Does the Chemistry of the Rio Grande River Change Seasonally?

By

Tyler Kraften

Canyon Hills Middle School, El Paso, Texas, USA

Kathy Kraften and Eloy Salamanca, Teachers

Abstract

The purpose of my project was to determine if the chemistry in the Rio
Grande River changes from season to season. Using the GLOBE hydrology
protocols for taking turbidity, temperature, dissolved oxygen (DO),
total dissolved solids (TDS), nitrates, pH and alkalinity measurements;
I began collecting monthly water samples from the Courchesne Bridge in
September 2001 for a science fair project. The Courchesne Bridge
separates the city of El Paso, Texas from Sunland Park, New Mexico. The
results show that there are noticeable differences in the chemistry of
the Rio Grande River from season to season. Changes in turbidity,
temperature, DO, TDS and nitrates show the greatest changes, while pH
and alkalinity showed the least. I gradually extended my study up river
from El Paso to Radium Springs, New Mexico, a town about 25 km north of
Las Cruces, New Mexico. This was done to see if some of the seasonal
changes observed were being influenced by land use, which indeed they
had. I also incorporated into my study, a significant amount of
hydrology data input from other GLOBE schools.

Hypothesis

Does the chemistry of the Rio Grande River change seasonally? I believe
the chemical changes that occur in the Rio Grande River from season to
season are due to many factors. My investigation is to identify those
factors and to find out which are due to seasonal changes alone and
which are the results of land use. By monitoring the river through the
seasons and graphing the data from this collection I hope to find the
answers to my questions.

![](media/image1.png){width="6.122222222222222in"
height="4.591666666666667in"}

**Map 1: "Does the Chemistry of the Rio Grande River Change
Seasonally?**

**Study Area**

![](media/image1.png){width="6.122222222222222in"
height="4.591666666666667in"}

**Map 1: "Does the Chemistry of the Rio Grande River Change
Seasonally?**

**Study Area**

![](media/image2.png){width="6.122222222222222in"
height="4.591666666666667in"}

**Image 2: Satellite Image of the El Paso, TX, Juarez, Mexico and Las
Cruces, New Mexico Area. Study Area: West of the Franklin Mountains
heading northwest along the agricultural valley of the Rio Grande
River.**

Purpose and Method of Investigation

The purpose of this investigation is fourfold: (1) test the waters of
the Rio Grande River at selected sites using GLOBE hydrology protocols,
(2) graph the data collected, (3) incorporate data input by other GLOBE
schools along the stretch of river investigated in this study, and (4)
analyze the information revealed by these graphs.

The investigation began with the testing of the Rio Grande River at the
Courchesne (Anapra) Bridge, which separates El Paso, Texas from Sunland
Park, New Mexico and Anapra, Mexico (map 1). After graphing the data
collected over a short period of time (2 to 3 months) it was obvious
that the chemistry of the river varied significantly. This led me to the
question of whether the changes were seasonal. Before this could be
determined it was necessary to test the river over longer periods of
time. The period of study was from September 2001 to the present. Graphs
of the data collected at the Canutillo, Texas Bridge, by Joel Gilbert, a
teacher at Canutillo High School, and the Radium Springs, New Mexico
Bridge by Rivers Academy student David Mooney were also analyzed. It was
found that the chemistry of the river not only changed seasonally, but
also varied from site to site. Furthermore, the chemistry changed from
year to year. It was immediately apparent that the data was indicating a
lot more than seasonal changes, which caused the purpose of the study to
broaden. What change could be attributed to mere seasonal changes and
which were influenced by river use? The Rio Grande's course stretches
3000 km. It begins in southwestern Colorado, and ends at the Gulf of
Mexico near Brownsville, Texas. Along approximately two thirds of this
distance it forms the boundary between the United States and Mexico. The
Rio Grande is a working river. Ninety percent of the waters in the river
are allocated to agriculture. Elephant Butte Dam located near Truth or
Consequences, New Mexico, releases water to the Mesilla Valley (Las
Cruces, New Mexico area) and El Paso, Texas, around March 1 to October 1
each year. As the population south of the dam increases, so does the
demand for water from the river. These demands have an affect on our
water quality. North of El Paso, the EPA has deemed the Rio Grande as
unsuitable for fishing and recreation. The area south of El Paso and its
sister city Juarez, Mexico is most probably far more unsuitable (image
2). The 3-year drought in the southwest has further deepened the
problems of the river system.

