Transcript Slide 1

Applications of landscape analyses
and ecosystem modeling to
investigate land-water nutrient
coupling processes in the
Guadalupe Estuary, Texas
Sandra Arismendez, Hae-Cheol Kim, Jorge Brenner
and Paul Montagna
Harte Research Institute for Gulf of Mexico Studies
Texas A&M University – Corpus Christi
March 2009
Introduction

Nutrient enrichment resulting from nonpoint sources of
pollution is the largest pollution problem facing coastal U.S.
waters (Howarth et al 2000).

More than 60% of coastal U.S. waters are moderately to
severely degraded.

Coastal waters along the Gulf of Mexico have been
identified as those among the most severely degraded.

Comprehensive studies that address the effects of landwater nutrient coupling processes along the Texas coast are
lacking.
Research Objectives

To characterize the San Antonio and Guadalupe
River Basins.

To determine effects of basin characteristics on
nutrient concentrations.

To determine estuarine ecosystem response to
the addition of varying nutrient concentrations
from the two river basins.
National Land Cover
Dataset (1992, 2001)
Approach
TCEQ Historical Water
Quality Monitoring Data
(1968-2007)
Landscape
Analysis
Water Climate Center
Oregon State University
PRISM Precipitation Data
USGS Water Resources
Data (1920s-2007)
Estuary Ecosystem
Response Box Model
Study Area

Two River Basins
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Guadalupe
San Antonio
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Four HUCs in each
basin
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Guadalupe Estuary
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Centrally located
along Texas coast
Microtidal
Small bay area but
large watershed
relative to other Texas
systems
Basin Characteristics
Characteristic
Size (ha)
Human
Population
1 San
Antonio
River Basin
1.08 x 106
2
1.8 x 106
4.0 x 105
Permitted Point 83 industrial
Sources
34 municipal
1San
Antonio River Basin Highlights Report 2003
2Guadalupe River Basin Highlights Report 2006
Guadalupe
River Basin
1.55 x 106
51 industrial
19 municipal
Precipitation and Flow
8000
GRB
SARB
Flow (cfs)
6000
4000
2000
0
1940
(PRISM)
1950
1960
1970
1980
1990
Year
Annual Average Precipitation
3Annual
1GRB:
GRB: 56.76 m3/s (2004.62 cfs )
76-94 cm/yr
2SARB:
66-97 cm/yr
1Guadalupe
River Basin Highlights Report 2006
2San Antonio River Basin Highlights Report 2003
Average Flow
SARB: 22.61 m3/s (798.39 cfs )
3USGS,
Water Resources Data
2000
2010
Landscape Analysis
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(2001 National Land Cover Data)
ArcGIS
Two years: 1992, 2001
21 LULC categories
Aggregated similar
categories
 Developed
 Water
 Agriculture
 Barren
 Wetlands
 Forest
 Shrubland
Land Use Change
8
6
From 2 to 6 %
4
Change (%)
2
0
-2
-4
-6
From 7 to 13 %
-8
GRB
SARB
-10
-12
Agriculture Barren Developed Forest
Land Use
Shrub
Water
Wetlands
Less
developed
land use
NLCD and TCEQ WQ Correlation

PC scores for 1992
and 2001 only
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Positive correlation

Areas with higher
nutrients reflect
areas with more
developed land use
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Areas with lower
nutrients reflect
areas with less
developed land use
GRB
SARB
2
R = 0.70
LC PC1 (36%)
1
0
More
developed
land use
-1
-2
-3
-2
-1
0
1
2
WQ PC1 (44%)
Less
nutrients
More
nutrients
3
Nitrogen Concentrations (1976-2007)

