FRONTIER RESEARCH ON EARTH EVOLUTION, VOL. 2
Turbidity variations seen at a sediment surface in meromictic Lake Kaiike, Japan
Kazumsa Oguri1, Saburo Sakai1, Hisami Suga1, Yoji Nakajima2¶, Yoshikazu Koizumi3*, Hisaya Kojima3,
Manabu Fukui3† and Hiroshi Kitazato1
1 Research
Program for Paleoenvironment and Earth System Evolution, Institute for Research on Earth Evolution (IFREE)
School of Earth and Planetary Sciences, Hokkaido University
3 Graduate School of Biology, Tokyo Metropolitan University
¶ Now at Asahi Glass Co. LTD.
*Now at Environmental Technology Center Co. LTD.
† Now at Institute for Low Temperature Science, Hokkaido University
2 Graduate
bar, and forms strong saline stratification in all the seasons. We
carried out water sampling and time-series observation of sediment surface at the deepest part of Lake Kaiike on March 12
through 14/ 2003.
1. Introduction
Observing sea bottom provides much information about sedimentological and benthic ecological features directly. In previous
studies, periscope camera was developed and used for the observation at sediment-water interface in situ [Rhoads, 1974, Rhoads
and Germano, 1982]. For time-series observation at sediment surface, long-term observation at north Atlantic abyssal plain had
conducted and it clearly illustrated the deposition processes of the
phytodetritus and the quick consumption by benthic activities
[Rice et al., 1994; Brian et al., 2003]. In JAMSTEC, sea floors
have been monitoring with deep-sea observatory [Momma et al.,
1994; Fujiwara et al., 1998] Despite of the advantage of direct
observation, such results have limited because of the difficulty of
constructing the camera system and the settings.
Although direct observations of sea floor provide impressive
insights, such observations have been limited for the ‘normal’
oceans where sea bottom is well oxidized by the dissolved O2 in
the water, and the observations in anoxic lake floor have not yet
reported. However, such applications can confirm sedimentary
processes of laminated sediments considered to the reflection of
the seasonal-annual environmental changes.
Recently, technologies of digital camera and Peripheral
Interface Controllers made it easy to build these instruments. In
this paper, we report our in situ time-series observation camera
newly designed and reveals with the results observed the bottom
of anoxic lake, Kaiike, Japan. This lake is known as the welldeveloped anoxic body and considered to the gateway of the past
anoxic ocean associated with the existence of the huge amount of
bacterial activity not only in the water column but also at the lake
bottom [Oguri et al., 2002]. The aim of this research is to obtain
sedimentological information to observe the anoxic lake bottom
directly in order to understand the processes of sedimentation and
the formation of such anoxic environments.
2.2 Lake water chemistry
Basic water profiles such as salinity, temperature and turbidity
were measured with a probe sensor (Quanta®, Hydrolab). Water
samples were subsequently collected with a convertible Niskin
sampler. The sampling interval was every 1m, except from 4 to 6
m where samples were collected every 50cm. Water samples were
used for both dissolved oxygen (DO), sulfate (SO42-) and sulfide
(Total S2-) measurements. The DO was measured with Winkler
titration [Winkler, 1888]. The SO42- was measured with HPLC
analysis, and the total S2- was measured with an improved method
based on Cline [1969].
2.3 Bottom water sampling
In order to collect bottom water near the lake bottom, short
core was collected using with an undisturbed short core sampler
(Rigosha). When core was recovered, lake water at the top part
was taken in the plastic bottle. The water sample was served to
HPLC analysis after bring back to the laboratory.
