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Investigators
Fred
Phillips
James
Hogan
Jan
Hendrickx
Graduate
Students
Suzanne Mills
Naomi Roseneau
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The Murray-Darling River
in southern Australia (1) is the sole water
supply for the major city of Adelaide, as
well as much of the surrounding region.
The drainage basin is semi-arid, with deep
vadose zones, and natural vegetation is
highly water-efficient mallee scrub. Clearing
of the natural vegetation for agriculture
and grazing has greatly increased water
fluxes through the vadose zone. Enhanced
recharge is rapidly flushing highly saline
vadose pore water (which is a natural result
of concentration of the precipitation by
mallee scrub) into the ground-water system,
which discharges into the rivers. As a result,
river salinity is already above drinking
water limits for much of the year and is
predicted to continue rising by ~5 ppm every
decade (2). Although the sequence of events
was initiated in the last century, the response
time of the subsurface system was so long
that the salinity trend was not noticed
until a few decades ago and the cause identified
less than 10 years ago. The damage appears
to be irreversible.
(1) Wolley, D.R.,
Hydrogeological maps for resource management
in the Murry-Darling drainage basin, Southeast
Australia, In Future Groundwater Resources
at Risk, International Association of Hydrological
Science, p.222, 1994.
(2) Allison, G.B., Cook, P.G. Barnett,
G.R., Walker, G.R., Jolly, I.D., and Hughes,
M.W., Land clearance and river salinization
in the western Murry Basin, Australia, Journal
of Hydrology, 119, 1-20, 1990.
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Overview
The quality of available water
is as significant a problem as the availability of water
in many arid-region drainage basins. River salinity
commonly increases downstream. The origins of this increase
in salinity are often difficult to determine. Potential
salinity sources include atmospheric deposition, saline
groundwater, anthropogenic sources, soil leaching in
irrigated areas, and evapotranspirative concentration
of the water. A comprehensive understanding of the sources
of salinity and the processes affecting its increase
are necessary for basin-scale salinity management. The
example of the Murray/Darling Basin (sidebar) shows
how even apparently benign human activities, such as
clearing land for grazing, can result in damaging long-term
fluctuations in water quality that may ultimately threaten
sustainable use.
The water quality of the Rio Grande,
like many arid region rivers, degrades with distance
downstream. In particular, salinity levels limit the
municipal and industrial use of the Rio Grande in the
El Paso region. The causes of salinization are often
complex, with multiple natural (saline groundwater,
hydrothermal springs, and dissolution of evaporite deposits)
and anthropogenic (agricultural return flow and wastewater
from sewage treatment plants) sources, in addition to
the concentrating effect of evapotranspiration. A comprehensive
understanding of the sources of salinity and the processes
affecting its increase are necessary for basin-scale
salinity management. For the past three years we have
conducted twice-annual synoptic sampling of the Rio
Grande. We have employed a variety of environmental
tracers to separate different salinity sources as well
as the effects of evapotranspiration. Our research is
focused around the following questions:
- What are the major sources of
solutes and how are they partitioned between natural
and anthropogenic origins?
- What are the relative roles of
solute input and evapotranspirative concentration
in producing the observed salinity in the lower basin?
- What is the solute-burden history
of the river basin and why has it varied in time?
- Are significant transients in
solute burden likely in the future?
- What management alternatives
are available for reducing salinity?
The immediate goal of this research
project is to identify and quantify the sources of salinity
to the Rio Grande. The long-term goal of this research
is to develop a water/solute mass balance model for the
Rio Grande that is capable of modeling past temporal variation
and can investigate future-use scenarios.
Activities and Results
We have conducted five synoptic
samplings of the Rio Grande. During these sampling campaigns
roughly 100 sites were sampled along the river. Samples
were analyzed in the field for TDS, EC, pH and in the
laboratory for Cl and Br concentrations. Salinity increases
in a stepwise fashion, with roughly five localized sections
of the river where there are significant increases,
that is remarkably consistent with minimal seasonal
or interannual variability (Figure 6A and 6B). Some
of these increases are correlated with known sources
(agricultural drains, hydrothermal areas). Others are
not correlated with known discharges but occur at the
lower end of sedimentary basins leading to the speculation
that they are the result of discharge of deep, saline,
groundwaters. Of particular interest is the Albuquerque
basin where, in two distinct steps, the TDS of the river
doubles from ~150 mg/L to ~300 mg/L and Cl increases
from ~10 mg/L to 30-40 mg/L (Figure 6A). With little
change in river discharge for this reach, this represents
a significant increase in the solute burden of the river.