Data Summary

![](media/image3.png){width="6.0in" height="4.5in"}

**Graph 1 shows plots of Temperature data**

![](media/image4.png){width="6.0in" height="4.5in"}

**Graph 2 shows plots of Turbidity data**

![](media/image5.png){width="6.0in" height="4.5in"}

**Graph 3 shows plots of Dissolved Oxygen data**

![](media/image6.png){width="6.0in" height="3.75in"}

**Graph 4 shows the inverse relationship between Temperature and
Dissolved Oxygen**

![](media/image7.png){width="6.0in" height="4.5in"}

**Graph 5 shows plots of pH data**

![](media/image8.png){width="6.0in" height="4.5in"}

**Graph 6 shows plots of Alkalinity data**

![](media/image9.png){width="6.0in" height="4.5in"}

**Graph 7 shows plots of TDS data**

![](media/image10.png){width="6.0in" height="4.5in"}

**Graph 8 shows plots of Nitrate plus Nitrite data**

![](media/image11.png){width="5.677083333333333in"
height="8.988888888888889in"}

**Graph 9 shows a stacked graph of the Nitrate plus Nitrite data**

Analysis

Using hydrology protocols and GLOBE graphs makes analyzing data
relatively easy for interpretation. Inspection of the graphs clearly
shows seasonal changes where they are present and where they have little
effect. As expected the temperature of the water increases and decreases
during the summer and winter months. The amount of this increase and
decrease in temperature reflects yearly averages. When there is less
water in the river during the winter months the depth of the river is
much shallower this causes much more fluctuation of the waters
temperature since the water responds more rapidly to the change in air
temperatures. Notice how little the temperature varies between June 1
and October 1, 2002 compared to the rest of the year (graph 1).

Turbidity or water clarity varies from a few centimeters during the
summer months to over 100 cm during the winter months. The river becomes
laden with sediment during the summer months due to flood irrigation.
The waters of the rivers are diverted through canals to the cotton,
chili, alfalfa fields and pecan groves from March to October. When the
water returns to the river via drainage canals, it not only carries back
sediment, but unused fertilizers and pesticides on its return. Water
clarity is the highest at the Radium Springs, New Mexico Bridge. Below
Radium Springs heavy demands of the agricultural areas between Las
Cruces and El Paso cause the decrease in water clarity (graph 2).

Dissolved oxygen varies from as much as 13 mg/l during the winter months
to as low as 6 mg/l during the summer months (graph 3). As the
temperature rises during the spring and summer months, the dissolved
oxygen in the water decreases. This inverse relationship is clearly
demonstrated on and graph 4.

The pH of the river seems to vary little and averages out over the year
at about 8.5. The deserts of the southwest are alkaline and during the
summer when rain is scarce and temperature is high many alkali flats are
created. Many of the mountains along the route of the Rio Grande are
made of limestones. When these limestones weather calcium carbonate is
released into the environment (graph 5).

Calcium carbonate in the waters of the Rio Grande is mainly from
weathered limestone outcrops. The calcium carbonate is carried into the
river by runoff from rainstorms. Alkalinity, unlike pH does reflect
seasonal changes and a decrease in the amount of water in the river
during the winter months of 2002 and 2003, also appears to have
increased the alkalinity readings (graph 6).

Total dissolved solids in the river vary seasonally. The dissolved
solids are more concentrated when the amount of water in the river is
reduced in the winter months. Due to the drought in the southwest and
the subsequent decline in the water being released by Elephant Butte
Dam, the amount of TDS in the Rio Grande have increased over the same
period last year. In fact since early December 2002 the level of TDS
have been in excess of 1990 microsiemens. The Oakton TDS pen used to
measure the water has a limit of 1990 and the reading recently obtained
at the Courchesne Bridge site has been OR which means out of range of
the instrument (graph 7).

Nitrate is reported as nitrate + nitrite in mg/l. Nitrates do not seem
to reflect seasonal changes as the other protocols do. However, nitrates
in the river are higher at most test sites for the period extending from
October 2002 to February 2003. The exception is where the river is
tested at the Radium Springs, New Mexico Bridge. Here nitrate readings
are never higher than .25 mg/l. Most times no nitrate is present (graph
8). A stacked graph of nitrate data recorded from each site clearly
shows this relationship more clearly. The readings taken at this site
probably reflect a more normal state for the river (graph 9).

The majority of the study was taken up with collecting data over an
extended period of time. A picture of how the chemistry of the river
changed quickly emerged as more data were added to the graphs. Bottles
of Rio Grande water have been sent to Suzanne Mills, a graduate student
at New Mexico Tech in Socorro, New Mexico. She will analyze the water
for total dissolved solids to determine the types of salts dissolved in
the river. These analyses are not yet in, but will be put into the GLOBE
website as Metadata when they are received.