2.4 Time-series observations of the sediment surface
In order to observe sediment surface in situ, we developed a
time-series observation camera, OGURI (On-Going Undersea
Research Instruments) view system (Fig. 2). The main part of this
camera consisted of a digital camera (Coolpix4300, Nikon), a
handmade shutter release unit with a programmable timer circuit
module (PIC sequencer kit, TriState Technology) and a 6 volt
rechargeable battery (Poralac, Yuasa). They were installed in the
waterproof housing (Super VideoMarine, UN). These equipments
and two underwater lights (LX-25, Sea & Sea) were set in a handmade frame made with steel tubing coated with plastic skin
(Creform, Yazaki) respectively. To synchronize the shutter trigger and the lighting, modified timer circuits were embedded in
these lights. Before observation, both shutter and lighting timings
were programmed to 30 minutes interval. After being programmed, three timer modules were started at the same time.
Subsequently the housing caps were closed. The camera was sunk
slowly from the boat toward the lake bottom by hand. When the
rope was loosening, a float was knot on the edge of the rope. With
the setting, the camera was set above 15cm height from the surface sediment, and the area taken was 10.2×7.3cm. The pictures
2. Materials and methods
2.1 Observation site-Lake Kaiike
Lake Kaiike is part of the Koshiki-jima lake group in
Kamikoshiki Island, located in 30 km westward of Kagoshima
prefecture, Kyushu, Japan. The lake is in the northern part of the
island bounded to the north by the “Nagame no Hama” gravel bar.
The size of the lake is approximately 700×200m, and the deepest
water depth is 10.7 meters (Figure 1). The lake water shows
brackish influenced by infiltrating seawater through the gravel
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FRONTIER RESEARCH ON EARTH EVOLUTION, VOL. 2
automatically taken were stored as a JPEG file into the compact
flash memory in the digital camera, and the image size was
1680x1200 pixels. The time taken the photo, shutter speed and the
focal number were also recorded as a plain text file. These images
were transferred to the PC after recovery of the camera. The
observation was carried out from 12.24PM on Mar./13th through
11.53AM on Mar./14th, and 48 pictures were obtained during the
period.
To make clear the mechanism, we compared the tide level and the
turbidity intensity. Because Lake Kaiike is neighbored to the sea
and the other meromictic lake, Namakoike, saline water is transparent through the gravel bar and the channel between these lakes,
respectively. Therefore, small tide is seen [Kobe Marine
Observatory, 1934; Aramaki et al., 1976]. The lake tide is greatly
reduced (centimeter scale) and delayed for several hours than the
sea tide associated with the lower conductance at the gravel bar,
and a pressure from the seaside should be added through the gravel bar and the lake bottom when the sea surface is higher than the
lake surface when tide level is higher than the lake surface level.
Therefore, seawater may intrude into the lake and the S0 at the
sediment surface subsequently form the turbidity with the short
time fluctuation by the upward and the horizontal currents.
To confirm the hypothesis, we compared to the relationships
between tide and the turbidity. As there are no tide stations in
Kamikoshiki Island, we estimated the tide at “Nagame no Hama”
gravel bar to compare the data from previous study with those
obtained from the nearest tide station, Makurazaki (Fig. 1) recorded at the same time. Aramaki et al. [1976] recorded the tidal
change at the seaside of the gravel bar. To compare their results
and the tide information at Makurazaki, the tide observed at the
gravel bar is delayed one hour. Therefore, we regarded the tide at
the gravel bar as to delay one hour from Makurazaki.
To obtain the turbidity intensity, quantification of the turbidity
from the images should be required. We attempted image processing with a MATLAB for all the pictures. Because the color of the
turbidity is white, it reflects red, green and blue colors when turbidity was high. On the other hand, the lake bottom absorbs blue
color when turbidity was absent. That is, variant from the blue
color image extracted from the RGB image should be low in high
turbidity. As the same, mean grayscale intensity calculated from
the RGB image tends to be high in high turbidity. Based on these
principles, we calculated “apparent turbidity index” by dividing
mean grayscale intensity by variant of the blue color image.
