Prepared in cooperation with Deschutes County

Ground Water Redox Zonation near La Pine, Oregon: Relation to 

River Position within the Aquifer–Riparian Zone Continuum

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2007–5239
Cover: Photograph showing process of installing a transect of wells in the Deschutes River at River Mile 206.4. 

(Photograph taken by Stephen R. Hinkle, U.S. Geological Survey, March 2006.)
Ground Water Redox Zonation near La Pine, 

Oregon: Relation to River Position within the 

Aquifer-Riparian Zone Continuum

By Stephen R. Hinkle, David S. Morgan, Leonard L. Orzol, and Danial J. Polette

Prepared in cooperation with Deschutes County

Scientific Investigations Report 2007–5239

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2007

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Suggested citation:

Hinkle, S.R., Morgan, D.S., Orzol, L.L., and Polette, D.J., Ground water redox zonation near La Pine, Oregon—Relation 

to River Position within the Aquifer-Riparian Zone Continuum: U.S. Geological Survey Scientific Investigations Report 

2007–5239, 30 p.
iii

Contents

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Purpose and Scope ..............................................................................................................................4

Description of Study Area ...................................................................................................................4

Study Design and Methods..........................................................................................................................5

Temporal and Spatial Considerations for Sampling Network .......................................................5

Site Selection.........................................................................................................................................7

Sample Collection and Analytical Methods .....................................................................................7

Particle Tracking ...................................................................................................................................8

Previous Near-River Redox Work in Study Area......................................................................................8

Results. .............................................................................................................................................................9

Transect Configurations.......................................................................................................................9

Ground-Water Transects on Deschutes River........................................................................9

Ground-Water Transects on Little Deschutes River..............................................................9

Redox Conditions, Nitrogen, and Chloride in Ground Water from Transects ...........................15

Spring and Slough Samples..............................................................................................................17

Discussion.....................................................................................................................................................17

Distribution of Dissolved Oxygen and Nitrate in Ground Water in the Near-River 

Environment............................................................................................................................17

Integration of Ground-Water Flow Paths at a Cut-Off Slough.....................................................19

Redox Controls at the Scale of River Reaches ..............................................................................19

Effects of Ground-Water Discharge to Rivers ...............................................................................20

Summary........................................................................................................................................................21

References Cited..........................................................................................................................................21

Appendix A. Project Quality-Control Data, Historical Near-River Ground-Water Data 

Collected near the Little Deschutes River Near La Pine, Oregon, and Project 

Discharge and Chemical Data from the Little Deschutes River near La Pine, 

Oregon, 2006....................................................................................................................................25
iv

Figures

Figure 1. Map showing location of study area near La Pine, Oregon ........................... 2

Figure 2. Graphs showing discharge in Deschutes and Little Deschutes Rivers at

selected sites near La Pine, Oregon, during calendar year 2006 ..................... 6

Figure 3. Cross sections showing configurations of ground-water transects at

Deschutes and Little Deschutes Rivers near La Pine, Oregon ........................ 12

Figure 4. Graphs showing relation between chemical constituents in samples from

wells at all ground water transects in the Deschutes and Little Deschutes

Rivers near La Pine, Oregon, March and October 2006................................. 16

Figure 5. Graph showing relation between δ15N and δ18O of nitrate in samples from

wells at ground-water transect LD24.9 (wells containing nitrite-plus-nitrate

concentrations greater than 0.5 mg N/L) and sand-filter effluent from septic

tanks near La Pine, Oregon ............................................................... 18

Tables

Table 1. Ground-water transect site wells and miscellaneous sites near La Pine,

Oregon, March and October 2006 ......................................................... 10

Table 2. Chemical and isotopic data for ground-water transect site wells and

miscellaneous sites near La Pine, Oregon, March and October 2006 ............... 11

Plate

Plate 1. Map showing transet sites, riparian zone extent (extent of cryaquoll soils and 

water), and ground-water particle pathlines for particles that remain in oxic zones 

near La Pine, Oregon
v

Conversion Factors, Datums, Abbreviations, and Acronyms

Conversion Factors

Multiply By To obtain

cubic foot per second (ft3

/s) 0.02832 cubic meter per second (m3/s)

inch (in.) 2.54 centimeter (cm)

foot (ft) 0.3048 meter (m)

gram (g) 0.03527 ounce, avoirdupois (oz)

liter (L) 33.82 ounce, fluid (fl. oz)

mile (mi) 1.609 kilometer (km)

square mile (mi2

) 2.590 square kilometer (km2) 

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F=(1.8×°C)+32.

River edges are referred to as “left edge” or “right edge” from a frame of reference of looking 

downstream.

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm at 

25°C).

Concentrations of chemical constituents in water are given either in milligrams per liter (mg/L) 

or micrograms per liter (μg/L).

Datums

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1927 (NAD 27) 

and North American Datum of 1983 (NAD 83).

Altitude, as used in this report, refers to distance above the vertical datum.
vi

Conversion Factors, Datums, Abbreviations, and 

Acronyms—Continued

Abbreviations and Acronyms

Abbreviation or Acronym Meaning

δ15N-NO3

- delta-15N (ratio of 15N to 14N, relative to the 

standard AIR, in units of per mil) of nitrate

δ18O-NO3

- delta-18O (ratio of 18O to 16O, relative to the standard 

VSMOW, in units of per mil) of nitrate

CH4 methane

Cl- chloride

Fe iron

FeS2 pyrite 

H2

S hydrogen sulfide

mg N/L milligram of nitrogen per liter

Mn manganese

MRL method reporting level

N nitrogen 15N nitrogen-15

NH4

+ ammonium

NO2

- nitrite

NO3

- nitrate

O2 dissolved oxygen

oxic oxygen-reducing; containing > 0.5 milligrams per 

liter of dissolved oxygen

‰ per mil

redox reduction/oxidation

SO4

2- sulfate

TMDL total maximum daily load

USGS U.S. Geological Survey

VSMOW Vienna Standard Mean Ocean Water
Abstract

Increasing residential development since in the 1960s has 

lead to increases in nitrate concentrations in shallow ground 

water in parts of the 247-square-mile study area near La 

Pine, Oregon. Denitrification is the dominant nitrate–removal 

process that occurs in suboxic ground water, and suboxic 

ground water serves as a barrier to transport of most nitrate in 

the aquifer. Oxic ground water, on the other hand, represents 

a potential pathway for nitrate transport from terrestrial 

recharge areas to the Deschutes and Little Deschutes Rivers. 

The effects of present and potential future discharge of 

ground-water nitrate into the nitrogen-limited Deschutes and 

Little Deschutes Rivers are not known. However, additions 

of nitrogen to nitrogen-limited rivers can lead to increases 

in primary productivity which, in turn, can increase the 

magnitudes of dissolved oxygen and pH swings in river water. 

An understanding of the distribution of oxic ground water 

in the near-river environment could facilitate understanding 

the vulnerability of these rivers and could be a useful tool for 

management of these rivers.

In this study, transects of temporary wells were installed 

in sub-river sediments beneath the Deschutes and Little 

Deschutes Rivers near La Pine to characterize near-river 

reduction/oxidation (redox) conditions near the ends of 

ground-water flow paths. Samples from transects installed 

near the center of the riparian zone or flood plain were 

consistently suboxic. Where transects were near edges 

of riparian zones, most ground-water samples also were 

suboxic. Oxic ground water (other than hyporheic water) 

was uncommon, and was only detected near the outside 

edge of some meander bends. This pattern of occurrence 

likely reflects geochemical controls throughout the aquifer 

as well as geochemical processes in the microbiologically 

active riparian zone near the end of ground-water flow paths. 

Younger, typically less reduced ground water generally enters 

near-river environments through peripheral zones, whereas 

older, typically more reduced ground water tends to discharge 

closer to the center of the river corridor. Such distributions of 

redox state reflect ground-water movement and geochemical 

evolution at the aquifer-scale. Redox state of ground water 

undergoes additional modification as ground water nears 

discharge points in or adjacent to rivers, where riparian zone 

processes can be important. Lateral erosion of river systems 

away from the center of the flood plain can decrease or even 

eliminate interactions between ground water and reducing 

riparian zone sediments. Thus, ground water redox patterns 

in near-river sediments appear to reflect the position of a river 

within the riparian zone/aquifer continuum. 

Spatial heterogeneity of redox conditions near the river/

aquifer boundary (that is, near the riverbed) makes it difficult 

to extrapolate transect-scale findings to a precise delineation 

of the oxic-suboxic boundary in the near-river environment of 

the entire study area. However, the understanding of relations 

between near-river redox state and proximity to riparian 

zone edges provides a basis for applying these results to the 

study-area scale, and could help guide management efforts 

such as nitrogen-reduction actions or establishment of Total 

Maximum Daily Load criteria. Coupling the ground-water 

redox-based understanding of river vulnerability with groundwater particle-tracking-based characterization of connections 

between upgradient recharge areas and receiving rivers 

demonstrates one means of linking effects of potential nitrate 

loads at the beginning of ground-water flow paths with river 

vulnerability.

Introduction

Nitrate (NO3

-

) ingestion may adversely affect human 

health (World Health Organization, 1996), and discharge 

of ground-water NO3

-

 into surface-water bodies can have 

detrimental effects on ecosystem health (U.S. Environmental 

Protection Agency, 1998; Howarth and Marino, 2006). 

Shallow aquifers are particularly susceptible to NO3

-

contamination because aquifers often receive nitrogen (N) 

inputs from anthropogenic activities at or near land surface. 

Shallow aquifers frequently have a direct connection to rivers, 

and hence represent a pathway for widely dispersed chemical 

constituents to enter rivers.

Ground Water Redox Zonation near La Pine, Oregon: 

Relation to River Position within the Aquifer–Riparian 

Zone Continuum

By Stephen R. Hinkle, David S. Morgan, Leonard L. Orzol, and Danial J. Polette
2 Ground Water Redox Zonation near LaPine, Oregon: Relation to River Position within the Aquifer-Riparian Zone Continuum

Ground water near La Pine, Oregon (fig. 1) is vulnerable 

to NO3

-

 contamination as a result of residential development 

using conventional (non-nitrogen-reducing) onsite wastewater 

treatment systems (septic tanks). In ground water near 

La Pine, NO3

-

 is derived primarily from septic tank effluent 

and occurs in the shallow part of the aquifer (approximately 

the uppermost 20 ft of saturated sediments). Evidence for a 

septic tank effluent source includes (1) similarity between δ15N 

values (nitrogen isotopic content) of NO3

-

 in shallow ground 

water and those in septic tank effluent, (2) relations between 

NO3

-

 and chloride (Cl-), (3) relations between NO3

-

 and 

tracer-based ground-water ages, (4) hydraulic gradients, and 

(5) occurrence of NO3

-

 in discrete plumes (Hinkle and others, 

2007). In coming years, NO3

-

 concentrations in ground water 

will increase in many parts of the aquifer as historically loaded 

NO3

-

 is transported farther along flow paths and as additional 

NO3

-

 from existing and new homes is added to the aquifer 

(Morgan and others, 2007).

Ammonium (NH4

+

), as well as NO3

-

, occurs in the 

aquifer. However, the distribution of NH4

+

 differs from that of 

NO3

-

. Ammonium at elevated concentrations (concentrations 

greater than 1 milligram nitrogen per liter [mg N/L]) occurs 

in deep ground water (100–400 ft below the water table), 

or in shallow ground water near rivers where deep, NH4

+

-

rich ground water discharges to rivers. This NH4

+

 is derived 

from decomposition of sedimentary organic matter (not from 

reduction of NO3

-

), as indicated by (1) δ15N values of NH4

+

, 

(2) relations between NH4

+

 and Cl-, (3) relations between NH4

+

and carbon, (4) occurrence of NH4

+

 in old ground water, and 

(5) location of NH4

+

 in deep and downgradient regions of the 

aquifer (Hinkle and others, 2007).

Ground water reduction/oxidation (redox) conditions 

in the aquifer near La Pine evolve from oxygen-reducing 

(oxic) conditions near the water table in recharge areas to 

increasingly reducing (suboxic, or post-oxygen-reducing) 

conditions farther downgradient. (A dissolved oxygen [O2] 

concentration of 0.5 mg/L was used by Hinkle and others 

[2007] as a threshold between oxic and suboxic conditions; 

this threshold value is used in this report.) N is a redoxsensitive element that usually occurs as NO3

-

 under oxic 

conditions. In redox processes, NO3

-

 becomes reduced 

(typically, in ground water, through denitrification, with an 

end product of nitrogen gas [N2]) once most O2 is reduced. 