Conclusions

The chemistry in the Rio Grande River does change seasonally, but not
all the changes in chemistry are due to seasons alone. As expected the
river's water temperature increases and decreases as the seasons change.
The pH readings of the river probably show the least change of all and
vary little from an average of 8.5. One observation about alkalinity was
that readings rise during the winter months and drop during the summer
months. This is probably due more to low water volume than an increase
or decrease in actual alkalinity. The turbidity or water clarity of the
river is greatest in the winter when the river is not being used to
irrigate crops. It becomes very turbid during the growing season when
the water's clarity falls too as little as 7 cm. The amount of dissolved
oxygen (DO) in the river increases and decreases with temperature, and
reflects the change of the seasons. Total dissolved solids readings in
the river show seasonal changes. However the decrease in the amount of
water in the river certainly increases the TDS. All sites show an
increase in TDS over the same period last year. At the Courchesne Bridge
readings have been in excess of 1990 microsiemens. Nitrate (nitrate +
nitrite) shows little seasonal change. The high readings in the later
part of 2002 and the beginning of 2003 most than likely reflect the low
amount of water in the river. At this time the Elephant Butte Dam is
releasing 3.5 cfs as compared with 350 cfs last winter (image 3) Sand
bars in the river are at an all time high. The river is so shallow, that
the bottom in the channels where it is still flowing appears to be less
a foot deep. (Image 4, 5) Of all the tests taken on the river's water,
the increase in nitrate is probably most alarming. We have had less than
125 mm of rain a year for the last 3 years. Nitrates in our river are
certainly not due to rain. The major routes of entry of nitrogen into
the Rio Grande are municipal and industrial wastewater, septic tanks,
animal wastes from the dairies, and runoff from agricultural areas.
South of El Paso, Texas, the city of Juarez, Mexico allows untreated
sewage to flow into the Rio Grande. This Mexican city of a million and a
half people has but a single sewage treatment plant (built in 2000),
which is hardly adequate to handle the amount of sewage that a
population of that size can generate.

![](media/image12.jpeg){width="5.9875in" height="4.490277777777778in"}

**Image 3: Elephant Butte Dam.** **The building in the foreground was
previously underwater for many years. It was used as an underwater
training site for scuba diving. The lighter areas shown on the rock
formation show how the level of water in the lake** **has dropped in the
past two years.** Oct. 2002

![](media/image13.jpeg){width="5.9875in" height="4.490277777777778in"}

**Image 4: Rio Grande River underneath I - 25 bridge just south of
Caballo Dam.** (Looking northeast) Photo taken 2/23/03

![](media/image14.jpeg){width="5.9875in" height="4.490277777777778in"}

**Image 5: Rio Grande River underneath I - 25 bridge just south of
Caballo Dam.** (Looking southwest) Photo taken 2/23/03

Discussion

Water covers roughly 79% of the Earth's surface. Despite its abundance,
people do not have access to the use of most of that water. In the
Introduction of the "Big Picture" for the hydrology protocols, the GLOBE
program states, "If we represent the Earth's water as 100 liters, 97% of
them would be seawater. Most of the remaining three liters would be ice,
and only about 3 ml would be water that we can consume; that is the
water pumped from the ground or taken from fresh water rivers or lakes."
The Rio Grande River is the nation's second longest river, but water in
the river has been over allocated to the farms, ranches and cities along
its path. The health of the river is in jeopardy, and very little
consideration has been given to the ecosystem along its route. A
continued monitoring of the river over the coming years would make an
excellent model for scientists studying the impact of population growth
on our river systems. Their research may turn the tide in favor of
protecting and restoring rivers such as the Rio Grande. It would be
interesting to compare data from other GLOBE schools existing along our
nations rivers. A study on macro invertebrates in the Rio Grande would
further indicate the health of our river.

> References

1\. The GLOBE Program - Hydrology Protocols. Washington DC 1997 edition.
[www.globe.gov](http://www.globe.gov/)

2\. Environmental Protection Agency. www.epa.gov

3\. \"Chemical Analysis - City Water" El Paso Water Utilities. El Paso,
Texas. 2001

4.  \"Water Quality Criteria and Standards Plan" Health and Ecological
    Criteria Division, U.S. EPA, Office of Water, Washington DC. 1997

5.  Dr. Robin Hoffer, GLOBE Program Director at The University of Texas
    at El Paso.

6\. USGS
<http://waterdata.usgs.gov/nm/nwis/uv/?site_no=08361000&PARAmeter_cd=00065,00060>