We have used several solute ratios (e.g. Cl/Br, Ca/Sr,
Cl/SO4) in
conjunction with a two component mixing - evaporation
model to study the solute balance of the Rio Grande.
Results indicate the importance of solute inputs, especially
from Albuquerque to Elephant Butte Reservoir where ~60%
of the solutes enter the system.
During the past 10 months much of
our focus has been on applying isotopic tracers to "fingerprint"
and quantify the sources of solutes at these locations.
We are currently employing four solute isotopic systems:
(1) 87Sr/86Sr
in collaboration with J. Ruiz at University of Arizona;
(2) 36Cl/Cl
at the PRIME Lab facility; (3) d32S
in collaboration with C. Eastoe; and (4) d11B in collaboration
with C.P. Chamberlain at Stanford University. In addition,
samples have been analyzed for oxygen and hydrogen isotopes
(with C. Eastoe) (Figure 6C). Oxygen and hydrogen isotopes
reveal the importance of evaporation, especially from
reservoirs. Preliminary results from solute isotope
systems do "fingerprint" saline groundwaters
as the solute source (e.g. low 36Cl/Cl
and high 87Sr/86Sr
ratios). In order to quantify saline groundwater inputs,
one must understand the chemical composition of the
groundwater system. In order to do this we have developed
partnerships with the USGS (Albuquerque basin), New
Mexico Interstate Stream Commission (Socorro basin),
and through SAHRA's partnership with CEA-CREST (Project
2.9: Hueco Bolson - El Paso area). We are currently
in the process of analyzing end member groundwater samples
obtained through these partnerships.
Finally, during the past reporting
period we have begun our efforts on dynamic simulation
modeling. We started with modeling the Elephant Butte
Reservoir system where we have observed increase in
Cl concentration from ~40 to ~60 mg/L during our three
years of sampling. The increase is clearly correlated
with the decrease in storage volume during this same
period. The situation allowed for a critical test of
both water and solute mass balance modeling. We developed
a model covering the period from 1997-2002 with a monthly
time-step. Results of this initial model were successful.
The water balance was easily modeled using USGS gauge
data from surface water input and output in addition
to simple precipitation and evaporation input. In order
to successfully model the chloride mass balance we needed
additional saline groundwater input into the reservoir.
Study Area
This study is focused on the Rio
Grande above Fort Quitman Texas
(Figure
1). The drainage area is just over 32,000 square
miles. Within the upper Rio Grande drainage there are
over one million inhabitants, mostly centered in the
two large population centers of Albuquerque NM and El
Paso TX. Irrigated agriculture is common along the Rio
Grande. There are close to one million acres land currently
being irrigated for agriculture along the length of
the Rio Grande. The greatest concentration of agriculture
occurs in the San Luis Valley, CO, Albuquerque Basin,
NM, and Mesillia Valley NM.
Take
a virtual field trip along the Rio Grande
Plans
Activities in the coming year will
be focused on three goals:
- Continue river sampling but with
a reduced number of samples; the next sampling trip
is planned for August 2002. We will continue to collect
filtered samples for organic/nutrient analysis (3.9).
- Wrap up the isotopic analysis.
Determine the geochemical composition of saline groundwaters.
Quantify saline groundwater fluxes using isotopic
mass balance.
- Continue construction of a steady-state
water/solute dynamic simulation model. Begin analysis
of historic datasets using dynamic simulation model.
Long-term
Plans and Goals
Our long-term goals include the following:
- A detailed
understanding of the sources, fluxes, and reservoirs
of salinity in the basin.
- Pinpointing
major salinity sources that could be diverted or ameliorated.
- Assessment
of the likelihood of major salinity transients and
their possible causes.
In order to achieve these goals
we have the developed the following timeline:
2003-2004: Continue sampling.