Figure 5 shows the relationships between apparent turbidity
index and the tide. The turbidity fluctuated in a short time, suggesting an existence of the horizontal current. During the observation, high turbidities were appeared in both high (from 12:00 to
18:30 on 13th and from 2:30 to 9:30 on 14th) and low tide (from
21:00 to 23:00 on 13th) periods. These results, especially high turbidity in a low tide period suggest that the long time variation of
the turbidity was driven not only by tide but also by another physical mechanism. A possibility adding to the pressure to the lake
bottom in such period is a groundwater. Aramaki et al. [1976]
mentioned the relationships between salinity and the level of the
lake water surface at Lake Kaiike and Lake Namakoike. They
concluded that Lake Kaiike is under affection of both seawater
and the groundwater. Koizumi et al. [2004] reported that the concentrations of SO42-, sulfide and S0 in the sediment were varied
during the time. This implies that upward/downward currents
would be occurred by the contributions of the seawater and the
groundwater at the lake bottom, and they may enhance/reduce the
bottom turbidity at the sediment surface. Figure 6 shows a
schematic model of the occurrence of the turbidity. When high
tide period, upward current is made by the contribution from the
seawater, and the groundwater contributes in the low tide period.
Turbidity is decreased when the balance of each water pressure is
in equilibrium, when turbidity was minimum. This model is proposed from tide and the image processing from the time series
3. Results and discussions
3.1 Lake water chemistry
Chemical profiles on 2003/Mar./12th are shown in Figure 3.
Temperature was ranged from 11 to 22 °C, but it greatly increased
from 3.0 to 4.5m. As well, both salinity and SO42- was greatly
increased between 2.5 to 3 m, indicating strong seawater contribution and forming the density stratification of the lake water.
During 4.5 to 5.0m, O2-total S2- boundary was seen. In this boundary, higher turbidity indicating large assemblages of purple sulfur
bacteria, Chromatium sp. was also observed [Oguri et al., 2002;
Nakajima et al., 2003]. These results indicate that the lake environment is meromictic, and both anoxic characteristics and the
sulfur cycle play significant roles on the ecological features like
previously reported meromictic lake such as Jellyfish Lake, Palau
Island [Burnett et al., 1989].
3.2 Characteristics of the lake bottom
Figure 4 shows the lake bottom pictures taken on
2003/Mar./12th by the OGURI view system, that can be considered to typical situation of the lake bottom. According to the pictures, a network structure was developed at the sediment surface.
The network seems to be an aggregation of marine snow consisted
of Chromatium sp. from the water column, as to see the timeseries observation at the lake bottom (Figures 4a~4c). The filamentous marine snow settled to the bottom was trapped to the bottom surface, and formed a part of the network. Throughout the
observation, an existence of white-colored turbidity was found,
and the intensity of the turbidity was fluctuated during the time
(Figures 4c and 4d). The white turbidity was also seen in the bottom water just above surface sediment in undisturbed short core
sampler. And the particles of the turbidity consisted of elemental
sulfur, S0 (result from HPLC analysis). Although the origin of the
turbidity is not known, two pathways can be considered to supply
S0 to the lake bottom. The first source is supplied by purple sulfur
bacteria Chromatium sp. living in the O 2- total S 2- boundary
[Matsuyama and Shiromizu, 1978]. Below O2- total S2- boundary,
filamentous marine snows aggregated with Chromatium sp. were
observed [Oguri et al., 2002]. Because Chromatium sp. oxidizes
H2S into S0 and store the S0 particles in the cell [Matsuyama and
Shiromizu, 1978], the marine snows would be a significant source
of the S0. The second source is an in situ production by sulfur oxidation bacteria. Koizumi et al.[2004] described the epsilonProteobacteria including sulfur oxidation group from the surface
lake sediment, which are possible to oxidize H2S into S0 using
with some electron acceptors.
3.3 A development mechanism of the turbidity
As mentioned, we found a turbidity fluctuation at the lake bottom and proposed the possibilities of the origin of the turbid particles. However, physical process driving that turbidity is unknown.
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FRONTIER RESEARCH ON EARTH EVOLUTION, VOL. 2
photographs at the lake bottom, however, it would be necessary to
observe the three dimensional current at the lake bottom or a
numerical simulation to support the model.
cal gradients. Environmental Microbiology, 6, 6, 622-637, 2004.
