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Spring bloom in a hypereutrophic lake, lake Kasumigaura, Japan—III Phytoplankton abundance in standing stock of organic matter in lake water
Water Res. Vol. 17, No. 4, pp. 453-457, 1983 Printed in Great Britain. All rights reserved
0043-1354/83/040453-05S03.00/0 Copyright © 1983 Pergamon Press Ltd
SPRING BLOOM IN A HYPEREUTROPHIC LAKE, LAKE KASUMIGAURA, JAPAN--Ill PHYTOPLANKTON ABUNDANCE IN STANDING STOCK ORGANIC MATTER IN LAKE WATER
OF
HUMITAKE SEKI and AKIHITO MASAKI Institute of Biological Sciences, University of Tsukuba, Sakuramura, Ibaraki, Japan 305 (Received March 1982)
Abstract--The rapid increase of phytoplankton biomass was the major process for the increase of particulate organic matter in Lake Kasumigaura in 1980. During the first phytoplankton pulse in the bloom relative abundance of each component of organic matter in the lake water was: dissolved organic matter 100, phytoplankton 28, bacteria 27, and detrital particle 27. This relative abundance was maintained as a steady-state oscillation throughout the spring bloom similar to that usually observed in moderately__eutrophic waters. Thus phytoplankton abundance in the standing stock of organic matter of the hypereutrophic water during the spring bloom does not show any marked difference from that of moderately eutrophic waters.
INTRODUCTION Organic materials have been shown to exist both in the forms of solute and particles in natural waters (e.g. Parsons & Seki, 1970). The biogenic fraction of the particles is composed of bacteria, phytoplankton, zooplankton and nekton. As most zooplankters and nekton are comparatively rare and have a relatively quick response to escape from almost all regular sampling of water for microbiological analyses, only bacteria and phytoplankton in these water samples have qualitative and quantitative significance (Seki, 1976). The relative abundance of these latter organisms in particulate organic material is generally different in natural waters having different trophic levels. It has been shown that the fraction of particulate organic materials increases firstly in heterotrophic microorganisms, secondly in phytoplankton and finally in detritus according to the degree of eutrophication from oligotrophic to hypereutrophic system (Seki & Nakano, 1981). Seasonal variation of each fraction has also been demonstrated within each type of water. This kind of variation occurs during a short period such as that of the spring bloom when cycling of materials is far more dynamic than during the rather static winter season. The phytoplankton that comprise the major component of the community during a spring bloom plays a double role. It shifts the ecosystem into a more energy-rich level on the one hand and threatens the steady-state equilibrium of the ecosystem with too much energetic excitation on the other. Thus, during the spring bloom, feedback mechanisms in the aquatic ecosystem should work more actively than in other seasons to maintain the ecosystem. As a result, as Nakano & Seki (1981) have shown, the balance of 453
each component comprising the particulate organic materials is variable. This highly variable balance must be sensitive in order to work in favour of the stability of an ecosystem. This mechanism was examined for the aquatic ecosystem of Tsuchiura Harbor during the spring bloom in 1980.
MATERIALS AND METHODS
The location of the sampling station and water sampling methods were given in Seki & Takahashi (1983). Dissolved organic carbon (DOC) was measured in the lake water filtered (water sample: 200 ml) through a Whatman glass fiber filter GF/C soon after the sampling, using Beckman TOC analyzer model 915B. The filtered particles found on the Whatman glass fiber filter GF/C were measured for chlorophyll a by the method in Seki & Takahashi (1983). Particulate organic carbon (POC) was also measured on the same filtered particles as that for the chlorophyll measurement. Total number of bacterioplankton in the lake water was counted from raw lake water soon after the sampling, using Nikon phase contrast microscope with a bacterial counting chamber (Erma, Tokyo). To determine the carbon flux, i.e. Total carbon = Dissolved organic carbon + Bacterial carbon + Phytoplankton carbon + Detrital carbon, the following calculations were required: Average cell size of bacterioplankton in the lake water was 1.0 x 0.5/~m. On the basis of this cell volume, the average wet weight of the bacterioplankton was estimated to be 2.5 x 10 -7/tg. The dry weight of bacterioplankton, therefore, can be calculated to be 5 x 10 -s/~g, because approx. 80~ of the wet weight of a bacterial cell is water (Lamanna & Mallette, 1953). Assuming that 40~o of dry weight of the bacterial cell is organic carbon (Holm-Hansen & Booth, 1966), the organic carbon content of the bacterioplankton cell should approximate 2 x 10-S,ug C cell -1. This organic carbon content in a bacterial cell multiplied by the bacterial density in lake water (cells ml- 1 lake water) gives the organic carbon concentration of bacterioplankton in lake water (/~g C ml-1
454
Ih
',,ill \1,:1 ~ 1 K I
and
lake water). The standing stock of phy/oplankton (l~g C I ]) was calculated as the chlorophyll a concentration (itgl 1) multiplied by a conversion factor IParsons, 1969) of chlorophyll a into the phytoplankton density. This conversion factor was determined from the regression relationship between P O C and chlorophyll a throughout the spring b l o o m Subtraction of the organic carbon in phytoplankton and bacteria from P O C gives the organic carbon in detritus.
