pH, and Dissolved Oxygen at Selected Basic Fixed 

Sites in South-Central Texas, 1996–98

Open-File Report 03–087

U.S. Department of the Interior

U.S. Geological Survey
Cover:

Main orifice of Comal Springs, which provides habitat for threatened and endangered aquatic 

species.
U.S. Department of the Interior

U.S. Geological Survey

Comparison of Temperature, Specific Conductance, 

pH, and Dissolved Oxygen at Selected Basic Fixed 

Sites in South-Central Texas, 1996–98

By Patricia B. Ging and Cassi L. Otero

U.S. GEOLOGICAL SURVEY

Open-File Report 03–087

NATIONAL WATER-QUALITY ASSESSMENT PROGRAM

Austin, Texas

2003
ii

U.S. DEPARTMENT OF THE INTERIOR

Gale A. Norton, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

Any use of trade, product, or firm names is for 

descriptive purposes only and does not imply 

endorsement by the U.S. Government.

For additional information write to

District Chief

U.S. Geological Survey

8027 Exchange Dr.

Austin, TX 78754–4733

E-mail: dc_tx@usgs.gov

Copies of this report can be purchased from

U.S. Geological Survey

Information Services

Box 25286

Denver, CO 80225–0286

E-mail: infoservices@usgs.gov
CONTENTS iii

CONTENTS

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

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

Site Descriptions .................................................................................................................................................................. 1

Comparisons ......................................................................................................................................................................... 3

Summary .............................................................................................................................................................................. 6

References ............................................................................................................................................................................ 6

FIGURES

1. Map showing South-Central Texas National Water-Quality Assessment study unit and water-quality 

monitor locations .................................................................................................................................................. 2

2–5. Boxplots showing distribution of monthly mean: 

2. Water temperature for all sites, January 1996–December 1998 ................................................................ 4

3. Specific conductance for all sites, January 1996–December 1998 ............................................................ 4

4. pH for all sites, January 1996–December 1998 ......................................................................................... 5

5. Dissolved oxygen for all sites, January 1996–December 1998 ................................................................. 5

6–11. Hydrographs showing daily mean water temperature, specific conductance, pH, dissolved oxygen, and 

stream discharge for: 

6. Frio River at Concan, Texas (08195000), January 1996–December 1998 ................................................ 7

7. Blanco River at Wimberley, Texas (08171000), January 1996–December 1998 ...................................... 8

8. Comal River at New Braunfels, Texas (08169000), January 1996–December 1998 ................................ 9

9. Medina River at La Coste, Texas (08180640), January 1996–December 1998 ........................................ 10

10. Salado Creek (lower station) at San Antonio, Texas (08178800), January 1996–December 1998 ........... 11

11. San Antonio River near Elmendorf, Texas (08181800), January 1996–December 1998 .......................... 12

TABLES

1–6. Summary statistics by month for water temperature, specific conductance, pH, and dissolved oxygen at:

1. Frio River at Concan, Texas (08195000) ................................................................................................... 13

2. Blanco River at Wimberley, Texas (08171000) ......................................................................................... 14

3. Comal River at New Braunfels, Texas (08169000) ................................................................................... 15

4. Medina River at La Coste, Texas (08180640) ........................................................................................... 16

5. Salado Creek (lower station) at San Antonio, Texas (08178800) .............................................................. 17

6. San Antonio River near Elmendorf, Texas (08181800) ............................................................................. 18
Abstract 1

Comparison of Temperature, Specific Conductance, 

pH, and Dissolved Oxygen at Selected Basic Fixed 

Sites in South-Central Texas, 1996–98

By Patricia B. Ging and Cassi L. Otero

Abstract

One component of the surface-water part of 

the U.S. Geological Survey National Water-Quality 

Assessment Program is the use of continuous 

water-quality monitors to help characterize the 

spatial and temporal distribution of general water 

quality in relation to hydrologic conditions. During 

1996–98, six continuous water-quality monitors in 

the South-Central Texas study unit collected water 

temperature, specific conductance, pH, and dissolved oxygen data. The data were compared 

among the six sites using boxplots of monthly 

mean values, summary statistics of monthly values, 

and hydrographs of daily mean values. 

INTRODUCTION

In 1991, the U.S. Geological Survey (USGS) 

implemented the National Water-Quality Assessment 

(NAWQA) Program to describe the status and trends in 

water quality of a large, representative part of the 

Nation’s surface- and ground-water resources. This program is based on a multidiscipline approach using standard protocols to collect data in more than 50 study 

units (Hirsch and others, 1988; Leahy and others, 1990). 

The South-Central Texas (SCTX) study unit (fig. 1) is 

one of the NAWQA units that began in 1994. One component of the surface-water part of the NAWQA program is the basic fixed-site assessment (Gilliom and 

others, 1995). The purpose of the basic fixed-site 

assessment is to characterize the spatial and temporal 

distribution of general water quality in relation to 

hydrologic conditions and contaminant sources. Nine 

sites for the basic fixed-site assessment were chosen to 

represent the range of habitat and water-quality conditions in the SCTX study unit. One way to characterize 

general water-quality conditions at the basic fixed sites 

is by continuous monitoring of selected properties (Gilliom and others, 1995). Therefore monitors were 

installed at six of the basic fixed sites (fig. 1) to collect 

data on water temperature, specific conductance, pH, 

and dissolved oxygen. These monitors were in operation to assess seasonal variability during the 1996–98 

sampling period.

The main focus of the SCTX study unit is the 

Edwards aquifer in the San Antonio region. The 

Edwards aquifer is the source of water for about 1.5 million people in and near San Antonio and for ranchers 

and farmers in the region. Water from the aquifer also 

provides habitat for threatened and endangered species 

associated with major springs in the region. The 

Edwards aquifer is a sequence of extensively faulted, 

fractured, and dissolutioned limestone and dolostone 

that yields large quantities of water to wells and springs. 

The SCTX study unit extends beyond the Edwards aquifer to the Gulf Coast of Texas to include the complete 

watersheds of the Nueces, San Antonio, and Guadalupe 

River Basins (fig. 1); but to date (2003), the study has 

involved only the upper parts of the basins. The six basic 

fixed sites with continuous water-quality monitors are 

located in the upper parts of the basins.

The purpose of this report is to present the water 

temperature, specific conductance, pH, and dissolved 

oxygen data collected during 1996–98 at the six continuous water-quality monitors in the study unit. The data 

were compared among the sites using boxplots of 

monthly mean values, summary statistics of monthly 

values, and hydrographs of daily means values.

