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of experimental variables and precise measurements. The results of this work, and
those of Culberson (see Takahashi et al.
1970), show that precise, routine field determinations of the apparent pH of seawater are attainable.
Albert0
Zirino
Chemistry and Environmental
Sciences
Division
Code 406
Naval Undersea Center
San Diego, California
92132
References
eastern Pacific
Ocean.
J. Oceanogr.
Sot. Jap.
26: 95-99.
MCINNES, D. A. 1961. The principles of electrochemistry.
Dover.
PARK, P. K. 1966. Surface pH of the northeastern Pacific Ocean.
J. Oceanogr. Sot. Korea
1: l-6.
-.
1968. The processes contributing
to the
vertical distribution
of the apparent pH in the
J. Oceanogr. Sot.
northeastern Pacific Ocean.
Korea 3 : l-7.
PYTKOWICZ, R. M., D. R. KESTER, AND B. C.
of pH
BLJRGENER. 1966. Reproducibility
measurements
in seawater.
Limnol.
Oceanogr. 11: 417-419.
TAKAHASHI, T., AND OTHERS. 1970. A carbonate
chemistry profile at the 1969 GEOSECS intercalibration station in the eastern Pacific Ocean.
J. Geophys. Res. 75: 7648-7666.
Submitted: 11 February 1974
Accepted: 26 February 1975
CULBERSON, C., AND R. M. PYTKOWICZ. 1970.
Oxygen-total
carbon dioxide correlation
in the
An evaluation of sediment trap methodology
Abstract-Five
sediment traps with collecting areas ranging from 8 to 1,465 cm2 collected the same amount of material, as measured by dry weight,
ash weight,
and
phosphorus
content,
on a unit area basis.
Variances from different
size traps were not
significantly
different.
These results are presented as further illustration
that traps are a
meaningful
technique for measuring sedimentation in certain lakes.
Sediment traps afford a unique method
of measuring the downward movement of
materials within a lentic environment; they
enable us to estimate loss of materials from
the trophogenic zone or accumulation of
materials in the sediments. However, despite their apparent utility sediment traps
have not received the general acceptance
that might be expected. One factor leading
to the reluctance to use this method in
quantitative
studies is the suspicion that
the rate of sediment accumulation in a trap
does not necessarily equal that in a lake.
Kleerekoper ( 1952) and Golterman ( 1973)
have suggested that, by decreasing turbulence, sediment traps increase the sedimentation rate in their vicinity.
Although the
suggested effect is not supported by results
from studies of rain collectors (Bruce and
Clark 1969), concern over the effects of
turbulence seems justified.
One approach to evaluating the influence
of turbulence on catching efficiency is to
measure the catch per unit area for sediment traps with different collecting areas.
The rationale for this type of experiment is
that the effect of turbulence should be correlated with size of trap aperture: that is,
if traps increase turbulence the catch per
unit area should increase with increasing
diameter, since larger traps would have a
larger portion of their collecting area sufficiently distant from the circumference to
minimize the effect of the turbulence which
is presumably enhanced by the trap sides.
To date, five studies have dealt with the
effect of trap size on catch. As Table 1
shows, these studies have resulted in contradictory conclusions. In addition, certain
aspects of these studies limit their value.
Pennington (1974) h as shown that funnel
traps are not suitable collectors and therefore studies based on this design must be
discounted. Examination of the remaining
data in Table 1 reveals that the trap size
ranges used have all been rather narrow,
Notes
658
Table 1. The effect of sediment
catch of material on a unit area basis.
Trap size range
(diam in cm)
Reference
Davis
1.5 - 8.4"
4.2 - 10.6
(1967)
trap
Size
effect
NO
size on
Trap
type
cylinder
Table 2. Dry weight of material collected at
sta. 2. Results in grams per square meter per day.
Trap size represented by trap diameter in centimeters.
Collection
period
(1974)
Watanabe and
Hayashi (1971)
12.0 - 24.0
NO
funnel
Johnson and
Brinkhurst(l971)
5.0 - 41.0$
5.0 - 17.0
Yes
funnel 6r
cylinder
White and
Wetzel (1973)
4.8 - 13.3
No
cylinder
Pennington
2.2 - 7.0
Yes 7 cylinder
(1974)
3.2
* Upper values represent laboratory
experiments;
lower values field experiments.
tUpper values represent total range; lower values
+range excluding funnel traps.
