ACG33-01

Room:202

Time:May 26 09:00-09:18

Iron and spring water which have been ignored in material cycles in coastal marine
ecosystems
YAMAMOTO, Tamiji1∗
1

Grad Sch Biosph Sci, Hiroshima Univ.

Material cycles in coastal areas can be calculated by freshwater and salinity budgets using a standardized method proposed by
LOICZ (Land-Ocean Interaction in the Coastal Zones) Working Group if the targetted area is estuaries with an obvious salinity
gradient. In the manual, material loads from spring water can be ignored in case no data are available. However, it is assumed
that bottom spring water contains higher concentration of dissolved matter particularly minerals than that of river water, because
it passes through the underground lithosphere. Eventhough the water volume is smaller than that of river water, it may contribute
greatly to the material budget in coastal areas.
In enclosed coastal seas of Japan, the number of red tide occurrence has been decreased and the transparency has also significantly been increased by reduction measures of material loads from land. There are several areas in which the growth of fish andother organisms is depressed by nutrient depletion, which is called ”oligotrophication”.
Unexpectedly, the anoxic water mass is still formed in the bottom layer of coastal areas whereas the material loads was reduced.
This evidenced that the anoxic water mass may be formed not only by decomposition of organic matter but also by chemical
oxidation of hydrogen sulfide. This also suggests that depletion of iron which is an essential element for the growth of algae.
The author recently determined the concentration of dissolved iron from the upper area of the Ohta River which flowing into
Hiroshima Bay to lower river and seawater of the bay. Iron and nutrient concentrations in a spring in the bay were also investigated. The author hopes the presentation would be a hook to promote material cycle study of coastal seas.
Keywords: nutrient, material cycle, iron, spring

1/1

ACG33-02

Room:202

Time:May 26 09:18-09:36

Estimation of distribution and discharge flux of submarine groundwater using Rn-222 in
the Yatsushiro Bay
HOSONO, Takahiro1∗ ; NIKPEYMAN, Yaser2 ; ONO, Masahiko3 ; YANG, Heejun2 ; SHIMADA, Jun2 ;TAKIKAWA, Kiyoshi4
1

Priority Organization for Innovation and Excellence, Kumamoto University, 2 Department of Earth Sciences, GSST, Kumamoto
University, 3 The National Institute of Advanced Industrial Science and Technology, 4 Center for Marine Environment Studies,
Kumamoto University
Continuous Rn-222 monitoring method has been developed around a decade ago, and with this method, evaluation of spatial
distribution and flux of submarine groundwater discharge (SGD) in/along ocean coastal bay/line is becoming popular worldwide.
In this presentation, we will introduce a case study in Yatsushiro Bay, describing distribution and flux properties of SGD, deduced
by Rn-222 data collected during recent four years. We try to show and confirm the merit and limit of Rn-222 monitoring method
and propose a new approach to solve several potential problems on Rn-222 study.
Yatsushiro Bay is one of the largest inland sea in Japan, surrounded by Kyushu mainland to the east and Amakusa Islands tothe west. Its total area is around 1,200 km2 with a total coastal line of around 220 km. The hinterland of this bay is composedof watersheds with various topographic and geological features. Therefore, Yatsushiro Bay should provide an ideal setting tounderstand the factors, i.e., watershed area, topographical gradient, presence of tidal flat, geological constituent materials andgeological structure, controlling SGD distribution properties in wide scale coastal sea area. By summarizing these features, we
can confirm interesting SGD distributing natures in coastal environments.
After analyzing Rn-222 samples of 61 flowing rivers into Yatsushiro Bay, we realized that river waters contain considerable Rn222, which value cannot be ignored when interpreting Rn-222 signal in the sea. In order to evaluate the effect of river-originatedRn-222 in the coastal sea water, we developed sea water Rn-222 distribution model within whole Yatsushiro Sea, based on apreviously constructed ocean currency simulation model. The net SGD-originated Rn-222 concentrations were estimated bysubtracting simulated river-originated Rn-222 concentrations from the observed towing Rn-222 monitoring data.
A total SGD flux within the Yatsushiro Bay was evaluated following traditional box model concept, by multiplying advection
rate deduced from continuous Rn-222 monitoring results at mooring survey sites, and SGD patch area estimated by Rn-222
towing survey results. Consequently, it was concluded that 15% of the total water transported toward the Yatsushiro Sea fromthe land is SGD origin. Furthermore, we tried to understand the possible components contributing to Yatsushiro coastal water,
FSGD, RSGD, river water, and sea water, with their contribution degree quantitatively. Our analysis also suggested interesting
aspect that wind velocity on the coastal sea surface would be an important triggering factor of SGD.
As a result of our study, it was suggested within the Yatsushiro Sea that Rn-222 concentration could not play as a direct tracer
of groundwater because the Rn-222 in the coastal sea water can be partially derived from rivers flowing into the bay. Althoughprevious studies have not taken this effect into account in interpreting sea water Rn-222 observation results, our findings, and oursolution idea, would be essential to be incorporated in a future study in an area of similar climate and topographical condition likeYatsushiro area. With this topic, we will propose distribution property, estimated flux, and discharging mechanism of submarine
groundwater comprehended by a recent Rn-222 study in the Yatsushiro Sea.