SITE DESCRIPTIONS

Six basic fixed sites (fig. 1) had data from 

continuous water-quality monitors during the period 

1996–98. These sites were the Frio River at Concan 

(08195000), Blanco River at Wimberley (08171000), 

Comal River at New Braunfels (08169000), Medina 

River at La Coste (08180640), Salado Creek (lower 
2 Comparison of Temperature, Specific Conductance, pH, and Dissolved Oxygen at Selected Basic Fixed Sites in South-Central

Texas, 1996–98 

station) at San Antonio (08178800), and San Antonio 

River near Elmendorf (08181800).

The drainage basin of the Frio River at Concan 

site (08195000) is 389 square miles (mi2) (Gandara and 

others, 1997). Land use in the watershed is 95-percent 

rangeland and forest with about 1 percent containing 

resorts along the Frio River. The majority of streamflow 

is lost to the Edwards aquifer below the Frio River at 

0 20 40 60 MILES

1. Frio River at Concan, Texas (08195000)

2. Blanco River at Wimberley, Texas (08171000)

3. Comal River at New Braunfels, Texas (08169000)

4. Medina River at La Coste, Texas (08180640)

5. Salado Creek (lower station) at San Antonio, Texas (08178800)

6. San Antonio River near Elmendorf, Texas (08181800)

3 Water-quality monitor location and reference number

EXPLANATION

LOCATION MAP

TEXAS

Study unit

Frio

Hondo

River

Creek

SAN

Atascosa

River

RIVER

Leona

River

Aransas

River

RIVER

NUECES

Seco

River

Sabinal

Dry

Frio

Blanco

Ri ver

San

Marcos

RIVER River

GUADALUPE

MEDINA

RIVER

ANT ONIO

Cibolo

Creek

RIVER

M ission

Creek

Creek

Frio

River

NUECES

GULF OF MEXICO

Comal

 River

Creek

Salado

MEDINA

 LAKE

Brackettville

Uvalde

Kerrville

Bandera

Boerne Lockhart San Marcos

New

 Braunfels

Hondo

San

 Antonio

Cotulla

Victoria

Corpus Christi

Concan

Wimberly

La Coste

Elmendorf

97o

98o 99o

100o

30o

28o

29o

4

5

6

3

2

1

Figure 1. South-Central Texas National Water-Quality Assessment study unit and water-quality monitor locations. 
COMPARISONS 3

Concan site. This site is used as an indicator of rangeland with resorts for the SCTX study unit.

The drainage basin of the Blanco River at 

Wimberley site (08171000) is 355 mi2

 (Gandara and 

others, 1997). Land use in the watershed is 87-percent 

rangeland and forest, 11-percent pasture, and 1-percent 

urban. This site is used as an indicator of rangeland 

with small town development for the SCTX study unit.

The drainage basin of the Comal River at New 

Braunfels site (08169000) is 130 mi2

. Land use in 

the watershed is 69-percent rangeland and forest, 23-

percent pasture, 5-percent urban, and 3-percent barren 

land. Except during rainfall, streamflow at the New 

Braunfels site is from Comal Springs, which emerge 

from the Edwards aquifer in the Balcones fault zone. 

Comal Springs is located about 1 mile (mi) upstream of 

the monitoring site. Streamflow at the Comal River at 

New Braunfels site can be affected by discharge from 

flood-detention pools of five floodwater-retarding 

structures within Landa Park in the city of New Braunfels (Gandara and others, 1997). This site is an integrator site of ground-water discharges, urban development, 

and rangeland for the SCTX study unit.

The drainage basin of the Medina River at 

La Coste site (08180640) is 805 mi2

 of which 634 mi2

is above the dam forming Medina Lake located west of 

San Antonio. Therefore, streamflow at this monitoring 

site is controlled by the dam at Medina Lake (Gandara 

and others, 1997). The predominant land use in the 

watershed is rangeland with small towns; 10 percent of 

the land use in the watershed is agricultural. The 

Medina River at La Coste site is used as an agricultural 

indicator for the SCTX study unit because of the close 

proximity of predominantly cotton, corn, and sorghum 

fields. Some of the corn and sorghum fields are irrigated 

with Edwards aquifer water. Water quality at this site is 

affected by runoff from the agricultural fields into the 

stream.

The drainage basin of the Salado Creek (lower 

station) at San Antonio site (08178800) is 189 mi2. 

Land use in the watershed is 80-percent urban and 20-

percent undeveloped. The urban land use consists 

mostly of residential and commercial and only a small 

percentage of industrial. Streamflow at this site might 

be affected during storms by 11 floodwater-retarding 

structures located in the upper part of the watershed 

(Gandara and others, 1997). Closer to the site, streamflow is maintained by precipitation and ground-water 

discharges. The Salado Creek site is used as an indicator 

of urban development for the SCTX study unit.

The drainage basin of the San Antonio River near 

Elmendorf site (08181800) is 1,743 mi2. Land use in the 

watershed is 14-percent urban, 22-percent agricultural 

and pasture land, and 61-percent rangeland and forest. 

Streamflow at this site is somewhat regulated by 

Medina Lake and by Olmos Reservoir on Olmos Creek 

4 mi north of downtown San Antonio. Some water is 

diverted above the site for irrigation purposes. The city 

of San Antonio periodically discharges wastewater 

effluent into the San Antonio River from the Leon 

Creek, Salado Creek, and Dos Rios plants, which affects 

water quality at this site (Gandara and others, 1997). 

This monitoring site is used as an integrator site of all 

types of land use in the SCTX study unit but is primarily 

affected by urban land use and wastewater effluent in 

the city of San Antonio.

COMPARISONS

Each of the six basic fixed sites selected for this 

study contained a four-parameter monitor that recorded 

water temperature, specific conductance, pH, and dissolved oxygen at 15-minute intervals. Boxplots (Helsel 

and Hirsch, 1992) of monthly means for water temperature, specific conductance, pH, and dissolved oxygen 

are shown in figures 2–5. Sites are grouped on the basis 

of the predominant land use in each watershed. Summary statistics (minimum, maximum, and mean values) 

by month are listed for the period of record for the four 

properties at each site in tables 1–6 (at end of report). 

Hydrographs of the daily mean values for each property 

monitored at each site are shown in figures 6–11 (at end 

of report). Median values were computed from those 

used for boxplots.

