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. Themaximum 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 HarimaNada 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

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ACG33-P01

Room:Convention Hall

Time:May 26 18:15-19:30

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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

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ACG33-P03

Room:Convention Hall

Time:May 26 18:15-19:30

Geochemical investigation for evaluation of submarine groundwater discharge in Suruga
BayONO, 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 ofMt. 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 toSGD.

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
1Research 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 theWakasa area
YAMADA, Makoto1∗ ; SUGIMOTO, Ryo2 ; SHOJI, Jun4 ; HONDA, Hisami1 ; KOBAYASHI, Shiho3 ;TOMINAGA, Osamu2 ; TANIGUCHI, Makoto11Research 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. Inorder 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 wasdifferent 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

1/1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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