800
GRB
SARB
GRB < SARB
600
DIN (uM)
Long-term DIN
concentration:
400

Flow vs DIN

200

800
Mean: 101.37 uM
Min: 19.81 uM
Max: 480.35 uM
600
20
10
20
05
20
00
19
95
19
90
19
85
19
80
19
75
0
Positive correlation in GRB
Negative correlation
in SARB
800
Guadalupe River Basin
San Antonio River Basin
700
Mean: 284.06 uM
Min: 98.52 uM
Max: 738.23 uM
400
500
DIN (uM)
DIN (uM)
600
200
400
300
200
0
100
0
0
1000
2000
3000
4000
Flow (cfs)
5000
6000
7000
8000
0
500
1000
1500
2000
Flow (cfs)
2500
3000
3500
Model Inputs

DIN loads from coastal
HUCs used as model
inputs
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Load comparison - 1992 vs.
2001
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
35000
30000
Lower Guadalupe
Lower San Antonio
(a)

-1
DIN Load (kg d )
25000
20000
15000
Highest flows ever recorded
in both basins in 1992
2001 was a moderate flow
year
DIN loads differed in
Guadalupe but not much
difference in Lower San
Antonio
10000
5000
0
1985
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1990
1995
2000
2005
2010
What does this mean?
Landscape Analysis Conclusions

Basin characteristics are different, thereby influencing
nutrient concentrations
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As developed land use increases, nutrients increase
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High river flow events in a river with high nutrient
concentrations (SARB) appears to have a negative
effect on DIN concentrations.
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High river flow events in the GRB appears to result in
increased DIN concentrations.
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Increased flows do not affect loads in SARB as much as
it affects loads in GRB.
A generic ecosystem model
(3 components with 2 boundary conditions)
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Mass-balance model
Two boundaries:
LGRW & LSRW
Three components:
Nutrient (DIN) –
Phytoplankton –
Zooplankton
Re-mineralization and
implicit sinking (or
horizontal exchange)
were assumed to be
50%, respectively
Δ=1 hr & RK 4th
order scheme
Why Phytoplankton?
Phytoplankton are Indicators of Water Quality, Climate Change


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Primary producer that can maintain food web by providing
organic carbon upper trophic levels (food source)
Carbon sequestration (deterring climate change)
Biofuel (energy source)
But too much? > Eutrophication causing deterioration of
water quality, hypoxia, etc.
NSF Polar Program
Model Results (steady-state case)
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No boundaries open, thus, mass conserved
Each state variables approach steady state solutions
Boundary Conditions (DIN loadings)
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Monthly
climatology
(1976-2007)
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Flow rate (m3 s1)
DIN
concentration
(mg at-N m3)
DIN Loading =
Flow rate • DIN
÷ volume
Model Results
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No loadings (both
boundaries shut
down): Initial
nitrogen pool for
DIN, Phyto and Zoo
will get eventually
depleted
When LSRW (2nd
panel) or LGRW (3rd
panel) were open:
discharged DIN kept
nitrogen pool for
DIN, Phyto and Zoo
to a certain level
LSRW and LGRW
had a different
timing, duration and
magnitude in
responses of DIN,
Phyto and Zoo
Model Conclusions and Discussion

Estuary response differs with respect to varying
nutrient concentrations.
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Increases in nutrient concentrations due to human
alterations of the landscape may result in future
eutrophic conditions in the Guadalupe Estuary.
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Which nutrient species is more limiting to
phytoplankton, nitrate+nitrite and/or ammonium?

What is the role of DON?

What is the proper mixing time scale?
Estuary PCA Comparison
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Nitrogen species exhibit different
behavior
Lavaca-Colorado Estuary
Future Work
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Implement watershed model (e.g. SPARROW,
ArcHydro)
Develop nutrient budgets
Develop a more realistic ecosystem loadingsbased model
Expand work to other river basins along
Texas coast
Study Area:
Mission-Aransas Estuary, Texas
Mission
River
Aransas
River
Mission River
Aransas River
Discharge from
20 yr average salinity (psu):
upstream gauge
(Mooney, 2008)
 Copano Bay = 17.1
 Aransas Bay = 20.3
Did any changes in oyster populations occur because of
200
100
0
20
15
Salinity (psu)

Discharge (m3/s)
300
Copano Bay East
Copano Bay near
Aransas Rv. mouth
the changing salinities from 2007 2008?
10