PUB00070

• Year: 1998
• Title: Ground Water and Surface Water A Single Resource U.S. Geological Survey Circular 1139
• CWCB Section: Interstate & Federal
• Author: T.C. Winter, J.W. Harvey, O.L. Franke, W.M. Alley
• Description: Overview of current understandimg of interaction of ground water and surface water in terms of quality and quantity
• Publications - Doc Type: Historical

Many streams are contaminated, Therefore,
the need to determine the extent of the chemical
reactions that take place in the hyporheic
zone is widespread because of the concern that
the contaminated stream water will contaminate
shallow ground water (see Box G), Streams offer
good examples of how interconnections between
ground water and surface water affect chemical
processes, Rough channel bottoms cause stream
water to enter the streambed and to mix with
ground water in the hyporheic zone, This mixing
establishes sharp changes in chemical concentra-
tions in the hyporheic zone,
A zone of enhanced biogeochemical activity
usually develops in shallow ground water as a
result of the flow of oxygen-rich surface water into
the subsurface environment, where bacteria and
geochemically active sediment coatings are abun-
dant (Figure 19), This input of oxygen to the
streambed stimulates a high level of activity
by aerobic (oxygen-using) microorganisms if
dissolved oxygen is readily available, It is not
uncommon for dissolved oxygen to be completely
used up in hyporheic flow paths at some distance
into the streambed, where anaerobic microorgan-
isms dominate microbial activity. Anaerobic
bacteria can use nitrate, sulfate, or other solutes in
place of oxygen for metabolism, The result of these
processes is that many solutes are highly reactive
in shallow ground water in the vicinity
of streambeds,

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Direction of streamflow ~

\ High oxygen)
AerObic microbial
processes
Very fow or
no OXygen AnaerObic m' .
JCrObJal
Processes

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land Use 9 On geology,
, and presen
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ar On

The movement of nutrients and other chem-
ical constituents, including contaminants, between
ground water and surface water is affected by
biogeochemical processes in the hyporheic zone,
For example, the rate at which organic contami-
nants biodegrade in the hyporheic zone can exceed
rates in stream water or in ground water away
from the stream, Another example is the
removal of dissolved metals in the hyporheic
zone, As water passes through the hyporheic zone,
dissolved metals are removed by precipitation of
metal oxide coatings on the sediments,

Ferric irO)

Ferrous
iron

I
Inches
to
feet
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Feet
to
miles
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27

Figure 19, Microbial activity and
chemical transformations commonly
are e11hanced in the hyporheic zone
compared to those that take place
in ground water and swface water,
This diagram il/ustrates some of the
processes alld chemical transforma-
tions that may take place ;n the
hyporhe;c zone, Actual chemical
interactions depend on numerous
factors including aquifer mineralogy,
shape of the aquifer, types of organic
matter in surface water and ground
water, and nearby land use,