Keywords: SGD, Rn-222, simulation, tidal flat, discharge rate, distribution

1/1

ACG33-03

Room:202

Time:May 26 09:36-09:51

Analyses of submarine groundwater discharge based on Radon-222 concentrations of thecoastal water in JapanTANIGUCHI, Makoto1∗ ; HONDA, Hisami1 ; ONO, Masahiko2 ; HOSONO, Takahiro3 ; UMEZAWA, Yu4 ;SUGIMOTO, Ryo5 ; YAMADA, Makoto1
1

Research Institute for Humanity and Nature, 2 National Institute of Advanced Industrial Science and Technology, 3 Kumamoto
University, 4 Nagasaki University, 5 Fukui Prefectural University
Radon-222 is one of the useful tracers for evaluating submarine groundwater discharge (SGD), because the groundwater has
extremely high concentration in 222Rn compared with surface water. In this study, we attempted to compile and compare radon
data observed in ten study areas in Japan, with SGD observed by seepage meters as well as local environmental parameterssuch as precipitation, gradient, permeability, basin area, tidal range, and others. We used geographical information system (GIS)
and digital elevation model (DEM) to evaluate the characteristics of the basin. The highest 222Rn concentrations was recorded
in Yuza (Northwestern Tohoku area) in Japan, where the highest SGD by seepage meter was observed. 222Rn concentrations
increases with precipitation within the study areas of four bays in Yuza and four bays in Otsuchi. Multivariable analyses ofdriving factors of submarine groundwater discharge were performed in the ten study areas.

Keywords: submarine groundwater discharge, Radon, coastal groundwater

1/1

ACG33-04

Room:202

Time:May 26 09:51-10:06

The origin of submarine groundwater discharge in the coastal zone of Hiji, Oita prefecture
YAMADA, Makoto1∗ ; OHSAWA, Shinji2 ; MISHIMA, Taketoshi2 ; SHOJI, Jun3 ; TANIGUCHI, Makoto1
1

Research Institute for Humanity and Nature, 2 BGRL, Institute for Geothermal Sciences, Kyoto University, 3 Hiroshima University
It is believed that groundwater discharges from the seabed of the coastal zone of Hiji, Oita prefecture. The marbled sole which
lives around this submarine groundwater discharge (SGD) is called the ”Shirosita Karei”, and is held in high regard by the local
community. From ancient times, local people have believed that this Shirosita Karei grows because of SGD. However, the ecological link between marbled sole and SGD has not been well established. Moreover, although it is clear that there is SGD in thearea, there is almost no information about the origin and dissolved components of the SGD. In this study, we directly collected
SGD and analyzed its chemical composition and water stable isotopes. Additionally, we analyzed the chemical composition andwater stable isotopes of the inland cold spring water. We considered the origin of the SGD by comparing the result of the SGD
analysis and the inland cold spring analysis. Since we expected that the temperature of SGD would be different than seawater,
we used a thermometer for the identification of the discharge location. We inserted a stainless steel pipe in the identified locationand collected SGD water. The sodium concentration from the collected SGD water was 12.1 mg/l, indicating fresh water. The
isotopic composition of the SGD water resembled that of the inland cold spring water. The recharge area of the inland cold springwater is at an elevation of 200 m or more. These results suggest that the SGD water comes from an elevation of 200 m or more.
It indicates that the origin of SGD is water recharged in the forest area of the mountain slope, and that the water moves under theplain and is discharged at the seabed.
Keywords: Submarine groundwater discharge, Stable isotope, recharge area, Hiji

1/1

ACG33-05

Room:202

Time:May 26 10:06-10:21

Submarine groundwater discharge and nutrients state of around coastal seawater
HONDA, Hisami1∗ ; OHSAWA, Shinji2 ; SUGIMOTO, Ryo3 ; HEN, Teki2 ; MISHIMA, Taketoshi2 ;YAMADA, Makoto1 ; SHOJI, Jun4 ; TANIGUCHI, Makoto1
1

Research Institute for Humanity and Nature, 2 Kyoto University, 3 Fukui Prefectural University, 4 Hiroshima University

