Total Loads and Water Quality in the Corpus Christi Bay System

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Total Loads and Water Quality in the Corpus
Christi Bay System

Presented by
Ann Quenzer and Dr. David Maidment
Special Thanks
Corpus Christi Bay National Estuary
Program Ferdinand Hellweger Dr. Nabil Eid Dr.
George Ward Dr. Neal Armstrong
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Purpose

• To determine the rainfall/runoff relationship
• To estimate the point and non-point source loads
  to the bay system
• To quantify the relationship between the total
  loads and the bay system water quality

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Basic Concept
Steady-State Model
Linkage of the Two Models
Calculate Flow and Total Loads
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Purpose

• To determine the rainfall/runoff relationship

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Watershed Delineation
Sub-Watersheds
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Precipitation
Merged Precipitation Files
Precipitation Trend
Oregon State University
over Bay System
Precipitation Data


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Regression Inputs and Outputs
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Surface Water Runoff

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Surface Water Runoff
Land Use

Precipitation
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Precipitation and Runoff Gradient
Precipitation and Runoff Gradient from South (A)
to North (B) along the Bay System
Precipitation and Runoff Gradient Locations in
the South (A) and North (B)
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Runoff Into Each Bay System
North Bay System 40.5 m3/s 56 of total flow
Entire Bay System 72 m3/s
Middle Bay System 24.5 m3/s 34 of total flow
South Bay System 7 m3/s 10 of total flow
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Bay System Water Balance
Entire Bay System
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Bay System Water Balance
North Bay System
Middle Bay System
South Bay System
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Purpose

• To estimate the point and non-point source loads
  to the bay system

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Total Constituent Loading
Land Surface Load
Point Source Load
Atmospheric Load
? Sediment Load ?
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Land Surface Constituent Loading
Load Mass/Time Runoff Vol/Time x
Concentration Mass/Vol
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Land Use
USGS Land
Use (1970s)
Addition of
Missing
Land Use
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Percent Land Use
Total Study Area
Legend
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EMC Table
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Point Sources
Texas Natural Resources Conservation Commission
(TNRCC) Water Quality Segmentation
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Loads Routing
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Elevation Grid Modification Methodology
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Model Connection Methodology
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Load Routing Methodology
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Connection of Both Models
Bay Water Quality
Total Constituent Loads
Input for Water Quality Model
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Total Load to Bay System
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Load Sources
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Load Contribution
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Atmospheric Contribution
Total Nitrogen Atmospheric Load to Land Surface
2,700 Kg/d which is 35 of Land Surface Load
from agricultural land use. This calculation
is made assuming the EMC of 4.4 mg/l for
agriculture and a Nitrogen concentration of 1.1
mg/l in precipitation
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Purpose

• To quantify the relationship between the total
  loads and the bay system water quality

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Bay System Segmentation
Clipped Segmentation from Drs. Armstrong and Ward
Segmentation Used in the CCBNEP Project
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Bay System Model Methodology.
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Bay System Model Methodology.
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Water Quality Analysis
Salinity Concentration and Mass Fluxes in
Corpus Christi Bay.
Finite Segment Analysis
Flow of water
Transport of Constituents
Fluxes
Loads
Advection
Dispersion
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Observed vs. Expected
Total Nitrogen (mg/l)
Total Phosphorus (mg/l)
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Observed vs. Expected
Oil and Grease (mg/l)
Copper (µg/l)
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Observed vs. Expected
Zinc (µg/l)
Chromium (µg/l)
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T-Test Results
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Decay Rates (using three segment model)
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Decay Rates (using three segment model)
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Provisional EMC Data
Original EMC Values from USGS Study (Baird,
1996) Total Nitrogen 4.40 mg/l Total
Phosphorus 1.30 mg/l Provisional EMC Values
from Agricultural Runoff Studies at King Ranch
and Agricultural Field Near Edroy, TX (Mean
Values Obtained from Okerman of USGS) Total
Nitrogen 1.49 mg/l Total Phosphorus 0.47 mg/l
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Provisional EMC Values
Total Nitrogen and Total Phosphorus from Land
Surface Sources to Bay System Using Original and
Provisional EMC Values.
Total Nitrogen Reduction 54 Total Phosphorus
Reduction 60
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Provisional EMC Values
Total Nitrogen and Total Phosphorus from All
Sources to Bay System Using Original and
Provisional EMC Values.
Total Nitrogen Reduction 27 Total Phosphorus
Reduction 38
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Provisional EMC Values
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Provisional EMC Values
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Conclusions

• Strong South-North gradient in runoff from the
  land surface
• Nearly all water evaporates from bays, little
  exchange with the Gulf
• Nonpoint sources are main loading source for most
  constituents
• Nitrogen, phosphorus, oil grease loads are
  consistent with observed concentrations in the
  bays
• Metals loads from land account for only a small
  part of observed concentrations in bays - a
  reservoir of metals in the bay sediments?