Denitrification is the dominant NO3

-

 sink in ground water in 

the aquifer near La Pine (Hinkle and others, 2007). Following 

denitrification, manganese (Mn) and iron (Fe) reduction 

occur, followed by sulfate (SO4

2-) reduction and later by 

methanogenesis. Mn and Fe reduction usually involves 

reduction of solid-phase (sediment) Mn and Fe to aqueousphase Mn and Fe. SO4

2- reduction results in formation of 

hydrogen sulfide (H2S), and methane (CH4) is formed during 

methanogenesis. 

The typical redox progression in ground-water evolution 

is:

1. Aqueous O2 concentrations decrease as a result of O2

consumption; 

2. NO3

-

 concentrations decrease (if present in recharge 

water) due to denitrification;

3. Mn and Fe concentrations increase;

4. SO4

2- concentrations decrease and are accompanied by 

increased H2S concentrations; and then

5. CH4 occurs.

Complications to this redox sequence can occur. Redox 

conditions can evolve beyond Fe reduction without large 

increases in aqueous Fe concentrations if iron sulfide solid 

phases such as pyrite (FeS2) precipitate from solution, or if 

aquifer materials do not contain sufficient solid-phase Fe 

for Fe reduction. Nevertheless, this progression of redox 

state as inferred by the relative abundances of these redoxindicator species generally is observed during the evolution 

of ground water along flow paths through aquifers. An 

understanding of redox state inferred by the occurrence of 

redox-sensitive species in ground water can be used to infer 

zones of chemical (for example, NO3

-

) stability and instability 

in aquifers. Generally, NO3

-

 is not reduced to NH4

+

 in ground 

water, but patterns of NH4

+

 occurrence in ground water near 

La Pine largely correspond with redox conditions, with 

elevated concentrations of NH4

+

 in suboxic ground water, and 

negligible concentrations in oxic ground water (Hinkle and 

others, 2007).

Previous studies of ground water in the La Pine region 

focused on the overall aquifer and emphasized the effects of 

septic tank effluent on the ground-water resource (Morgan 

and others, 2007; Hinkle and others, 2007). In these previous 

works, a flow model was developed to evaluate alternatives 

for management of NO3

-

 loads from septic tanks to the aquifer 

system. The model simulated the three-dimensional groundwater velocity distribution in the upper 120 ft of alluvial 

sediments (Morgan and others, 2007). Redox zonation was 

used to conceptualize the occurrence and fate of NO3

-

 in the 

aquifer and to represent a reaction boundary for NO3

-

 in the 

flow model. These geochemical and modeling investigations, 

including aquifer redox zonation efforts, were not specifically 

designed to address questions about NO3

-

 transport to rivers 

such as the Deschutes and Little Deschutes Rivers. An 

understanding of NO3

-

 transport to rivers has been hampered 

by uncertainty in redox zonation near the rivers. Redox 

zonation near these rivers was poorly constrained in this 

previous work because (1) few data were available on redox 

conditions near rivers, and (2) redox conditions tend to exhibit 

tremendous spatial variability in the near-river environment 

(Hill, 1996). The thickness of the oxic zone in the aquifer 
Introduction 3

DESCHUTES

L A K E

KLAMATH

Wickiup

Reservoir

Paulina

River

RIVER

DESCHUTES

Deschutes

Little

Creek

Crescent Cr

River

Fall

Spring

River

97

97

31

31

Masten Road

River Spring

Century

South

Road

Road

Butte

Finley

Drive

Burgess Road

La Pine study area

Deschutes

Basin

Upper Deschutes

Basin

La Pine

region

OREGON

Bend

Sunriver

La

Pine

+

+

+

+

+

+

+

+

+

+

+

+

D194.8

D209.2

D194.1

D198.5

D206.4 LD13.4

LD16.1

LD24.9

LD32.8

LD37.8

LD2.4

LD5.7

RM 50

RM 40

RM 30

RM 20

RM 10

RM 200

RM 210

RM 220

RM 190

RM 180

Deschutes River

at Benham Falls

Little Deschutes River

near La Pine

RM 210

Deschutes River

at Benham Falls

LD13.4

D194.8

D209.2

0 4 KILOMETERS

0 4 MILES

EXPLANATION

Sewered area

Alluvium

Volcanic rocks

Location of well 

 transect

Location of 

slough

Location of 

spring

Location of 

gaging station

River mile

Base modified from U.S. Geological 

Survey

1:500,000 state base map, 1982 with 

digital data from U.S. Bureau of the 

Census, TIGER/Line (R), 1990 and

U.S. Geological Survey Digital Line 

Graphs published at 1:100,000

Publication projection is 

Lambert Conformal Conic

Standard parallels 42o20' and 44o40', 

central meridian -120o30'

Datum is NAD83

T 19 S

T 20 S

T 24 S

T 23 S

T 22 S

T 21 S

R 9 E R 10 E R 11 E

43°35'

40'

121°40' 35' 30' 25' 121°20'

45'

50'

43°55'

Figure 1. Location of study area near La Pine, Oregon.
4 Ground Water Redox Zonation near LaPine, Oregon: Relation to River Position within the Aquifer-Riparian Zone Continuum

in the near-river environment was estimated to be 10 ft by 

Morgan and others (2007), based on available but limited 

data from domestic and monitoring wells (Hinkle and others, 

2007). This estimate allowed for the possibility of shallow, 

oxic ground-water discharge to rivers, with the realization that 

the oxic zone in the near-river environment likely was thinner 

or nonexistent in some zones. 

A refined understanding of redox conditions near rivers in 

the study area is needed before the link between ground-water 

and river-water conditions can be more fully addressed. This 

work was initiated by a cooperative study by the Deschutes 

County Community Development Department and the U.S. 

Geological Survey (USGS). The resulting understanding 

could be used to help guide management decisions for river 

protection. For example, if NO3

-

 is loaded to ground water 

in the zone of contribution (beginning of ground-water flow 

paths) during the recharge process, that NO3

-

 can be carried 

into rivers where oxic ground water enters rivers. Removal 

of that NO3

-

 could be accomplished by reducing NO3

-

 loads 

in the zones of contribution. Alternatively, reduction of NO3

-

loads to rivers could be accomplished by altering geochemical 

conditions at the end of ground-water flow paths through, for 

example, the creation of NO3

-

-removing artificial wetlands in 

vulnerable discharge areas (Martin and others, 1999). 

Purpose and Scope

The purpose of this report is to provide a conceptual 

framework describing the distribution of redox conditions in 

aquifer sediments near the Deschutes and Little Deschutes 

Rivers. Suboxic ground water in the aquifer near La Pine, 

Oregon, represents a zone of NO3

-

 instability in which 

denitrification generally can be expected (Hinkle and others, 

2007). This framework will provide resource managers 

with a refined understanding of the NO3

-

 attenuation 

capacity of part of the aquifer that was poorly constrained in 

previous assessments of the overall aquifer. The improved 

understanding of redox state in the near-river ground-water 

environment may assist in evaluating river vulnerability to 

NO3

-

 from ground water or in identifying steps that can be 

taken to reduce that vulnerability.

This report characterizes redox conditions in the nearriver environment by presenting data from ground-water 

samples collected from sub-river sediments at various points 

along transects in the Deschutes and Little Deschutes Rivers 

and analyzed for redox indicator species (primarily O2). 

Multiple measurements were made at each of 10 transects, 

with sampling designed to characterize spatial variability 

in redox conditions along transects oriented perpendicular 

to the rivers. These data were used to relate ground water 

redox state to geomorphologic and landscape variables and 

features that can be used to extrapolate the results to the 

near-river ground-water environments of the Deschutes and 

Little Deschutes Rivers near La Pine. Particle tracking with 

an existing ground-water flow model demonstrated one way 

to relate potentially vulnerable river reaches to upgradient 

recharge areas.

The redox characterization work described in this report 

is limited to the near-river environment. Although study 

results were consistent with basic principles of ground-water 

geochemical evolution and ground-water/surface-water 

interactions, they were restricted by the limited number of 

transects installed for the study. Therefore, conclusions drawn 

from this work were inherently general and the patterns 

observed hold for many, but not all river segments.

Description of Study Area

The La Pine study area, as defined in previous 

investigations by Morgan and others (2007) and Hinkle and 

others (2005 and 2007), encompasses 247 mi2 of the upper 

Deschutes Basin in central Oregon (fig. 1). About 30 river 

miles of the Deschutes River and 50 river miles of the Little 

Deschutes River are represented in the study area. The area 

is underlain by Quaternary alluvial and lacustrine deposits in 

a structural basin of Quaternary and Tertiary basalt, andesite, 

vent deposits, and pyroclastic rocks (Lite and Gannett, 2002). 

These sediments contain an aquifer that provides the primary 

source of drinking water to most local residents, numbering 

about 18,000 in 2005 and expected to number 26,000 by 

approximately 2019 (Rich and others, 2005; Morgan and 

others, 2007).

Rain and snowmelt are the primary sources of recharge. 

Precipitation ranges from 15 to 20 in/yr over most of the area 

(Taylor, 1993), falling primarily from November through 

March. In addition to recharge from rain and snow, ground 

water also flows into the study area from neighboring highelevation areas (Gannett and others, 2001). Ground water 

discharges to the Deschutes and Little Deschutes Rivers, 

which meander across a flood-plain-and-wetland complex as 

much as one-quarter-mile or more wide.

The Deschutes and Little Deschutes Rivers are N limited 

(Jones, 2003), and are susceptible to increases in N loads. 

Increased N concentrations can increase primary productivity, 

which can increase the magnitudes of O2

 and pH swings in 

river water. Parts of the Deschutes River do not meet State 

of Oregon water-quality standards for O2 and are included 

in the state 303(d) list of water-quality-impaired streams. 

Data currently are insufficient to determine the status of O2

conditions in the Little Deschutes River (Anderson, 2000). 
Study Design and Methods 5

Study Design and Methods

Ground water was sampled to characterize the 

geochemistry of water discharging to the Deschutes and Little 

Deschutes Rivers. Where ground water discharges to rivers, 

that shallow ground water represents the ends of flow paths 

converging at and discharging into rivers. Ground-water 

samples were analyzed for O2, Fe, NO3

-

, NH4

+

, Cl-, as well 

as specific conductance and temperature. Dissolved oxygen 

was the primary redox indicator species of interest because 

previous work demonstrated that redox gradients in the study 

area are sharp and that most NO3

-

 is removed by denitrification 

near the oxic/suboxic boundary (Hinkle and others, 2007). 

Thus, the presence of suboxic ground water in sediment under 

a river could be used to indicate the presence of a barrier that 

would prevent most ground-water NO3

-

 from discharging to 

the river at that point. Note, however, that ground water at a 

point beneath the riverbed may not flow directly up into the 

river at that point. A point measurement beneath a river to 

determine the redox state of ground water entering the river 

above the measurement point is an approximation. Iron also 

was used as a redox indicator species. Nitrate and NH4

+

 can 

be used as redox indicator species. Alternatively, other redox 

indicator species (here O2 and Fe) can serve as predictor 

variables for the presence of conditions favorable for NO3

-

 and 

NH4

+

 occurrence. Chloride is useful as a tracer of septic tank 

effluent (Hinkle and others, 2007). 

Temporal and Spatial Considerations for 

Sampling Network

Exchanges between ground water and surface water 

are complex as a result of spatial and temporal variations in 

hydraulic gradients, spatial heterogeneities in aquifer hydraulic 

properties, and convergence of multiple ground-water flow 

paths at rivers (rivers commonly serving as regional drains 

for ground-water discharge). A network design that accounts 

for these complexities was used in this study. The network 

consisted of temporary wells installed directly in the riverbeds. 

Transects of wells were installed at 10 locations: 3 along 

the Deschutes River and 7 along the Little Deschutes River 

(fig. 1). At each transect, 2–9 wells (40 wells total among the 

10 transects) were installed to allow characterization of redox 

state at different points. Wells were installed with the center 

of the screen generally at a depth of 1.0 ft, but several were 

screened at 2.0 ft, and one at 3.0 ft. Shallow ground-water 

samples collected where ground water discharged to rivers 

represent the ends of flow paths converging at and discharging 

into rivers.

Aquifers may alternately discharge to rivers and receive 

recharge from rivers at different times, or at the same time 

but at different places. Given the need to characterize the 

geochemical nature of ground water discharging to rivers, 

water samples were collected during periods of low river flow. 

Previous field measurements of hydraulic gradients between 

ground water and the Deschutes and Little Deschutes Rivers 

in the study area indicated that at almost all measurement 

sites, vertical hydraulic gradients were upward (toward the 

rivers) during low flow (Morgan and others, 2007). Thus, in 

the present study, ground-water sampling occurred during 

periods of low river flow in March and October 2006 (fig. 2). 

This sampling structure minimized the potential for sampling 

ground water that originated in the river.

