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