Apply steady-state model to results. Begin (in cooperation
with C. Duffy) to construct transient water/solute balance
model. Begin analysis of socioeconomic implications
of findings.
2004-2005: Apply transient
model to results. Model past temporal variations of
solute burden. Explore future-use scenarios with model.
Analysis of socioeconomic implications.
Integration with other SAHRA
Activities
Research investigating solute sources
and balances in the Rio Grande has close ties with several
other SAHRA research projects (Figure
6). As described above, saline groundwaters are
a potentially significant source of solutes to the Rio
Grande. The work of Long and Eastoe, tracing groundwater
flowpaths will provide a useful constraint on where
saline groundwaters may discharge. Exploration of past
variation and future scenarios with our solute mass
balance model will be closely tied with Chris Duffy's
work on low-dimensional models. Duffy's research investigates
how long-term changes (climate, vegetation, human use)
propagate through a basin hydrologic system and result
in changes in river discharge and solute burden. The
combined results of this work will be incorporated into
a coarse resolution / lumped parameter systems model
as part of the Integrated basin-scale modeling effort
of TA4. Finally, this project has direct linkages to
nutrient cycling in riparian areas (TA3) (nutrients
are biologically important solutes) and to river management
in TA5 (URGWOM
Model, etc.).
This group has also developed several
important collaborations outside of SAHRA specifically
focused on developing partnerships with researchers
working on the groundwater system of Rio Grande valley.
As the Rio Grande travels from Colorado to Texas it
passes through several sedimentary basins. Past research
efforts have tended to be isolated and focused on one
groundwater basin at a time. Our study represents the
first attempt to gain a holistic understanding of salinity
sources through all basins. In order to understand these
sources one must also have an understanding of basin-scale
groundwater systems. To this end we have developed partnerships
with the
USGS (Albuquerque basin) , New
Mexico Interstate Stream Commission (Socorro basin)
, and through SAHRA's new partnership with the CEA-CREAST
(Hueco Bolson - El Paso area). It is our belief that
by linking these groundwater basin studies with our
sampling of the Rio Grande we will develop a holistic
understanding of salinity sources to the Rio Grande.
Finally, the isotopic analyses of the Rio Grande will
be incorporated into the International
Atomic Energy Agency's (IAEA) worldwide investigation
into isotopic mass balances for river basins.
Publications and Presentations
James F. Hogan, Fred M. Phillips,
Suzanne K. Mills, Jan M.M. Hendrickx, John Villinski,
Chris Eastoe, Paul Brooks, and Joquin Ruiz, Rio Grande
Water Quality: An Integrated Basin-Scale View, SAHRA
2002 Annual Meeting, Tucson, Arizona, March 2002.
View
abstract
View
poster
Suzanne K. Mills, Fred M. Phillips,
James Hogan, and Jan M.H. Hendrickx, The Salt of the
Earth: Using Environmental Tracers to Quantify Causes
of Salinity in semi-Arid Region Basins, Preliminary
Results from the Rio Grande, SAHRA 2002 Annual Meeting,
Tucson, Arizona, March 2002.
View
abstract
Hogan, J., F. M. Phillips and J.M.M.
Hendrickx, Solute Sources and Budget for the Rio Grande
above El Paso, Texas, AGU Fall Meeting, San Francisco,
CA, December, 2001.
View
abstract
View poster
Phillips, F.M., Hogan, J., Mills,
S.K., and Hendrickx, J.M.H., Environmental Tracers for
Assessing Water and Salt Balances in Arid-Region River
Basins (invited abstract) Dubai International Conference
On Water Resources and Integrated Management in the
Third Millenium, Dubai, UAE, February, 2002.
View
abstract
Download PDF of report
Download PDF of presentation
Roseneau, N. and F.M. Phillips,
Chloride/ bromide ratios in the Rio Grande, Poster Presentation
at the SAHRA Annual Meeting, Tucson, AZ, February, 2001.
Annual
Meeting Site
Springer E. P., C. J. Duffy, F.
M. Phillips, J. Hogan, and C. L. Winter, The Upper Rio
Grande Basin as a Long-Term Hydrologic Observatory -
Challenges and Opportunities, AGU Fall Meeting, San
Francisco, CA, December, 2001.
View
abstract
View poster
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