The medians for monthly mean water temperature at the six selected sites ranged from 18.6 degrees 

Celsius (°C) at the Blanco River at Wimberley site to 

24.1 °C at the San Antonio River near Elmendorf site 

(fig. 2). The smallest range of temperature was at the 

Comal River at New Braunfels site, which is a result of 

the ground-water influence at this site. As shown by the 

hydrographs of each site (figs. 6–11), water temperature 

fluctuates at all sites during the year with lows in winter 

and highs in the summer and daily means ranging from 

about 5 to 30 °C.

The medians for monthly mean specific conductance ranged from 415 microsiemens per centimeter at 

25 °C (μS/cm) at the Frio River at Concan site to 901 

μS/cm at the San Antonio River near Elmendorf site 

(fig. 3). The highest values and largest range in specific 
4 Comparison of Temperature, Specific Conductance, pH, and Dissolved Oxygen at Selected Basic Fixed Sites in South-Central

Texas, 1996–98 

conductance were at the two urban classified sites, 

Salado Creek (lower station) at San Antonio and San 

Antonio River near Elmendorf. Specific conductance 

at all sites indicates a correlation with discharge; as 

discharge increases, specific conductance decreases 

(figs. 6–11).

The medians for monthly mean pH ranged from 

7.4 standard units at the Comal River at New Braunfels 

site to 8.0 standard units at the Frio River at Concan 

(fig. 4). pH at all six sites appears to be fairly uniform 

most likely because of the limestone terrain in the study 

unit.

Rangeland Springflow Agriculture Urban

LAND USE

(20)

(17) (31) (34)

(36) (36)

SPECIFIC CONDUCTANCE, IN MICROSIEMENS

PER CENTIMETER AT 25 DEGREES CELSIUS

0

100

200

300

400

500

600

700

800

900

1,000

1,100

1,200

FRIO BLANCO COMAL MEDINA SALADO ELMENDORF

(34)

EXPLANATION

Sample size

Largest data value within 1.5 times

the IQR above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times

the IQR below the box

Data value greater than 1.5 times the IQR

outside the box

Interquartile

range (IQR)

Figure 3. Distribution of monthly mean specific conductance for all sites, January 1996–December 1998.

Rangeland Springflow Agriculture Urban

LAND USE

(20) (17)

(31)

(34) (36)

(36)

WATER TEMPERATURE, IN DEGREES CELSIUS

0

5

10

15

20

25

30

35

FRIO BLANCO COMAL MEDINA SALADO ELMENDORF

(34)

EXPLANATION

Sample size

Largest data value within 1.5 times

the IQR above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times

the IQR below the box

Interquartile

range (IQR)

Figure 2. Distribution of monthly mean water temperature for all sites, January 1996–December 1998.
COMPARISONS 5

The medians for monthly mean dissolved oxygen 

ranged from 6.8 milligrams per liter (mg/L) at the 

Salado Creek (lower station) at San Antonio site to 

9.8 mg/L at the Blanco River at Wimberley site (fig. 5). 

Dissolved oxygen varied from site to site with hydrographs for some sites indicating a correlation with water 

Rangeland Springflow Agriculture Urban

LAND USE

(16) (12)

(23)

(34)

(35) (36)

FRIO BLANCO COMAL MEDINA SALADO ELMENDORF

DISSOLVED OXYGEN, IN MILLIGRAMS PER LITER

0

2

4

6

8

10

12

14

(34)

EXPLANATION

Sample size

Largest data value within 1.5 times

the IQR above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times

the IQR below the box

Data value greater than 1.5 times the IQR

outside the box

Interquartile

range (IQR)

Figure 5. Distribution of monthly mean dissolved oxygen for all sites, January 1996–December 1998.

Rangeland Springflow Agriculture Urban

LAND USE

(20) (17)

(28)

(34)

(36) (36)

FRIO BLANCO COMAL MEDINA SALADO ELMENDORF

pH, IN STANDARD UNITS

7.0

7.8

8.0

8.2

8.4

8.6

8.8

9.0

7.6

7.4

7.2

(34)

EXPLANATION

Sample size

Largest data value within 1.5 times

the IQR above the box

75th percentile

Median (50th percentile)

25th percentile

Smallest data value within 1.5 times

the IQR below the box

Data value greater than 1.5 times the IQR

outside the box

Interquartile

range (IQR)

Figure 4. Distribution of monthly mean pH for all sites, January 1996–December 1998.
6 Comparison of Temperature, Specific Conductance, pH, and Dissolved Oxygen at Selected Basic Fixed Sites in South-Central

Texas, 1996–98 

temperature. Dissolved oxygen concentrations tend to 

be higher in the winter and lower in the summer because 

colder water can hold more oxygen (Hem, 1992).

Ranges in water temperature, specific conductance, pH, and dissolved oxygen were similar for all 

sites except for the Comal River at New Braunfels site 

and the urban sites, Salado Creek (lower station) at 

San Antonio and San Antonio River at Elmendorf. 

The Comal River at New Braunfels site had the smallest 

range in water temperature, specific conductance, 

and dissolved oxygen. The urban sites, Salado Creek 

(lower station) at San Antonio and San Antonio River 

at Elmendorf, had the largest range in specific 

conductance.

SUMMARY

One component of the surface-water part of 

the NAWQA Program is the use of continuous waterquality monitors to help characterize the spatial and 

temporal distribution of general water quality in relation 

to hydrologic conditions. Six continuous water-quality 

monitors in the SCTX study unit were used to obtain 

water temperature, specific conductance, pH, and dissolved oxygen data during 1996–98. 

Boxplots of mean monthly values for the four 

properties were plotted at each of the six sites. The 

boxplots (sites) were grouped on the basis of predominant land use in each watershed. Summary statistics of 

monthly values and hydrographs of daily mean values 

for each of the four properties are given for the six sites. 

The medians for monthly mean temperatures ranged 

from 18.6 to 24.1 °C, and the medians for monthly mean 

specific conductance ranged from 415 to 901 μS/cm for 

the six sites. The medians for monthly mean pH ranged 

from 7.4 to 8.0 standard units, and the medians for 

monthly mean dissolved oxygen ranged from 6.8 to 

9.8 mg/L. Ranges in water temperature, specific conductance, pH, and dissolved oxygen were similar for 

all sites except for the Comal River at New Braunfels 

site and the urban sites, Salado Creek (lower station) 

at San Antonio and San Antonio River at Elmendorf. 

The Comal River at New Braunfels site had the smallest 

range in water temperature, specific conductance, and 

dissolved oxygen. The urban sites, Salado Creek 

(lower station) at San Antonio and San Antonio River 

at Elmendorf, had the largest range in specific 

conductance.

