1 upscaling of site-specific nitrate-nitrogen measurements to the watershed scale in the santa fe...
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Upscaling of Site-Specific Nitrate-Nitrogen Measurements to the Watershed Scale in the Santa Fe
River Watershed
S. Lamsal, S. Grunwald, C. M. Bliss, I. Lopez-Zamora, N. B. Comerford and M.W. Clark
University of Florida
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Introduction
• The Santa Fe River watershed (SFRW) (3,585 km2) is part of the Suwannee Basin (≈ 25,900 km2)
• The Santa Fe River (SFR) Reach 2 covers 5.7 % of the basin
• In 1998, SFR Reach 2 (west) accounted for 15.9 % (1,130 tons) and SFR Reach 1 (east) accounted for 0.9 % (65.6 tons) of the total nitrate–nitrogen delivered to the Gulf of Mexico (SRWMD, 1998)
• In 2002, the contribution of SFR Reach 2 increased to 19.6 % (SRWMD, 2003)
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Objective
• Overall Goal
To gain a better understanding of the geo-temporal distribution and variability of nitrate –nitrogen (NO3-N) in the SFRW
• Objective
To upscale site-specific NO3-N measurements to the watershed-scale using field observations and ancillary environmental datasets
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Study Area• Santa Fe River Watershed in north-east Florida• Major soils: Ultisols (37 %), Spodosols (26 %), Entisols (15%), Histosols (2 %) (NRCS, SSURGO)
Data SourcesLand use: 1995 LANDSAT TM imagesprocessed by SRWMD & SJRWMDWatershed boundary: SRWMD
±Land use category
UrbanRangelandPine plantationsUpland forestWetlandImproved pastureForest regenerationCrops
0 12,500 25,000 37,500 50,000Meters
Land use categories in the SFRW
±Land use category
UrbanRangelandPine plantationsUpland forestWetlandImproved pastureForest regenerationCrops
0 12,500 25,000 37,500 50,000Meters
Land use categories in the SFRW
N
Land use
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Sampling Design
• Stratified random sampling: land use–soil combinations
• Composite sampling at 4 depth increments
0-30, 30-60, 60-120, 120-180 cm• Comprehensive space-time sampling, 2 years with 3
samplings per year (Sept. 2003, Jan. 2004, May 2004, and 3 future sampling events)
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Nitrate-Nitrogen Measurements
• NO3-N measurements at each site were profile averaged
• Distribution highly skewed to the right
Statistics Sept. 2003 Jan. 2004 May 2004
n 101 123 128
Mean 0.74 3.72 1.16
Min 0.01 0.06 0.10
Max 9.88 193.83 90.12
SD 0.11 1.84 0.68
Statistics of NO3-N (μg.g-1 soil) distribution
High values in Jan. followed by May and Sept sampling events
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NO3-N by Land Use
Land uses Sept 2003 Jan 2004 May 2004
Mean Max Mean Max Mean Max
Pine plantation 0.22 0.79 0.14 0.60 0.23 0.86
Crops 1.95 5.02 26.88 103.12 5.36 13.96
Forest regeneration 0.83 10.1 0.19 0.70 0.30 0.50
Improved pasture 1.17 6.54 11.40 103.70 3.01 19.92
Rangeland 1.58 4.30 8.38 41.80 1.49 6.50
Tree grove 3.07 6.06 2.79 5.36 4.22 8.86
Upland forest 0.78 4.58 3.66 67.42 0.22 0.39
Urban 0.14 0.39 0.19 0.61 0.38 1.12
Wetland 0.24 1.60 0.09 0.28 0.49 1.79
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NO3-N Trend Model
• Trend model based on mean NO3-N under land use Pixel based upscaling
0 10,000 20,000 30,000 40,0005,000Meters
±
OK prediction of nitrate-nitrogen residuals across the SFRW
Nitrate-Nitrogen(ug/g soil)
0.0990.1450.1900.1993.6608.38511.40626.880
Nitrate-Nitrogenμg.g-1 soil
Jan. 20040 10,000 20,000 30,000 40,0005,000
Meters
±
OK prediction of nitrate-nitrogen residuals across the SFRW
Nitrate-Nitrogen(ug/g soil)
0.0990.1450.1900.1993.6608.38511.40626.880
0.090.140.190.193.338.3811.4026.88 N
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Residual Modeling
• Residuals were computed for each sampling location • Spatial autocorrelation of residuals was modeled
using semivariograms• Residuals were interpolated using Ordinary Kriging• Residuals compensated for under- and over-
predictions made by the trend model
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Autocorrelation of Residuals
Spherical modelNugget:15Sill: 75Range: 6,500 m
D1
M1
0. 10. 20. 30.
Lag (km)
0.
25.
50.
75.
100.
125.
Semivaraince
January 2004
The residuals were interpolated using the fitted semivariograms
>=70.72
46.46
28.27
10.07
-8.12
<-26.31
Text stringResidual(ug/g)
Residual(μg.g-1 soil)
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Spatial Distribution of NO3-N
±0 11,000 22,000 33,000 44,000Meters
Distribution of nitrate-nitrogen across theSFRW
Nitrate-Nitrogen(ug/g soil)
0 - 0.20.2 - 0.50.5 - 1.01.0 - 1.51.5 - 2.02.0 - 3.2
±0 11,000 22,000 33,000 44,000Meters
Distribution of nitrate-nitrogen across theSFRW
Nitrate-Nitrogen(ug/g soil)
0 - 0.20.2 - 0.50.5 - 1.01.0 - 1.51.5 - 2.02.0 - 3.2
Nitrate-Nitrogenμg.g-1 soil
Trend model + Residual model NO3-N Model
Sept. 2003
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Spatial Distribution of NO3-N
± 0 12,500 25,000 37,500 50,000Meters
0 - 11 - 22 - 55 - 1010 - 2020 - 4040 - 87 ± 0 12,500 25,000 37,500 50,000
Meters
0 - 11 - 22 - 55 - 1010 - 2020 - 4040 - 87
Nitrate-Nitrogenμg.g-1 soil
Jan. 2004
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Spatial Distribution of NO3-N
May 2004
Nitrate-nitrogen distribution in the SFRW in May 2004
Nitrate-Nitrogen(ug/g soil)
0 - 0.50.5 - 1.01.0 - 2.02.0 - 5.05.0 - 10.010.0 - 15.015.0 - 20.5
±0 12,500 25,000 37,500 50,000Meters
Nitrate-nitrogen distribution in the SFRW in May 2004
Nitrate-Nitrogen(ug/g soil)
0 - 0.50.5 - 1.01.0 - 2.02.0 - 5.05.0 - 10.010.0 - 15.015.0 - 20.5
±0 12,500 25,000 37,500 50,000Meters
Nitrate-Nitrogenμg.g-1 soil
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Prediction Success
Prediction error is a composite of the error from the trend model and the residual model
Error statistics Sept. 2003 Jan 2004 May 2004
Mean -0.12 -0.37 -0.10
Variance 1.69 247.96 8.28
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Conclusions
• Soil NO3-N was variable in space and through time
• NO3-N was highest in Jan. 2004 and lowest in Sept. 2003
• High NO3-N was found in crops, improved pasture and rangeland
• Future research will focus on more advanced modeling of space-time distributions of NO3-N across the SFRW
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Thank you