/\KIII[I()
'%,'1\ S % K I
I
~' o,oi
oO~/
7
6
o 005 Jc 0
RESULTS
A highly significant regression relationship was found between POC and chlorophyll a in lake water throughout the spring bloom in 1980: Y = 0.0446 X - 0.103 (r = 0.817, n = 228) where X is the concentration of POC and Y is the concentration of chlorophyll a. This relationship shows that the concentration of chlorophyll a was greater when POC was more abundant in the lake. Similar relationships (Figs 1-4) were observed in four individual periods within the spring bloom: Y = 0.0338 X - 0.0767 (r = 0.699, n = 36) in the first period from 24 March to 3 April; Y = 0.0421 X - 0.0976 (r = 0.763, n = 78) in the second period from 5 April to 29 April; Y = 0 . 0 4 2 8 X - 0 . 0 9 0 4 ( r = 0 . 7 9 2 , n = 5 4 ) in the third period from 1 May to 17 May; and Y = 0.0453 X - 0.1079 (r = 0.808, n = 60). These periods are the same as those reported by Seki & Takahashi (1983). The relationship between POC and chlorophyll a during every period in the spring bloom shows that phytoplankton made a great contribution to the standing stock of particulate organic matter. The slope of the regression increased from the first to the second period, but changed little after the second period. Thus the increase of phytoplankton biomass caused a rapid increase of POC only at the early stage of the spring bloom in 1980. The similarity in the relationship between POC and chlorophyll a in different periods within the spring bloom is in contrast to what was seen in winter seasons just before the bloom. Concentrations of POC and chlorophyll were very low before the bloom, and their correlation was not significant. Dur010 Y ~
.
0.0338X-00767
F~
¢)
0
0
0
202.90 (F'o,o* = 7,19)
0.05
5 POC,
,~o mg t -I
Fig. 1. Relationship between POC and chlorophyll a in lake water of Lake Kasumigaura during the first period of the spring bloom. Each plot shows the value for each water sample. Three lines indicate the regression line (central line) and the range of 95~o confidence limit (outer two lines). F value shows that the regression line is highly significant.
o
I 5
I I0
POC, mg t-I Fig. 2. Relationship between POC and chlorophyll a in lake water of Lake Kasumigaura during the second period of the spring bloom. Symbols and statistic explanation are as in Fig. 1. ing this period, therefore, the variation of phytoptankton density had little affect on the standing stock of particulate organic matter. The quantitative variation of phytoplankton during the bloom could be clearly shown in relation to other components of the particulate matter, when each component was expressed on a relative scale based on 100 for the amount of dissolved organic matter in lake water (Figs 5-8, Table 1). Before the spring bloom, detritus comprised the greatest fraction of particles in lake water. Bacteria were second in importance. When the spring bloom started, phytoplankton increased rapidly in their population density. Already in the first period of the spring bloom the phytoplankton fraction increased to a high steady-state level. Bacteria also increased and detritus decreased, possibly due to active bacterial decomposition of detrital particles. Thereafter through periods two and three every component of particulate matter maintained a constant level, although the bacterial fraction tended to decrease a little as time elapsed (Table 1). In the fourth period, when Ch/amydomonas species became predominant by excluding other phytoptankters, the diversity index decreased to below 3.0 (Hara et al., 1983) and the phytoplankton fraction increased again to another higher steady-state level. In this period, blue-green algae began to become dominant numbers of the phytoplankters. Therefore, the fourth period of the spring bloom in 1980 can be regarded as the transition stage from the spring bloom to the summer bloom.