In recent years, the importance of nutrient input to the coastal seawater through submarine groundwater discharge (SGD)
has been pointed out in several studies. The coastal area of Hiji town in Oita Prefecture, it is known that there is a submarine
groundwater discharge. However, the effects of SGD-derived nutrients has not yet been clarified in this area. Therefore, weinvestigated the spatial distribution of SGD using radon-222 isotope as a groundwater tracer and assessed the impact on the
nutrient (DIN and DIP) concentrations of surrounding seawater. In May 26-30, 2014, we monitored 222 Rn and nutrients along
the coast of Hiji. In addition, we collected the spring water on the land and the spring water of a salt water mixture discharged on
the coast. As a results, 222 Rn concentrations was clearly highest on SGD point. Nutrients concentrations around the SGD point
were higher DIP concentrations than elsewhere and the N/P ratios lower than the Redfield ratio. These results imply that SGD ismain source of DIP in coastal area of Hiji.
Keywords: Submarine groundwater discharge, 222Rn, Nutrients, Primary production

1/1

ACG33-06

Room:202

Time:May 26 10:21-10:36

The influence of groundwater discharge on primary production in a shallow coastal sea,
Obama bay,Japan
KOBAYASHI, Shiho1∗ ; SUGIMOTO, Ryo2 ; MIYATA, Youji1 ; HONDA, Hisami3 ; YAMADA, Makoto3 ;TOMINAGA, Osamu2 ; TAHARA, Daisuke2 ; SHOJI, Jun4 ; TANIGUCHI, Makoto3
1

Kyoto University, 2 Fukui Prefectural University, 3 Research Institute for Humanity and Nature, 4 Hiroshima University

Submarine groundwater discharge (SGD) often influences on biogeochemical properties in coastal seas. We observed spatial
and temporal variations in SGD using 222 Rn and seepage meter along the shoreline of Obama bay, Japan. The results showed
SGD exists even in the shallow sea adjacent to the small water catchment area (˜1 km2 ), where the range of the tide is relatively
small (10 ˜30 cm). The spatial and temporal variations in chlorophyll observed at the same time suggest that the SGD influenceson primary production.
Keywords: land-ocean interaction, submarine groundwater discharge, costal ecosystem, primary production

1/1

ACG33-07

Room:202

Time:May 26 11:00-11:15

Location estimation of submarine groundwater discharge from Mt. Fuji in Suruga Bay(II)
MURANAKA, Yasuhide1∗ ; KAMITANI, Takafumi1 ; ITO, Akira1 ; OHYAMA, Koichi1 ; WATANABE, Masayuki2 ;ONO, Masahiko3 ; MARUI, Atsunao3
1

Shizuoka Institute of Environment and Hygiene, 2 Industrial Research Institute of Shizuoka Prefecture, 3 National Institute ofAdvanced Industrial Science and Technology
Around the foot of Mt. Fuji, the main flow passages of groundwater are thought to be in the Younger Fuji volcano, which
consists of the pervious basaltic lavas in new volcanic stage. Especially, the Fujikawa-kako fault zone, which stretches south
to north in the southwestern side of Mt. Fuji, has a potentially effect on the local groundwater flow system into Suruga Bay.
Therefore, precipitation at Mt. Fuji have been considered to be discharging partly from seabed in Suruga Bay and making a great
impact on the biological production at the coastal sea area.
For the purpose of contribution to make sense of the rich coastal ecosystem in Suruga Bay, we conducted a survey for submarine
groundwater discharge (SGD) in Oku-Suruga Bay: from the mouth of the Fuji River, at which the fault is found, to Tagonoura,
where the lavas of the Younger Fuji volcano are distributed from 100 to 200 m below sea level. We are trying to estimate somelocations of SGD from bottom topography, condition of seabed and geological structure by using multibeam sonar, side scansonar and sub-bottom profiler, respectively. We also use a remotely operated vehicle (ROV) for photographing for the image ofthe extrapolated spring points. In this presentation, we introduce our works noted above.

Keywords: submarine groundwater discharge (SGD), Mt. Fuji, multibeam sonar, side scan sonar, sub-bottom profiler, remotely
operated vehicle (ROV)

1/1

ACG33-08

Room:202

Time:May 26 11:15-11:30

Effects of submarine groundwater discharge on coastal fishery production: emphasizing
on fish community
SHOJI, Jun1∗ ; SUGIMOTO, Ryo2 ; HONDA, Hisami3 ; TOMINAGA, Osamu2 ; KOBAYASHI, Shiho4 ;YAMADA, Makoto3 ; TANIGUCHI, Makoto3
1

Hiroshima University, 2 Fukui Prefectural University, 3 RIHN, 4 Kyoto University

Biotic and abiotic surveys were conducted at four sites in Japan, where submarine groundwater discharge has been confirmed.
In order to evaluate the contribution of nutritional input from the terrestrial ecosystems to production of fishery resources incoastal areas, sampling for fish and their prey organisms were conducted. Number of fish species, fish abundance and biomass
were compared between areas of different levels of Radon concentration at each site.