Within a single cross section of a river, ground water 

often consists of multiple flow paths of varying ages that 

can vary from days to millennia (Winter and others, 1998). 

Characterization of ground-water inputs to a river requires 

attention to this spatial variability. According to one 

conceptual model that describes the nature of ground-water 

discharge to a gaining river, the oldest ground water (generally 

the most geochemically evolved) enters in the center of the 

river channel. The age of ground water decreases as the point 

of entry into the river moves from the center to the edges of 

the river (Modica and others, 1998). “Geochemically evolved” 

is a relative term that refers to ground water that has changed 

to a relatively great extent due to chemical reactions with 

geologic materials. Geochemically evolved ground water 

may be more reduced, may contain higher concentrations of 

dissolved solids, and (or) may be older than ground water that 

has had less interaction with geologic materials. 

Browne and Guldan (2005) suggest an alternative 

conceptual model in which a river meanders across a relatively 

flat valley floor and ground water discharges to this valleyfloor system rather than solely into the river. In this conceptual 

model, the river intercepts relatively young ground water 

where the river bends toward the edge of the valley floor, and 

intercepts relatively old ground water where the river course 

lies near the center of the valley. The oldest ground water 

within a given transect might enter the river at the inside edge 

of a meander bend (edge closest to the center of the valley 

floor), and the youngest ground water might enter the river 

at the outside edge (edge closest to the margin of the valley 

floor) (Brown and Gulden, 2005). Therefore, in any given 

river transect, younger ground water may tend to enter a river 

by flow paths near one edge of the river (Browne and Guldan, 

2005) or near both edges (Modica and others, 1998). In either 

conceptual model, though, ground water entering a river near 

the edges may be particularly young, and river edges may be 

particularly vulnerable to discharge of young ground water. To 

account for such spatial variability in ground-water age, and 

implicitly, geochemical character, the sampling regime used in 

this study incorporated multiple samples across river transects. 
6 Ground Water Redox Zonation near LaPine, Oregon: Relation to River Position within the Aquifer-Riparian Zone Continuum

or19-0152_fig02

2,500

2,000

1,500

1,000

500

600

700

800

900

500

400

300

200

100

0

0

JAN. FEB. MAR. APR. MAY JUNE JULY AUG. SEPT. OCT. NOV. DEC.

A. Deschutes River at Benham Falls, Oregon

B. Little Deschutes River near La Pine, Oregon

DISCHARGE, IN CUBIC FEET PER SECOND

Period of field 

 data collection

Continuous 

 discharge

2006

Figure 2. Discharge in Deschutes and Little Deschutes Rivers at 

selected sites near La Pine, Oregon, during calendar year 2006.

(Source: U.S. Bureau of Reclamation, 2007). 
Study Design and Methods 7

Ten transects were installed to represent some of the 

spatial variability of ground water redox state along the axes 

of the rivers. The geochemical character of ground water 

flowing into a river may vary along the length of the river 

in response to a spatially variable geologic and hydrologic 

framework and to spatially varying qualities of the riparian 

environment. The riparian zone has been broadly defined as 

the zone at which terrestrial and aquatic ecosystems overlap 

(Gregory and others, 1991; Martin and others, 1999). Riparian 

zone sediment tends to be a zone of enhanced geochemical 

cycling; therefore, riparian zones can be particularly effective 

zones of denitrification (Hill, 1996). In riparian zones, NO3

-

loss primarily is due to denitrification; plant and microbial 

uptake generally is less important than denitrification (Martin 

and others, 1999). Denitrification in riparian zones is due, 

in large part, to the abundance of labile (reactive) organic 

carbon derived from wetland plants and other riparian zone 

plants, as well as that available in sediment deposited by 

rivers. This organic carbon serves as an electron donor for 

redox reactions including denitrification. Therefore, riparian 

zone processing of ground-water NO3

-

 potentially represents a 

useful explanatory variable for ground water redox conditions 

along rivers. Published literature on N cycling in riparian 

environments has tended to focus on individual sites rather 

than on larger spatial scales (Vidon and Hill, 2004), and 

elucidation and characterization of N dynamics at larger 

spatial scales (for example, river scales) currently is in its 

infancy (Boyer and others, 2006). For an effective river-scale 

assessment, identification of differences among transect sites 

is needed to understand the processes governing redox state 

along rivers.

Site Selection

The sampling framework calls for installation of multiple 

wells along multiple transects. Site selection within this 

framework was designed to provide broad coverage within 

the study area (fig. 1). Site selection also was designed to 

emphasize the identification of oxic ground water. This 

emphasis was introduced into the sampling design because 

it was assumed that most ground water discharging to the 

Deschutes and Little Deschutes Rivers in the study area would 

be suboxic. Although identifying suboxic ground water is 

highly useful for constraining the redox character of ground 

water discharging to rivers, oxic ground water presents the 

dominant vulnerability for NO3

-

 transport into the rivers; these 

factors that accommodate retention of O2 in ground water need 

elucidation.

The site selection focus on identifying oxic ground 

water lead to emphasizing coarse-grained sediments (sand, 

gravel) and avoiding macrophyte beds. Oxic ground water 

more commonly is detected in coarse-grained sediments 

than in fine-grained sediments (silt and clay) because of 

greater concentrations of organic carbon in and slower water 

movement through fine-grained sediments (Vidon and Hill, 

2004; Pinay and others, 2007). Macrophyte beds were avoided 

because macrophytes can trap fine-grained sediments, and 

exudates from macrophyte roots could create local conditions 

of anoxia (Martin and others, 1999).

Transect site names begin with a “D” (Deschutes River) 

or “LD” (Little Deschutes River), followed by the location 

in river miles (as indicated on USGS topographic maps). For 

example, “D194.1” is a site on the Deschutes River at river 

mile 194.1. Individual wells are assigned a name beginning 

with the transect site name, followed by a decimal and a 

number to represent the well. For example, “D194.1.1” is one 

well in the transect “D194.1”.

Sample Collection and Analytical Methods

 Ground-water samples were collected by installing 

temporary stainless steel wells in riverbed sediment. Screen 

lengths were 0.25 ft (36 wells) and 0.05 ft (4 wells). Wells 

were developed and then sampled by pumping with a 

peristaltic pump. 

Field parameters (O2, specific conductance, and 

temperature) were measured on-site in flow-through cells. 

The flow-through cell for O2 measurements was created from 

a capped, high-density polyethylene beaker fitted with a 

fluorocarbon polymer inlet tube to which the pump tubing was 

attached and with an outlet hole to allow sample water to exit 

the flow-through cell. The inlet tube allowed sample water to 

enter the bottom of the flow-through cell, where the tip of the 

O2 probe was located. The outlet hole was located at the top of 

the flow-through cell. The flow-through cell was large enough 

to accommodate the O2 probe, but sized sufficiently small as 

to allow operation with low pumping rates. The flow-through 

cell allowed O2 measurements on ground water that was not 

exposed to atmospheric gasses during measurement. A similar 

flow-through cell was used for specific conductance and 

temperature measurements.

Following well purging (more than three well bore 

volumes) and stabilization of field parameters, wells were 

sampled for nitrite-plus-nitrate (NO2

-

 + NO3

-

), NH4

+

, Fe, and 

Cl- (U.S. Geological Survey, 1999). In this report, NO2

-

 + NO3

-

is assumed to contain negligible NO2

-

; this assumption is based 

on previous experience in this basin (Hinkle and others, 2007) 

and in other aquifers. Thus, NO2

-

 + NO3

-

 is referred to as NO3

-

. 

Four wells also were sampled for isotopes of NO3

-

 (δ15N–NO3

-

and δ18O–NO3

-

) (isotopic content of N and O in NO3

-

).

Samples were filtered through in-line 0.45-μm nominalpore-size one-time-use capsule filters. Capsule filters were 

flushed with 1 L of deionized water and then flushed with 

sample water to remove deionized water prior to use. 
8 Ground Water Redox Zonation near LaPine, Oregon: Relation to River Position within the Aquifer-Riparian Zone Continuum

Samples for NO3

-

 and NH4

+

 were preserved by chilling to 

near-freezing. Fe samples were preserved with ultrapure nitric 

acid (pH < 2). 

Samples for NO3

-

, NH4

+

, Fe, and Cl- were analyzed at 

the USGS National Water Quality Laboratory in Denver, 

Colorado. Methods are described in Fishman and Friedman 

(1989) and Fishman (1993).

Samples for δ15N–NO3

-

 and δ18O–NO3

-

 were analyzed at 

the USGS Reston Stable Isotope Laboratory (http://isotopes.

usgs.gov). Analyses were done by bacterial conversion of 

NO3

-

 to N2O and subsequent measurement on a continuous 

flow isotope-ratio mass spectrometer (Sigman and others, 

2001; Casciotti and others, 2002; Coplen and others, 2004), 

with values of δ15N and δ18O reported relative to N2 in air 

(AIR) and Vienna Standard Mean Ocean Water (VSMOW), 

respectively. Analyses of δ15N–NO3

-

 and δ18O–NO3

-

 were 

calibrated by analyzing laboratory solutions with known 

isotopic compositions, and data were normalized against 

internationally distributed reference materials (Böhlke and 

Coplen, 1995, Böhlke and others, 2003) for: δ15N–NO3

-

, 

IAEA-N3 = +4.7 per mil (‰) and USGS32 = +180 ‰, and 

for δ18O–NO3

-

, IAEA-N3 = +25.6 ‰ and USGS34 = –27.9 ‰. 

Average reproducibility of normalized values for samples 

analyzed more than once was about ±0.2 ‰ for δ15N–NO3

-

 and 

±0.4 ‰ for δ18O–NO3

-

. 

For plotting purposes, NO3

-

 and NH4

+

 concentrations less 

than the method reporting level (MRL) were plotted at onehalf of the MRL. The MRL for NO3

-

 was 0.016 mg N/L, and 

for NH4

+

, 0.04 mg N/L.

Project quality-control data are presented in table A1

(appendix A). These data demonstrate contaminationfree sampling and analysis, tight analytical precision, and 

negligible analytical bias.

Particle Tracking

Potential ground-water flow paths for advection of 

NO3

-

 from septic tank sources to near-river environments 

were delineated using a numerical ground-water flow 

model (Morgan and others, 2007) in conjunction with the 

MODPATH particle tracking program (Pollock, 1994). For 

these simulations, four particles were placed at the water table 

in each water-table cell in the model and tracked to the river 

location where they were simulated to discharge. Aquiferscale denitrification was represented in the flow model using 

the redox-boundary approach in which NO3

-

 transported 

across the redox boundary (from oxic to suboxic conditions) 

was assumed to be instantaneously denitrified. Pathlines for 

particles that were transported into the suboxic part of the 

system were removed from the ensemble of oxic and suboxic 

pathlines. In these simulations, aquifer-scale denitrification 

processes were the only chemical reactions represented in the 

model; additional near-river reactions were not represented. 

Although flow-model boundary conditions accounted 

for and allowed evapotranspiration and discharge to wells, 

particles in the particle-tracking simulations were not allowed 

to leave the system by evapotranspiration or discharge to 

wells and particles did not represent volumes of ground-water 

discharge. Therefore, greater densities of pathlines should not 

be interpreted as greater volumes of ground-water discharge to 

rivers.

Previous Near-River Redox Work in 

Study Area

Hydraulic gradients between ground water and surface 

water at 32 sites in the study area were measured with a 

minipiezometer during autumn 2000 (Morgan and others, 

2007). One or more measurements of hydraulic gradient were 

made at each site, at depths of 1.0, 2.0, and (or) 3.0 ft. In 

conjunction with that work, reconnaissance-level geochemical 

data were collected at seven sites along the Little Deschutes 

River (table A2, appendix A). One sample was collected at 

the center of the river at each site. Additional samples were 

collected at one of the seven sites: one sample half-way 

between the center of the river and the edge of the river in 

each direction. Thus, six sites were represented by single 

samples, and one site (at river mile 24.9) was represented by 

three samples.

Samples were analyzed for NO3

-

 and NH4

+

. O2 was 

not measured, but the presence or absence of H2S odor was 

noted (the presence of H2S odor indicates highly reducing 

water). Samples were analyzed by Oregon Department of 

Environmental Quality, by methods described in Hinkle and 

others (2007). Collection and processing protocols were the 

same as those used in the current study.

Samples collected at each of the six single-sample sites 

contained H2S, indicating the presence of highly reducing 

water; these samples were considered to be suboxic. These 

six samples contained NH4

+

 at concentrations ranging from 

0.34 to 2.6 mg N/L and NO3

-

 at concentrations less than 0.1 

mg N/L, reflecting the suboxic conditions. The presence 

of suboxic ground water is consistent with concepts that 

describe mechanisms by which ground water may evolve to 

suboxic conditions in the aquifer prior to reaching the nearriver environment, or may become reduced in the near-river 

environment.