DISCUSSION
By the first phytoptankton pulse of the spring bloom, in 1980, there was a fine balance among the relative abundance of each component comprising organic matter. Large diatoms of Synedra were~ the major phy!oplankters among more t h a n 27 dominant phytoplankton species comprising the first phytoplankton pulse (Hara et al., 1983). The maximum
Spring bloom in Lake Kasumigaura--III
455
0.15
L 0.10
~
O
O•/•// 0
/
/
~
Y =
0.0428X-0.0904
F =
fill07
(F0.01 = 7.17)
0.05
/%/
O
o
I
i
5
io
mg L~I
POC,
Fig. 3. Relationship between POC and chlorophyll a in lake water of Lake Kasumigaura during the third period of the spring bloom. Symbols and statistic explanation are as in Fig. 1.
standing stock of phytoplankters in the first pulse was observed about 4 days after the initiation of rapid phytoplankton multiplication. The bacteria, on the other hand, also multiplied rapidly to achieve in their highest level among the population densities observed during the spring bloom. Thereafter, their abundance tended to decrease as time elapsed. This prompt bacterial response corresponding with the rapid phytoplankton increase may be very favourable for stability in the natural balance, otherwise excess accumulation of organic matter in an aquatic ecosystem leads the system into disequilibrium (Seki & Nakano, 1981).
0.30
025
Actually the relative abundance of each component comprising the organic matter in lake water continued to stay in balance during the spring bloom. Phytoplankton, bacteria and detritus are major components comprising the particulate organic matter. The abundance of each components was approx. 30 when expressed on a relative scale based on 100 for the amount of dissolved organic matter. These relative values of organic components in lake water of Lake Kasumigaura during the spring bloom in 1980 are the same as those usually observed in the upper range of moderately eutrophic waters (Seki, 1982; Seki & Nakano, 1981). Thus this typical hypereutrophic lake during the spring bloom in 1980 shared common characteristics with moderately eutrophic waters from the viewpoint of biochemistry (Seki & Takahashi, 1983) in this study. The same conclusion may also be drawn from the viewpoint of taxonomy, i.e. the phytoplankters found in Lake Kasumigaura are also found commonly in moderately eutrophic waters (Hara et al., 1983; Mizuno, 1971). If eutrophic
020 IO0
0.15
"o c
& A
so
,1= u 0.10
OOA
O0
0
g
0
0,05
I 3
D0C,
1 5
o
P0C,
I IO
mgt -~
Fig. 4. Relationship between POC and chlorophyll a in lake water of Lake Kasumigaura during the fourth period of the spring bloom. Symbols and statistic explanation are as in Fig. 1.
I 4
t 5
m g t -r
Fig. 5. Organic carbon of each component of particulate matter as expressed on a relative scal.~ased on 100 for the amount of dissolved organic matter in lake water of Lake Kasumigaura during the first period of the spring bloom. Each symbol shows the component of particulate matter: O--phytoplankton; IS]--bacteria; /X--detritus. Vertical bar with each symbol on the left of the figures shows the average (site of each symbol) and the standard deviation (width of the bar).
45b
HUMllAKI, SEKI and AKIHtF() MASAKI I00
A
6
q9
6 AAA
50
,t
O0
~'
(~
A
aA
I
I
I
I
I
3
4
5
6
7
DO(;,
mgt - I
Fig. 6. Organic carbon of each component of particulate matter as expressed on a relative scale based on 100 for the amount of dissolved organic matter in lake water of Lake Kasumigaura during the second period of the spring bloom. Symbols are as in Fig. 5.
I00
c .~
'&
•
50
o o
I
I
0
Doe,
I
I
4
3
mgL
-I
5
6
Fig. 7. Organic carbon of each component of particulate matter as expressed on a relative scale based on 100 for the amount of dissolved organic matter in lake water of Lake Kasumigaura during the third period of the Spring bloom. Symbols are as in Fig. 5.