Keywords: coast, water-food NEXUS, Fishery resources, biodiversity, submarine ground water, biological production

1/1

ACG33-09

Room:202

Time:May 26 11:30-11:45

The evaluation of the effectiveness of the d13C signature in bivalve shells as proxy forenvironment of SGD
TOMINAGA, Osamu1∗ ; HORIBE, Nanami1 ; NISHI, Saori1 ; SUGIMOTO, Ryo1 ; YAMADA, Makoto2 ; SHOJI, Jun3 ;HONDA, Hisami2 ; KOBAYASHI, Shiho4 ; TANIGUCHI, Makoto2
1

Fukui Prefectural University, 2 Research Institute for Humanity and Nature, 3 Hiroshima University, 4 Kyoto University

Submarine groundwater discharge (SGD) is often characterized by high concentration of nutrients and documented as an important pathway between land and sea contributing to the biological productivity in coastal waters. However, to our knowledge,
no scientific information about the relationship between environmental conditions of SGD and the extent of biological productivity of the primary consumers is available. The carbon stable isotope composition of dissolved inorganic carbon (δ 13 C{DIC})
is generally different between SGD (low δ 13 CDIC ) and sea water (high δ 13 CDIC ). Bivalves record chemical and biologicalenvironment-signal in their shell. In this study, to examine whether the δ 13 C of bivalve shell (δ 13 CSHELL ) reflect the δ 13 CDICof the ambient water or not, we conducted the rearing experiments of Manila clam Ruditapes philippinarum under laboratory
and field conditions. Manila clam was reared at three different salinity in the laboratory; 100% sea water (100 % SW), 80%
sea water + 20% underground water (80 % SW) and 60 % sea water + 40% underground water (60 % SW). Water temperatureof three salinity groups was maintained at 25 ℃ and the same amount of diet (Chaetoceros gracillis ) was fed every day duringexperiments (3 months). There was a high positive correlation between δ 13 CDIC and salinity (r2 = 0.997, n = 32, p <0.001). Although the significant difference among 100 % SW, 80 % SW and 60% SW was not found (ANOVA, p >0.05), the δ 13 CSHELLof 80 % SW and 60 % SW was tend to be lower than that of 100 % SW. The field experiment was carried out at 6 sites under
different SGD condition in Obama Bay, Japan from July to August 2013. Manila clam was reared in the small containers withbottom sand, which were kept at the depth of 2 m under natural condition. There was a high negative linear relation between
δ 13 CSHELL and Radon 222 (222 Rn) concentration at surface layer of each rearing site ,which is a useful tracer of SGD (r2 =0.920, n = 6, p<0.01). Thus, it seems that the δ 13 CSHELL shows some possibility of being proxy for environmental reconstitutions of submarine groundwater discharge. However, the value of the δ 13 CSHELL was lower by about 5 ‰ than that of theδ 13 CDIC of ambient water in the laboratory experiment. It was the possible reason that isotopically light metabolic carbon,
derived from food, is incorporated into shell carbonated.
Keywords: Dissolved inorganic carbon, metabolic carbon, bivalve shell, carbon stable isotope ratio, submarine groundwater
discharge

1/1

ACG33-10

Room:202

Time:May 26 11:45-12:00

The application of regional groundwater flow model to the underground dam in the ryukyu
limestone aquifer
ABE, Masami1∗ ; HATA, Kyoko1 ; YASUMOTO, Jun2 ; NAKANO, Takuzi2
1

IDEA Consultants, Inc., 2 Ryukyu University

The underground dam was construction in the Ryukyu limestone aquifer and groundwater is used to agricultural water. Water
quality change of groundwater and that affect to sea water quality through submarine groundwater discharge to be expected due
to agricultural use.
Groundwater model for understanding and predicting hydraulics and contaminant transport in aquifer make assumptions about
the distribution and hydraulic properties of geologic features that may not always apply to karst aquifers. In this study, afinite difference groundwater model (MODFLOW-NWT) was applied to construct an equivalent single layer two-dimensional
mathematical model of the Ryukyu limestone aquifer, which is located a southern part of Okinawa main islands. In orderto handle problems at regional scale groundwater model in the aquifer, automated parameter estimation method (PEST) andcoupling the conduit flow process was used in this model. Groundwater level measurements collected in 1994 were used tocalibrate a steady state model of the study area. This study shows the ability of MODFLOW-NWT and PEST to simulate
regional groundwater flow in highly karstified aquifer such as Ryukyu limestone aquifer, which is important for water resource
and groundwater management in the area.
Keywords: Underground dam, groundwater flow, conduit flow, PEST, submarine water discharge