Samples collected at the multi-sample site (Little 

Deschutes River at river mile 24.9) indicated spatially 

variable redox conditions. The sample near the left edge of 

water (defined from a position facing downstream) contained 

H2

S, NH4

+

 at a concentration of 0.31 mg N/L, and NO3

-

 at a 

concentration of only 0.011 mg N/L, consistent with reduced 

conditions. The other two samples contained no detectable 
Results 9

H2S, contained NH4

+

 at concentrations less than the Oregon 

Department of Environmental Quality MRL of 0.02 mg 

N/L, and contained NO3

-

 at elevated concentrations (1.29 

and 2.73 mg N/L). These data indicate that less reduced 

(apparently either O2- or NO3

-

-reducing) ground water was 

present in these two samples. The samples were collected from 

the center of the river and from a point near the right edge of 

water. The site was where the Little Deschutes River bends 

toward the eastern edge of the riparian zone. Less reduced 

ground water entering the river in the center and right edge 

where the right edge of the river cuts toward the edge of the 

riparian zone also is consistent with concepts presented earlier 

in this report.

Of these seven sites, the site on the Little Deschutes River 

at river mile 24.9 was particularly valuable because (1) NO3

-

was detected in some ground water under the river, and (2) the 

boundary between NO3

-

-bearing (either O2- or NO3

-

-reducing) 

and more reduced ground water was identified. This site was 

resampled in greater detail as part of this study.

Results

The locations of the 10 ground-water transect sites are 

shown in figure 1. Well locations and screen depths are listed 

in table 1. Geochemical data are listed in table 2.

Transect Configurations

Transects generally consisted of a well installed in the 

center of the river, and one or more wells toward each edge of 

the river (lateral wells) (fig. 3). Lateral wells generally were 

installed near the river edge in coarse sediments and not in 

sloughed bank material. These wells tapped sediments likely 

to have a relatively direct connection to aquifer sediments, 

rather than collapsed-bank sediments that may behave 

more as a barrier than a conduit for aquifer discharge to the 

river. Most wells were screened at 1.0 ft below the riverbed. 

Transect configurations that deviated from these guidelines are 

discussed below.

Ground-Water Transects on Deschutes River

Site D194.1 consisted of two wells (table 1). River depth 

prevented installation of a well in the center.

Site D198.5 consisted of four wells: one in the center, 

one at each bank, and one toward the left edge of water. In 

attempting to install a well near (but not at) the left edge 

of water to complement the well at the left edge, multiple 

attempts at increasingly greater distances away from the 

left edge failed to yield a well that would produce water, 

until a well installed 18.8 ft from the left edge produced 

water. Sediment on the riverbed at this point was silt with 

macrophytes—conditions that generally were avoided but 

were accepted in this instance due to difficulty in finding a 

suitable location closer to the left edge of water. Sub-riverbed 

sediments between this well and the left edge of water 

probably are heterogeneous and have little correlation to 

lithologies on the riverbed itself.

Ground-Water Transects on Little Deschutes 

River

Site LD16.1 consisted of five wells. One nest of two 

wells (depths of 1.0 and 2.0 ft) was installed in the center 

of the river, another nest (depths of 1.0 and 2.0 ft) toward 

the left edge, and a single well toward the right edge. The 

shallow (1.0 ft) ground water in the center and near the left 

edge contained oxic, dilute ground water. Values of specific 

conductance (related to dissolved-ion content) were 53 and 

58 μS/cm at 25°C, respectively (table 2), similar to the value 

of 54 μS/cm at 25°C measured in the river water during well 

installation. The presence of oxic ground water with specific 

conductance values similar to the specific conductance of 

river water suggested the presence of hyporheic water. The 

hyporheic zone is a place of interaction between river and 

ground water, commonly occurring in near-river sediments. 

Physical processes occurring at small spatial scales can 

promote hyporheic exchanges against a backdrop of 

unidirectional hydraulic gradients at larger spatial scales. 

For example, hyporheic exchanges can occur in response to 

localized hydraulic gradients arising from pool-and-riffle 

sequences in rivers (Harvey and Bencala, 1993). The apparent 

presence of hyporheic water prompted the decision to install 

deeper wells because the presence of oxic, hyporheic water in 

sediments under a river does not provide information about the 

redox state of ground water moving from terrestrial recharge 

areas to the river. The deeper (2.0 ft) ground water in the 

center and near the left edge contained suboxic ground water 

with slightly greater values of specific conductance (63 and 

71 μS/cm at 25°C, respectively). The deeper ground water 

was more geochemically evolved than the shallower ground 

water, indicating that either hyporheic water had undergone a 

longer geochemical evolution, or ground water had entered the 

sediments from recharge areas away from the river. Regardless 

of the origin of the deeper ground water, the presence of 

suboxic ground water at a depth of 2.0 ft at these two points 

represents a NO3

-

-reducing zone between the river at these 

locations and terrestrial recharge areas.
10 Ground Water Redox Zonation near LaPine, Oregon: Relation to River Position within the Aquifer-Riparian Zone Continuum

Table 1. Ground-water transect site wells and miscellaneous sites near La Pine, Oregon, March and October 2006. 

[Well and site locations are shown in figure 1. Depth, depth of center of screen below riverbed. Latitude and longitude of center of transect: in 

degrees, minutes, seconds; North American Datum of 1927 (NAD 27). Abbreviations: LEW, left edge of water looking downstream; RM, river mile; 

–, not collected]

Well or 

site No.

Distance from 

LEW

(feet)

Depth

(feet)

Width

(feet) Station No. Latitude Longitude

Ground-water transect site wells near Deschutes River

D194.1.1 3.0 1.0 88 435033121275501 43°50'33.0" 121°27'54.8"

D194.1.2 85.0 1.0 88 435033121275502 43°50'33.0" 121°27'54.8"

D198.5.1 37.5 1.0 75 434920121292201 43°49'19.7" 121°29'22.5"

D198.5.2 .0 1.0 75 434920121292202 43°49'19.7" 121°29'22.5"

D198.5.3 75.0 1.0 75 434920121292203 43°49'19.7" 121°29'22.5"

D198.5.4 18.8 1.0 75 434920121292204 43°49'19.7" 121°29'22.5"

D206.4.1 30.5 1.0 61 434638121304301 43°46'38.0" 121°30'42.8"

D206.4.2 3.0 1.0 61 434638121304302 43°46'38.0" 121°30'42.8"

D206.4.3 58.0 1.0 61 434638121304303 43°46'38.0" 121°30'42.8"

Ground-water transect site wells near Little Deschutes River

LD2.4.1 29.0 1.0 58 435018121265001 43°50'18.1" 121°26'50.0"

LD2.4.2 3.0 1.0 58 435018121265002 43°50'18.1" 121°26'50.0"

LD2.4.3 55.0 1.0 58 435018121265003 43°50'18.1" 121°26'50.0"

LD5.7.1 19.0 1.0 38 434908121265401 43°49'07.9" 121°26'54.1"

LD5.7.2 9.0 1.0 38 434908121265402 43°49'07.9" 121°26'54.1"

LD5.7.3 29.0 1.0 38 434908121265403 43°49'07.9" 121°26'54.1"

LD13.4.1 19.0 1.0 38 434623121283601 43°46'23.1" 121°28'36.3"

LD13.4.2 6.0 1.0 38 434623121283602 43°46'23.1" 121°28'36.3"

LD13.4.3 30.0 1.0 38 434623121283603 43°46'23.1" 121°28'36.3"

LD16.1.1 27.0 1.0 54 434512121290301 43°45'12.3" 121°29'02.6"

LD16.1.2 5.5 1.0 54 434512121290302 43°45'12.3" 121°29'02.6"

LD16.1.3 52.5 1.0 54 434512121290303 43°45'12.3" 121°29'02.6"

LD16.1.4 5.5 2.0 54 434512121290304 43°45'12.3" 121°29' 02.6"

LD16.1.5 27.0 2.0 54 434512121290305 43°45'12.3" 121°29' 02.6"

LD24.9.1 26.5 1.0 53 434212121295201 43°42'12.4" 121°29' 52.4"

LD24.9.2 .0 1.0 53 434212121295202 43°42'12.4" 121°29'52.4"

LD24.9.3 40.0 1.0 53 434212121295203 43°42'12.4" 121°29'52.4"

LD24.9.4 26.5 2.0 53 434212121295204 43°42'12.4" 121°29'52.4" 1

LD24.9.5 40.5 1.0 54 434212121295205 43°42'12.4" 121°29'52.4" 2

LD24.9.6 25.6 1.0 35 434212121295206 43°42'12.4" 121°29'52.4"

LD24.9.7 53.0 1.0 53 434212121295207 43°42'12.4" 121°29'52.4"

LD24.9.8 53.0 2.0 53 434212121295208 43°42'12.4" 121°29'52.4"

LD24.9.9 53.0 3.0 53 434212121295209 43°42'12.4" 121°29'52.4"

LD32.8.1 25.0 2.0 41 434016121325301 43°40'16.4" 121°32'52.7"

LD32.8.2 3.0 1.0 41 434016121325302 43°40'16.4" 121°32'52.7"

LD32.8.3 38.0 2.0 41 434016121325303 43°40'16.4" 121°32'52.7"

LD32.8.4 31.5 2.0 41 434016121325304 43°40'16.4" 121°32'52.7"

LD37.8.1 16.5 2.0 33 433848121352901 43°38'48.5" 121°35'29.2"

LD37.8.2 1.0 2.0 33 433848121352902 43°38'48.5" 121°35'29.2"

LD37.8.3 29.0 2.0 33 433848121352903 43°38'48.5" 121°35'29.2"

LD37.8.4 6.0 2.0 33 433848121352904 43°38'48.5" 121°35'29.2"

Miscellaneous sites near Deschutes River

Slough at RM 194.8 – – – 435014121274900 43°50'13.7" 121°27'49.0"

Spring at RM 209.2 – – – 434627121321001 43°46'27.2" 121°32'09.6"

1

 At thalweg (deepest point in the river cross section), 16 feet downstream of primary transect.

2

 At thalweg, 69 feet downstream of primary transect.
Results 11

Table 2. Chemical and isotopic data for ground-water transect site wells and miscellaneous sites near La Pine, Oregon, March and 

October 2006.

[Well locations are shown in figure 1. Depth, depth of center of screen below riverbed. Abbreviations: mg/L, milligram per liter; μS/cm, microsiemens per 

centimeter at 25°C; °C, degrees Celsius; mg N/L, milligram of nitrogen per liter; μg/L, microgram per liter; RM, river mile; ‰, per mil; <, less than; –, not 

collected]

Well or 

site No. Date Time Depth(feet)

Dissolved 

oxygen

(mg/L)

Specific 

conductance

(μS/cm)

Temperature

(°C)

Chloride

(mg/L)

Ammonium

(mg N/L)

Nitriteplusnitrate

(mg N/L)

Iron

(μg/L)

δ15NNO3

-

(‰)

δ18ONO3

-

(‰)