200
o 150 o A o
*o c
0o
fO0 AO0
o ne
A
0 g
o8
50
J_
0
~
t
0
O0 A ° o A ~.
a I
I
3
4
•
DOC,
o D
I
I
J
5
6
7
m g L- I
Fig. 8. Organic carbon of each component of particulate matter as expres,~d on a relative scale based on 100 for the amount of dissolved Organic matter in lake water of Lake Kasumigaura during the fourth period of the Spring bloom. Symbols are as in Fig. 5,
Spring bloom in Lake Kasumigaura--IlI
457
Table 1. Average value of each component comprising particulate organic matter as expressed on a relative scale based on 100 for the amount of dissolved organic material in lake water of Lake Kasumigaura Period
Phytoplankton
Bacteria
Detritus
16
21
35
28
27
27
28
25
29
26
18
28
46
19
32
Before the spring bloom (17 February-22 March) During the spring bloom 1st period (24 March-3 April) 2nd period (5 April-29 April) 3rd period (1 May-17 May) 4th period (19 May-6 June)
and hypereutrophic ecosystem are different, and if elements comprising each system function differently, such overlapping of common characteristics in both systems is not to be expected. The elements comprising the hypereutrophic system should remain in a steady-state oscillation within an upper part of the eutrophic system (detailed discussion in Seki, 1982). Thus the hypereutrophic system is not another energized state independent from other less eutrophied systems. Incidentally, Wetzel (1966) calls an extreme type of eutrophic equilibrium as hypereutrophic.
Acknowledgements--The authors wish to thank Drs T. R. Parsons and R. J. LeBrasseur for valuable comments. This work was partly supported by a special research project of the Ministry of Education of Japan (203012).
REFERENCES
Hara Y., Tsuchida A. & Seki H. (1983) Spring bloom in a hypereutrophiclake, Lake Kasumigaura, Japan--II. Succession of phytoplankton species. Water Res. 17, 447-451. Holm-Hansen O. & Booth C. R. 0966) The measurement of adenosine triphosphate in the ocean and its ecological significance. Limnol. Oceanogr. II, 510--519.
Lamanna C. & Mallette M. F. (1953) Basic Bacteriology. Its Biological and Chemical Background, 853 pp. Williams & Wilkins, Baltimore. M izuno T. (1971) Illustrations of the Freshwater Plankton of Japan, 351 pp. Hoikusha, Osaka (in Japanese). Nakano H. & Seki H. (1981) Impact of nutrient enrichment in a waterchestnut ecosystem at Takahama-iri Bay of Lake Kasumigaura, Japan. V. Dynamics of organic debris. WASP 14, 133-157, Parsons T. R. (1969) The use of particle size spectra in determining the structure of a plankton community. J. Oceanogr. Soc. Japan 25, 172-181. Parsons T. R. & Seki H. (1970) Importance and general implications of organic matter in aquatic environments. Organic Matter in Natural Waters (Edited by Hood D. W.), pp. 1-27. University of Alaska. Seki H. (1976) Methods for Microbial Ecology in Aquatic Environments, 126 pp. Kyoritsu Shuppan Co., Tokyo (in Japanese). Seki H. (1982) Dynamics of Organic Materials in Aquatic Ecosystems, 201 pp. CRC Press, Florida. Seki H. & Nakano H. (1981) Production of bacterioplankton with special reference to dynamics of dissolved organic matter in a ~hypereutrophic lake. Kieler Meeresforsch. Sonderh. 5, 408-415. Seki H. & Takahashi.E. (1983) Spring bloom in a hypereutrophic lake, Lake Kasumigaura, Japan--I. Succession of phytoplankters with different accessory pigments. Water Res. 17, 441-445. Wetzel R. G. (1966) Variations in productivity of Goose and hypereutrophic Sylvan lakes, Indiana. Invest. Indiana Lakes Stream 7, 147-184.
0043-1354/83/040453-05S03.00/0 Copyright © 1983 Pergamon Press Ltd
SPRING BLOOM IN A HYPEREUTROPHIC LAKE, LAKE KASUMIGAURA, JAPAN--Ill PHYTOPLANKTON ABUNDANCE IN STANDING STOCK ORGANIC MATTER IN LAKE WATER
OF
HUMITAKE SEKI and AKIHITO MASAKI Institute of Biological Sciences, University of Tsukuba, Sakuramura, Ibaraki, Japan 305 (Received March 1982)
Abstract--The rapid increase of phytoplankton biomass was the major process for the increase of particulate organic matter in Lake Kasumigaura in 1980. During the first phytoplankton pulse in the bloom relative abundance of each component of organic matter in the lake water was: dissolved organic matter 100, phytoplankton 28, bacteria 27, and detrital particle 27. This relative abundance was maintained as a steady-state oscillation throughout the spring bloom similar to that usually observed in moderately__eutrophic waters. Thus phytoplankton abundance in the standing stock of organic matter of the hypereutrophic water during the spring bloom does not show any marked difference from that of moderately eutrophic waters.