1/1ACG33-11

Room:202

Time:May 26 12:00-12:15

Analysis about the condition of sea water intrusion to Yodo River estuary by the fluid
model
NAKAMURA, Ippei1∗ ; KOYAMA, Yuto1 ; NAKADA, Satoshi1 ; HAYASHI, Mitsuru1
1

Kobe University

Red tide of Alexandrium tamarense occurred in Yodo River estuary in recent years. A. tamarense is marine phytoplankton
and causes shellfish poisoning. Sea water intrusion to Yodo River is one of the reasons of marine phytoplankton survive. We
investigated the distribution of the sea water intrusion by in-situ observation, then reproduced it by the fluid model. Fluid
structure of Yodo River estuary consists by the runoff of fresh water, the esturey circulation, the tidal current and the wind driven
circulation. These had contributed at almost same rate to sea water ascension.

Keywords: Yodo River, sea water intrusion, Red tide, shellfish poison, fluid model

1/1

ACG33-12

Room:202

Time:May 26 12:15-12:30

Diurnal variation of pH in Oshoro Bay, Hokkaido: A monitoring study assessing andprojecting impacts of ocean acidific
TAKAO, Shintaro1 ; FUJII, Masahiko1∗
1

Faculty of Environmental Earth Science, Hokkaido University

Coastal marine species have already been experiencing a low pH environment (<7.9) that is not predicted until 2100 in open
oceans in a high CO2 world. To properly assess impacts of ocean acidification on them inhabiting wide ranges of diurnal variationof pH, we need to conduct long-term and high-frequency monitoring measurements of environmental parameters. In this study,
to investigate the diurnal variation of pH in subarctic region, which is less known than tropical and subtropical regions, we
conducted monitoring measurements of pH, seawater temperature, and salinity in Oshoro Bay, Hokkaido from 2013 to 2014.
Mean, maximum, and minimum pH values obtained by a pH meter were 8.02, 8.47, and 7.33, respectively. Although ranges ofdiurnal variation of pH were different with season, increases in pH during the day and decreases during the night were foundin all periods. There are no statistically significant relationships between the variation of pH and that of seawater temperatureor salinity except in some cases. These results suggest that observed diurnal variations of pH may be driven by photosynthesis
and/or respiration in resident organisms in Oshoro Bay.
Keywords: subarctic region, ocean acidification, coastal ecosystem, diurnal variation

1/1

ACG33-13

Room:202

Time:May 26 12:30-12:45

Ongoing stress of transboundary pollution: Assessment of atmospheric N deposition influence by means of nitrate isotopes
SUGIMOTO, Ryo1∗ ; NEGISHI, Kouki1 ; ASAI, Kazuyoshi2 ; MIYASHITA, Yuji3 ; TAHARA, Daisuke1
1

Fukui Prefectural University, 2 Geo Science Laboratory, 3 Hot Springs Research Institute of Kanagawa Prefecture

Anthropogenic emissions of reactive nitrogen (N) due to fossil fuel combustion and modern agriculture practices have dramatically increased in global scale. In the Japanese watershed along the Sea of Japan, large amounts of reactive N emitted
from northeastern Asia have deposited onto forest ecosystems, and thus N concentrations in rivers and groundwaters have been
increased year to year. Remotely modified N concentrations of terrestrial waters in local watersheds would affect coastal ecosystems. However, quantitative influence of N deposition on the watershed along the Sea of Japan is still unclear. In this study, we
assessed the influence of atmospheric reactive N deposition on the watershed in Wakasa Bay by means of the 17 O anomaly (⊿17O) in nitrate, which is an alternative tracer for atmospheric nitrate (NO3 − atm ). As a result, fractions of NO3 − atm in stream
waters of the Kita River observed in 2014 changed from >10% in winter to 6% in summer. This seasonal variation corresponded
to monthly changes in reactive N (= NO3 − , NH4 + and others) deposition rates onto the watershed. However, most of NO3 − instream water was derived from remineralized NO3 − by nitrification (NO3 − re ) within the watershed. Apparent nitrification rates
estimated by ⊿ 17 O were significantly higher than total N deposition rates. Although fractions of NO3 − atm in groundwater andspring water (mean±SD = 4.3±0.3%), which was dated from 2001 to 2009 by SF6 , were significantly lower than that in stream
water, yearly variation in NO3 − atm fractions showed exponential increasing trend in the recent decade. These results imply that
atmospheric reactive N deposition would affect severe influence on not only the forest ecosystem but also the coastal ecosystems.
Keywords: transboundary pollution, atmospheric nitrogen deposition, triple oxygen isotope, nitrogen saturation, retrospective
analysis, Sea of Japan

