the sparrow water-quality model as a tool
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The SPARROW water-quality model as a tool for watershed analysis of nutrient sources and transport
Anne Hoos, U.S. Geological Survey, TennesseeSherry Wang, Tennessee Division of Water Pollution Control
Sources
Land-to-water transport
Instream transport
1. Science
2. Management
Watershedanalysis:
• SPAtially-Referenced Regression On Watershed Attributes
• Developed (~1995-ongoing) by USGS,applied on a national scale (1987 conditions)http://water.usgs.gov/nawqa/sparrow/
• Applied at regional scales (New England, Chesapeake, Interior Low Plateau) in collaboration with water-quality management authorities
SPARROW background
• Interior Low Plateau ecoregion, in collaboration with Tennessee Division of Water Pollution Control
• In development: southeastern U.S. (NAWQA Major River Basin program)
SPARROW modeling in Tennessee/Alabama
1. Assess water quality: What is the annual mean load and concentration of total nitrogen in the Elk River at its confluence with Tennessee River? 5,500 tons per year, 1.5 mg/L
Examples of the basin-scale questionsSPARROW can address
1. Assess water quality
2. Establish linkage between source inputs and instream flux: What portion of annual instream load is contributed by wastewater (versus atmospheric deposition, fertilizer applied to cropland, urban land, etc.)? 3%
Examples of basin-scale questionsSPARROW can address
1. Assess water quality
2. Establish linkage between source inputs and instream flux
3. Track flux from upstream origin to downstream destination: What portion of the annual load was contributed by Tennessee watersheds (versus Alabama watersheds)? 85%
Examples of basin-scale questionsSPARROW can address
• A strong advantage for its use in management decisions: estimate of uncertainty calculated for all model output
How certain are the answers?
1. Annual mean load = 5,500 tons per year;95% confidence interval: 4,150 – 7,950 tons (error ~20%)
2. Portion of annual load contributed by wastewater from all watersheds upstream = 3 percent; 95% confidence interval: 1 – 7 percent
SPAtially-Referenced Regression On Watershed Attributes
Response variable: measured load at monitoring stations
What is SPARROW?
Predictor variables: measured watershed attributes
“Expensive” information “Inexpensive” information
“Moving from Monitoring to Prediction”
Point-level water-quality data
Predictions for unmonitored, comparable areas
SPARROW model structure for Ecoregion 71
Network of stream reaches and associated catchment
- Average reach length ~8 miles- Average catchment area ~30 sq mi
30 MILES0
Sources
Land-to-water delivery
Instream decay
Stream load Sources Land-to-water
deliveryInstream
decay Error
http://water.usgs.gov/nawqa/sparrow
Stream load Sources Land-to-water
deliveryInstream
decay Error
Source variables:
wastewater load,applied fertilizer,animal waste,atmospheric deposition,urban area
Stream load Sources Land-to-water
delivery Instream
decay Error
Delivery variables:(landscapecharacteristics)
air temperature *,soil permeability,slope,drainage density
Stream load Sources Land-to-water
delivery Instream
decay Error
Instream decay variables(waterbody characteristics)
reservoir residence time *,stream depth,stream-reach travel time
Calibrating SPARROW model for Ecoregion 71:Results (draft) for nitrogen
Fit statistics: r2 = 0.9, RMSE = 0.2 (average prediction error = 20 percent)
Elk River Basin and Embayment
SPARROW Total Phosphorus Model (Draft)Elk River Basin (Tenn., Ala.)
0 - 11 - 22 - 33 - 4>4
Phosphorus entering stream network from incremental watershed, tons/sq.mile/year
Annual mean concentration (model predicted): 0.6 mg/L
SPARROW Total Phosphorus Model (Draft)Elk River Basin (Tenn. Ala.)
0
0.2
0.4
0.6
0.8
1
1.2
Phosphorus delivered to
Elk River embayment
(tons/sq mi/yr)
TN AL
Wastewater 'Natural' source Animal waste
SPARROW Total Phosphorus Model (Draft)Elk River Basin (Tenn. Ala.)
0
0.5
1
1.5
2
2.5
Nitrogen delivered to
Elk River embayment
(tons/sq mi/yr)
TN AL
Urban land
Animal Waste
Fertilizer
AtmosphericDeposition
Wastewater
SPARROW Total Nitrogen Model (Draft)Elk River Basin (Tenn. Ala.)
Example Application of SPARROW Model
Total
Nitrogen
lb/ac/yr
Total
Phosphorus
lb/ac/yr
East Fork (Reference) 5.84 0.41
West Fork 10.56 0.63
% Reduction 44.70 34.92
SPARROW Estimates of Source Share Contribution
Total N % Total P %
Wastewater 24 Wastewater 91Atm. Dep. 22 P Rich Rock 0Animal Waste 9 Animal Waste 9Fertilizer 19Urban 26
Total N- Sources Allocations
Wastewater Atm.Dep. Fertilizer Animal Waste Urban Total
Existing Load (lb/ac/yr) (SPARROW estimates) 2.625 2.438 2.0 0.906 2.844 10.813
Required Load Reduction 44.7%
New Load (lb/ac/yr) 5.979
No Load Reduction 2.438
New Load Allocate-able (lb/ac/yr) 3.541
Existing Load (lb/ac/yr) 2.625 2.0 0.906 2.844 8.375
Required Load Reduction 57.7%
New Load Allocations (lb/ac/yr) 1.11 0.864 0.383 1.202 3.541
Total P- Sources Allocations
Wastewater P rich Rock Animal Waste
Total
Existing Load (lb/ac/yr) 0.594 0.00 0.063 0.656
Required Load Reduction 34.9%
New Load (lb/ac/yr) 0.427
No Load Reduction 0.00 0.00
New Load Allocate-able (lb/ac/yr) 0.656
Existing Load (lb/ac/yr) 0.594 0.063 0.427
Required Load Reduction 34.9%
New Load Allocations (lb/ac/yr) 0.387 0.041 0.427
STP Permit Limits
Drainage Area (sq. mi.) 253
Design Flow (MGD) 16
STP WLA (lb/ac/yr) - TN 1.11
STP Load (lb/yr) - TN 179,731
Mean Avg, Permit Limit –
TN (mg/l)
3.69
STP WLA (lb/ac/yr) - TP 0.387
STP Load (lb/yr) - TP 62,663
Mean Avg, Permit Limit –
TP (mg/l)
1.28
• The SPARROW water-quality model is a tool for addressing basin-scale questions about stream nutrient loads/concentrations (assess water quality, source shares, track flux from upstream origin to downstream target)
• A strong advantage for its use in management decisions – estimate of uncertainty(percent error for Ecoregion 71 models: 20% for nitrogen, 60% for phosphorus)
Main Ideas
Calibrated coefficients establish the linkage (average)
between source inputs and instream flux
1.1 x
0.7 x
Coeff.
0.2 x
0.1 x
11 x
SPARROW Total Phosphorus Model (Draft)Elk River Basin (Tenn., Ala.)
0 - 11 - 22 - 33 - 4>4
Phosphorus entering stream network from incremental watershed, tons/sq.mile/year
Phosphorus delivered to target waterbody from incremental watershed
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