Ground-water transect site wells near Deschutes River

D194.1.1 03-07-06 1300 1.0 0.3 144 3.9 3.44 1.19 <0.016 7,360 – –

D194.1.2 03-07-06 1400 1.0 .5 195 3.6 2.20 .30 <.016 12,700 – –

D198.5.1 03-06-06 1800 1.0 .1 115 4.4 .74 .17 <.016 609 – –

D198.5.2 03-06-06 1700 1.0 5.1 170 5.1 5.30 <.04 .131 <6 – –

D198.5.3 03-08-06 1000 1.0 .1 323 2.3 .86 1.37 <.016 12,000 – –

D198.5.4 03-08-06 1300 1.0 .2 125 4.0 .89 .23 <.016 4,790 – –

D206.4.1 03-09-06 1100 1.0 .3 95 2.2 .81 <.04 <.016 25 – –

D206.4.2 03-09-06 1300 1.0 .3 243 2.0 .80 .33 <.016 9,040 – –

D206.4.3 03-08-06 1700 1.0 .4 117 3.9 1.24 <.04 <.016 2,580 – –

Ground-water transect site wells near Little Deschutes River

LD2.4.1 03-14-06 1200 1.0 0.2 108 1.4 1.95 <0.04 <0.016 38 – –

LD2.4.2 03-14-06 1400 1.0 .2 184 2.1 2.58 .52 <.016 12,000 – –

LD2.4.3 03-14-06 1500 1.0 .3 209 3.2 1.49 .69 <.016 14,400 – –

LD5.7.1 03-15-06 1500 1.0 .4 118 2.8 2.56 .51 <.016 11,000 – –

LD5.7.2 03-15-06 1400 1.0 .3 106 2.9 2.22 <.04 <.016 350 – –

LD5.7.3 03-15-06 1300 1.0 .3 138 4.3 4.35 .60 <.016 10,400 – –

LD13.4.1 10-11-06 1300 1.0 .4 73 10.8 .96 .21 <.016 218 – –

LD13.4.2 10-11-06 1400 1.0 .4 228 11.9 .84 1.59 <.016 16,700 – –

LD13.4.3 10-11-06 1600 1.0 .4 125 12.1 .38 .24 <.016 186 – –

LD16.1.1 03-16-06 1200 1.0 4.6 53 3.1 1.21 <.04 .048 751 – –

LD16.1.2 03-16-06 1000 1.0 3.5 58 2.2 1.20 <.04 .088 15 – –

LD16.1.3 03-13-06 1600 1.0 .2 206 2.9 3.24 .99 .021 14,600 – –

LD16.1.4 03-16-06 1100 2.0 .2 71 2.7 1.15 <.04 <.016 1,710 – –

LD16.1.5 03-16-06 1400 2.0 .2 63 2.9 1.09 .07 <.016 2,680 – –

LD24.9.1 10-02-06 1600 1.0 1.0 52 13.5 .66 <.04 .098 35 – –

LD24.9.2 10-03-06 1000 1.0 .1 62 11.5 .58 .11 <.016 2,060 – –

LD24.9.3 10-02-06 1800 1.0 .1 173 12.6 6.14 <.04 1.57 296 9.7 -4.0

LD24.9.4 10-02-06 1700 2.0 .2 94 13.3 1.49 .05 .068 35 – – 1

LD24.9.5 10-03-06 1100 1.0 .2 105 12.1 1.80 .22 <.016 4,570 – – 2

LD24.9.6 10-03-06 1300 1.0 .2 254 12.9 9.44 .50 <.016 10,700 – –

LD24.9.7 10-12-06 1700 1.0 .7 184 10.2 6.74 <.04 .701 45 14.3 -.5

LD24.9.8 10-12-06 1730 2.0 .7 181 9.1 6.71 <.04 1.24 17 10.5 -3.0

LD24.9.9 10-12-06 1800 3.0 1.1 178 8.7 6.39 <.04 1.30 20 9.1 -4.4

LD32.8.1 10-05-06 1500 2.0 .1 90 11.7 .73 1.83 .080 169 – –

LD32.8.2 10-05-06 1400 1.0 .1 67 12.2 .66 1.17 <.016 2,150 – –

LD32.8.3 10-05-06 1300 2.0 .2 213 9.2 1.03 7.73 <.016 3,900 – –

LD32.8.4 10-05-06 1600 2.0 .1 153 11.4 .91 4.17 <.016 1,100 – –

LD37.8.1 10-04-06 1200 2.0 .2 50 11.9 .48 <.04 <.016 77 – –

LD37.8.2 10-04-06 1400 2.0 2.8 46 12.4 .59 <.04 .118 57 – –

LD37.8.3 10-04-06 1430 2.0 .1 95 10.4 .58 .12 <.016 6,790 – –

LD37.8.4 10-04-06 1500 2.0 2.4 42 12.6 .57 <.04 .156 76 – –

Miscellaneous sites near Deschutes River

Slough at RM 194.8 03-07-06 1000 – 5.2 171 0.9 13.2 0.63 0.278 1,650 11.9 -1.0

Spring at RM 209.2 03-09-06 1500 – .2 131 6.3 .75 .15 <.016 3,460 – –

1

 At thalweg (deepest point in the river cross section), 16 feet downstream of primary transect.

2

 At thalweg, 69 feet downstream of primary transect.
12 Ground Water Redox Zonation near LaPine, Oregon: Relation to River Position within the Aquifer-Riparian Zone Continuum

OR19_0152_LaPine_fig_03

0.0

1.0

2.0

3.0

4.0

5.0 0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0

0.0

1.0

2.0

3.0

4.0

DEPTH BELOW WATER SURFACE, IN FEET

5.0 0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0

0.0

1.0

2.0

3.0

4.0

5.0 0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0

RIVER MILE 194.1

DESCHUTES RIVER

RIVER MILE 198.5

RIVER MILE 206.4

DISTANCE FROM LEFT EDGE OF WATER, IN FEET

VERTICAL EXAGGERATION X 5

1

144

3.44

1.19

<0.016

2

195

2.20

0.30

<0.016

2

170

5.30

<0.04

0.131

1

115

0.74

0.17

<0.016

3

323

0.86

1.37

<0.016

4

125

0.89

0.23

<0.016

1

95

0.81

<0.04

<0.016

2

243

0.80

0.33

<0.016

3

117

1.24

<0.04

<0.016

Oxic conditions

Sub-oxic conditions

Center of screened interval of well

1

95

0.81

<0.04

<0.016

Well sequence number

Specific conductance (μS/cm)

Chloride (mg/L) 

Ammonium (mg N/L)

Nitrate (mg N/L) 

Gravel

Sand

Silt

Clay

Macrophyte bed

River bed lithology

EXPLANATION

Figure 3. Configurations of ground-water transects at Deschutes and Little Deschutes Rivers near La Pine, Oregon. 

(Two wells at river mile 24.9 on the Little Deschutes River were installed downstream of the cross section and are not 

shown.)
Results 13

OR19_0152_LaPine_fig_03_B

0.0

1.0

2.0

3.0

4.0

5.0 0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0

0.0

1.0

2.0

3.0

4.0

DEPTH BELOW WATER SURFACE, IN FEET 5.0 0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0

0.0

1.0

2.0

3.0

4.0

5.0 0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0

0.0

1.0

2.0

3.0

4.0

5.0 0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0

RIVER MILE 2.4

RIVER MILE 5.7

RIVER MILE 13.4

RIVER MILE 16.1

DISTANCE FROM LEFT EDGE OF WATER, IN FEET

VERTICAL EXAGGERATION X 5

LITTLE DESCHUTES RIVER

1

53

1.21

<0.04

0.048

2

58

1.20

<0.04

0.088

1

108

1.95

<0.04

<0.016

2

184

2.58

0.52

<0.016

3

209

1.49

0.69

<0.016

1

118

2.56

0.51

<0.016

2

106

2.22

<0.04

<0.016

3

138

4.35

0.60

<0.016

1

73

0.96

0.21

<0.016

2

228

0.84

1.59

<0.016

3

125

0.38

0.24

<0.016

3

206

3.24

0.99

0.021

4

71

1.15

<0.04

<0.016

5

63

1.09

0.07

<0.016

Oxic conditions

Sub-oxic conditions

Center of screened interval of well

1

95

0.81

<0.04

<0.016

Well sequence number

Specific conductance (μS/cm)

Chloride (mg/L) 

Ammonium (mg N/L)

Nitrate (mg N/L) 

Gravel

Sand

Silt

Clay

Macrophyte bed

River bed lithology

EXPLANATION

Figure 3.—Continued
14 Ground Water Redox Zonation near LaPine, Oregon: Relation to River Position within the Aquifer-Riparian Zone Continuum

OR19_0152_LaPine_fig_03_C

0.0

1.0

2.0

3.0

4.0

5.0 0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0

0.0

1.0

2.0

3.0

4.0

DEPTH BELOW WATER SURFACE, IN FEET

5.0 0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0

0.0

1.0

2.0

3.0

4.0

5.0 0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0

RIVER MILE 24.9

LITTLE DESCHUTES RIVER—CONTINUED

RIVER MILE 32.8

RIVER MILE 37.8

DISTANCE FROM LEFT EDGE OF WATER, IN FEET

VERTICAL EXAGGERATION X 5

1

52

0.66

<0.04

0.098

2

62

0.58

0.11

<0.016

3

173

6.14

<0.04

1.57

4

94

1.49

0.05

0.068

7

184

6.74

<0.04

0.701 8

181

6.71

<0.04

1.24

9

178

6.39

<0.04

1.30

1

90

0.73

1.83

0.080

2

67

0.66

1.17

<0.016

3

213

1.03

7.73

<0.016

4

153

0.91

4.17

<0.016

1

50

0.48

<0.04

<0.016

2

46

0.59

<0.04

0.118

3

95

0.58

0.12

<0.016

4

42

0.57

<0.04

0.156

Oxic conditions

Sub-oxic conditions

Center of screened interval of well

1

95

0.81

<0.04

<0.016

Well sequence number

Specific conductance (μS/cm)

Chloride (mg/L) 

Ammonium (mg N/L)

Nitrate (mg N/L) 

Gravel

Sand

Silt

Clay

Macrophyte bed

River bed lithology

EXPLANATION

Figure 3.—Continued
Results 15

Site LD24.9, with nine wells, was more densely 

instrumented than the other sites in an attempt to provide a 

more detailed characterization of the nature and geometry 

of the oxic/suboxic boundary in the near-river environment 

(table 1). Seven of the nine wells were installed along one 

transect, and the other two wells were installed in the river 

thalweg (deepest part of the channel) 16 and 69 ft downstream 

of the primary transect. One nest of two wells (depths of 1.0 

and 2.0 ft) was installed in the center of the river. One well 

was installed at the left edge of water, another well between 

the center of the river and the right edge of the river, and a nest 

of three wells at the right (east) edge of water (depths of 1.0, 

2.0, and 3.0 ft).

The shallow well in the center of the river (LD24.9.1) 

yielded oxic water with a specific conductance of 

52 μS/cm at 25°C, similar to the specific conductance of the 

river water during well installation (46 μS/cm at 25°C). The 

deeper well in the center (LD24.9.4) was suboxic, with a 

specific conductance of 94 μS/cm at 25°C. As was observed at 

site LD16.1, a layer of oxic hyporheic water appears to overlie 

a deeper layer of suboxic ground water in part of the transect 

at LD24.9.

The nest of three wells at the right edge of water at site 

LD24.9 (fig. 3) was installed to provide increased definition 

of the geochemical nature of ground water entering the 

river from the east—the presumed source area for NO3

-

previously measured in ground water near this site (table A2, 

appendix A). The nest of wells was installed at the transect 

edge where the riverbed was composed of silt. However, there 

was no obvious bank slough, and the river reach at this site 

was primarily sand and gravel, indicating an overall coarsetextured sedimentary geologic framework.

The two off-transect wells at site LD24.9 were installed 

to provide information about the longitudinal scale of the 

NO3

-

–bearing ground-water plume at this site. These wells 

also helped characterize the spatial heterogeneity of oxic and 

suboxic ground water occurrence in near-river ground water. 

At site LD32.8, an island caused most water to flow in 

a right channel, and a small amount of water to flow in a left 

channel. Site LD32.8 consisted of three wells in the right 

channel, including one in the center of that channel, plus one 

well near the left edge of the left channel. The three wells in 

the right channel were installed at a depth of 2.0 ft because of 

concern that the well-sorted, coarse gravel in the bed of the 

right channel at this site could promote hyporheic flow. The 

left channel, however, was sandy, and the well depth there was 

set at 1.0 ft.

Site LD37.8 consisted of four wells. The riverbed at 

site LD37.8 consisted primarily of well-sorted, coarse gravel 

(some gravely sand near the right edge), so the wells were 

installed at depths of 2.0 ft in an attempt to sample below 

possible hyporheic water.

Redox Conditions, Nitrogen, and Chloride in 

Ground Water from Transects

The previous section described well nests at transects 

LD16.1 (two nests) and LD24.9 (one nest) that yielded oxic 

ground water in shallower wells and suboxic ground water 

in deeper wells. Other wells yielding oxic ground water 

were (1) the well at the left edge of water at D198.5, (2) all 

three wells in the nest at the right edge of water at LD24.9, 

and (3) the two wells near the left edge of water at LD37.8. 

(The O2 concentration in ground water near the right edge 

of water at D194.1.2, 0.5 mg/L was borderline oxic/suboxic. 

This ground water had a H2S odor and an Fe concentration of 

12,700 μg/L—one of the highest Fe concentrations measured 

in this study. These data indicate strongly reducing conditions. 

Thus, this sample is considered to be suboxic.)

Origin of water and solutes, availability of nutrients, 

and additional characterization of redox conditions can 

be inferred by evaluating concentrations of and relations 

between O2

, NO3

-

, NH4

+

, Fe, and Cl-. Relations between Fe 

and O2 concentrations (fig. 4A) reflect the suppression of Fe 

dissolution in the presence of O2 and in the absence of strongly 

acidic (for example, acid-mine drainage) conditions. This 

pattern is consistent with basic principles of redox progression 

in aquifers.

Relations between Fe and NO3

-

 concentrations (fig. 4B) 

also are consistent with the expected sequence of redox 

progression in aquifers. Concentrations of NO3

-

 are low or less 

than the MRL in Fe-rich ground water.

