Transcript Effects of Freshwater Inflow on Water Quality in the Nueces Delta Andrea Kopecky

Effects of Freshwater
Inflow on Water Quality
in the Nueces Delta
Andrea Kopecky
Marine Science Department
CE 394K Term Project – Fall 2001
Where is the Nueces Delta?
The Nueces Delta is upstream of Corpus Christi Bay
on the coast of South Texas
One threat to the Nueces Delta
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Decrease in freshwater
– Population increase (more water usage)
– Dams, reservoirs, diversions, etc.
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Result = increase in salinity
– Decrease in primary productivity and diversity
– Causes stress, creates a harsh environment
– Delta is now considered a reverse estuary
Fixing the inflow problem…
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Rincon Bayou Demonstration Project
– Included people from U.S. Bureau of
Reclamation, UT Marine Science Institute,
CRWR, TWDB
– Project from 1994-1999 with purpose of
increasing freshwater inflow to the Nueces Delta
– 2 channels were created to divert water from the
Nueces River
Nueces River Overflow Channel
Rincon Overflow Channel
Map of Nueces Delta
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Made by David Eckhardt from the U.S. Bureau of Reclamation
It is a mosaic of eight color-infrared USGS DOQQ's (Digital Orthophoto
Quarter Quadrangles)
The map is a raster image data set projected in UTM coordinates
Project objectives
Find out how an increase in freshwater
influences water quality
 Use salinity, ammonium, nitrate/nitrite,
and silica concentrations at 10 stations
in the area
 Look for correlations between
freshwater and the amount of each
nutrient
 Consider other factors that could
influence the water quality
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Water data used

Rincon gauge data
– Precipitation
– Freshwater inflow from the Nueces River
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Station data for Nueces Delta
– Monthly averages for salinity, ammonium
(NH4+), nitrate (NO32-), nitrite (NO2-), and
Silica at 10 stations for September 1998
to March 2001
Narrowing down the data set
I chose 3 months out of a possible 31
 Based on missing data and amount of
inflow
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– Narrowed down to October 1998, April 1999,
November 1999
Results
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Salinity
As freshwater inflow
increases, salinity decreases
What else affects salinity
(besides freshwater inflow)?

Temperature / Evaporation
– As temp increases, evaporation increases, which
increases salinity
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Amount of tidal inflow
– This could decrease or increase salinity,
depending on the salinity of the estuary

Precipitation
– Causes a decrease in salinity
Results

Ammonium
– More variation
– Trends not clear
– Other factors are influencing
the concentration
Factors that could influence [NH4+]
Uneven distribution of freshwater
throughout the Delta
 Amount of fertilizer in agricultural
runoff varies
 Sensitive ammonium test – error prone
 Nitrifying bacteria – Cyanobacteria
convert atmospheric nitrogen to NH4+
 Amount of phytoplankton and
zooplankton
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Results

Nitrate and
Nitrite
- At 8 of the stations, NO32- and
NO2- were the highest during
October ’98, which had highest
inflow
- At stations 50 and 54, April ’99
had the highest concentrations
What’s affecting nitrate &
nitrite?
Nitrifying bacteria can convert NO32- to
NO2- to NH4+
 Tidal inflow
 Ground water inflow
 Agricultural runoff
 Seasonal fluctuations

Results

Silica
- Highest silica levels during Oct
’98 at river stations (4, 4A, 4B)
-April ’99 and November ’99 had
similar concentrations
-More freshwater = more silica
What influences silica
concentrations?

Amount of runoff
– Erosion of clays
– Weathering of igneous rocks
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Diatoms and other phytoplankton
– Essential for their growth (used in cell walls)
– Recycling of their cell walls
Conclusions
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Freshwater inflow positively affects the
water quality in the Nueces Delta
– Causes a decrease in salinity
– Increases the concentration of nutrients,
including ammonium, nitrate, nitrite, and silica
– An increase in nutrients can lead to an increase
in biological productivity and diversity
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There are other factors that also influence
the concentration of nutrients
More Conclusions
 GIS is helpful for…
– Studying water quality
– Visualizing data from multiple stations
– Comparing data over time
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Project expansion
– Other water quality parameters
– Other estuaries
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Relationship between inflow & nutrients
– Predict what effects dams/reservoirs will have
– THE MORE WE KNOW ABOUT THE IMPACTS
OF HUMAN ACTIVITIES ON WATER QUALITY,
THE MORE WE CAN DO TO PROTECT OUR
ESTUARIES!
Acknowledgements
Heather Alexander-Mahala and Dr.
Kenneth Dunton, University of Texas
Marine Science Institute
 Dr. Maidment
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