SPARROW Modeling Case Study

Research Question: What is the impact of land use change in the U.S. from 1992 to 2001 on nitrogen delivery?

By Jahangir Alam and Jonathan GoodallDept of Civil EngineeringUniversity of South Carolina

Observations Database: 400 sites

For each NAWQA site where flow and concentration are available for time period of interest, relate spatially-referenced watershed characteristics to observed in-stream load.

SPARROW Equations

TNi = observed nitrogen loading at station iSn,j = nitrogen source n for reach jZj = watershed attributes for reach jTi,j = travel time from reach j to station iβn , α, and k = calibration parameters

Smith, R.A., Schwarz, G.E., and Alexander, R.B., 1997, Regional interpretation of water-quality monitoring data, Water Resources Research, 33, 12, 2781-2798.

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

SPARROWSPARROW considers tobasic processes innitrogen transport:

(1.) Overland transport (2.) In-stream transport

(both are assumed tofollow 1st order decay)

Overland Transport

In-stream Transport

Eno River Basin

Little Creek

SPARROW Calibration

Nitrogen Observation Site

Example of Previous SPARROW Application: Nitrogen Transport to the Gulf

Agriculture Atmosphere

Point Sources

Alexander, R.B., Smith, R.A., and Schwarz, G.E., 2000, Effect of stream channel size on the delivery of nitrogen to the Gulf of Mexico, Nature, 403, 758-761.

Procedure

1. Prepare land cover data2. Prepare loading data3. Update “baseline” SPARROW inputs with

1992 and 2001 specific data

Procedure

1. Prepare land cover data2. Prepare loading data3. Update “baseline” SPARROW inputs with

1992 and 2001 specific data

National Land Cover Dataset (NLCD)

• Products include classifications for 1992, 2001, and 2006 (in development), and change product (1992 to 2001)• 30m resolution; 25 classes • http://www.epa.gov/mrlc

Urbanization in Columbia, SCChange Product (1992 to 2001)

map of NLCD 2001

Colored Pixels are 2001 NLCDBlack Pixels Change to Urban from 1992 to 2001

Urbanization in Charlotte, NCChange Product (1992 to 2001)

map of NLCD 2001

Colored Pixels are 2001 NLCDBlack Pixels Change to Urban from 1992 to 2001

Land Cover Change in the South East U.S.

* all areas reported in units of km2

from

to Open Water Urban Barren Forest Grassland/Shrub Agriculture Wetlands Ice/Snow sum

Open Water - 82 26 194 13 190 244 0 749

Urban 33 - 2 2,563 185 720 591 0 4,094

Barren 46 7 - 350 23 71 75 0 572

Forest 30 127 7 - 4,032 5,111 401 0 9,707

Grassland/Shrub 118 55 7 13,961 - 481 782 0 15,404

Agriculture 72 171 4 6,606 701 - 820 0 8,373

Wetlands 477 92 11 1,879 411 996 - 0 3,866

Ice/Snow 0 0 0 0 0 0 0 - 0

sum 775 451 31 25,359 5,352 7,379 2,668 0

Land Cover Change in South East U.S.(1992 to 2001)

Summarizing Land Cover

1992

2001

WatershedID Urban

1 534322

2 453221

… …

Modeling Units

WatershedID Urban

1 534322

2 453221

… …

1992 2001

61,215 Watersheds

Procedure

1. Prepare land cover data2. Prepare loading data3. Update “baseline” SPARROW inputs with

1992 and 2001 specific data

Data Preparation Workflow

Time Series Data

Identify time series of interest

Create sites.csv file

Run FetchWaterML.exe

tool to create WaterML Cache

Reformat files from WaterML to LOADEST inputs

Runkel, R.L., Crawford, C.G., and Cohn, T.A., 2004, Load Estimator (LOADEST): A FORTRAN Program for Estimating Constituent Loads in Streams and Rivers: U.S. Geological Survey Techniques and Methods Book 4, Chapter A5, 69 p.

Creating a Cache of HIS DataSites.csv

c:> FetchWaterML.exe sites.csv ./daily-discharge-2/

output directoryinput sites file

Downloaded WaterML Files (one for each time series requested)

Estimating Load from Flow and Concentration

TN Loading Data

1988-1996

< 5.0x106

5.0x106 - 10.0x106

10.0x106 - 20.0x106

20.0x106 - 50.0x106

> 50.0x106

Average Loading (kg/yr)

1997-2005

Difference, ‘92 and ‘01 Loadings

> - 5.0x106

-5.0x106 - 00 - 5x106 > 5.0x106

Loading Difference (kg/yr)

+ (orange/red) increase in loading from 92 to 01- (blue) decrease in loading

Procedure

1. Prepare land cover data2. Prepare loading data3. Update “baseline” SPARROW inputs with

1992 and 2001 specific data

Results

Results

Conclusions • Our model suggests that nitrogen loadings to streams have

decreased from the 1990s to the 2000s by on average 1 kg/ha/yr (or roughly 10%). It also shows a shift in the relative contribution of nitrogen sources with a greater contribution from urban land use areas in the 2000s compared to the 1990s. That said, the current model assumes fertilizer application rates, point sources loadings, and animal populations are constant over time because it is difficult to obtain differences between these numbers of the two time periods of analysis.