SAlthough data presented show no effect,
Pennington stated larger traps caught less material.
the greatest being a factor of four in trap
diameter. Also, only relatively small traps
were used.
White and Wetzel (1973) found that
the variance increased directly with trap
size, suggesting still another apparent problem in sediment trap methodology.
The sediment traps that I used were
made of 6-mm-wall Plexiglas which was
purchased either as tubing or, for the largest trap, a sheet which was formed into a
cylinder. A 5-cm layer of sodium chloride
solution in the bottom of each trap established a density gradient to eliminate disturbance of the collected material during
raising of the traps (Rigler et al. 1974). A
dye was also included in the bottom layer
to act as an indicator in the event of trap
disturbance.
Samples in which the dye
mixed with the overlying water were discarded. All. traps were 25 cm tall and their
diameters were 3.2, 9.3, 19.5, 29.8, and 43.2
cm. The smallest trap was just large
enough to yield a sufficient quantity of material to analyze, while the largest took two
people to manipulate.
The five traps were individually
buoyed
by Styrofoam collars and equally spaced
along a 2.4-m wooden dowel, attached to
a rope running through two pulleys anchored in the bottom and to a float on the
31
2
17
19
Jul
Aug
Aug
Aug
21 Aug
2.6Aug
28 Aug
11 Sep
19 Sep
-
2
7
19
21
26
28
30
16
25
Aug
Aug
Aug
Aug
Aug
Aug
Aug
Sep
Sep
0.67
2. 8
1.2
1.6
1.4
1.5
2.5
1.8
0.52
Trap size
9.3 19.5
0.42
0.86
2.1
1.5
1.2
1.8
4.7
1.3
0.51
0.68
1.2
1.3
2.0
1.3
2.0
3.3
1.4
0.83
29.8
43.2
0.48
1.0
1.3
1.7
1.4
1.9
3.6
1.3
0.74
0.42
0.45
1.1
1.5
1.7
2.3
1.4
0.68
0.68
surface. The pulleys were about 4 m apart,
ensuring that movement of the surface line
would not disturb water in the vicinity of
the traps.
The traps were raised by detaching the
surface line from the float and allowing the
dowel-trap assembly to float slowly to the
surface. When the traps reached the surface the water was pumped out through a
rebent glass tube. The trap was emptied
until the water level reached about 2.5 cm
above the top of the dye layer. The remaining water and sedimented material
was then agitated and subsamples were
taken for dry weight and ash weight (in
duplicate)
and phosphorus analysis (in
triplicate).
Samples were taken at two stations in
Crawford
Lake (79”57’N,
43”28’W),
a
2.5-ha meromictic lake in southern Ontario.
The traps at station 1 were positioned about
1 m below the chemocline, those at station
2 an equal distance above the chemocline,
exposing the two sets of traps to different
amounts of turbulence. Collecting periods
extended from l-10 days during July
through October 1974, a period of considerable variation in seston levels as indicated
by Secchi disk.
Sedimenting material was collected in
the five traps simultaneously
over eight
periods at sta. 1 and nine at sta. 2. The relationship between the material collected,
659
Notes
Table 3. ANOVA table for sta. 1. Data in descending order is dry weight, ash weight, phosphorus. ns = value not significant
at Fo.o,.
Trap size
Collecting
Error
Total
period
4
7
28
39
16.3
251.5
46.5
314.3
4.1
35.9
1.7
2.5 ns
21.6
Trap size
Collecting
Error
Total
period
3
3697 1232
7 269734 38276
21 85017 4048
31 358448
0.3 ns
9.5
as measured by phosphorus content, dry
weight and ash weight on a unit area basis,
and trap size was examined by two-way
analysis of variance without
replication
(Sokal and Rohlf 1969). Table 2 contains
the dry weight results from sta. 2 as an illustration. The ANOVA tables for stations
1 and 2 are presented in Tables 3 and 4. As
these tables show, the size of the trap had
no significant effect ( F0.05) on the catch
per unit area except in the case of dry
weight at sta. 1.