Matsuyama, M. and E. Shiromizu, Importance of photosynthetic sulfur bacteria, Chromatium sp. as an organic matter producer in
Lake Kaiike, Japanese Journal of the Limnology, 39, 3, 103-111
1978.
Matsuyama, M., Disturbance of Chromatium population at mid-depth
of lake Kaiike, Microbes and Environments, 17, 3, 134-138, 2002.
Momma, H., K. Mitsuzawa, Y. Kaiho, and H. Hotta. Long term and
real time observation on the deep sea floor off Hatsushima Island
in Sagami Bay. JAMSTEC Journal of Deep-Sea Research, 10,
363-371. 1994.
Nakajima, Y., H. Okada, K. Oguri, H. Suga, H. Kitazato, Y. Koizumi,
M. Fukui and N. Ohkouchi. Distribution of chloropigments in suspended particle matter and benthic microbial mat of a meromicitc
lake, Lake Kaiike, Japan. Environmental Microbiology, 5, 11031110, 2003.
Oguri, K., M. Itou, Hirano, T. Hisamitsu, S. Sakai, M. Murayama, H.
Kitazato, Y. Koizumi, M. Fukui and A. Taira, Toward the understanding on anoxic ocean: environment and characteristics of
water and sediments of bacterial activity of the Lake Kaiike,
Kamikoshiki Island, Kagoshima Prefecture, The Journal of the
Geological Society of Japan, 108, 12, 2002.
Rice, A. L., M. H. Thurston, and B. J. Bett. The IOSDL DEEPSEAS
programme: introduction and photographic evidence for the presence and absence of a seasonal input of phytodetritus at contrasting abyssal sites in the northeastern Atlantic. Deep-Sea Research I,
41, 9, 1305-1320, 1994.
Rhoads, D.C. Organism-sediment relations on the muddy sea floor.
Marine Biology Annual Review. 12, 263-300, 1974.
Rhoads. D.C., and J.D. Germano. Characterization of organism-sediment relations using sediment profile imaging: an efficient method
of remote ecological monitoring of the seafloor (REMOTS
System). Marine Ecological Progress Series, 8, 115-128, 1982.
Winkler, L. W., Die Bestimmung des im Wasser gelösten
Sauerstoffes, Berichte der Deutschen Chemischen Gesellschaft,
21, 2843-2855, 1888.
4. Summary
We made the observation at the deepest part of the Lake Kaiike
on 2003/Mar. with water sampling, core collection and time-series
observation at the lake bottom using OGURI view system.
Throughout the observation, we found three aspects for the lake:
(1) The lake water was strongly stratified influenced by the seawater, and the lake environments showed meromictic. From 4.5 to
5.0 m, the O2-total S2- boundary was observed. At the depth, high
turbidity consisting of purple sulfur bacteria, Chromatim sp. was
confirmed. (2) At the lake bottom, we found the network structure. It seems to consist of the aggregations of Chromatium sp.
from the O2-total S2- boundary. Moreover, white turbidity consisting of S0 particle at the lake bottom of the lake Kaiike. The origin
of the S0 was considered to the two sources: from the marine snow
consisted of bacterium Chromatium sp. living in the O2-sulfide
boundary and in situ production by sulfur oxidation bacteria. (3)
The intensity of the turbidity fluctuated during the time. Short
time variation is possible to be a reflection of the horizontal current at the lake bottom, and it enhanced by the upward current
from the sediment surface. Such current may possible to be generated by water pressure driven by the seawater and the groundwater, respectively, and the contributions of these water sources were
depended on each water level.