INTRODUCTION Organic materials have been shown to exist both in the forms of solute and particles in natural waters (e.g. Parsons & Seki, 1970). The biogenic fraction of the particles is composed of bacteria, phytoplankton, zooplankton and nekton. As most zooplankters and nekton are comparatively rare and have a relatively quick response to escape from almost all regular sampling of water for microbiological analyses, only bacteria and phytoplankton in these water samples have qualitative and quantitative significance (Seki, 1976). The relative abundance of these latter organisms in particulate organic material is generally different in natural waters having different trophic levels. It has been shown that the fraction of particulate organic materials increases firstly in heterotrophic microorganisms, secondly in phytoplankton and finally in detritus according to the degree of eutrophication from oligotrophic to hypereutrophic system (Seki & Nakano, 1981). Seasonal variation of each fraction has also been demonstrated within each type of water. This kind of variation occurs during a short period such as that of the spring bloom when cycling of materials is far more dynamic than during the rather static winter season. The phytoplankton that comprise the major component of the community during a spring bloom plays a double role. It shifts the ecosystem into a more energy-rich level on the one hand and threatens the steady-state equilibrium of the ecosystem with too much energetic excitation on the other. Thus, during the spring bloom, feedback mechanisms in the aquatic ecosystem should work more actively than in other seasons to maintain the ecosystem. As a result, as Nakano & Seki (1981) have shown, the balance of 453
each component comprising the particulate organic materials is variable. This highly variable balance must be sensitive in order to work in favour of the stability of an ecosystem. This mechanism was examined for the aquatic ecosystem of Tsuchiura Harbor during the spring bloom in 1980.
MATERIALS AND METHODS
The location of the sampling station and water sampling methods were given in Seki & Takahashi (1983). Dissolved organic carbon (DOC) was measured in the lake water filtered (water sample: 200 ml) through a Whatman glass fiber filter GF/C soon after the sampling, using Beckman TOC analyzer model 915B. The filtered particles found on the Whatman glass fiber filter GF/C were measured for chlorophyll a by the method in Seki & Takahashi (1983). Particulate organic carbon (POC) was also measured on the same filtered particles as that for the chlorophyll measurement. Total number of bacterioplankton in the lake water was counted from raw lake water soon after the sampling, using Nikon phase contrast microscope with a bacterial counting chamber (Erma, Tokyo). To determine the carbon flux, i.e. Total carbon = Dissolved organic carbon + Bacterial carbon + Phytoplankton carbon + Detrital carbon, the following calculations were required: Average cell size of bacterioplankton in the lake water was 1.0 x 0.5/~m. On the basis of this cell volume, the average wet weight of the bacterioplankton was estimated to be 2.5 x 10 -7/tg. The dry weight of bacterioplankton, therefore, can be calculated to be 5 x 10 -s/~g, because approx. 80~ of the wet weight of a bacterial cell is water (Lamanna & Mallette, 1953). Assuming that 40~o of dry weight of the bacterial cell is organic carbon (Holm-Hansen & Booth, 1966), the organic carbon content of the bacterioplankton cell should approximate 2 x 10-S,ug C cell -1. This organic carbon content in a bacterial cell multiplied by the bacterial density in lake water (cells ml- 1 lake water) gives the organic carbon concentration of bacterioplankton in lake water (/~g C ml-1
454
Ih
',,ill \1,:1 ~ 1 K I
and
lake water). The standing stock of phy/oplankton (l~g C I ]) was calculated as the chlorophyll a concentration (itgl 1) multiplied by a conversion factor IParsons, 1969) of chlorophyll a into the phytoplankton density. This conversion factor was determined from the regression relationship between P O C and chlorophyll a throughout the spring b l o o m Subtraction of the organic carbon in phytoplankton and bacteria from P O C gives the organic carbon in detritus.
