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
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