REFERENCES

Gandara, S.C., Gibbons, W.J., Andrews, F.L., Jones, R.E., 

and Barbie, D.L., 1997, Water Resources Data, Texas, 

Water Year 1996—Volume 3: U.S. Geological Survey 

Water-Data Report TX–96–3, 347 p.

Gilliom, R.J., Alley, W.M., and Gurtz, M.E., 1995, Design of 

the National Water-Quality Assessment Program—

Occurrence and distribution of water-quality conditions: 

U.S. Geological Survey Circular 1112, 33 p.

Helsel, D.R., and Hirsch, R.M., 1992, Studies in environmental science 49—Statistical methods in water resources: 

New York, Elsevier, 522 p.

Hem, J.D., 1992, Study and interpretation of the chemical 

characteristics of natural water: U.S. Geological Survey 

Water-Supply Paper 2254, 263 p.

Hirsch, R.M., Alley, W.M., and Wilber, W.G., 1988, Concepts 

for a National Water-Quality Assessment Program: 

U.S. Geological Survey Circular 1021, 42 p.

Leahy, P.P., Rosenshein, J.S., and Knopman, D.S., 1990, 

Implementation plan for the National Water-Quality 

Assessment Program: U.S. Geological Survey OpenFile Report 90–174, 10 p.
Figure 6 7

Figure 6

10

100

1,000

10,000

100,000

0

10

20

30

40

200

300

400

500

600

7.50

7.75

8.00

8.25

8.50

5

7

9

11

13

15

DISCHARGE, IN CUBIC

FEET PER SECOND

DISSOLVED OXYGEN, IN

MILLIGRAMS PER LITER

pH, IN

STANDARD UNITS

SPECIFIC CONDUCTANCE,

IN MICROSIEMENS PER

CENTIMETER AT

25 DEGREES CELSIUS

WATER TEMPERATURE, IN

DEGREES CELSIUS

1996 1997 1998

1996 1997 1998

1996 1997 1998

1996 1997 1998

1996 1997 1998

Figure 6. Daily mean water temperature, specific conductance, pH, dissolved oxygen, and stream discharge for 

Frio River at Concan, Texas (08195000), January 1996–December 1998.
8 Comparison of Temperature, Specific Conductance, pH, and Dissolved Oxygen at Selected Basic Fixed Sites in South-Central

Texas, 1996–98 

Figure 7

1996 1997 1998

1996 1997 1998

1996 1997 1998

1996 1997 1998

1996 1997 1998

0

10

20

30

40

200

400

600

800

7.0

7.5

8.0

8.5

4

6

8

10

12

14

10

100

1,000

10,000

100,000

DISCHARGE, IN CUBIC

FEET PER SECOND

DISSOLVED OXYGEN, IN

MILLIGRAMS PER LITER

pH, IN

STANDARD UNITS

SPECIFIC CONDUCTANCE,

IN MICROSIEMENS PER

CENTIMETER AT

25 DEGREES CELSIUS

WATER TEMPERATURE, IN

DEGREES CELSIUS

Figure 7. Daily mean water temperature, specific conductance, pH, dissolved oxygen, and stream discharge for 

Blanco River at Wimberley, Texas (08171000), January 1996–December 1998. 
Figure 8 9

Figure 8

1996 1997 1998

1996 1997 1998

1996 1997 1998

1996 1997 1998

1996 1997 1998

15

20

25

30

300

400

500

600

700

6.5

7.0

7.5

8.0

8.5

6

8

10

12

14

10

100

1,000

10,000

DISCHARGE, IN CUBIC

FEET PER SECOND

DISSOLVED OXYGEN, IN

MILLIGRAMS PER LITER

pH, IN

STANDARD UNITS

SPECIFIC CONDUCTANCE,

IN MICROSIEMENS PER

CENTIMETER AT

25 DEGREES CELSIUS

WATER TEMPERATURE,

IN DEGREES CELSIUS

100,000

Figure 8. Daily mean water temperature, specific conductance, pH, dissolved oxygen, and stream discharge for 

Comal River at New Braunfels, Texas (08169000), January 1996–December 1998 
10 Comparison of Temperature, Specific Conductance, pH, and Dissolved Oxygen at Selected Basic Fixed Sites in South-Central

Texas, 1996–98 

Figure 9

1996 1997 1998

1996 1997 1998

1996 1997 1998

1996 1997 1998

1996 1997 1998

10

20

30

40

200

400

600

800

7.5

8.5

10

12

14

10

100

1,000

10,000

100,000

0

7.0

8.0

9.0

4

6

8

DISCHARGE, IN CUBIC

FEET PER SECOND

DISSOLVED OXYGEN, IN

MILLIGRAMS PER LITER

pH, IN

STANDARD UNITS

SPECIFIC CONDUCTANCE,

IN MICROSIEMENS PER

CENTIMETER AT

25 DEGREES CELSIUS

WATER TEMPERATURE, IN

DEGREES CELSIUS

Figure 9. Daily mean water temperature, specific conductance, pH, dissolved oxygen, and stream discharge for 

Medina River at La Coste, Texas (08180640), January 1996–December 1998. 
Figure 10 11

Figure 10

1996 1997 1998

1996 1997 1998

1996 1997 1998

1996 1997 1998

1996 1997 1998

10

20

30

40

200

400

600

800

1,000

1,200

1,400

7.0

7.5

8.0

8.5

9.0

0

2

4

6

8

10

12

14

0.01

0.1

10

100

1,000

10,000

100,000

0

0

1

DISCHARGE, IN CUBIC

FEET PER SECOND

DISSOLVED OXYGEN, IN

MILLIGRAMS PER LITER

pH, IN

STANDARD UNITS

SPECIFIC CONDUCTANCE,

IN MICROSIEMENS PER

CENTIMETER AT

25 DEGREES CELSIUS

WATER TEMPERATURE, IN

DEGREES CELSIUS

3

Figure 10. Daily mean water temperature, specific conductance, pH, dissolved oxygen, and stream discharge for 

Salado Creek (lower station) at San Antonio, Texas (08178800), January 1996–December 1998. 
12 Comparison of Temperature, Specific Conductance, pH, and Dissolved Oxygen at Selected Basic Fixed Sites in South-Central