1/1

ACG33-P01

Room:Convention Hall

Time:May 26 18:15-19:30

Primary production in the eastern part of the Seto Inland Sea
ANBUTSU, Kaori1∗ ; ICHIMI, Kazuhiko2 ; YAMAGUCHI, Hitomi3 ; OMI, Hiroiaki4 ; AKIYAMA, Satoshi4 ;MIYAHARA, Kazutaka5 ; YAMAMOTO, Masayuki6 ; KASAI, Akihide7
1

CoHHO Eucational Unit, Kyoto Univ, 2 Seto Inland Sea Regional Res Cntr, Kagawa Univ, 3 Faculty of Agriculture, Kagawa
Univ, 4 Res Ins Env Agr Fish, Osaka Pref, 5 Hyogo Fish Technol Inst, 6 Kagawa Pref Fish Exp Stn, 7 FSERC, Kyoto Univ
In the 1970’s and 80’s, the Seto Inland Sea was affected by eutrophication. Since the 1980’s anthropogenic nutrient loads fromrivers have been reduced and subsequently the occurrence of environmental problems has decreased. However, new problems
such as reduced fishery yields and nutrient deficiencies for seaweed culture have occurred. This implies a change in the ecosystem
structure from the 1970’s to the present. Primary production in the Seto Inland Sea was extensively surveyed during the 1960’s- 90’s, but recently information is more limited. In this study, we investigated primary production in the eastern part of the Seto
Inland Sea and compared the results with those in the 1980’s and 90’s.
We measured primary production at 7 stations in Osaka Bay (2), Harima Nada (2), Bisan Seto (2), Hiuchi Nada (1). Water
samples were taken from five different depths, corresponding to 100, 48, 33, 14, 8.3% photon fluxes. The water samples werethen transferred into replicate 1-L polycarbonate bottles in the laboratory. After the addition of NaH13 CO3 , the samples wereincubated for 2 hours in a Plant Growth Chamber. The incubations were conducted at in situ temperature under the corresponding
light intensity regulated using filters. Photosynthetic rate at each depth was calculated according to the 13 C methods of Hamaet al. (1983). A trapezoidal integration was applied to calculate primary production throughout the euphotic zone. These
investigations were carried out in September, November, 2013, and February, May, August, 2014.
The estimated primary production varied among the dates (Fig. 1). Primary production in February and May, 2013, was lower
than that in September and November, 2013, and August, 2014. Uye et al. (1987) and Tada et al. (1998) described that primary
production in the Seto Inland Sea was low in winter. Their results also showed that the primary production in spring was similar
to those in summer and autumn. The trends shown in our results differ with the previous studies.
Primary production measured in summer and autumn (September and November, 2013 and August, 2014) varied widely
among the stations. Primary production in the central part of Osaka Bay and Hiuchi Nada were consistently lower throughout
the investigation period. Primary production changed largely at the inner part of Osaka Bay, Harima Nada and Bisan Seto. The
maximum production was observed at Harima Nada in September and November, 2013, and at the inner part of Osaka Bay inAugust, 2014. Primary production showed a peak at the inner part of Osaka Bay and showed decreasing trends through Harima
Nada to Bisan Seto in February, May and August, 2013. On the other hand, primary production showed a different distribution
pattern in September and November, 2014, when high primary production was also observed at Bisan Seto. These results aredifferent from those of Tada et al. (1998), in which they noted low primary production in Bisan Seto.
In the present study, the maximum primary production ranged from 1.0 to 1.6 gC m−2 day−1 in summer and autumn. This
range was similar to the value observed in the same season in the 1990’s. However, we also found differences in trends between
previous studies and the present study. In order to examine structural changes in the primary production in this region, further
analysis is needed on the factors controlling the distribution pattern of primary production.
References
Hama et al. (1983): Marine Biology, 73, 31-36.
Tada et al. (1998): J. Oceanogr., 54, 285-295.
Uye et al. (1987): J. Oceanogr. Soc. Japan, 42, 421-434.

Keywords: the Seto Inland Sea, primary production, phytoplankton

1/2

ACG33-P01

Room:Convention Hall

Time:May 26 18:15-19:30

2/2

ACG33-P02

Room:Convention Hall

Time:May 26 18:15-19:30

Distribution of benthicmicroalgae and nutrients in tidalflat sediments estimating fromchemical composition and delta13C
YAMAMOTO, Mariko1∗ ; HARADA, Naomi2 ; SATOU, Miyako2 ; UENO, Shinichiro1 ; SUGITANI, Kenichiro1
1

Graduate School of Environmental Studies, Nagoya University, 2 Japan Agency for Marine-Earth Science and Technology