Nitrate and NH4

+

 appear to be mutually exclusive 

(fig. 4C). NH4

+

 is a reduced form of N, but reduction from 

NO3

-

 to NH4

+

 generally is for assimilation (Brock and 

Madigan, 1988), and most NO3

-

 reduction in ground water is 

by denitrification, usually to N2 (Freeze and Cherry, 1979). 

However, NO3

-

 or NH4

+

 occurrence does reflect environmental 

redox state—NO3

-

 is stable and mobile in oxic ground water, 

whereas elevated concentrations of NH4

+

 tend to occur in 

suboxic ground water (fig. 4D).

Patterns of NO3

-

 and NH4

+

 in ground water near La Pine 

also reflect different sources of NO3

-

 and NH4

+

. Concentrations 

of Cl- also reflect NO3

-

 and NH4

+

 origin; Cl- is a particularly 

useful tracer because it is nonreactive in most ground 

water systems. Septic tank effluent contains several tens of 

milligrams of N and Cl- per liter, and NO3

-

 and Cl- co-occur in 

ground water receiving septic tank effluent. Other potential Clsources, such as road salt applications, agricultural fertilizers, 

and dissolution of evaporites, generally are negligible in the 

study area (Hinkle and others, 2007). Ground water in the La 

Pine study area with background concentrations of Cl- (on 

the order of a few milligrams per liter or less) indicate that 

ground water is unimpacted or minimally impacted by septic 

tank effluent, whereas concentrations of more than several 

milligrams per liter frequently indicate a septic tank effect. 
16 Ground Water Redox Zonation near LaPine, Oregon: Relation to River Position within the Aquifer-Riparian Zone Continuum

OR19-0152_fig03

DISSOLVED OXYGEN, IN MILLIGRAMS PER LITER

IRON, IN MICROGRAMS PER LITER

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

18,000

IRON, IN MICROGRAMS PER LITER

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

18,000

AMMONIUM, IN MILLIGRAMS N PER LITER

0

1

2

3

4

5

6

7

8

A. Dissolved oxygen and Iron D. Dissolved oxygen and ammonium

B. Nitrite-plus-nitrate and iron

C. Nitrite-plus-nitrate and ammonium

E. Chloride and ammonium

NITRITE-PLUS-NITRATE, IN MILLIGRAMS N PER LITER CHLORIDE, IN MILLIGRAMS PER LITER AMMONIUM, IN MILLIGRAMS N PER LITER

0

1

2

3

4

5

6

7

8

NITRITE-PLUS-NITRATE, IN MILLIGRAMS N PER LITER

AMMONIUM, IN MILLIGRAMS N PER LITER

0

1

2

3

4

5

6

7

8

0 1 2 3 4 5 6

0 0.5 1.0 1.5 2.0 0 1 2 3 4 5 6 7 8 9 10

0 0.5 1.0 1.5 2.0

DISSOLVED OXYGEN, IN MILLIGRAMS PER LITER

0 1 2 3 4 5 6

Figure 4. Relation between chemical constituents in samples from wells at all ground water transects in the 

Deschutes and Little Deschutes Rivers near La Pine, Oregon, March and October 2006. 
Discussion 17

Mineralization of sedimentary organic matter, however, yields 

ground water characterized by elevated concentrations of 

NH4

+

 but low concentrations of Cl-. Patterns of NH4

+

 and Cl-

(fig. 4E) reflect this source of NH4

+

.

Redox data presented in figure 4 demonstrate 

understandable patterns of solute occurrence within a redox 

framework. Such a framework can be used to infer the 

sources of some solutes and to predict the occurrence of 

redox-sensitive solutes within a given redox zone. 

Spring and Slough Samples

Ground water enters rivers through sediments beneath the 

rivers; this part of the resource was the component intercepted 

by transect wells. Ground water also enters rivers by discharge 

from springs and seeps. Data collection activities often 

relied on canoe access, an activity that, along with additional 

scouting from roads and trails, provided opportunities for 

identification of springs and seeps. Numerous seeps and 

minor springs were observed, but only one flowing spring was 

found (river mile 209.2 on the Deschutes River) that yielded 

sufficient water volume for meaningful measurement of O2

and for collection of water samples with a peristaltic pump 

(fig. 1, tables 1 and 2). The spring water was suboxic.

Samples were collected from one slough, a cut-off 

meander bend of the Deschutes River at river mile 194.8 

(fig. 1, tables 1 and 2). At the time of sampling, the water 

elevation in the slough was greater than the elevation of the 

Deschutes River, and drainage occurred through a narrow, 

flowing stream connecting the slough to the river. The slough 

water was oxic, as would be expected for such a surface-water 

body. However, other data from the slough indicated the 

presence of complex geochemistry.

Discussion

Distribution of Dissolved Oxygen and Nitrate in 

Ground Water in the Near-River Environment

Oxic ground water was uncommon in transect samples, 

in spite of a sampling design that emphasized identification 

of oxic ground water. Some well nests at transects LD16.1 

and LD24.9 yielded oxic ground water in shallower wells 

and suboxic ground water in deeper wells. In these well 

nests, shallow, oxic ground water was attributed to hyporheic 

processes, whereas deeper, suboxic ground water represented a 

NO3

-

–reducing zone between the river and terrestrial recharge 

areas. Other occurrences of oxic ground water are discussed in 

the following three paragraphs.

Oxic ground water from the well at the left edge of 

water at D198.5.2 appears to have originated in terrestrial 

recharge areas. The specific conductance, 170 μS/cm at 

25°C, and Cl- concentration, 5.30 mg/L, suggest such an 

origin. The concentration of Cl- could indicate a possible 

septic tank influence on the ground water. However, the 

NO3

-

 concentration, 0.131 mg N/L, does not support such a 

link. Furthermore, the region upgradient from this transect 

is one of the few sewered neighborhoods in the La Pine 

study area (fig. 1). Wastewater is treated nearby; wastewater 

lagoons are within 0.25 mi of the transect, and land-based 

wastewater disposal occurs adjacent to the lagoons. Such 

wastewater would be expected to be low in N but still retain 

wastewater Cl-. This could be a source of the slightly elevated 

Cl- concentration for water from the well at the left edge of the 

transect. Although specific conductance and Cl- data indicate 

that this oxic sample has a terrestrial recharge origin, the 

sample possibly represents a mixture of (1) ground water that 

is relatively enriched in solutes but is suboxic, and (2) river 

water that is relatively dilute but is oxic. However, the Clconcentration, 5.30 mg/L, is typical of wastewater-impacted

ground water in the study area (Hinkle and others, 2007), 

indicating minimal dilution, whereas the O2 concentration, 

5.1 mg/L, would require a considerable component of river 

water.

Oxic ground water in two wells near the left edge 

of water at LD37.8 (LD37.8.2 and LD37.8.4) could have 

originated as terrestrial recharge or as hyporheic water. 

The wells were screened at 2.0 ft, and deeper wells were 

not installed. The dilute nature of the water from these 

wells—specific conductance 46 and 42 μS/cm at 25°C and 

Cl- concentrations 0.59 and 0.57 mg/L, respectively—would 

be consistent with water originating as hyporheic water. 

Alternatively, such dilute ground water could have been 

recharged locally, such as ground water originating from 

near-river flood plains that receive recharge from precipitation 

or dilute river water during floods. The dilute nature of this 

ground water indicates that distal terrestrial recharge areas 

are a less likely source of this water than local or hyporheic 

recharge areas. The presence of oxic but dilute ground water 

at these locations, without additional data from deeper wells, 

leaves delineation of the oxic/suboxic boundary for the left 

side of the transect at LD37.8 ill-defined because the redox 

state of ground water upgradient (earlier in the flow paths) 

from the dilute, oxic ground water is not known. 

Oxic ground water in samples collected from all three 

wells (LD24.9.7, LD24.9.8, and LD24.9.9) in the nest at 

the right edge of water at LD24.9 probably originated in 

terrestrial recharge areas. Specific conductance values for 

water from these three wells, 178–184 μS/cm at 25°C, and 

Cl-

 concentrations, 6.39–6.74 mg/L, were similar. Dissolved 
18 Ground Water Redox Zonation near LaPine, Oregon: Relation to River Position within the Aquifer-Riparian Zone Continuum

oxygen (and NO3

-

) concentrations were lower at the 1.0-ft 

zone than at the 3.0-ft zone (table 2). This redox sequence 

is inverted from the sequence typically observed in recharge 

areas, where ground-water flow has a downward component 

and redox conditions tend to progress from less reduced 

at shallow depths to more reduced at greater depths. The 

physically inverted redox sequence at this well nest is 

consistent with the typical mechanism of discharge through a 

riverbed, in which ground water moves through the near-river 

environment toward the river with an upward component of 

flow, and in which redox conditions evolve from less reduced 

toward more reduced conditions along the flow path. In this 

case, redox conditions in some ground water sampled from 

this transect remained oxic to the end of the flow path at the 

river, or at least to within 1 vertical foot of the river edge. 

Four transect wells at LD24.9 yielded ground water with 

NO3

-

 concentrations greater than 0.2 mg N/L. All four wells 

were at LD24.9, a transect near the outskirts of the city of 

La Pine where residential development has been in place for 

several decades. These four wells included the nest of three at 

the right edge of water (LD24.9.7, LD24.9.8, and LD24.9.9), 

and the well 13 ft from the right edge of water (LD24.9.3). 

Concentrations of NO3

-

 ranged from 0.701 to 1.57 mg N/L 

(table 2). The three wells at the right edge of water were oxic, 

but well LD24.9.3 was suboxic.

In the redox boundary approach developed to represent 

the occurrence of denitrification in the La Pine study area, 

Hinkle and others (2007) observed that the oxic/suboxic 

boundary closely matched the denitrification boundary, and 

as such, was a useful representation of denitrification at 

the aquifer scale. However, a redox boundary that appears 

relatively sharp at the aquifer scale may appear more 

gradational at smaller spatial scales. Some NO3

-

 may be 

denitrified on the oxic side of the boundary in response to 

denitrification in reduced microenvironments, and some 

NO3

-

 may be advected beyond the oxic/suboxic boundary as 

microbial systems adjust from O2-reducing to NO3

-

-reducing 

conditions. Thus, the occurrence of NO3

-

 in suboxic ground 

water in one well is reasonable, especially in light of the 

geochemical structure at this site, where oxic, NO3

-

-bearing 

ground water apparently migrated to the right edge of the 

river without evolving to suboxic conditions. The redox 

sequence at the right edge of water, in which both O2 and 

NO3

-

 concentrations decreased with increasing proximity to 

the riverbed, also is consistent with redox boundary concepts 

in that some NO3

-

 may undergo denitrification at microsites 

of anoxia within the oxic zone prior to arrival at the redox 

boundary.

Samples collected from the four wells at and near the 

right edge of water at LD24.9 were analyzed for stable 

isotopes of NO3

-

 (fig. 5). The mean and standard deviation 

0

0 5

Ground-water samples

Septic-tank sand-filter effluent—Mean, with error bars indicating one 

 standard deviation for 27 samples collected as part of a previous study 

 in the La Pine area (U.S. Geological Survey, unpub. data). 

 Mean and median values were within 0.1 per mil.

10 15 20

-2

-4

-6

-8

-10

δ15N–NO3

-

, PER MIL

δ18O–NO3

- , PER MIL

EXPLANATION

of a set of 27 samples of septic tank effluent collected after 

percolation through unsaturated volcanic sand in the study 

area, approximating the isotopic character of septic tank 

NO3

-

 loaded to the aquifer, also are shown in figure 5. The 

enrichment in both δ15N–NO3

-

 and δ18O–NO3

-

 in the transect 

samples is indicative of fractionation during denitrification 

(Groffman and others, 2006), and indicates that NO3

-

 in 

these sediments had been partially denitrified. Thus, 

the oxic/suboxic boundary can be seen as an imperfect 

representation of the denitrification boundary, insofar as 

denitrification actually can begin before NO3

-

 reaches the 

boundary (as evidenced by the isotopes of NO3

-

) and can 

continue to occur downgradient from the boundary (as 

evidenced by the presence of NO3

-

 in ground water beyond the 

oxic/suboxic boundary). In locations where the oxic/suboxic 

boundary is near the river, some NO3

-

 can migrate beyond the 

boundary and potentially discharge to the river. On the other 

hand, as NO3

-

 approaches the oxic/suboxic boundary, some 

denitrification can occur prior to arriving at the oxic/suboxic 

boundary, lessening the mass of NO3

-

 available for discharge 

to the river.

