P3)
Vertical profile and diversity of sediment Phosphorus in an artificle lake and bay of seto inland sea Japan*Guangzhe Jin1, Shin-ichi Onodera1, Atsuko Amano2, Takaharu Sato1 , Yuta,Shimizu1
12

Graduate School of Integrated Arts and Sciences, Hiroshima University,

Marine Geology research Group Institute of geology and Geoinformation Geological Survey of Japan , AISTcontent,

1. Introduction

thenearbottomwater

samplesshows

The Kojima bay is located in Okayama prefecturecomparably higher in Kojima bay than Kojima lake

and is an important water flow to the Seto inland sea .thesediment P forms which are the redox sensitive P boundP load to the Seto inland sea appears to have importantto oxides of reducible metals which mainly are Fe andeffect to the eutrophication in this area. Kojima Lake is

Mn consist of the biggest part of the P forms (Figure .1)

formed by enclosing the dike in 1959, so research of theIn Kojima lake core samples the redox sensitive P

effect of formation to the environment is important andforms leads the decreasing in Kojima lake while the P

interesting. Our study is mainly focused on the effect offrom Al oxides and non-reducible metals and Apatite andphosphorus in sediment and the overlying water samples

other inorganic P shows the dominate P forms in Kojima

in Kojima bay and Kojima Lake.

Bay.
The SiO2-Si content in pore water profile shows

2. Method
The field observations of this study were taken indiversity in the dating of enclosing the dike and the water

2009. 27 surface and 3 core sediment samples were taken

silica content shows lower in Kojima Lake than inin September 2009 in Kojima bay seto inland sea，TheKojima bay which means the changing of fresh water innutrients of surface water samples and near bottom water

Kojima lake decrease the water Silica content.

samples were determined by auto analyzer. Sediment TP

In this study, part of bay changed to artificial Lake 50

and P forms were also determined by Aspila method

years ago, the environment changes leads to very

137

210

Pb activity were determined tointeresting results. In Kojima bay the surface sediment P

calculate the dating data of different depth and also thefractionation and sediment core seems to be more

sedimentation accumulation rate (SAR rate).

uniform and of same size of P pool rather than P

3. Results and Discussion

fractionation in Kojima Lake. The content and the more(1976).

CS andThe SAR values shows that the sedimentation has

rivers supply more uniform quality and quantity of P

been much slower in the Kojima Lake than in the outerresources deposited in the sediment in Kojima bay.

side in the Kojima bay .while after the dike constructed

The low SAR value in Kojima bay may suggest that it is(table 1) .the Kojima Lake seems to act as a trap for

more vulnerable to be the transportation of sedimentationmaterial transported from the open sea. In surface

process .the Kojima Lake has higher sedimentation value

sediment samples the Kojima lake samples has thethan the bay samples. But with lower burial of P andhigher TP content in sediment while lower pore water P

higher efflux of P,P fractionation revealed that most part of P sediment indike of Kojima lake is enclosed and the severe water

sub layer of sediment is in forms prone to be stable withquality was reflected in pore water P and P content in

the depth increasing. While in surface layer is prone tosediment which is mostly reflected by NaBD-iP .In ourbe release under anoxic condition or other digenetic

research. The erosion of sediment and vertical and spatialprocess. The reactive P forms are higher in the Lakeheterogeneity in the sediment should also be consideredenvironment with the higher SAR value. And theand needs more evidences in the future research.

immobile P forms are dominated in the bay sedimentcores and surface sediment samples. The Lake samples
appear to have higher content of P than Bay samples
while the increasing part is mostly NaBD-iP. Through thedating data, P content is increasing in sediment after theTable 1 Sediment accumulation rates (SAR), sedimentation of extractable P, burial fluxes of immobile P,
long-term average for P efflux, and burial efficiency of P at two different sites in Kojima bay and Kojima
LakeBurialsite

SAR

sedimentation of P

burial of P

Long term aver.efflux of Pefficiency-2-1-2gm ymmol m y-2-1-1-2gm ymmol m y-1-2-1-2

gm ymmol m y-1-2-1

gm y(％)

Lake core

4300

140.93

4.37

37.72

1.17

0.97

30.09

27

Bay core

3500

82.42

2.56

45.10

1.40

0.71

21.95

55700

NRP
resdue P form
Ca bound P
oxide metal bound P
redox sensitive P
loosely sorbed P

600
500
400
300
200
100
0123456

78910 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27

0.16
0.14
0.12
0.1
0.08
0.06
0.04
0.02

1.4
1.2
10.8
0.6
0.4
0.2
0Figure.1 The different P forms of surface sediment samples (upper),the surfacewater(middle) and pore water PO4-P content(down) . The X-axis represents the sites
number the Y-axis represents the sediment P content (μg/g ) PO4-P content( mg/L)