Texas, 1996–98 

Figure 11

1996 1997 1998

1996 1997 1998

1996 1997 1998

1996 1997 1998

1996 1997 1998

0

10

20

30

40

7.0

7.5

8.0

8.5

9.0

0

200

400

600

800

1,000

1,200

1,400

2

4

6

8

10

12

14

10

100

1,000

10,000

100,000

DISCHARGE, IN CUBIC

FEET PER SECOND

DISSOLVED OXYGEN, IN

MILLIGRAMS PER LITER

pH, IN

STANDARD UNITS

SPECIFIC CONDUCTANCE,

IN MICROSIEMENS PER

CENTIMETER AT

25 DEGREES CELSIUS

WATER TEMPERATURE, IN

DEGREES CELSIUS

Figure 11. Daily mean water temperature, specific conductance, pH, dissolved oxygen, and stream discharge for 

San Antonio River near Elmendorf, Texas (08181800), January 1996–December 1998. 
Table 1 13

Table 1

Table 2

Table 1

Table 1. Summary statistics by month for water temperature, specific conductance, pH, and dissolved oxygen at 

Frio River at Concan, Texas (08195000)

[°C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, milligrams per liter; --, monitor not in 

operation or probe malfunction during month] 

Date

Temperature

(°C)

Specific conductance

(μS/cm)

pH

(standard units)

Dissolved oxygen

(mg/L)

MinimumMaximum

Mean

MinimumMaximum

Mean

MinimumMaximum

Mean

MinimumMaximum

Mean

Jan. 1997 7.0 17.3 11.8 416 436 424 8.0 8.2 8.1 9.3 12.8 10.9

Feb. 1997 10.6 18.6 14.0 394 424 416 7.9 8.3 8.0 8.9 11.8 10.3

Mar. 1997 14.7 22.6 18.2 383 428 417 7.9 8.2 8.1 8.1 10.7 9.3

Apr. 1997 15.5 24.6 19.3 215 462 446 7.9 8.3 8.0 7.5 10.9 9.4

May 1997 18.6 28.4 23.2 418 463 444 7.8 8.1 8.0 6.9 10.0 8.5

June 1997 19.8 28.5 25.0 120 469 415 7.8 8.3 8.0 -- -- --

July 1997 24.1 29.6 26.4 421 467 446 7.8 8.0 7.9 -- -- --

Aug. 1997 24.3 30.1 27.4 405 437 419 7.8 8.0 7.9 6.5 9.1 7.7

Sept. 1997 22.0 29.2 26.4 401 423 411 7.7 8.0 7.8 6.2 9.3 7.5

Oct. 1997 15.3 26.7 21.4 379 421 407 7.7 8.0 7.9 7.2 10.8 8.7

Nov. 1997 12.2 20.1 16.3 407 421 416 7.9 8.1 8.0 8.7 12.7 10.7

Dec. 1997 7.9 16.2 12.2 407 425 416 7.9 8.0 7.9 9.8 14.1 11.8

Jan. 1998 10.7 18.0 14.0 128 415 397 7.8 8.2 8.0 8.2 12.5 9.8

Feb. 1998 12.5 20.3 15.5 290 435 423 7.9 8.1 8.0 6.7 9.7 8.1

Mar. 1998 12.4 23.8 17.2 384 431 415 8.0 8.1 8.1 6.7 10.6 8.3

Apr. 1998 16.6 25.1 21.0 404 417 412 7.7 8.1 8.0 6.9 9.9 8.3

May 1998 20.5 30.3 25.3 394 416 406 7.8 8.3 7.9 5.9 9.0 7.4

June 1998 24.0 31.9 28.1 367 410 395 7.7 8.1 7.9 5.4 9.4 7.1

July 1998 26.4 32.5 29.3 377 400 389 7.6 8.0 7.8 -- -- --

Aug. 1998 24.9 32.6 28.3 342 413 387 7.7 8.2 8.0 -- -- --
14 Comparison of Temperature, Specific Conductance, pH, and Dissolved Oxygen at Selected Basic Fixed Sites in South-Central

Texas, 1996–98 

Table 3

Table 2. Summary statistics by month for water temperature, specific conductance, pH, and dissolved oxygen at 

Blanco River at Wimberley, Texas (08171000)

[°C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, milligrams per liter; --, monitor not in 

operation or probe malfunction during month] 

Date

Temperature

(°C)

Specific conductance

(μS/cm)

pH

(standard units)

Dissolved oxygen

(mg/L)

MinimumMaximum

Mean

MinimumMaximum

Mean

MinimumMaximum

Mean

MinimumMaximum

Mean

Jan. 1997 4.0 17.6 10.7 493 516 505 7.9 8.2 8.0 10.3 11.9 11.3

Feb. 1997 7.5 18.7 12.6 422 514 500 7.8 8.0 7.9 8.8 11.7 10.3

Mar. 1997 14.1 22.7 17.7 455 513 491 7.8 8.0 7.9 7.8 10.8 9.2

Apr. 1997 15.3 23.8 18.6 361 526 489 7.7 8.1 7.8 7.6 10.9 9.1

May 1997 14.6 28.5 22.5 225 506 461 7.8 8.1 8.0 6.5 11.4 8.5

June 1997 -- -- -- -- -- -- -- -- -- -- -- --

July 1997 -- -- -- -- -- -- -- -- -- -- -- --

Aug. 1997 -- -- -- -- -- -- -- -- -- -- -- --

Sept. 1997 21.1 30.2 26.2 435 465 452 7.8 8.1 7.9 5.4 8.8 7.7

Oct. 1997 14.6 26.2 20.3 419 500 476 7.7 7.9 7.8 7.0 10.3 8.3

Nov. 1997 10.0 20.3 15.0 484 504 495 7.7 7.9 7.8 7.4 11.6 9.8

Dec. 1997 6.5 16.0 11.4 378 500 436 7.7 7.9 7.8 9.1 12.9 10.9

Jan. 1998 9.6 19.1 14.2 228 513 461 7.8 8.0 7.9 8.9 11.5 10.2

Feb. 1998 11.8 18.8 14.9 227 479 426 7.9 8.1 8.0 8.5 10.9 9.8

Mar. 1998 12.2 22.5 16.4 -- -- -- 6.3 8.7 7.9 8.4 11.5 9.9

Apr. 1998 17.7 24.3 20.4 377 434 406 7.8 8.1 7.9 -- -- --

May 1998 19.6 30.8 24.9 396 481 430 7.8 8.1 8.0 -- -- --

June 1998 24.2 32.3 28.3 430 492 462 7.7 8.1 8.0 -- -- --

July 1998 24.9 33.3 29.5 280 484 437 7.7 8.1 7.9 -- -- --

Aug. 1998 24.6 33.1 28.4 268 475 427 7.7 8.2 7.9 -- -- --
Table 3 15

Table 3. Summary statistics by month for water temperature, specific conductance, pH, and dissolved oxygen at 