Community compositions of microalgae that respond to environmental fluctuations have been often used as indicators of paleoenvironmental ploxis, organic water pollution, and so on. Benthic microalgae potentially adapt to wide ranges of environmental
conditions, and their growth is mainly controlled by intensity of light and feeding pressure. However it is possible that specificnutrients determine the community compositions under the similar physical conditions. In order to contribute to our knowledge
about relationship between community compositions of benthic microalgae and nutrients in estuarine tidal flat, this study provides the results of analyses of chlorophyll a , elemental compositions, δ 13 C ratio and δ 15 N ratio in tidal flat sediments.
Study site is located at Fujimae-higata inner part of Nagoya Port in Aich Prefecture, central Japan. Samples of surface sediments (1.5 cm depth, n=25) were subjected to analyses of chlorophyll a , TOC, TN, SiO2 , TiO2 , Al2 O3 , Fe2 O3 , MgO, MnO,
CaO, Na2 O, K2 O, P2 O5 , Cr, Cu, Pb, Zn, Zr, δ 13 C and δ 15 N.
The surface sediments are characterized by high positive correlations of chlorophyll a with TN (r = 0.70, p<0.001) and TOC(r = 0.68, p<0.001). On the other hand the correlation between chlorophyll a and excess-P that is available for microalgae isvery low (r = 0.09, p>0.5). Based on analysis of principal component chlorophyll a and other elements can be categorized into
three groups, i) elements associated with coarse-grained materials, such as Al, Ca, and K, ii) elements adsorbed and /or bounded
to fine-grained materials such as Cr, Cu, Pb, Zn, Fe, and P, iii) elements associated with organic matter, such as TOC, TN, andchlorophyll a . According to these results, three segments were identified for Fujimae-higata, including Segment 1 closest to theriver mouth where sediments are dominated by coarse-grained materials, Segment 2 away from the river mouth, characterized byfine-grained materials, and Segment 3 between Segments 1 and 2, characterized with organic matter. Values of δ 13 C of surface
sediments (average = -25.99 ‰, n = 25) are almost the same as those of suspended matter in the closest river (average = -25.94‰, n = 9). Benthic microalgae tend to have heavier δ 13 C ratio (approx. -18 ‰) than phytoplankton and the highest δ 13 C ratio
in the analyzed sediment samples is -24.6 ‰. This suggests that the contribution of benthic microalgae to the sediment organic
matter is small. The organic matter in Fujimae-higata sediments is likely supplied largely by riverine inflow.

Keywords: benthic microalgae, nutrients, tidal flat sediments

1/1

ACG33-P03

Room:Convention Hall

Time:May 26 18:15-19:30

Geochemical investigation for evaluation of submarine groundwater discharge in Suruga
Bay
ONO, Masahiko1∗ ; IKAWA, Reo1 ; MACHIDA, Isao1 ; MARUI, Atsunao1 ; MURANAKA, Yasuhide2 ;KAMITANI, Takafumi2 ; OHYAMA, Koichi2 ; ITO, Akira2
1

National Institute of Advaneced Industrial Science and Technology, 2 Shizuoka Institute of Environmental and Hygiene

Submarine groundwater discharge (SGD) has been recognized as an important pathway for material transport from land toocean and it is expected as ubiquitous phenomenon in coastal area. Our study site, Suruga Bay is adjacent to the southern foot of
Mt. Fuji where the permeable lava flow deposits and the active groundwater flow system exist. Therefore, large amount of SGD
could be occurred at the coastal area.
To estimate the spatial distribution of SGD, geophysical surveys such as multi-beam sonar, side scan sonar and sub-bottom
profiler, have been conducted in this area. This study attempts to evaluate SGD by using geochemical tracers, such as radon andradium in coastal water. We will show the spatial distribution of these tracers in Suruga Bay and discuss their relationship to
SGD.

Keywords: submarine groundwater discharge, Suruga Bay, geochemical tracer

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ACG33-P04

Room:Convention Hall

Time:May 26 18:15-19:30

Investigation of environmental factors related to regional differences in radon concentration in Japanese coasts
HONDA, Hisami1∗ ; TANIGUCHI, Makoto1 ; ONO, Masahiko2 ; HOSONO, Takahiro3 ; UMEZAWA, Yu4 ;SUGIMOTO, Ryo5 ; YAMADA, Makoto1
1