/\KIII[I()
'%,'1\ S % K I
I
~' o,oi
oO~/
7
6
o 005 Jc 0
RESULTS
A highly significant regression relationship was found between POC and chlorophyll a in lake water throughout the spring bloom in 1980: Y = 0.0446 X - 0.103 (r = 0.817, n = 228) where X is the concentration of POC and Y is the concentration of chlorophyll a. This relationship shows that the concentration of chlorophyll a was greater when POC was more abundant in the lake. Similar relationships (Figs 1-4) were observed in four individual periods within the spring bloom: Y = 0.0338 X - 0.0767 (r = 0.699, n = 36) in the first period from 24 March to 3 April; Y = 0.0421 X - 0.0976 (r = 0.763, n = 78) in the second period from 5 April to 29 April; Y = 0 . 0 4 2 8 X - 0 . 0 9 0 4 ( r = 0 . 7 9 2 , n = 5 4 ) in the third period from 1 May to 17 May; and Y = 0.0453 X - 0.1079 (r = 0.808, n = 60). These periods are the same as those reported by Seki & Takahashi (1983). The relationship between POC and chlorophyll a during every period in the spring bloom shows that phytoplankton made a great contribution to the standing stock of particulate organic matter. The slope of the regression increased from the first to the second period, but changed little after the second period. Thus the increase of phytoplankton biomass caused a rapid increase of POC only at the early stage of the spring bloom in 1980. The similarity in the relationship between POC and chlorophyll a in different periods within the spring bloom is in contrast to what was seen in winter seasons just before the bloom. Concentrations of POC and chlorophyll were very low before the bloom, and their correlation was not significant. Dur010 Y ~
.
0.0338X-00767
F~
¢)
0
0
0
202.90 (F'o,o* = 7,19)
0.05
5 POC,
,~o mg t -I
Fig. 1. Relationship between POC and chlorophyll a in lake water of Lake Kasumigaura during the first period of the spring bloom. Each plot shows the value for each water sample. Three lines indicate the regression line (central line) and the range of 95~o confidence limit (outer two lines). F value shows that the regression line is highly significant.
o
I 5
I I0
POC, mg t-I Fig. 2. Relationship between POC and chlorophyll a in lake water of Lake Kasumigaura during the second period of the spring bloom. Symbols and statistic explanation are as in Fig. 1. ing this period, therefore, the variation of phytoptankton density had little affect on the standing stock of particulate organic matter. The quantitative variation of phytoplankton during the bloom could be clearly shown in relation to other components of the particulate matter, when each component was expressed on a relative scale based on 100 for the amount of dissolved organic matter in lake water (Figs 5-8, Table 1). Before the spring bloom, detritus comprised the greatest fraction of particles in lake water. Bacteria were second in importance. When the spring bloom started, phytoplankton increased rapidly in their population density. Already in the first period of the spring bloom the phytoplankton fraction increased to a high steady-state level. Bacteria also increased and detritus decreased, possibly due to active bacterial decomposition of detrital particles. Thereafter through periods two and three every component of particulate matter maintained a constant level, although the bacterial fraction tended to decrease a little as time elapsed (Table 1). In the fourth period, when Ch/amydomonas species became predominant by excluding other phytoptankters, the diversity index decreased to below 3.0 (Hara et al., 1983) and the phytoplankton fraction increased again to another higher steady-state level. In this period, blue-green algae began to become dominant numbers of the phytoplankters. Therefore, the fourth period of the spring bloom in 1980 can be regarded as the transition stage from the spring bloom to the summer bloom.
DISCUSSION
By the first phytoptankton pulse of the spring bloom, in 1980, there was a fine balance among the relative abundance of each component comprising organic matter. Large diatoms of Synedra were~ the major phy!oplankters among more t h a n 27 dominant phytoplankton species comprising the first phytoplankton pulse (Hara et al., 1983). The maximum
Spring bloom in Lake Kasumigaura--III
455
0.15
L 0.10
~
O
O•/•// 0
/
/
~
Y =
0.0428X-0.0904
F =
fill07
(F0.01 = 7.17)
0.05
/%/
O
o
I
i
5
io
mg L~I
POC,
Fig. 3. Relationship between POC and chlorophyll a in lake water of Lake Kasumigaura during the third period of the spring bloom. Symbols and statistic explanation are as in Fig. 1.
standing stock of phytoplankters in the first pulse was observed about 4 days after the initiation of rapid phytoplankton multiplication. The bacteria, on the other hand, also multiplied rapidly to achieve in their highest level among the population densities observed during the spring bloom. Thereafter, their abundance tended to decrease as time elapsed. This prompt bacterial response corresponding with the rapid phytoplankton increase may be very favourable for stability in the natural balance, otherwise excess accumulation of organic matter in an aquatic ecosystem leads the system into disequilibrium (Seki & Nakano, 1981).