Comal River at New Braunfels, Texas (08169000)

[°C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, milligrams per liter; --, monitor not in 

operation or probe malfunction during month] 

Date

Temperature

(°C)

Specific conductance

(μS/cm)

pH

(standard units)

Dissolved oxygen

(mg/L)

MinimumMaximum

Mean

MinimumMaximum

Mean

MinimumMaximum

Mean

MinimumMaximum

Mean

Mar. 1996 20.3 24.8 22.5 501 537 521 -- -- -- 8.1 10.4 8.9

Apr. 1996 20.6 25.6 23.3 431 548 514 -- -- -- 8.2 10.2 9.1

May 1996 22.2 26.2 24.3 468 541 518 -- -- -- 7.8 9.9 8.8

June 1996 23.0 26.8 25.2 486 544 517 7.4 7.8 7.6 6.8 9.8 8.3

July 1996 24.3 26.5 25.7 426 596 520 6.7 7.7 7.5 5.7 10.1 7.3

Aug. 1996 23.6 26.6 25.2 332 599 516 7.4 7.8 7.6 6.4 11.8 8.5

Sept. 1996 21.6 25.8 24.3 249 569 517 7.4 7.9 7.7 6.5 11.0 8.6

Oct. 1996 21.0 24.9 23.3 486 594 543 7.4 7.8 7.6 8.0 10.6 9.0

Nov. 1996 19.5 24.2 22.3 426 610 537 7.5 7.9 7.7 -- -- --

Dec. 1996 19.0 23.6 21.9 432 650 542 7.5 8.0 7.8 -- -- --

Jan. 1997 19.2 24.0 21.5 493 611 539 7.6 8.1 7.8 -- -- --

Feb. 1997 19.7 24.0 21.8 458 587 534 7.4 7.8 7.6 -- -- --

Mar. 1997 21.1 25.1 22.9 507 571 537 7.3 7.7 7.4 8.0 10.1 8.8

Apr. 1997 20.2 25.2 22.9 370 587 528 7.2 7.5 7.3 7.9 9.9 8.8

May 1997 22.5 25.4 23.8 459 570 536 7.3 7.6 7.4 8.3 10.0 9.0

June 1997 22.1 25.8 24.2 224 585 514 7.3 7.6 7.4 7.4 10.1 9.1

July 1997 23.5 25.6 24.4 492 552 542 7.3 7.6 7.4 8.2 10.9 9.5

Aug. 1997 23.4 25.7 24.3 497 553 533 7.3 7.6 7.5 7.3 10.6 8.9

Sept. 1997 22.9 25.5 24.1 468 554 537 7.3 7.6 7.4 7.3 9.9 8.7

Oct. 1997 21.9 25.0 23.4 462 577 536 7.0 7.5 7.3 7.7 9.6 8.6

Nov. 1997 21.0 23.8 22.6 412 552 523 7.2 7.7 7.4 7.8 9.9 8.8

Dec. 1997 20.9 23.5 22.1 411 553 530 7.2 7.5 7.3 8.5 10.9 9.8

Jan. 1998 19.4 23.7 22.5 466 551 529 7.1 7.5 7.3 -- -- --

Feb. 1998 20.4 24.1 22.6 464 559 531 7.1 7.4 7.2 -- -- --

Mar. 1998 18.7 24.7 22.8 389 564 527 7.1 7.6 7.3 -- -- --

Apr. 1998 22.3 25.0 23.4 526 551 537 7.0 7.8 7.3 -- -- --

May 1998 22.8 25.9 24.0 530 546 538 7.5 7.8 7.6 8.1 10.4 9.1

June 1998 22.8 26.4 24.6 445 553 541 7.4 7.9 7.6 7.4 9.7 8.5

July 1998 23.6 26.4 24.9 233 551 538 7.2 7.7 7.5 7.2 9.7 8.3

Aug. 1998 23.4 26.4 24.6 327 566 533 7.1 7.6 7.3 -- -- --

Sept. 1998 23.3 25.4 24.1 394 551 532 7.1 7.6 7.3 -- -- --
16 Comparison of Temperature, Specific Conductance, pH, and Dissolved Oxygen at Selected Basic Fixed Sites in South-Central

Texas, 1996–98 

Table 4

Table 4. Summary statistics by month for water temperature, specific conductance, pH, and dissolved oxygen at 

Medina River at La Coste, Texas (08180640) 

[°C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, milligrams per liter] 

Date

Temperature

(°C)

Specific conductance

(μS/cm)

pH

(standard units)

Dissolved oxygen

(mg/L)

