Transcript 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

Decrease in freshwater
– Population increase (more water usage)
– Dams, reservoirs, diversions, etc.

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…

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

Water data used

Rincon gauge data
– Precipitation
– Freshwater inflow from the Nueces River

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

– Narrowed down to October 1998, April 1999,
November 1999
Results

Salinity
As freshwater inflow
increases, salinity decreases
What else affects salinity
(besides freshwater inflow)?

Temperature / Evaporation
– As temp increases, evaporation increases, which
increases salinity

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

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

Diatoms and other phytoplankton
– Essential for their growth (used in cell walls)
– Recycling of their cell walls
Conclusions

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

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

Project expansion
– Other water quality parameters
– Other estuaries

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
