『Abstract
Silicon isotope compositions of main channel samples of the Yangtze
River were systematically investigated along with their chemical
compositions. The concentration of suspended matter in the Yangtze
River tends to decrease from the upper reaches to the lower reaches,
corresponding to settling of the sediments in the lakes and reservoirs
due to reduction of the velocity of water flow. The silica contents
of suspended matter vary from 52.1% to 56.9% and their δ30Si
values vary from 0 to -0.7‰, both similar to those of shales.
From the upper to lower reaches, the silica contents of suspended
matter tend to increase, whilst their δ30Si values
tend to decrease. Both trends reflect the increase of clay minerals
and decrease of carbonates in suspended matter.
The concentrations of dissolved silicon vary from 97 to 121μmol/L
and their δ30Si values vary over a wide range from
0.7 to 3.4‰. From the upper to lower reaches, dissolved silica
concentrations tend to decrease and their δ30Si values
tend to increase. These trends mainly reflect the change of chemical
and isotopic characteristics of the tributaries from the upper
to lower reaches. The major factors responsible for these changes
may be the high meteoric precipitation and significant silicon
absorption by grass (in wetlands) and rice (in paddy fields) in
drainage areas of the middle and lower reaches.
There is no correlation between δ30Si of dissolved
silicon and that of suspended matter. The Δ30SiDiss-SPM values vary over a wide range of 1.0-3.7‰,
indicating that (1) they are out of isotopic equilibrium, (2)
dissolved silicon and the associated suspended matter do not belong
to one physico-chemical system, and (3) isotopic exchange rate
between them is very slow.
The δ30Si value of dissolved silicon output from the
Yangtze River to the East Sea is estimated to be 3.0‰, much higher
than the values reported for the Amazon and Congo rivers. This
increases the δ30Si range of dissolved silicon in the
world's rivers from 0.4-1.2‰; to 0.4-3.47‰.』
『揚子江の主要な河川試料のケイ素同位体組成が、それらの化学組成とともに系統的に調べられた。揚子江の浮遊物濃度は上流域から下流域へ減少する傾向にあり、水流の流速減少による湖や貯水池での堆積物の沈殿に対応する。浮遊物のシリカ含有量は52.1%から56.9%まで変動し、それらのδ30Si値は0から-0.7‰まで変動して、共に頁岩の値と似ている。上流から下流へ、浮遊物のシリカ含有量は増加する傾向にあるが、それらのδ30Siは減少する傾向にある。両方の傾向とも、浮遊物中の粘土鉱物の増加と炭酸塩の減少を反映している。
溶存ケイ素の濃度は 97から121μmol/Lまで変動し、それらのδ30Si値は0.7から3.4‰までの広い範囲で変動する。上流から下流へ、溶存シリカ濃度は減少傾向にあり、それらのδ30Si値は増加傾向にある。これらの傾向は主に、上流から下流までの支流の化学的および同位体的特性の変化を反映している。これらの変化に対応する主要な要因は、中流と下流の集水域における高い降水量ならびに草(湿地の)と稲(水田の)によるケイ素の重大な吸着であるだろう。
溶存ケイ素のδ30Siと浮遊物のそれとは相関はない。Δ30SiDiss-SPM値は1.0〜3.7‰の広い範囲で変動し、これは次のことを示す:(1)これらは同位体平衡にない、(2)溶存ケイ素とそれに伴う浮遊物は一つの物理-化学系に属していない、そして(3)これらの間の同位体交換速度は非常に遅い。
揚子江から東シナ海への溶存ケイ素アウトプットのδ30Siは3.0‰と見積られ、アマゾン川およびコンゴ川で報告された値よりも非常に高い。
これは、世界の河川中の溶存ケイ素のδ30Si範囲を、0.4〜1.2‰から0.4-3.47‰へ増加させる。』
1. Introduction
2. Geographic and hydrological background of the Yangtze River
3. Samples and experiments
4. Results
5. Discussion
5.1. Concentration of SPM in the Yangtze River
5.2. SiO2 contents and δ30Si
values of SPM in the Yangtze River
5.3. DSi and some δ30SiDiss in the Yangtze waters
5.3.1. DSi and some cation contents in
the Yangtze River waters
5.3.2. Silicon isotope compositions of dissolved silicon in
the Yangtze River
5.3.4. Relation between DSi and δ30SiDiss of the Yangtze water
5.4. Relation between δ30SiDiss
andδ30SiSPM in Yangtze waters
5.5. Silicon isotope compositions of dissolved silicon in world
river system
6. Conclusion
Acknowledgments
References