MinimumMaximum

Mean

MinimumMaximum

Mean

MinimumMaximum

Mean

MinimumMaximum

Mean

Mar. 1996 13.9 17.8 15.8 550 555 553 7.9 8.0 8.0 8.7 9.9 9.3

Apr. 1996 14.5 24.0 19.8 533 554 543 7.9 8.1 8.0 6.5 9.8 8.0

May 1996 19.3 28.2 24.9 506 541 526 8.0 8.3 8.1 5.5 8.1 6.5

June 1996 25.0 29.7 27.5 475 517 504 7.8 8.1 7.9 5.1 7.3 6.1

July 1996 27.0 29.6 28.3 410 507 492 7.6 7.9 7.8 5.2 7.4 6.3

Aug. 1996 25.2 29.5 27.4 469 525 514 7.6 8.2 7.9 6.0 7.8 6.8

Sept. 1996 21.1 27.8 26.0 329 552 503 7.7 8.2 7.9 4.9 7.9 6.3

Oct. 1996 17.4 22.9 21.1 542 569 552 7.7 8.0 7.9 6.6 9.1 7.6

Nov. 1996 12.2 22.3 17.3 468 552 542 7.8 8.0 7.9 6.8 9.1 8.0

Dec. 1996 7.6 16.3 12.5 526 576 558 7.7 7.9 7.8 7.7 11.0 9.3

Jan. 1997 5.8 17.0 10.9 562 584 573 7.8 7.9 7.9 8.2 13.9 11.2

Feb. 1997 10.0 16.5 12.9 507 579 556 7.7 7.8 7.7 8.9 12.3 10.4

Mar. 1997 14.4 21.1 18.0 535 593 571 7.6 7.9 7.7 6.6 10.2 8.1

Apr. 1997 15.9 21.9 18.9 424 618 557 7.7 7.9 7.8 7.7 10.5 8.7

May 1997 20.1 26.6 22.9 439 546 527 7.6 7.9 7.8 6.2 8.9 7.4

June 1997 21.2 28.5 25.5 175 548 459 7.6 8.0 7.8 4.9 7.8 6.3

July 1997 25.4 30.1 27.9 370 500 468 7.8 8.1 8.0 5.0 7.4 6.8

Aug. 1997 24.3 32.0 28.0 530 582 563 7.8 8.0 7.9 5.1 9.2 7.3

Sept. 1997 23.5 27.5 26.1 504 538 521 7.7 8.0 7.9 6.1 7.7 6.8

Oct. 1997 16.8 25.1 21.4 430 532 505 7.7 8.0 7.8 6.1 8.9 7.5

Nov. 1997 12.9 19.0 15.8 466 519 496 7.7 8.0 7.9 7.9 10.6 9.3

Dec. 1997 9.8 16.3 12.5 440 497 477 7.8 8.2 8.0 8.2 12.8 10.7

Jan. 1998 10.8 16.5 13.9 404 484 462 7.9 8.2 8.0 8.5 12.6 10.5

Feb. 1998 13.1 17.6 14.9 364 474 440 7.8 8.1 8.0 8.5 10.6 9.7

Mar. 1998 12.5 20.5 16.4 230 464 412 7.7 8.1 7.9 8.4 11.7 10.2

Apr. 1998 17.6 22.5 20.1 395 537 461 7.8 8.0 7.9 7.7 9.5 8.5

May 1998 20.6 27.1 24.3 503 540 524 7.8 8.1 7.9 6.8 8.9 7.6

June 1998 25.4 29.4 27.6 466 514 503 7.7 8.1 7.9 6.5 8.2 7.4

July 1998 27.5 29.9 28.5 470 507 500 7.7 7.8 7.7 6.6 7.9 7.2

Aug. 1998 25.5 29.4 27.3 296 503 461 7.5 7.8 7.7 6.7 8.1 7.4

Sept. 1998 24.5 27.2 26.0 447 522 494 7.6 7.8 7.7 6.6 8.0 7.2

Oct. 1998 19.1 26.9 22.6 144 531 472 7.6 7.9 7.7 6.5 9.0 7.9

Nov. 1998 17.9 22.6 19.5 387 436 410 7.8 8.2 8.1 7.5 9.9 9.1

Dec. 1998 10.6 21.0 15.8 432 485 457 8.2 8.5 8.3 8.1 13.1 10.3
Table 5 17

Table 5

Table 5. Summary statistics by month for water temperature, specific conductance, pH, and dissolved oxygen at 

Salado Creek [lower station] at San Antonio, Texas (08178800) 

[°C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, milligrams per liter; --, monitor not in 

operation or probe malfunction during month] 

Date

Temperature

(°C)

Specific conductance

(μS/cm)

pH

(standard units)

Dissolved oxygen

(mg/L)