Research Institute for Humanity and Nature, 2 National Institute of Advanced Industrial Science and Technology, 3 Kumamoto
University, 4 Nagasaki University, 5 Fukui Prefectural University
In recent years, submarine groundwater discharge (SGD) have received considerable attention in hydrology and oceanography.
Radon-222 (222 Rn) is a useful tracer to detect SGD because 222 Rn in groundwater has extremely high concentration comparedwith surface waters. In Japanese coasts, many researches have been done SGD observations using 222 Rn tracer techniques. If
we compiled 222 Rn data from many coasts with different environmental condition, we can get generality related environmental parameters to SGD. Therefore, objectives of this study are to compile the existing observed data in Japanese coasts and toevaluate environmental parameters concerning the regional difference in 222 Rn activities. Firstly, we consolidated 222 Rn data incoastal waters at 10 sites from the northern part to the southern part of Japan. We also prepared environmental parameters in eachwatershed such as precipitation, geological data and geomorphological characteristics to examine and effect of driving forces on
the regional difference of 222 Rn activity. In this presentation, we will show the regional difference of 222 Rn activities in Japanese
coasts and statistical analysis results of relationship between compiled 222 Rn data and environmental parameters.
Keywords: 222Rn, SGD

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ACG33-P05

Room:Convention Hall

Time:May 26 18:15-19:30

Using stable isotopes to measure the groundwater connection between land and sea in the
Wakasa area
YAMADA, Makoto1∗ ; SUGIMOTO, Ryo2 ; SHOJI, Jun4 ; HONDA, Hisami1 ; KOBAYASHI, Shiho3 ;TOMINAGA, Osamu2 ; TANIGUCHI, Makoto1
1

Research Institute for Humanity and Nature, 2 Fukui Prefectural University, 3 Kyoto University, 4 Hiroshima University

The Wakasa area within Obama city, Fukui Prefecture is a very small area where the mountain and the sea connect. Thoughgroundwater is abundant, there is no conspicuous surface outflow in this area. Groundwater may flow into the sea directly. In
order to clarify the connection of groundwater between the seabed of the coastal zone and the land, we sampled groundwater
under the seabed and at inland wells, and analyzed the water’s stable isotopes in this area. The piezometers for collecting
groundwater samples in the seabed (depth: 1m) were installed in eight places along the shoreline. The groundwater from inlandwell was collected at six wells. The results of isotope analysis of these samples show that the groundwater from the seabed was
different from groundwater from the inland well. The origin of groundwater collecting near the shore line recharged from a low
elevation area. This result shows the possibility that the groundwater from inland well at the village flows at a deeper place, anddischarges at a more offshore seabed.
Keywords: Submarine groundwater discharge, Stable isotope, Discharge area

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ACG33-P06

Room:Convention Hall

Time:May 26 18:15-19:30

Seasonal variation in saline submarine groundwater discharge and associated nutrient
fluxes into Obama Bay
SUGIMOTO, Ryo1∗ ; OMIYA, Kenji1 ; YAMADA, Makoto2 ; TANIGUCHI, Makoto2
1

Fukui Prefectural University, 2 Research Institute for Humanity and Nature

Submarine groundwater discharge (SGD) is now recognized as a major conveyor of dissolved materials from land to the sea.
Nutrient loads carried by SGD are commonly calculated as the product of SGD rate and concentrations of coastal fresh groundwater with the assumption that chemical transport through the coastal aquifer is conservative. However, most of the discharging
water is usually saline groundwater (recirculated seawater) except in some karstic, volcanic and glacial areas where it is composed principally of fresh meteoric water. Recent studies have shown that biogeochemical processes in the subterranean estuarywould have an important effect on concentrations of the dissolved species. Therefore, it still remains unclear how to identify
endmember concentrations in a subterranean estuary for calculating SGD-derived nutrient fluxes. In this study, to evaluate nutrient fluxes through the saline SGD and their seasonality, we conducted monthly observation from March to November 2014
in the shallow coast in Obama Bay using a Lee-type seepage meter for SGD rate and piezometers for nutrient endmembers inthe subterranean estuary. Estimated SGD rates which mainly composed of recirculated seawater ranged from 0.01 cm d−1 to3.86 cm d−1 . This seasonal variation was dominated by integrated precipitation for 30 days before observation date with timelags of 1.5-2.5 months, suggesting that the recharging water takes time to percolate through the unsaturated zone to the watertable. Assuming that endmember of nutrients concentrations is derive from saline groundwater in 0.9 m beneath the bottom,
fluxes of dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorous (DIP) and dissolved silica (DSi) were 1.9-479.7µmol m−2 d−1 , 0.1-15.1 µmol m−2 d−1 and 7.4-1092.6 µmol m−2 d−1 , respectively. If we used nutrient concentrations infresh groundwater, fluxes of DIN and DSi were overestimated while DIP was underestimated, because nutrient concentrationsin fresh groundwater were enriched in DIN and DSi while depleted in DIP. These results show that biogeochemical processes insubterranean estuary affect crucial impact on nutrient loads carried by saline SGD.
Keywords: saline submarine groundwater discharge, nutrient flux, seasonal variation, subterranean estuary

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