0.30
025
Actually the relative abundance of each component comprising the organic matter in lake water continued to stay in balance during the spring bloom. Phytoplankton, bacteria and detritus are major components comprising the particulate organic matter. The abundance of each components was approx. 30 when expressed on a relative scale based on 100 for the amount of dissolved organic matter. These relative values of organic components in lake water of Lake Kasumigaura during the spring bloom in 1980 are the same as those usually observed in the upper range of moderately eutrophic waters (Seki, 1982; Seki & Nakano, 1981). Thus this typical hypereutrophic lake during the spring bloom in 1980 shared common characteristics with moderately eutrophic waters from the viewpoint of biochemistry (Seki & Takahashi, 1983) in this study. The same conclusion may also be drawn from the viewpoint of taxonomy, i.e. the phytoplankters found in Lake Kasumigaura are also found commonly in moderately eutrophic waters (Hara et al., 1983; Mizuno, 1971). If eutrophic
020 IO0
0.15
"o c
& A
so
,1= u 0.10
OOA
O0
0
g
0
0,05
I 3
D0C,
1 5
o
P0C,
I IO
mgt -~
Fig. 4. Relationship between POC and chlorophyll a in lake water of Lake Kasumigaura during the fourth period of the spring bloom. Symbols and statistic explanation are as in Fig. 1.
I 4
t 5
m g t -r
Fig. 5. Organic carbon of each component of particulate matter as expressed on a relative scal.~ased on 100 for the amount of dissolved organic matter in lake water of Lake Kasumigaura during the first period of the spring bloom. Each symbol shows the component of particulate matter: O--phytoplankton; IS]--bacteria; /X--detritus. Vertical bar with each symbol on the left of the figures shows the average (site of each symbol) and the standard deviation (width of the bar).
45b
HUMllAKI, SEKI and AKIHtF() MASAKI I00
A
6
q9
6 AAA
50
,t
O0
~'
(~
A
aA
I
I
I
I
I
3
4
5
6
7
DO(;,
mgt - I
Fig. 6. Organic carbon of each component of particulate matter as expressed on a relative scale based on 100 for the amount of dissolved organic matter in lake water of Lake Kasumigaura during the second period of the spring bloom. Symbols are as in Fig. 5.
I00
c .~
'&
•
50
o o
I
I
0
Doe,
I
I
4
3
mgL
-I
5
6
Fig. 7. Organic carbon of each component of particulate matter as expressed on a relative scale based on 100 for the amount of dissolved organic matter in lake water of Lake Kasumigaura during the third period of the Spring bloom. Symbols are as in Fig. 5.
200
o 150 o A o
*o c
0o
fO0 AO0
o ne
A
0 g
o8
50
J_
0
~
t
0
O0 A ° o A ~.
a I
I
3
4
•
DOC,
o D
I
I
J
5
6
7
m g L- I
Fig. 8. Organic carbon of each component of particulate matter as expres,~d on a relative scale based on 100 for the amount of dissolved Organic matter in lake water of Lake Kasumigaura during the fourth period of the Spring bloom. Symbols are as in Fig. 5,
Spring bloom in Lake Kasumigaura--IlI
457
Table 1. Average value of each component comprising particulate organic matter as expressed on a relative scale based on 100 for the amount of dissolved organic material in lake water of Lake Kasumigaura Period
Phytoplankton
Bacteria
Detritus
16
21
35
28
27
27
28
25
29
26
18
28
46
19
32
Before the spring bloom (17 February-22 March) During the spring bloom 1st period (24 March-3 April) 2nd period (5 April-29 April) 3rd period (1 May-17 May) 4th period (19 May-6 June)
and hypereutrophic ecosystem are different, and if elements comprising each system function differently, such overlapping of common characteristics in both systems is not to be expected. The elements comprising the hypereutrophic system should remain in a steady-state oscillation within an upper part of the eutrophic system (detailed discussion in Seki, 1982). Thus the hypereutrophic system is not another energized state independent from other less eutrophied systems. Incidentally, Wetzel (1966) calls an extreme type of eutrophic equilibrium as hypereutrophic.
Acknowledgements--The authors wish to thank Drs T. R. Parsons and R. J. LeBrasseur for valuable comments. This work was partly supported by a special research project of the Ministry of Education of Japan (203012).
REFERENCES
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