Figure 5. Relation between δ15N and δ18O of nitrate in 

samples from wells at ground-water transect LD24.9 (wells 

containing nitrite-plus-nitrate concentrations greater than 

0.5 mg N/L) and sand-filter effluent from septic tanks near 

La Pine, Oregon.
Discussion 19

Integration of Ground-Water Flow Paths at a 

Cut-Off Slough

The slough that enters the Deschutes River at river mile 

194.8 (fig. 1) provided an opportunity to characterize surface 

water that likely received sizable contributions from multiple 

ground-water flow paths. Slough water may have contained 

a component of river water that entered the slough during a 

period of high river stage and (or) a component of surface 

runoff from snowmelt. However, slough water contained 

1,650 μg/L of Fe, indicating a component of suboxic ground 

water. (Oxic ground water may also discharge to the slough.) 

The balance between the kinetically controlled nature of Fe 

oxidation and precipitation, and the relatively short residence 

times of most surface water relative to most ground water, 

accounts for the presence of both O2 and Fe in the slough 

water. Slough water contained 0.278 mg N/L of NO3

-

 and 

0.63 mg N/L of NH4

+

, also indicating non-equilibrium redox 

conditions (table 2).

Nitrate in slough water could have been present in 

ground water that discharged to the slough (the area near the 

slough was developed earlier and more densely than most 

other locations in the study area). Alternatively, NO3

-

 in the 

slough could have been produced by nitrification of NH4

+

 in 

the presence of O2 in the slough. The δ15N–NO3

-

 value, 11.9 

‰ (table 2), suggests that NO3

-

 in the slough water primarily 

was from ground water (with possible denitrification of some 

NO3

-

). The Cl- concentration (13.2 mg/L) also is consistent 

with a ground-water source for the NO3

-

. Although slough 

water was not analyzed for δ15N–NH4

+

, other ground-water 

δ15N–NH4

+

 values measured in the La Pine area ranged from 

2.5 to 3.9 ‰ (Hinkle and others, 2007), and NO3

-

 derived from 

nitrification of NH4

+

 would be isotopically depleted (lighter) 

than source NH4

+

 (Hübner, 1986). The δ15N–NO3

-

 value for 

the slough water indicates that nitrification of NH4

+

 was not a 

dominant source of NO3

-

 in the slough at the time of sampling. 

The occurrence of both NO3

-

 and NH4

+

 in the slough water 

reflects distinct contributions of N from various sources: NO3

-

apparently from septic tank effluent (based on Cl-

 and stable 

isotopes of NO3

 -) and NH4

+

 apparently from natural sources 

(based on the presence of Fe).

Redox Controls at the Scale of River Reaches

The widespread occurrence of suboxic ground water 

beneath the Deschutes and Little Deschutes Rivers represents 

an extensive denitrifying zone between rivers and upgradient 

recharge areas that appears to remove much of the NO3

-

 being 

transported from upgradient recharge areas. However, oxic 

ground water does occur in sediments directly beneath these 

rivers in places, and these oxic zones are potential pathways 

for NO3

-

 transport from terrestrial recharge areas to rivers.

Oxic ground water, where detected, tended to be present 

near the outside edge (edge closest to the margin of the valley 

floor) of a river meander bend (pl. 1). The three transects 

where oxic ground water was detected (excluding sites where 

oxic hyporheic water was underlain by suboxic water) were: 

(1) D198.5 (left or western edge), (2) LD24.9 (right or eastern 

edge), and (3) LD37.8 (left or western edge; oxic, but possibly 

hyporheic or otherwise of local origin). The pattern of oxic 

ground water occurrence relative to river meander bends is 

apparent on plate 1: oxic ground water was detected at the 

western edge of D198.5, where the river bends toward the 

west, in the eastern part of LD24.9, where the river bends 

towards the east, and in the western part of LD37.8, where 

the river hugs the western edge of the flood plain. Oxic water, 

when detected, was near the outside edge of meander bends, 

but not all ground water near the outside edge of meander 

bends was oxic.

Occurrence of oxic ground water also was related to 

riparian zone extent. Oxic ground water was detected in zones 

where the width of the riparian environment adjacent to a site 

on the outside edge was narrow relative to the overall width of 

the riparian zone in the valley at the site (pl. 1). Plate 1 shows 

the riparian zone extent using a geographical information 

system (GIS) representation the cryaquoll soils (Natural 

Resources Conservation Service, 2006). GIS coverage is 

available for 9 of the 10 transect sites. Relations between 

ground water redox state and riparian zone size are hampered 

because transect D198.5 is not represented by GIS coverage. 

However, field observations indicated that the west bank 

(but not the east bank) at this site had essentially no riparian 

zone; the west bank consisted of a beach of eroded aquifer 

gravel and a near absence of vegetation. Some transects with 

a relatively narrow riparian zone extent between the river and 

the outside edge (for example, LD2.4), or even, in the case of 

D194.1, essentially lacking a riparian zone, were largely free 

of oxic ground water (no oxic ground water was detected). 

As a consequence, establishing quantitative estimates of 

riparian zone width associated with suboxic (or, alternatively, 

oxic) ground water in the near-river environment is difficult. 

The inability to draw quantitative conclusions reflects the 

limited number of transects available for making such an 

analysis. However, it also reflects the facts that the near-river 

geochemical environment is highly heterogeneous, and that 

ground water redox conditions in the near-river environment 

are controlled not only by near-river redox processes, but also 

by redox processes occurring in parts of the aquifer upgradient 

from the near-river environment.
20 Ground Water Redox Zonation near LaPine, Oregon: Relation to River Position within the Aquifer-Riparian Zone Continuum

Although oxic ground water appears to be relatively 

uncommon in sub-river sediments, the redox state of ground 

water discharging to rivers through springs and seeps in the 

study area has received little attention. Seeps usually were 

located near the outside bends of river meanders (near the 

edge of the flood plain, which closely corresponds to the edge 

of the riparian zone). Although seeps were not represented in 

this analysis, they tended to be located in the same types of 

sites (outside bends of river meanders) as sites where oxic subriver ground water was detected.

Particle tracking analysis can be used in combination 

with an understanding of occurrence patterns of near-river 

ground water redox conditions to infer relative degrees of 

river reach vulnerability to ground-water NO3

-

. Particle 

tracking results delineate areas where NO3

-

 reaching the water 

table from septic tanks could be transported to the near-river 

environment, subject to the aquifer-scale redox controls 

discussed earlier. In this analysis, pathlines for particles 

transported into the suboxic part of the system (most pathlines) 

were removed. Only pathlines for particles that remain in the 

oxic part of the ground-water system were retained, providing 

a delineation of oxic ground-water contributing zones to rivers 

as represented by the aquifer-scale model (pl. 1). (Pathlines 

for particles that travel through suboxic zones, although not 

shown on plate 1, generally lie beneath pathlines for particles 

in oxic zones.) Because the thickness of the oxic zone in the 

near-river environment was represented in the aquifer-scale 

model by a 10-ft minimum thickness, the suite of particle 

pathlines shown on plate 1 should be considered to represent 

the maximum number of pathways for NO3

-

 transport into 

rivers.

Particle tracking results provide insights at scales ranging 

from the scale of transects to the scale of the aquifer. At the 

aquifer scale, oxic pathlines primarily occur near the rivers 

(pl. 1). Oxic ground-water pathlines extend farther from the 

river in the northern part of the study area, where (primarily 

forested) volcanic uplands contain thick oxic zones. These 

results indicate that rivers generally are less vulnerable to 

residential development farther from rivers than development 

closer to rivers.

Particle tracking results at the scale of transects are 

consistent with study results. For example, simulated oxic 

pathlines on the west at D198.5, east at LD24.9, and west at 

LD37.8 (pl. 1) are consistent with the measurement of oxic 

ground water at the same sites, as well as the detection of 

NO3

-

 at wells near the east edge of LD24.9. Simulated oxic 

pathlines near the slough that enters the Deschutes River at 

river mile 194.8 (pl. 1), together with the observation that the 

area near the slough contains residential development, are 

consistent with the detection of NO3

-

 in the slough (table 2). 

At other transect sites, ground water simulated to remain oxic 

in the aquifer scale model appears to be suboxic based on field 

measurements. For example, oxic pathlines were simulated 

for D194.1 and D206.4, but field measurements identified 

only suboxic ground water. These results also are consistent 

with study results, insofar as near-river redox processes not 

represented in the aquifer-scale model still are expected to 

occur in some areas.

The combination of particle tracking analysis with 

near-river redox characterization has potential application in 

a variety of hydrologic or environmental assessments. For 

example, resource managers attempting to reduce potential 

N loads to rivers could prioritize N-reduction efforts in 

recharge areas or could prioritize locations for riparian zone 

protection or establishment in discharge areas by focusing 

on oxic pathlines that link unsewered neighborhoods with 

river reaches that occur near the edges of riparian zones. 

Residential neighborhoods are approximately represented 

on plate 1 by the networks of roads. Alternatively, strategies 

for establishing river Total Maximum Daily Load (TMDL) 

guidelines could use an analysis in which a range of scenarios 

for pathline redox state, based on a range of riparian zone 

widths, is used to bracket likely NO3

-

 loads to river reaches. 

Actual identification of pathlines that would likely remain oxic 

along their entire lengths (including during transport through 

near-river sediments) was not depicted on plate 1 because 

(1) uncertainty remains regarding the potential for ground 

water to remain oxic along the near-river parts of the pathlines, 

and (2) different potential applications of this analysis 

preclude the presentation of a single subset of pathlines. 

However, the absence of a more quantitative assessment does 

not prevent useful applications. For example, at LD5.7, oxic 

pathlines essentially do not extend beyond the riparian zone 

extent, suggesting a relatively small degree of vulnerability 

to NO3

-

. Near LD13.4, oxic pathlines do extend beyond the 

riparian zone, but do not appear to extend to residential areas, 

again suggesting a relatively small degree of vulnerability. 

However, large areas of the Deschutes River between river 

miles 190 and 200 contain residential development and large 

numbers of oxic pathlines, indicating a potentially large degree 

of vulnerability.

Effects of Ground-Water Discharge to Rivers

Ground water is a potential source of both NO3

-

 and 

NH4

+

 to rivers in the study area. The cut-off slough adjacent 

to the Deschutes River at river mile 194.8 demonstrates this 

potential, with 0.278 mg N/L of NO3

-

 and 0.63 mg N/L of 

NH4

+

 at the time of sampling. The magnitude of the NO3

-

concentration and the ratio of NO3

-

 to NH4

+

 in the slough 

sample indicate the existence of a considerable contribution of 

oxic ground water to the slough, consistent with the extension 

of the slough 0.6 mi away from the riparian zone (pl. 1). 
References Cited 21

Most river reaches, however, likely would be less vulnerable 

to NO3

-

 from sub-river ground water sources because of the 

widespread occurrence of suboxic ground water in sub-river 

sediments and large amounts of water for dilution.

Contributions of oxic ground water, and therefore, 

potential contributions of NO3

-

 to rivers in the study area 

probably are limited primarily to areas where rivers bend 

toward the outside of the riparian environment. Thus, 

contributions of NO3

-

 to rivers likely are restricted to relatively 

small areas of river reaches. However, the potential effects 

of such N loads to rivers might not be negligible because 

rivers can be highly sensitive to changes in nutrient fluxes 

(nutrient over-enrichment represents the single greatest 

source of impairment to rivers in the United States; U.S. 

Environmental Protection Agency, 1998). A seepage run 

(series of river discharge measurements along a section of 

river) with water sampling was done on the Little Deschutes 

River during a period of stable low flow in October 2006 

(table A3, appendix A). Total N concentrations were less than 

0.10 mg N/L in all samples, whereas dissolved orthophosphate 

concentrations were about 0.04 mg/L, indicating N-limited 

conditions. Generally increasing discharge, specific 

conductance, and Cl- downstream (figure A1, appendix A) 

indicate a river receiving ground-water discharge. 

Concentrations of N were variable and may have been 

depressed by plant uptake; rivers in the study area contain 

extensive algae and macrophytes. Concentrations of NO3

-

 in 

study area ground water likely will increase over time as NO3

-

currently in the aquifer is transported farther along groundwater flow paths and as continued residential development 

leads to increasing NO3

-

 loads to the water table (Morgan and 

others, 2007), but potential effects of future increased groundwater NO3

-

 contributions to rivers in the study area have not 

been investigated.

Summary

The redox state of ground water exerts a strong control 

on nitrate (NO3

-

) stability, and therefore on NO3

-

 discharge 

from aquifers to rivers. Oxic ground water was uncommon in 

sub-river ground-water samples in the La Pine area. Groundwater samples from transects of temporary wells installed near 

the center of the riparian zone were always suboxic. Where 

transects were located near edges of riparian zones, groundwater samples from transect centers were always suboxic, 

as were ground-water samples from points on the inside part 

of each transect (toward the center of the river/riparian zone 

system). Oxic ground water (other than hyporheic water), if 

detected, was detected only near the outside edge of transects 

at meander bends. However, zones in which oxic ground 

water discharges to rivers represent locations of potential river 

vulnerability to NO3

-

.

