『Abstract
Mixing between meteoric water and sea water produces brackish
to saline water in many coastal aquifers. In this mixing zone,
chemical reactions of the salty water with aquifer solids modify
the composition of the water, much as riverine particles and suspended
sediments modify the composition of surface estuarine waters.
To emphasize the importance of mixing and chemical reaction in
these coastal aquifers, I call them subterranean estuaries. Geochemical
studies within subterranean estuaries have preceded studies that
attempt to integrate the effect of these systems on the coastal
ocean. The mixing zone between fresh ground water and sea water
has long been recognized as an important site of carbonate diagenesis
and possibly dolomite formation. Biologists have likewise recognized
that terrestrial inputs of nutrients to the coastal ocean may
occur through subterranean processes. Further evidence of the
existence and importance of subterranean estuaries comes from
the distribution of chemical tracers in the coastal ocean. These
tracers originate within coastal aquifers through chemical reactions
of the saline water with aquifer solids. They reach the coastal
ocean as the surface and subterranean systems exchange fluids.
Exchange between the subterranean estuary and the coastal ocean
may be quantified by the tracer distribution in the coastal ocean.
Examples from the east and Gulf coasts of the U.S., as well as
the Bay of Bengal, will be used to evaluate the importance of
these unseen estuaries in supplying not only chemical tracers,
but also nutrients, to coastal waters. Anthropogenic effects on
subterranean estuaries are causing significant change to these
systems. Ground water mining, sea level rise, and channel dredging
impact these systems directly. The effects of these changes are
only beginning to be realized in this vital component of the coastal
ecosystems.
Keywords: estuary; ground water; coastal aquifer; radium』
『要旨
天水と海水の混合が、多くの海岸帯水層に汽水〜塩水をつくりだす。河川粒子と浮遊堆積物が地表河口水の組成を変えるように、この混合帯では帯水層の固体と塩を含む水との化学反応が水の組成を変える。このような海岸帯水層での混合と化学反応の重要性を強調するために、私はこれらを地下河口と呼ぶ。地下河口の地球化学的研究は、沿岸海洋へのこれらの系の影響をまとめることを試みる研究の前に行われた。淡水地下水と海水の間の混合帯は、炭酸塩の続成作用およびおそらくドロマイト形成の重要な場所として長い間認められてきた。生物学者も同様に、沿岸海洋への陸上栄養分の流入が地下過程をつうじて起こる可能性を認識してきた。地下河口の存在と重要性についてのあらたな証拠が、沿岸海洋における化学トレーサーの分布から得られる。これらのトレーサーは、帯水層の固体との塩水の化学反応をつうじて沿岸帯水層内に生じている。地表系と地下系が流体を交換しながら、それらは沿岸海洋に達する。地下河口と沿岸海洋間の交換は、沿岸海洋でのトレーサー分布によって定量化できるだろう。ベンガル湾のほかに米国の東部と湾岸地域からの例が、化学トレーサーだけでなく栄養分を沿岸水に供給しているこれらの目に見えない河口の重要性を評価するために用いられるだろう。地下河口への人類の影響は、これらの系に重大な変化をもたらしている。地下水採取、海水準上昇、そして水路浚渫はこれらの系に直接影響する。これらの変化の影響は、沿岸生態系のこのきわめて重要な構成要素においていま生じ始めている。』
1. Introduction
2. Mechanisms of flow in subterranean estuaries
3. Use of tracers to study subterranean aquifers
4. Case studies of tracer applications
5. Effects of sea level change on the subterranean estuary
6. Anthropogenic effects on the subterranean estuary
7. Summary
Acknowledgements
References
地表河口 |
地下河口 |
Mixing zone of river and sea water 河川水と海水の混合帯 |
mixing zone of meteoric and sea water 天水と海水の混合帯 |
Tidal and river forces, estuarine circulation, residual flow
to sea, short residence time 潮汐力と河川水力、河口循環、海への残留流、短い滞留時間 |
hydraulic and tidal forces, circulation? residual flow may be
either way, long residence time 水圧と潮汐力、循環? 残留流はたぶん両方へ、長い滞留時間 |
High particle concentrations lead to strong particle-water interactions 大きい粒子濃度は強い粒子-水相互作用を引き起こす |
direct water contact with solids leads to strong particle-water
interactions 固体とじかに接する水は強い粒子-水相互作用を引き起こす |
Sea level exerts a major control 海水準が大きく支配する |
sea level exerts a major control 海水準が大きく支配する |
Human impacts is often significant 人類の影響はしばしば重要 |
human impact is often significant 人類の影響はしばしば重要 |
In contact with atmosphere, high oxygen, oxidized Fe and Mn (sediments
may be different) 大気との接触で、高酸素、酸化されたFeとMn(堆積物はたぶん違っている) |
no contact with atmosphere, low to high oxygen, high p
CO2, Fe and Mn may be reduced 大気と接触しない、低〜高酸素、高いp CO2、FeとMnはたぶん還元されている |
Abundant, diverse life 豊富で多様な生物 |
bacteria are primary life 細菌が主要な生物 |
Major ions dominated by sea salts 主要イオンは海水塩分が優勢 |
major ions may reflect diagenesis 主要イオンは続成作用を反映 |