Acknowledgements. We are deeply grateful to Mr. Yasuhiko
Morio, Sadao Higashi and all the members of the planning department
of Kamikoshiki village (Now Satsuma-Sendai city). This study is
sponsored by promoting fund for frontier research, JAMSTEC and
Grant-in-Aid for Scientific Research: 16740290, Japanese Society for
the Promotion of Science
References
Aramaki, M., M. Yamaguchi and Y. Tanaka, A geomorphological and
hydrological study on lagoons of Kamikoshiki island, Japan,
Senshu-Shizenkagaku-Kiyo, 9, 1-80, 1976.
Bett, B. J., M. G. Malzone, B. E. Narayanaswamy, and B. D. Wigham.
Temporal variability in phytodetritus and megabenthic activity at
the seabed in the deep Northeast Atlantic. Progress in
Oceanography, 50, 349-368, 2001.
Burnett, W. C., Landing, W. M., Lynos, W. B. and Orem, W. Jellyfish
Lake, Palau A model anoxic environment for geochemical studies,
Eos Trans., AGU, 70, 33, 777-778, 783, 1989.
Cline, J. D., Spectrophotometric determination of hydrogen sulfide in
natural water, Limnology and Oceanography, 14, 454-458, 1969.
Fujiwara et al., In situ spawning of a deep-sea vesicomyid clam:
Evidence for an environmental cue. Deep-Sea Research I, 45,
1881-1889, 1998.
Kobe Marine Observatory, The Reports of the limnological observations in the Koshiki-zima lake group in June and July 1934, Kaiyo
Jiho, 8, 2, 163-199, 1935.
Koizumi. Y., H. Kojima, K. Oguri, H. Kitazato and M. Fukui. Vertical
and temporal shifts in microbial communities in the water column
and sediment of saline meromictic Lake Kaiike (Japan), as determined by 16S rDNA-based analysis, and related to physicochemi-
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FRONTIER RESEARCH ON EARTH EVOLUTION, VOL. 2
Figure 1. Location of the Lake Kaiike: (a) Lake Kaiike is in the Kamikoshiki Island where located in the 30 km westward from the Kyushu Island, Japan. Makurazaki in the map is the nearest tide station from the Kamikoshiki Island.
(b) The lake located in the northern part of the island, and is isolated from the sea by “Nagame no Hama” gravel bar.
(c) The size of the lake is ca. 700x200m, and the water depth at the deepest part is 10.7m.
Figure 2. Schematic drawing of the time-series observation camera: (a) frame, (b) light, (c) shutter release unit, (d) digital camera, (e) water resistant housing, (f) scale, (g) battery, (h) sequencer circuit, and (i) handling rope.
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FRONTIER RESEARCH ON EARTH EVOLUTION, VOL. 2
Figure 3. Chemical properties in the lake water observed on 2003/Mar./12th: SO42- (open diamond),
salinity (black circle), temperature (open cross), total S2- (open circle), DO (open box with dot), and turbidity (black box).
Figure 4. Photographs of the lake bottom taken by OGURI view system: (a) image taken at 17:54 on
2003/Mar./13th. Network structure was developed at the bottom. The image is just recorded that the filamentous marine snow (shown in the red circle) was settling. (b) image taken at 18:24. Marine snow was settled
and was fixed to the bottom. (c) image taken at 20:54. Fixed marine snow was assimilating to the network
structure. (d) image taken at 3:24 on Mar./14th. White turbidity was developed upon the lake bottom. To compare with another pictures (a~c), we can identify that the intensity of the turbidity was fluctuating during the
time. Scale bars in the each image represent 1 cm, respectively.
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FRONTIER RESEARCH ON EARTH EVOLUTION, VOL. 2
Figure 5. Relationship between tidal level (closed diamond) and apparent turbidity index (closed circle).
Tidal level data was used to subtract one hour observed at Makurazaki tide station (see text). Apparent turbidity index was calculated from dividing the grayscale intensity by the variant of blue color intensity.
Figure 6. Three source model to explain upward current at the lake bottom. When tide was higher than the
lake surface, upward current occurred by the pressure from the sea. When both tide and the lake surface
lower than the groundwater level, upward current was driven by the groundwater input. The turbidity was
low when the balance was in equilibrium.
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