MinimumMaximum

Mean

MinimumMaximum

Mean

MinimumMaximum

Mean

MinimumMaximum

Mean

Jan. 1996 5.1 16.4 11.1 942 1,080 1,020 7.8 8.2 8.0 6.4 16.3 10.3

Feb. 1996 4.6 21.2 13.9 558 1,150 1,070 7.8 8.2 7.9 4.4 14.8 9.0

Mar. 1996 8.9 21.8 15.3 512 1,080 959 7.8 8.4 8.0 4.5 16.7 8.6

Apr. 1996 13.2 23.8 19.5 266 1,140 1,040 7.6 8.3 7.9 1.2 9.4 5.8

May 1996 19.0 27.3 24.6 417 1,170 908 7.6 8.1 7.8 .80 5.5 2.7

June 1996 23.7 30.0 26.8 300 1,200 737 7.3 8.1 7.7 1.0 8.3 4.7

July 1996 26.2 30.9 27.7 502 1,130 782 7.3 8.1 7.6 .60 6.6 2.9

Aug. 1996 25.0 29.8 26.8 218 1,170 783 7.5 8.5 7.8 .70 11.6 4.6

Sept. 1996 19.7 27.5 25.3 183 685 440 7.4 8.1 7.8 2.8 12.9 7.8

Oct. 1996 16.4 23.0 20.5 532 1,160 888 7.6 8.0 7.8 2.4 7.7 4.7

Nov. 1996 10.6 23.0 16.7 260 1,280 924 7.6 8.0 7.9 1.5 10.8 5.7

Dec. 1996 5.3 17.0 12.3 400 852 634 7.6 8.1 7.8 3.9 10.5 8.0

Jan. 1997 3.3 19.0 10.7 438 965 824 7.7 8.2 7.9 5.6 15.0 10.3

Feb. 1997 9.2 18.3 12.7 258 1,050 704 7.6 8.2 7.9 7.5 15.1 9.9

Mar. 1997 14.1 21.4 18.0 290 859 621 7.7 8.0 7.8 3.9 9.6 6.8

Apr. 1997 14.6 21.9 18.2 169 992 640 7.7 9.0 8.0 5.6 9.1 7.5

May 1997 20.0 26.3 23.1 167 851 538 7.5 8.5 8.1 3.7 6.4 5.1

June 1997 22.4 28.0 25.7 158 757 453 7.4 8.2 7.8 4.1 7.7 5.7

July 1997 26.8 29.1 28.0 494 747 603 7.8 8.2 8.0 4.9 8.0 6.3

Aug. 1997 25.5 29.0 27.7 585 895 657 7.7 8.2 7.9 4.4 7.8 6.2

Sept. 1997 22.5 28.2 26.1 396 884 568 7.4 8.1 7.8 3.2 9.2 6.2

Oct. 1997 16.4 25.7 21.9 227 639 518 7.8 8.2 8.0 5.4 9.2 7.1

Nov. 1997 12.2 21.6 16.9 260 701 554 7.6 8.2 8.0 3.4 10.1 8.1

Dec. 1997 9.1 18.4 13.4 189 723 579 7.2 8.2 7.8 3.2 11.8 8.5

Jan. 1998 12.8 20.3 16.3 204 721 573 7.5 8.4 8.1 3.4 12.4 9.0

Feb. 1998 12.3 18.8 14.9 182 711 480 7.4 8.0 7.7 7.1 10.1 8.6

Mar. 1998 11.4 22.8 17.0 171 973 666 7.5 8.1 7.8 6.2 14.6 9.1

Apr. 1998 17.6 22.8 19.9 725 898 812 7.7 8.0 7.8 3.6 8.3 6.9

May 1998 19.4 27.9 24.4 724 985 885 7.7 8.1 7.9 2.0 7.8 4.8

June 1998 24.6 28.9 27.5 695 998 856 7.6 8.1 7.8 2.2 4.5 3.6

July 1998 26.3 29.7 28.0 774 940 883 7.6 8.1 8.0 -- -- --

Aug. 1998 24.6 29.2 27.3 130 981 481 7.4 8.2 7.7 2.3 8.6 5.5

Sept. 1998 23.8 28.2 26.4 207 846 582 7.3 8.0 7.7 4.1 7.1 5.3

Oct. 1998 18.0 27.5 22.8 74.0 835 452 7.4 8.8 7.8 3.5 8.2 5.3

Nov. 1998 15.8 21.6 18.3 401 1,010 743 7.5 7.8 7.7 5.3 8.9 7.1

Dec. 1998 7.8 22.1 14.7 812 1,130 947 7.6 8.3 7.9 5.6 10.5 7.9
18 Comparison of Temperature, Specific Conductance, pH, and Dissolved Oxygen at Selected Basic Fixed Sites in South-Central

Texas, 1996–98 

Table 6

Table 6. Summary statistics by month for water temperature, specific conductance, pH, and dissolved oxygen at 

San Antonio River near Elmendorf, Texas (08181800) 

[°C, degrees Celsius; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, milligrams per liter] 

Date

Temperature

(°C)

Specific conductance

(μS/cm)

pH

(standard units)

Dissolved oxygen

(mg/L)

MinimumMaximum

Mean

MinimumMaximum

Mean

MinimumMaximum

Mean

MinimumMaximum

Mean

Jan. 1996 13.5 21.2 17.3 966 1,080 1,040 7.8 8.1 7.9 8.8 12.4 10.3

Feb. 1996 12.5 24.2 19.0 827 1,080 961 7.8 8.1 7.9 7.9 13.2 9.8

Mar. 1996 13.7 24.8 20.0 623 1,020 951 7.6 8.0 7.8 8.1 11.7 9.6

Apr. 1996 18.3 28.3 23.7 605 1,100 995 7.4 8.0 7.8 5.8 9.9 8.1

May 1996 22.4 31.3 27.7 490 1,070 995 7.4 8.1 7.9 2.4 9.6 7.5

June 1996 27.0 33.4 29.9 430 1,090 971 7.4 8.3 7.9 4.7 9.6 7.1

July 1996 27.4 33.2 30.7 469 1,100 972 7.4 8.1 7.9 3.9 8.7 7.0

Aug. 1996 26.7 33.2 30.0 446 1,060 962 7.4 8.1 7.8 6.3 9.6 7.5

Sept. 1996 23.9 33.7 28.1 218 986 708 7.2 7.9 7.7 2.5 8.1 7.1

Oct. 1996 21.0 27.8 25.3 933 1,050 999 7.7 8.0 7.9 6.8 8.8 7.7

Nov. 1996 15.6 26.7 21.7 387 1,060 936 7.8 8.1 8.0 6.8 9.8 8.2

Dec. 1996 13.7 22.6 18.6 533 1,060 939 7.9 8.2 8.0 6.9 10.5 8.6

Jan. 1997 10.8 22.6 16.9 744 1,060 989 7.8 8.2 8.1 7.2 12.5 9.6

Feb. 1997 13.5 21.6 17.6 501 1,090 948 7.6 8.0 7.8 7.8 12.4 9.4

Mar. 1997 17.7 24.7 21.2 427 1,060 935 7.5 8.2 8.0 7.3 9.5 8.5

Apr. 1997 16.5 26.3 21.6 234 1,070 882 7.7 8.3 8.0 7.2 9.1 8.1

May 1997 22.0 28.9 25.4 182 1,030 809 7.6 8.1 7.9 4.6 8.0 6.9

June 1997 22.3 30.8 27.0 218 986 684 7.8 8.4 8.1 4.8 8.6 6.4

July 1997 26.8 30.9 28.7 493 865 696 7.9 8.3 8.0 6.2 8.4 7.3

Aug. 1997 27.9 31.8 29.8 779 973 908 7.7 8.2 8.0 5.3 8.3 6.8

Sept. 1997 25.9 30.9 28.8 666 985 894 7.7 8.2 8.0 6.2 8.8 7.2

Oct. 1997 20.3 28.5 24.6 291 983 771 7.7 8.1 8.0 4.8 7.6 6.5

Nov. 1997 16.3 23.1 19.3 678 981 856 7.9 8.2 8.0 7.4 9.6 8.6

Dec. 1997 13.7 20.2 16.9 265 975 835 7.8 8.2 8.0 6.6 10.7 9.0

Jan. 1998 15.5 21.2 18.0 247 977 836 7.9 8.4 8.1 4.7 10.5 8.0

Feb. 1998 14.0 21.1 17.7 311 915 732 7.7 8.2 7.9 6.4 9.2 8.3

Mar. 1998 15.7 23.5 19.0 223 903 687 7.5 8.2 8.0 7.5 10.4 9.0

Apr. 1998 20.0 25.3 22.8 605 958 778 7.7 8.0 7.9 7.1 9.2 8.2

May 1998 23.3 31.1 27.2 857 1,010 941 7.6 8.3 7.9 6.4 9.0 7.5

June 1998 24.9 32.8 29.9 745 1,030 918 7.5 8.2 7.9 6.1 9.0 7.4

July 1998 28.8 33.0 30.8 776 987 927 7.5 8.2 7.9 5.1 10.4 7.1

Aug. 1998 25.4 33.1 29.3 150 1,010 729 7.5 8.4 7.9 2.7 9.9 6.1

Sept. 1998 25.5 30.8 28.6 321 951 817 7.7 8.2 8.0 4.4 7.4 6.8

Oct. 1998 20.1 29.8 24.4 102 959 727 7.6 8.3 7.8 5.4 14.3 8.2

Nov. 1998 18.2 24.4 20.7 461 820 653 7.6 8.2 8.0 3.8 15.7 7.2

Dec. 1998 12.7 23.1 17.9 690 831 760 7.8 8.0 7.9 3.3 10.0 7.7
Ging and Otero— Comparison of Temperature, Specific Conductance, pH, and Dissolved Oxygen 

at Selected Basic Fixed Sites in South-Central Texas, 1996–98