The relationship between trap size and
sample variance was examined with BartTable 4. ANOVA
same as Table 3.
table for sta. 2. Explanation
Source of
variation
df
Trap size
Collecting
Error
Total
4 124.2
8 2224.3
32 980.4
44 3328.9
Trap size
Collecting
Error
Total
Trap size
Collecting
Error
Total
period
period
period
SS
MS
31.1
278.0
30.1
Fs
1.0 ns
9.3
2.9
42.0
3.3
0.9 ns
12.6
3 29282 9757
8 376126 47016
24 260175 10341
35 665583
0.9 ns
4.3
4
8
32
44
11.5
335.9
106.7
454.1
Table 5. Analysis of variance of heterogeneity
among trap sixes. A nonsignificant
ratio ( ns ) indicates that different size traps do not exhibit different variances. DW-dry
weight; AW-ash
weight;
P-phosphorus
content. ns-value
not significant
at x20.1.
-Station
Parameter
df
x2
1
1
1
2
2
2
DW
AIJ
P
DW
AW
P
437
4,7
397
498
438
398
4.94
1.54
1.98
4.91
3.07
3.59
ns
ns
ns
ns
ns
ns
lett’s test of variance homogeneity (Sokal
and Rohlf 1969). As Table 5 illustrates,
there were no significantly
different variances among samples from different trap
sizes.
There is growing evidence that sediment
traps do, in fact, measure the “real” sedimentation in certain lakes. Studies such
as mine and those summarized in Table 1
have shown that the collection of sedimenting material on a unit area basis is independent of sediment trap aperture size.
Still more convincing are those studies involving an absolute calibration.
Pennington ( 1974) found sedimentation in traps to
be similar to that expected from radioactive
dating of sediment accumulation and Rigler et al. (1974) found amazing agreement
between the number of zooplankton exuviae shed and the number collected in their
traps. Pennington did find some discrepancies between radioactive sediment accumulation and sedimentation rates as measured
by traps, but these differences were attributed to resuspension of bottom material.
The agreement between alternate methods
was apparently related to the percentage of
the lake deeper than 15 m. This is consistent with the results of Davis (1973) who
found that the effect of resuspension was
insignificant in the deepest ( 10 m ) area of
the lake. Davis (1968) also showed that
thermal stratification prevents resuspension
of bottom materials. These explanations,
in conjunction with the work presented
660
Notes
herein, seem to indicate that except in shallow and unstratified lakes traps are a dependable method of measuring sedimentation.
I thank F. H. Rigler for many discussions.
D. Evans and P. Hesse assisted in the field
and laboratory work. The Halton Region
Conservation Authority permitted the use
of Crawford Lake. The suspension apparatus was modified from a design by L. Ewers.
W. B. Kirchner
Department of Zoology
University of Toronto
Toronto, Ontario
M5S 1Al
References
BRUCE, J. P., AND R. H. CLARK. 1969. Introduction to hydrometeorology.
Pergamon.
DAVIS, M. B. 1967. Pollen deposition in lakes as
measured by sediment traps.
Geol. Sot. Am.
Bull. 78: 849-858.
-.
1968. Pollen grains in lake sediments:
Redeposition caused by seasonal water circulation.
Science 162: 796-799.
-.
1973. Redeposition
of pollen grains in
Limnol. Oceanogr. 18: 44lake sediments.
52.
GOLTERMAN, H. L. 1973. Vertical movement of
phosphate in freshwater,
p. 509-538.
In E.
J. Griffith
et al. [eds.], Environmental
phosphorus handbook. Wiley.
JOIINSON, M. G., AND R. 0. BRINKHURST. 1971.
Benthic
community
metabolism
in Bay of
J. Fish. Res. Bd.
Quinte and Lake Ontario.
Can. 28: 1715-1725.
KLEEREKOPER, H. 1952. A new apparatus
for
the study of sedimentation
in lakes.
Can. J.
Zool. 30: 185-190.
PENNINGTON, W.
1974. Seston and sediment
formation in five Lake District lakes. J. Ecol.
62 : 215-251.
RIGLER, F. H., M. E. MACCALLUM, AND J. C. ROFF.
1974. Production
of zooplankton
in Char
Lake.
J. Fish. Res. Bd. Can. 31: 637-646.
SOKAL, R. R., AND F. J. ROHLF. 1969. Biometry.
Freeman.
WATANABE, Y., AND H. HAYASHI.
1971. Investigation on the method for measuring
the
amount of freshly precipitating
matter in lakes.
Jap. J. Limnol. 32: 40-45.
1973. A modWHITE, W. S., AND R. G. WETZEL.
ified sedimentation
trap.
Limnol. Oceanogr.
18 : 986-988.
Submitted:
Accepted:
26 December 1974
20 March 1975