hydrodynamic pro
cesses and biotic activity. Limnol. Oceanogr. 31:
779-787.
Ludlam, S. D. 1969. Fayelteville Green Lake, New
York. 3. The laminated sediments. Limnol.
Oceanogr. 14: 848-857.
. 1974. Fayetteville Green Lake, New York.
6. The role of turbidity currents in lake sedimen
tation. Limnol. Oceanogr. 19: 656-664.
Muller, H. E. 1977. Observations of interactions
between water and sediment with a 30-kHz-sediment echosounder, p. 448-452. In H. L. Goiterman [ed.], Interactions between sediments and fresh
water. Junk.
Murphy, J., and J. P. Riley. 1962. A modified single
solution method for the determination of phos
phate in natural waters. Anal. Chim. Acta 27: 3136.
Nakashima,B.S.,andW.C. Leggett.
1975. Yellow
perch (Perca Jlavescens) biomass responses to dif
ferent levels of phytoplankton and benthic bio
mass in Lake Memphremagog, Quebec-Vermont.
J. Fish. Res. Bd. Can. 32: 1785-1797.
Nicholls, K. H., and P. J. Dillon. 1978. An eval
uation of phosphorus, chlorophyll, phytoplankton
relationships for lakes. Int. Rev. Gesamten Hy-
drobiol. 63: 141-154.
Nikaido, M. 1978. Ratios of organic carbon to ni
trogen in the core sediments from Lake Kojima.
Jpn. J. Limnol. 39: 15-21.
Parsons, T. R., and R. J. LeBrasseur. 1970. The
availability of food to different trophic levels in
457
the marine food chain, p. 325-343. In J. H. Steele
[ed.], Marine food chains. Univ. Calif.
Pelletier, B. R.
1968. Submarine physiography,
bottom sediments, and models of sediment trans
port in Hudson Bay, p. 100-135. In Earth Sci.
Symp. on Hudson Bay. Geol. Surv. Can. Pap. 6853.
Petr, T. 1977. Bioturbation and exchange of chem
icals in the mud-water interface, p. 216-226. In
H. L. Golterman [ed.], Interactions between sed
iments and fresh water. Junk.
Premazzi, G., and O. Ravera. 1977. Chemical char
acteristics of Lake Lugano sediments, p. 121-124.
In H. L. Golterman [ed.], Interactions between
sediments and fresh water. Junk.
Rath, L. C. 1986. Le rapport entre l'heterogeneite
du benthos et les sediments lacustres dans les zones
profondes et littoriprofondes. M.S. thesis, Univ.
Montreal. 139 p.
Reynoldson, T. B., Jr., and H. R. Hamilton. 1982.
Spatial heterogeneity in whole lake sediments—
towards a loading estimate. Hydrobiologia 91:235240.
Rhoads, D. C. 1974. Organism-sediment relations
on the muddy sea floor. Oceanogr. Mar. Biol. Annu.
Rev. 12: 263-300.
Rippey, B., and D. H. Jewson. 1982. The rates of
sediment-water exchange of oxygen and sediment
bioturbation in Lough Neagh, Northern Ireland.
Hydrobiologia 92: 377-382.
Ross, P. R., andJ. Kalff. 1975. Phytoplankton pro
duction in Lake Memphremagog, Quebec (Canada)-Vermont (USA). Int. Ver. Theor. Angew.
Limnol. Verh. 19: 760-769.
Sanger, J. E., and E. Gorham. 1970. The diversity
of pigments in lake sediments and its ecological
significance. Limnol. Oceanogr. 15: 59-69.
Shapiro, J., W. T. Edmondson, and D. E. Allison.
1971. Changes in the chemical composition of
sediments of Lake Washington, 1958-1970. Lim
nol. Oceanogr. 16: 437-452.
Slater, S. J. E., and A. J. Boag. 1978. The phos
phorus status of the sediments of three eutrophic
lakes in Victoria. Aust. J. Mar. Freshwater Res.
29: 263-274.
Sly, P. G. 1977. Sedimentary environments in the
Great Lakes, p. 76-82. In H. L. Golterman [ed.],
Interactions between sediments and fresh water.
Junk.
Staub, T. 1977. Stratigraphy of diatoms and chlo
rophyll derivatives in the uppermost sediment of
a Swiss lake, p. 161-164. In H. L. Golterman [ed.],
Interactions between sediments and fresh water.
Junk.
Strickland, J. D. H., and T. R. Parsons.
1968. A
practical handbook of seawater analysis. Bull. Fish.
Res. Bd. Can. 167.
Swain, E. B. 1985. Measurement and interpretation
of sedimentary pigments. Freshwater Biol. IS: 5375.
SWEERTS, J. P., J. W. M. RUDD, AND C. A. KjELLEY.
1986. Metabolic activities in flocculent surface
sediments and underlying sandy littoral sedi
ments. Limnol. Oceanogr. 31: 330-338.
458
Notes
Twinch, A. J., and R. H. Peters. 1984. Phosphate
exchange between littoral sediments and overlying
water in an oligotrophic north-temperate lake. Can.
Williams, J. D. H., J.-M. Jaquet, and R. L. Thomas.
1976. Forms of phosphorus in the surficial sediments of Lake Erie. J. Fish. Res. Bd. Can. 33:
J. Fish. Aquat. Sci. 41: 1609-1617.
Vodopich, D. S., and B. C. Cowell. 1984. Interaction of factors governing the distribution of a
predatory aquatic insect. Ecology 65: 39-52.
413-429.
, J. K. Syers, S. S. Shukla, R. F. Harris, and
Wentz, D. A., and G. F. Lee.
1969.
Sedimentary
phosphorus in lake cores-observations on depo-
sitional pattern in Lake Mendota. Environ. Sci.
Technol. 3: 754-759.
Whitehead, D. R., H. Rochester, Jr., S. W. Rissing,
C.B.Douglass,andM.C.Sheehan. 1973. Late
glacial and postglacial productivity changes in a
New England pond. Science 181: 744-747.
D. E. Armstrong. 1971. Levels ofinorganic and
total phosphorus in lake sediments as related to
other sediment parameters. Environ. Sci. Technol.
5: 1113-1120.
Wood, L. E. 1964. Bottom sediments of Saginaw
Bay, Michigan. J. Sediment. Petrol. 34: 173-184.
.
VuhmitiP/i- 7 ? Anrii 1QR1
Submitted. 23 April 198/
Accepted: 18 September 198/
Revised: 27 January 1988