The redox state of ground water in near-river sediment 

is controlled by geochemical processes occurring throughout 

the aquifer and also by geochemical processes occurring near 

the intersection of riparian zones and ground-water discharge 

zones. Younger, less geochemically evolved ground water 

generally enters the near-river environment near the edges 

of the river corridor, whereas older, more geochemically 

evolved ground water (water that generally has traversed 

more of the aquifer) tends to be in more regional flow systems 

that discharge to locations closer to the center of the river 

corridor. Riparian zone processes that occur in many nearriver sediments become important as ground water nears 

discharge points in or adjacent to rivers; lateral erosion of 

river systems away from the center of the flood plain can 

decrease interactions between ground water and reducing 

riparian zone sediments. Thus, ground water redox patterns in 

near-river sediments reflect the position of a river within the 

river/riparian zone/aquifer continuum. Spatial heterogeneity 

of redox conditions in the near-river environment reflects the 

interplay of these (aquifer and riparian zone) processes, and 

makes it difficult to quantitatively define conditions under 

which oxic ground water might be expected in near-river 

sediments. Nevertheless, this general understanding of factors 

controlling near-river redox state, particularly if coupled to 

a ground-water-flow-path-based understanding of linkages 

between upgradient recharge areas and rivers, may be useful 

for managing river water quality.

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pubs_dir/Pdf/00-386.pdf

Böhlke, J.K., and Coplen, T.B., 1995, Interlaboratory 

comparison of reference materials for nitrogen-isotope-ratio 

measurements, in Reference and intercomparison materials 

for stable isotopes of light elements (IAEA-TECDOC-825): 

Vienna, International Atomic Energy Agency, p. 51–66.

Böhlke, J.K., Mroczkowski, S.J., and Coplen, T.B., 2003, 

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Boyer, E.W., Alexander, R.B., Parton, W.J., Li, C., ButterbachBahl, K., Donner, S.D., Skaggs, R.W., and Del Grosso, S.J., 

2006, Modeling denitrification in terrestrial and aquatic 

ecosystems at regional scales: Ecological Applications, v. 

16, p. 2123–2142.
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microorganisms (5th ed.): Englewood Cliffs, New Jersey, 

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Browne, B.A., and Guldan, N.M., 2005, Understanding 

long-term baseflow water quality trends using a synoptic 

survey of the ground water–surface water interface, central 

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Casciotti, K.L., Sigman, D.M., Hastings, M.G., Böhlke, 

J.K., and Hilkert, A., 2002, Measurement of the oxygen 

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using the denitrifier method: Analytical Chemistry, v. 74, 

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dual-bacterial denitrification to improve δ15N determinations 

of nitrates containing mass-independent 17O: Rapid 

Communications in Mass Spectrometry, v. 18, p. 245–250.

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determination of inorganic substances in water and fluvial 

sediments: U.S. Geological Survey Techniques of WaterResources Investigations, book 5, chapter A1, 545 p.

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Englewood Cliffs, New Jersey, Prentice Hall, 604 p.

Gannett, M.W., Lite, K.E., Jr., Morgan, D.S., and Collins, 

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streambed topography on surface-subsurface water 

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evaluation of alternative approaches for management 

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La Pine, Oregon: U.S. Geological Survey Scientific 

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and Décamps, H., 2007, Patterns of denitrification rates in 

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24 Ground Water Redox Zonation near LaPine, Oregon: Relation to River Position within the Aquifer-Riparian Zone Continuum

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Appendix A 25

Appendix A. Project Quality-Control Data, Historical Near-River Ground-Water 

Data Collected near the Little Deschutes River Near La Pine, Oregon, and Project 

Discharge and Chemical Data from the Little Deschutes River near La Pine, 

Oregon, 2006

Project quality-control data are shown in table A1. 

Geochemical data collected from sediments beneath the Little 

Deschutes River during October 2000 (Morgan and others, 

2007) are shown in table A2.

River discharge was measured, and chemistry data 

were collected, at five sites along the Little Deschutes River 

during low-flow conditions October 9–10, 2006 and are listed 

in table A3 and shown in figure A1. For these discharge 

Table A1. Project quality-control data, March and October 2006.

[Standard reference samples prepared by M.C. Doyle, U.S. Geological Survey. Abbreviations: mg/L, milligram per liter; mg N/L, milligram of nitrogen per 

liter; μg/L, microgram per liter; ‰, per mil; NWQL, National Water Quality Laboratory; –, not collected]

Sample type Station No. Date Time Chloride

(mg/L)

Ammonium

(mg N/L)

Nitrite + 

nitrate

(mg N/L)

Iron

(μg/L)

δ15N-NO3

-

 

(‰)

δ18O-NO3

-

 

(‰)

Replicate 434212121295203 10-02-06 1800 6.14 <0.04 1.57 296 – –

Replicate 434212121295203 10-02-06 1801 6.18 <.04 1.56 287 – –

Replicate 434212121295203 10-02-06 1802 6.15 <.04 1.55 302 – –

Standard deviation of 

replicates

.02 – .01 8 – –

Replicate 435014121274900 03-07-06 1000 – – – – 11.9 -1.0

Replicate 435014121274900 03-07-06 1001 – – – – 11.9 -.7

Standard deviation of 

replicates

– – – – .0 .2

Equipment blank – 03-01-06 1508 <.20 <.04 <.016 <6 – –

Standard reference sample 1

Standard concentration – 03-01-06 1603 5.20 .53 1.00 – – –

Reported by NWQL – 03-01-06 1603 5.14 .54 .99 – – –

Reported concentration, as 

percentage of standard

98.8 102 99 – – –

Standard reference sample 2

Standard concentration – 03-01-06 1613 11.9 .91 2.78 – – –

Reported by NWQL – 03-01-06 1613 11.0 .93 2.68 – – –

Reported concentration, as 

percentage of standard

92.4 102 96.4 – – –

Standard reference sample 3

Standard concentration – 03-01-06 1623 15.4 1.93 3.06 – – –

Reported by NWQL – 03-01-06 1623 14.5 1.86 2.97 – – –

Reported concentration, as 

percentage of standard

94.2 96.4 97.1 – – –

measurements, tributary inflows along the studied reaches 

accounted for less than 0.2 ft3/s. Water samples were collected 

using isokinetic, depth-integrated, equal-width-increment 

sampling methods. Collection and processing methods were 

those described by U.S. Geological Survey (1999). Analytical 

techniques used were those described by Fishman (1993) and 

Patton and Kryskalla (2003).
26 Ground Water Redox Zonation near LaPine, Oregon: Relation to River Position within the Aquifer-Riparian Zone Continuum

Table A2. Historical ground-water data for samples collected from sediments beneath the Little Deschutes River, Oregon.

[Historical data from Morgan and others, 2007. Nitrogen samples analyzed by Oregon Department of Environmental Quality, using methods described in 

Hinkle and others, 2007. River mile, as indicated on U.S. Geological Survey topographic maps. Depth, depth of center of screen below riverbed. Latitude and 

longitude: North American Datum of 1927 (NAD 27). Abbreviations: LEW, left edge of water looking downstream; mg N/L, milligram of nitrogen per liter; 

<, less than]

River 

mile Sample location Depth (feet) Latitude Longitude Date

Dominant 

river bed 

lithology

Nitrite+ 

nitrate

(mg N/L)

Ammonium 

(mg N/L)

Hydrogen 

sulfide 

odor

7.8 Center of river 1.0 43° 48' 6.2" 121° 27' 10.7" 10-27-00 Sand <0.005 0.34 Present

9.8 Center of river 3.0 43° 47' 30.2" 121° 27' 29.1" 10-27-00 Sand <.005 1.6 Present

12.5 Center of river 3.0 43° 46' 41.5" 121° 28' 12.0" 10-27-00 Sand .006 .44 Present

16.7 Center of river 1.0 43° 44' 58.2" 121° 29' 15.8" 10-26-00 Sand <.005 1.3 Present

19.1 Center of river 2.0 43° 44' 15.8" 121° 29' 21.4" 10-26-00 Sand .071 2.3 Present

21.2 Center of river 2.0 43° 43' 32.5" 121° 29' 26.8" 10-26-00 Sand .006 2.6 Present

24.9 One-fourth of distance 

across from LEW

3.0 43° 42' 12.3" 121° 29' 52.4" 10-23-00 Gravel .011 .31 Present

24.9 Center of river 3.0 43° 42' 12.3" 121° 29' 52.4" 10-23-00 Gravel 1.29 <.02 Absent

24.9 Three-fourths of 

distance across 

from LEW

3.0 43° 42' 12.3" 121° 29' 52.4" 10-23-00 Gravel 2.73 <.02 Absent

Table A3. Discharge measurements and chemical samples collected from Little Deschutes River near La Pine, Oregon, October 2006.

[Total nitrogen and field parameters on unfiltered samples; other analyses on filtered samples. Latitude and longitude: North American Datum of 1927 (NAD 

27). Abbreviations: NAVD 88, North American Vertical Datum of 1988; RM, river mile, as indicated on U.S. Geological Survey topographic maps. ft3/s, cubic 

foot per second; mg/L, milligram per liter; μS/cm, microsiemens per centimeter at 25°C; °C, degrees Celsius; mg N/L, milligram of nitrogen per liter; mg P/L, 

milligram of phosphorus per liter; <, less than]

Site Station 

No. Date Time Latitude Longitude

Altitude 

(feet above 

NAVD 88)

Instantaneous 

discharge 

(ft3

/s)

Dissolved 

oxygen 

(mg/L)

Specific 

conductance 

(μS/cm)

RM 37.8 433846121352800 10-09-06 1610 43° 38' 45.7" 121° 35' 28.1" 4,235 30.3 10.2 55

RM 32.6 434022121324600 10-10-06 1110 43° 40' 22.2" 121° 32' 46.5" 4,205 29.5 9.8 57

RM 24.9 434212121295700 10-10-06 1340 43° 42' 12.4" 121° 29' 52.4" 4,195 31.1 10.4 61

RM 16.0 434515121290200 10-10-06 1510 43° 45' 14.7" 121° 29' 02.0" 4,170 33.9 10.6 66

RM 5.4 434917121270000 10-10-06 1720 43° 49' 16.8" 121° 26' 59.8" 4,165 36.9 10.3 68

Site Station 

No.

Temperature 

(°C)

Chloride 

(mg/L)

Ammonium 

(mg N/L)

Nitrite+ 

nitrate 

(mg N/L)

Nitrite 

(mg N/L)

Total 

nitrogen 

(mg N/L)

Orthophosphate 

(mg P/L)

RM 37.8 433846121352800 11.5 0.67 <0.02 <0.06 <0.002 0.08 0.039

RM 32.6 434022121324600 7.1 .66 <.02 <.06 <.002 .09 .040

RM 24.9 434212121295700 8.9 .82 <.02 <.06 <.002 .08 .041

RM 16.0 434515121290200 9.7 .95 <.02 <.06 <.002 <.06 .053

RM 5.4 434917121270000 10.3 1.10 <.02 <.06 <.002 .06 .041
 Appendix A 27

or19-0152_figA1

10

15

20

25

30

35

40

INSTANTANEOUS DISCHARGE 

IN CUBIC FEET PER SECOND 

10

20

30

40

50

60

70

80

SPECIFIC CONDUCTANCE IN 

MICROSIEMENS PER CENTIMETER

 AT 25 DEGREES CELCIUS 

0

0.20

0.40

0.60

0.80

1.00

1.20

510152025303540 0

RIVER MILE

CHLORIDE IN MILLIGRAMS PER LITER

0

5

0

Figure A1. Spatial patterns of instantaneous 

discharge, specific conductance, and chloride, 

Little Deschutes River near La Pine, Oregon, 

October 9–10, 2006.
28 Ground Water Redox Zonation near LaPine, Oregon: Relation to River Position within the Aquifer-Riparian Zone Continuum

This page intentionally left blank.
Manuscript approved for publication, September 29, 2007

Prepared by the USGS Publishing Network, 

Publishing Service Center, Tacoma, Washington

Bill Gibbs 

Debra Grillo

Jackie Olson

Bobbie Jo Richey

Sharon Wahlstrom

For more information concerning the research in this report, contact 

Director, Oregon Water Science Center

U.S. Geological Survey, 2130 SW 5th Avenue

Portland, Oregon 97201

http://or.water.usgs.gov
Hinkle and others—Ground Water Redox Zonation near La Pine, Oregon: Aquifer-Riparian Zone Continuum—Scientific Investigations Report 2007–5239