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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, Tennessee Sherry Wang, Tennessee Division of Water Pollution Control. Sources. Land-to-water transport. Instream transport. Watershed analysis:.

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slide1

The SPARROW water-quality model as a tool

for watershed analysis of nutrient sources and transport

Anne Hoos, U.S. Geological Survey, Tennessee

Sherry Wang, Tennessee Division of Water Pollution Control

Sources

Land-to-water

transport

Instream

transport

Watershed

analysis:

1. Science

2. Management

slide2

SPARROW background

  • 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
slide3

SPARROW modeling in

Tennessee/Alabama

  • Interior Low Plateau ecoregion, in collaboration with Tennessee Division of Water Pollution Control
  • In development: southeastern U.S. (NAWQA Major River Basin program)
slide4

Examples of the basin-scale questions

SPARROW can address

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

slide5

Examples of basin-scale questions

SPARROW can address

1. Assess water quality2. 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%

slide6

Examples of basin-scale questions

SPARROW can address

1. Assess water quality2. 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%

slide7

How certain are the answers?

  • A strong advantage for its use in management decisions: estimate of uncertainty calculated for all model output

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

slide8

What is SPARROW?

SPAtially-Referenced Regression On

Watershed Attributes

Response variable: measured load at monitoring stations

Predictor variables: measured watershed attributes

“Expensive” information

“Inexpensive” information

slide9

“Moving from Monitoring to Prediction”

Point-level

water-quality data

Predictions for unmonitored,

comparable areas

slide10

SPARROW model structure for Ecoregion 71

Network of stream reaches and associated catchment

  • Average reach length ~8 miles
  • Average catchment area ~30 sq mi
slide11

Stream load

Sources

Land-to-water delivery

Instream

decay

Error

Sources

Land-to-water

delivery

Instream

decay

http://water.usgs.gov/nawqa/sparrow

slide12

Stream load

Sources

Land-to-water delivery

Instream

decay

Error

Source variables:

wastewater load,

applied fertilizer,

animal waste,

atmospheric deposition,

urban area

slide13

Stream load

Sources

Land-to-water delivery

Instream

decay

Error

Delivery variables:

(landscape

characteristics)

air temperature *,

soil permeability,

slope,

drainage density

slide14

Stream load

Sources

Land-to-water delivery

Instream

decay

Error

Instream decay variables

(waterbody

characteristics)

reservoir residence

time *,

stream depth,

stream-reach travel time

slide15

Calibrating SPARROW model for Ecoregion 71:

Results (draft) for nitrogen

Fit statistics: r2 = 0.9,

RMSE = 0.2 (average prediction error = 20 percent)

slide17

SPARROW Total Phosphorus Model (Draft)

Elk River Basin (Tenn., Ala.)

Phosphorus entering stream network from incremental

watershed, tons/sq.mile/year

Annual mean concentration (model predicted): 0.6 mg/L

slide18

SPARROW Total Phosphorus Model (Draft)

Elk River Basin (Tenn. Ala.)

slide19

SPARROW Total Phosphorus Model (Draft)

Elk River Basin (Tenn. Ala.)

slide20

SPARROW Total Nitrogen Model (Draft)

Elk River Basin (Tenn. Ala.)

slide26

Main Ideas

  • 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)
slide27

Coeff.

1.1 x

0.7 x

0.2 x

0.1 x

11 x

Calibrated coefficients establish the linkage (average)

between source inputs and instream flux

slide28

SPARROW Total Phosphorus Model (Draft)

Elk River Basin (Tenn., Ala.)

Phosphorus entering stream network from incremental

watershed, tons/sq.mile/year

Phosphorus delivered to target waterbody from incremental watershed